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This is to certify that the
thesis entitled

BIODEGRADATION OF COMMERCIALLY AVAILABLE
BIODEGRADABLE PACKAGES IN REAL AND SIMULATED
COMPOSTING CONDITIONS

presented by

GAURAV KALE

has been accepted towards fulfillment
of the requirements for the

 

 

 

 

Masters of degree in Packaging
Science
Major Wr'é Signature
®°t l 291 N 1
Date

MSU is an affirmative-action, equal-Opportunity employer

 

PLACE IN RETURN BOX to remove this checkout from your record.
To AVOID FINES return on or before date due.
MAY BE RECALLED with earlier due date if requested.

 

DATE DUE I DATE DUE

DATE DUE

 

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6/07 p:/ClRC/DateDue.indd-p.1

BIODEGRADATION OF COMMERCIALLY AVAILABLE BIODEGRADABLE
PACKAGES IN REAL AND SIMULATED COMPOSTING CONDITIONS

BY

Gaurav Kale

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

School of Packaging

2007

 

 

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ABSTRACT

BIODEGRADATION OF COMMERCIALLY AVAILABLE BIODEGRADABLE
PACKAGES IN REAL AND SIMULATED COMPOSTING CONDITIONS

By
Gaurav Kale
There is currently incentive and growth for the adoption of biodegradable polymers for
packaging applications. Standards developed so far address the biodegradability of these
polymers in simulated controlled composting conditions but they are limited to the
assessment of plastic material and not whole package. As a result, it is necessary to assess
biodegradability performance of biodegradable packages. The first part of this thesis
presents a review of: 1) the current standards and methodologies used for evaluating
biodegradability; 2) the commonly employed composting processes and the actual
biodegradation environments; and 3) the certifications process used for biodegradable
plastics. In the second part, biodegradation studies of polylactide (PLA) based packages
were carried out in real composting and ambient exposure conditions using a novel
technique. In the third part, biodegradation of PLA bottles was investigated in simulated
composting conditions as prescribed by ASTM D5338, ISO 14855-1 (titration method)
and a new method based on ISO 14855-2 (gravimetric method). Finally, in the fourth
part, the biodegradation of poly(butylene adipate terephthalate) films and its blends was
carried out in real composting conditions. PLA packages disintegrated very fast in real
composting conditions based on visual inspection and variation in physical properties.
The comparison of both simulated laboratory methods and real composting conditions for
PLA bottles showed that much variability occur in biodegradation in real composting

conditions.

DEDICATION

To my Parents and their more than 20 years of dedicated service in Packaging

 

 

 

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ACKNOWLEDGEMENTS

First and foremost, I would like to thank Dr. Rafael Auras for guiding me
throughout this thesis work. I would like to thank him for all his support and help in
doing composting studies and setting up experiments, writing paper for journals and
giving me opportunity to present my work at professional conferences. Thanks to Dr.
Rafael Auras for always keeping his door open for me and providing guidance whenever
needed. His guidance in improving writing and presentation skills has been very helpful.
Thanks to Dr. Paul Singh for his guidance, initiatives in starting the project and help in
providing the PIA samples. Thanks to Dr. Ramani Narayan for giving continuous
guidance and sharing his expertise whenever needed, allowing use of MODA system at
CHEMS, providing Ecoflex samples and his feedback in finishing the literature review.
Thanks to Dr. Susan Selke for answering graduate program questions and reviewing
manuscripts of journal papers. Thanks to Dr. Amar Mohanty for allowing use of DSC and
TGA. Thanks to Dr. Robert Clarke for giving opportunity to work as TA for PKG432 for
two semesters. Thanks to the entire faculty at MSU School of Packaging for providing
excellent education and instruction in all packaging classes.

Special thanks to Tony Boughton for allowing me to use compost pile at his
facility and answering all my questions related to composting. Thanks to Dr. John
Biembaum for allowing use of composting lab at MSU Horticulture department. Thanks
to Andy Fogiel for teaching basics in composting and providing reading material on
same. Thanks to Dr. Gregory Baker and quei Jiang for allowing use of GPC at
Chemistry Department. Thanks to Bob for his help in making boxes and all other

engineering work. Thanks to NatureWorks LLC (NE) for providing PLA bottles and

 

 

 

 

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Wilkinson Manufacturing (NE) for providing thermoforrned PLA packages. Thanks to
Keith Edwards (BASF Chemical Co.) for answering questions and providing literature
regarding Ecoflex. Thanks to Dr. Shogo Uematsu (Japan) for providing guidance in
running MODA system. Thanks to Patrizia Sadocco (Italy) for her review and comments
on the MODA results. Thanks to Guoren Cheng for help in setting up the MODA system.
Thanks to Brendan Buckley (Fresh Express INC) for giving me Opportunity to work as a
packaging technologist intern at Fresh Express INC.

Thanks to Santosh Madival for looking after CMR system when I was away; and
being a good roommate and friend. Thanks to Turk for all his help in setting up
composting experiments and writing the literature review. Thanks to Pankaj Kumar for
help in making the 3D box figure. Thanks to Eva for all her guidance and help. Thanks to
Nitin, Ben, Gaurav and Sukeewan for their feedback during the research group meetings.
Thanks to Yash and Rahul for giving me training on DSC and TGA. Thanks to Jonathan
Falls for conducting my labs when I was away on conferences.

Thanks to Gaurav Dabholkar and Amol Khanapurkar for being good friends and
roommates; and tolerating smell of manure on my shoes. Thanks Mitzi Ma for being such
a nice friend, making tiramisu, helping in my experiments, entertaining me and sharing
such a wonderful time with me. Thanks Shantanu, Kathy, Aileen for being nice friends.

I want to thank my parents; Nandkishor and Shashi Kale for believing in me;
encouraging me and making me who I am today.

Thanks to everyone else that I have failed to mention for all their help and support

throughout my thesis work.

TABLE OF CONTENTS

Page

LIST OF TABLES ................................................................... ix

LIST OF FIGURES .................................................................. xi
1. INTRODUCTION ................................................................... 1
2. LITERATURE REVIEW ........................................................... 5
Summary ........................................................................ 6
2.1 Introduction ................................................................. 7

2.2 Compostable Packages .................................................... 12

2.1.1 Compostable Materials ......................................... 13

2.2.2 Biodegradable polymers and degradation mechanism 13

2.2.2.1 Natural polymers .................................... 14

2.2.2.2 Carbon chain polymers .............................. 15

2.2.2.3 Hetero chain polymers ............................... 15

2.2.3 Factors affecting rate of biodegradation ..................... 18

2.2.3.1 Exposure conditions ................................. 18

2.2.3.2 Polymer factors ....................................... 21

2.3 Composting ................................................................. 24

2.3.1 Waste materials ................................................. 25

2.3.1.1 Yard waste ............................................ 25

2.3.1.2 Food waste ............................................ 26

2.3.1.3 Manure waste ........................................ 28

2.3.1.4 Packaging waste ..................................... 29

2.3.2 Composting techniques ........................................ 33

2.3.2.1 Commercial composting ............................ 33

2.3.2.2 Advances in composting techniques .............. 35

2.3.2.3 Home composting (Backyard) ..................... 37

2.3.3 Plastics in compost ............................................. 38

2.3.4 Uses of compost ................................................ 40

2.3.5 Environmental impacts of the composting process 41

2.4 Standards .................................................................... 41

2.4.1 ASTM standards ................................................ 42

2.4.2 European and ISO standards .................................. 48

2.5 Labeling and certification ................................................. 54

2.6 Life cycle analysis ......................................................... 57

2.7 Conclusion .................................................................. 60

REFERENCES .................................................................. 62

3. DEGRADATION OF COMMERCIAL BIODEGRADABLE PACKAGES

vi

UNDER REAL COMPOSTING AND AMBIENT EXPOSURE

CONDITIONS ........................................................................ 68
Summary ..................................................................... 69
3.1 Introduction ............................................................. 70
3.2 Materials and methods ................................................ 75

3.2.1 Packages ..................................................... 77
3.2.2 Compost pile ................................................ 77
3.2.3 Box ............................................................ 77
3.2.4 Placement of packages ..................................... 79
3.2.5 Compost property testing .................................. 79
3.2.6 Ambient conditions ......................................... 80
3.2.7 Visual inspection ............................................ 82
3.2.8 Physical properties .......................................... 82
3.4 Results and discussion ................................................. 84
3.4.1 Visual inspection ............................................ 85
3.4.2 Physical properties .......................................... 99
3.5 Conclusion ............................................................... 106

REFERENCES .............................................................. 107

4 COMPARISON OF THE DEGRADABILITY OF POLY (LACTIDE)
PACKAGES IN COMPOSTING AND AMBIENT EXPOSURE

CONDITIONS ........................................................................ 111
Abstract ....................................................................... 1 12
4.1 Introduction ............................................................. 113
4.2 Materials and methods ................................................ 1 18

4.2.1 Packages ..................................................... 118

4.2.2 Compost pile ................................................ 119

4.2.3 Box ........................................................... 121

4.2.4 Plastic containers ........................................... 121

4.2.5 Placement of packages ..................................... 122

4.2.6 Compost parameters ........................................ 122

4.2.7 Ambient parameters ........................................ 123

4.2.8 Visual inspection ............................................ 125

4.2.9 Physical properties .......................................... 125

4.2.10 Statistical analysis ......................................... 126

4.3 Results and discussion ................................................. 127
4.3.] Visual inspection ............................................ 129

4.3.2 Physical properties .......................................... 132

4.3.2.1 Molecular weight ................................. 132

4.3.2.2 Glass transition and melting temperature 138

4.3.2.3 Decomposition temperature ..................... 142

4.4 Conclusions ............................................................. 146
REFERENCES .............................................................. 147

vii

5 BIODEGRADABILITY OF POLYLACTIDE BOTTLES IN REAL AND

SIMULATED COMPOSTIN G CONDITIONS ................................. 151
5.1 Introduction ............................................................. 151
5.2 Materials and methods ................................................ 153
5.2.1 Samples ...................................................... 153
5.2.2 Real composting conditions ............................... 157
5.2.3 Molecular weight ............................................ 166
5.2.4 Cumulative measurement respirometric system 166
5.2.5 Microbial oxidative degradation analyzer ............... 160
5.3 Results and discussion ................................................. 163
5.3.1 Real composting conditions ................................ 163
5.3.2 Cumulative measurement respirometric system 167
5.3.3 Microbial oxidative degradation analyzer ................ 168
5.3.4 Comparison of all methods ................................. 171
5.4 Conclusion ............................................................... 176
REFERENCES .............................................................. 178
6 BIODEGRADABILITY OF PACKAGING FILMS IN REAL
COMPOSTING CONDITIONS ................................................... 181
6.1 Introduction ............................................................. 181
6.2 Materials and methods ................................................ 183
6.2.1 Samples ...................................................... 183
6.2.2 Compost pile ................................................ 183
6.2.3 Compost parameters ....................................... 186
6.2.4 Ambient conditions ........................................ 186
6.2.5 Placement of films in compost pile ...................... 186
6.2.6 Visual inspection ........................................... 186
6.2.7 Molecular weight analysis ................................. 186
6.3 Results and discussion ................................................. 186
6.3.] Visual inspection ............................................ 186
6.3.2 Molecular weight ........................................... 195
6.4 Conclusion .............................................................. 199
REFERENCES ............................................................. 195
7 FUTURE WORK RECOMMENDATIONS .................................... 196

viii

 

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LIST OF TABLES

Table Page
Table 2.1 Food and yard waste generated during 2003 in the USA ............... 29
Table 2.2 List of current ASTM Standards sorted by category .................... 43

Table 2.3 Maximum heavy metal content of packaging material and whole
packaging from EN 13432 Annex A] ................................................ 49

Table 3.1. Physical properties of the poly(lactide) bottles, trays, and deli
containers .................................................................................. 84

Table 3.2. First order equation (MW: a*exp(-b*t)) of the degradation process
of poly(lactide) bottles, trays, and deli containers ................................... 94

Table 3.3. Variation of glass transition T8: Tg(0)+d*t as a function of time for
poly(lactide) bottles, trays, and deli containers ....................................... 98

Table 3.4. Variation of glass transition T3: Tam) — A/Mn as a function of
average molecular weight number for poly(lactide) bottles, trays, and deli
containers .................................................................................. 99

Table 3.5. Variation of decomposition temperature TD: Too + e*t as a function
of time (equation 6) and Molecular number for poly(lactide) bottles, trays, and
deli containers. Variation of decomposition temperature TD: TWO) — B/Mn as a
function of Mn ............................................................................. 104

Table 4.1. Physical properties of the poly(lactide) bottles and deli containers 127

Table 4.2. F irst-order equation [MW x 103 = a*exp(—b*t)] of the degradation
process of poly(lactide) bottles and deli containers .................................. 137

Table 4.3. Variation of glass transition T8 = Tgm) + d*t as a function of time for
poly(lactide) bottles and deli containers ............................................... 141

Table 4.4. Variation of decomposition temperature T D = T D0 + e*t as a function

of time (equation 4) and molecular number for poly(lactide) bottles and deli
containers. Variation of decomposition temperature T D = T 0(a)) — B/Mn as a

function of Mn ............................................................................. 144

ix

LIST OF FIGURES
Figure
Figure 2.1 Structures of poly(lactide), poly(caprolactone), and
poly(hydroxyalkanoates) ................................................................

Figure 2.2 Hydrolyzable functional group commonly found in biodegradable
polymers ...................................................................................

Figure 2.3 (Left) Poly(glycolic acid), (Right) Poly(lactide) ........................

Figure 2.4. Pictorial view of PLA bottles exposed at 30 day of compost
conditions (5815 C, 60i5%RH) .......................................................

Figure 2.5. Pictorial View of Ecoflex films exposed at 60 day of compost
conditions (48°Cdz5°C, 52il6%RH) ....................................................

Figure 2.6. Pictorial view of LDPE with oxo-additive exposed at 60 day of
compost conditions (48°C15°C, 52i16%RH) ..........................................

Figure 2.7. Commercial composting system and operations ........................
Figure 2.8. Compostable materials identification flowchart ........................
Figure 2.9 a & b. Accumulative and direct method to measure biodegradation.

Figure 2.10 Flowchart of evaluation of organic recoverability of packaging
based on EN 13432 standard ............................................................

Figure 2.1] Percentage of mineralization of PLA and PET bottles and corn
starch measured according ASTM D 5338 and ISO 14855 .........................

Figure 2.12 (a) BPI compostable logo, (b) DIN CERTCO compostable logo,
(0) AV OK compost logo ................................................................

Figure 3.1. PLA containers a) bottle; b) tray; c) deli .................................

Figure 3.2. Temperature distribution inside the compost pile at the beginning
of the testing ..............................................................................

Figure 3.3. 3D view of Box .............................................................
Figure 3.4. a) 30 days maximum and minimum temperature data; b) 30 days

maximum and minimum relative humidity data; c) 30 days average total solar
radiation ....................................................................................

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Figure 3.5. a) Temperature and relative humidity of the compost pile at time of
package removal, b) pH of the compost pile at time of package removal ........

Figure 3.6. Pictorial View of the PLA bottles exposed at 30 day of compost
conditions ..................................................................................

Figure 3.7. Pictorial view of the PLA trays exposed at 30 day of compost
conditions ..................................................................................

Figure 3.8. Pictorial view of the PLA deli exposed at 30 day of compost
conditions ...................................................................................

Scheme 3.1. PLA hydrolysis and molecular weight loss ............................

Figure 3.9. Comparison of the variation of the molecular weight and
polydispersity index (PDI) as a function of time for a) bottles, b) trays, c) deli
containers exposed to the ambient for 30 days; and (1) bottles, e) trays, f) deli
containers exposed to composting conditions for 30 days ...........................

Figure 3.10. 2nd run of DSC showing the glass transition and melting

temperature variation of the PLA bottle exposed to composting conditions for
30 days .....................................................................................

Figure 3.11. Glass transition and melting temperature variation of a) bottles b)
trays c) deli containers exposed to the ambient conditions for 30 days; (1)
bottles e) trays f) deli containers exposed to composting conditions for 30
days ..........................................................................................

Figure 3.12. Tg vs M“ of the 3) bottles b) trays, and c) deli containers exposed
to compost conditions for 30 days ......................................................

Figure 3.13. a) Weight percent reduction vs temperature .............................

Figure 3.14. Decomposition temperature a) bottles b) trays c) deli containers
exposed to ambient and composting conditions for 30 days ........................

Figure 4.1.. PLA containers: (a) bottle and (b) deli container .......................

Figure 4.2. Temperature distribution inside the compost pile at the beginning
of the testing ................................................................................

Figure 4.3. 3D view ofthe box .........................................................

Figure 4.4. (a) 30 days maximum and minimum temperature data. (b) 30 days
maximum and minimum relative humidity data. (c) 30 days average total solar

xi

85

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87

88

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93

96

97

100

101

103

119

120

121

radiation ....................................................................................
124

Figure 4.5 (a) Temperature and relative humidity of the compost pile at time of
package removal. (b) pH of the compost pile at time of package removal ........ 128

Figure 4.6. Pictorial View of the PLA bottles exposed at day 30 of compost
conditions .................................................................................. 129

Figure 4.7. Pictorial view of the PLA bottles exposed for 30 days under
ambient conditions ........................................................................ 130

Figure 4.8. Pictorial view of the PLA deli containers exposed at day 30 of
compost conditions ....................................................................... 131

Figure 4.9. Pictorial view of the PLA deli containers exposed for 30 days under
ambient conditions ........................................................................ 131

Scheme 4.1. PLA hydrolysis and molecular weight loss ............................ 133

Figure 4.10. Variation of the molecular weight and polydispersity index (PDI)
as a function of time for (a, b) bottles exposed to composting (D) and ambient
(0) conditions for 30 days and (c, d) deli containers exposed to composting (1:1)
and ambient (0) conditions for 30 days ................................................ 135

Figure 4.11. Second run of DSC showing the glass transition and melting
temperature variations of the PLA (a) bottle and (b) deli container exposed to
composting conditions for 30 days ..................................................... 139

Figure 4.12. Variation of the glass transition and melting temperature as a
function of time for (a, b) bottles exposed to composting (c1) and ambient (0)
conditions for 30 days and (c, d) deli containers exposed to composting (c1) and
ambient (0) conditions for 30 days .................................................... 140

Figure 4.13. Variation in decomposition temperature as a function of time for
(a) bottles exposed to composting (c1) and ambient (0) conditions for 30 days
and (b) deli containers exposed to composting (El) and ambient (0) conditions
for 30 days .‘ ................................................................................ 143
Figure 5.1. PLA Bottle ................................................................... 154

Figure 5.2. Placement of packages in compost pile .................................. 156

Figure 5.3. Schematic of CMR system ................................................ 159
Figure 5.4. Schematic of MODA system .............................................. 159

xii

Figure 5.5. Schematic of the reaction column for MODA system .................

Figure 5.6. Biodegradation of PLA bottles in real composting conditions .......

Figure 5.7. Variation in molecular weight (0) and PDI (CI) for PLA bottles in
real composting conditions ..............................................................

Figure 5.8. Percentage mineralization as a function of time for cellulose (O)
and PLA bottles (E1) in CMR system ...................................................

Figure 5.9. Percentage mineralization as a function of time for cellulose (O)
and average of PLA bottles (CI) in MODA. Turning days are represented by
(x) ...........................................................................................
Figure 5.10. Comparison of variation in molecular weight (:1) due to

biodegradation and % mineralization values for PLA bottles in CMR (o) and
MODA (O) systems .......................................................................

Figure 6.1. Monomer unit of Ecoflex .................................................

Figure 6.2. (a) Temperature (0), (b) %RH (c1) and (c) pH (A) of compost pile;
and (d) ambient maximum“) and minimum(c1) temperatures, (e) ambient
maximum(0) and minimum(c1) %RH and (f) solar radiation (A) as a function
of time for 60 day period ................................................................

Figure 6.3. Visual inspection of PBAT films in real composting conditions.

Figure 6.4. Pictorial representation of four samples of PBAT films on 60th day.
Samples B and C were more towards interior of the pile ............................

Figure 6.5. Visual inspection of PBAT + talc films in real composting
conditions ..................................................................................

Figure 6.6. Variation in molecular weight for PBAT films (O) and PBAT with

talc additive (:1) films in real composting conditions.
* 60”I day data point shows average of 3 points for PBAT films ...................

xiii

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CHAPTER 1 - INTRODUCTION

There has been a recent growth in adoption of biodegradable polymers for
packaging applications due to concerns of growth in municipal solid waste (MSW) and
the contribution of polymeric packaging waste in it. For example, in 2005 in United
States; 6.55 million tons of plastics packaging waste was generated, out of which 0.58
million tons was recovered through recycling [1]. The common recycled products were
carbonated beverage bottles, milk bottles and water bottles which has a good waste
collection infrastructure in many states in USA; due to the bottle bill first introduced in
Vermont in 1953. The rest of plastic packaging material went to landfill and could not be
recycled mainly because of the contamination caused due to the food and other biological
substances in it.

Also recently sustainable packaging systems has gained lot of attention and
according to Sustainable Packaging Coalition (USA); one of the criteria of definition of
sustainable packaging is that the “packaging should be sourced, manufactured,
transported and recycled using a renewable energy”. Currently many commercially
available biodegradable polymers like polylactide (PLA), polyhydroxybutyrate (PHB),
etc. come from renewable sources and the consumption of same for packaging
applications can go up due to the packaging sustainability initiatives. Chemical nature of
those renewable biodegradable polymeric materials are discussed in detail in the
literature review.

As those new biodegradable polymers are emerging for packaging applications, it
is necessary to address its biodegradability, and avail its unique functionality to reduce

the waste generation problem. Standards are developed by ASTM and ISO (International

 

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simulated controlled composting conditions. Those standards, their scope and comparison
are also discussed in detail in the literature review. It also become essential to study
various systems where those biodegradable polymeric packages could be successfully
biodegraded, hence commonly used composting processes and materials are discussed in
literature review.

As mentioned above, the standards provide guidelines for testing plastic materials
for biodegradability in simulated externally controlled composting conditions. There is a
need to develop a testing procedure which can test a complete biodegradable package and
report its biodegradability which can be useful and applied in successful
biodegradation/composting operations. At the same time, it is also necessary to address
the degradation performance of those packages in ambient conditions as opposed to
composting conditions (where microorganisms are involved). Chapter 3 and 4 discusses
one such procedure of testing biodegradable packages based on polylactide (PLA) in real
composting conditions and ambient conditions.

Although the simulated composting conditions are operated with externally
controlled parameters, but are difficult to resemble the real composting conditions due to
the variability’s associated with it. Those variability’s need to be investigated and proper
comparison report of biodegradation performance in both real and simulated composting
conditions is necessary. A PLA based bottle was used for this comparison and is
discussed in chapter 5.

Polymeric flexible packaging materials such as LDPE are used in variety of

packaging applications in food and consumer goods. At the end of its life cycle, those

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flexible packages end up in landfill as no known waste management initiatives are
deployed in this case. Also majority of flexible packaging materials are blend or
laminations used for property enhancement of package, hence recycling of those
packages becomes difficult due to its non-uniformity. Some biodegradable resins such as
Ecoflex® commercialized by BASF has desirable properties needed for some flexible
packaging applications. Biodegradability of such materials was carried out in real
composting conditions and discussed in detail in chapter 6.

Chapter 7 discusses the future recommendations derived based the results
obtained in this study.

In short, the main objectives of this study were:

1. To review and compare the current methodologies and standards associated with
biodegradable testing of plastic materials; and its scope in regards with the
packaging.

2. To develop a method of testing whole packages and polymeric films in real
composting conditions; which can give a correct representation of its
biodegradation performance.

3. To evaluate biodegradation of biodegradable polymeric package on basis of
existing standards and standards under development; and comparison of its results

with real composting conditions.

 

 

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REFERENCES

1. EPA. Municipal Solid Waste. 2005-Facts and Figures. 2005 [cited 04-10—2007];
Available fiom: http://www.epa.gov/garbage/pubs/mswcharOS .mf.

 

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CHAPTER TWO

Gaurav Kale, Thitisilp Kijchavengkul, Rafael Auras, Maria Rubino, Susan E. Selke, Sher
Paul Singh. (2006). An overview of compostability of bioplastic packaging materials;
Macromolecular Bioscience, 7 (3): 255-277

 

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CHAPTER 2 - LITERATURE REVIEW
SUMMARY

Annually, packaging waste accounts for 78.81 million tons (31.6% of the total
municipal solid waste, MSW) in 2003 in the USA, 56.3 million tons (25% of MSW) in
2005 in Europe, and 3.3 million tons in 2004 (10% of MSW) in Australia. Currently, in
the USA the dominant method of packaging waste disposal is landfill, followed by
recycling, incineration, and composting. Since landfill occupies valuable space and
results in generation of greenhouse gases and contaminants, recovery methods such as
reuse, recycling or composting are encouraged as a way of reducing packaging waste
disposal. Most of the common materials used in packaging (i.e., steel, aluminum, glass,
paper and paperboard, plastics and wood) can be efficiently recovered by recycling;
however, if packaging materials are soiled with foods or other biological substances,
physical recycling of these materials may be impractical. Therefore, composting of some
of these packaging materials is a promising way to reduce MSW. As biopolymers are
developed and increasingly used in applications such as food, pharmaceutical, and
consumer goods packaging, composting could become one of the prevailing methods for
disposal of packaging waste provided that industry, governments, and consumers
encourage and embrace this alternative.

The main objective of this article is to provide an overview of the current situation
of packaging compostability, to describe the main mechanisms that make a biopolymer
compostable, to delineate the main methods to compost these biomaterials, and to explain
the main standards for assessing compostability, and the current status of biomaterial

labeling.

 

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Biopolyrners such as poly(lactide) and poly(hydroxybutyrate) are increasingly becoming
available for use in food, medical and consumer goods packaging applications. The main
claims of these new biomaterials are that they are obtained from renewable resources and
that they can be biodegraded in biological environments such as soil and compost.
Although recycling could be energetically more favorable than composting for these
materials, it may not be practical due to excessive sorting and cleaning requirements.
Therefore, the main focus is to dispose them by composting. So far, there is no formal
agreement between companies, governments and consumers as to how this packaging
composting will take place; therefore, the main drivers for their use have been green
marketing and pseudo environmental consciousness related to high firel prices. Packaging
compostability could be an alternative for disposal of biobased materials as long as
society as a whole is willing to formally address the challenge to clearly understand the
cradle-to-grave life of a compostable package, and to include these new compostable

polymers in food, manure, or yard waste composting facilities.

2.1 INTRODUCTION

Packaging waste is a major contributor in generation of municipal solid waste
(MSW). In the USA, containers and packaging waste accounted for 74.81 million tons
(31.6% of the total MSW) in 2003 [1]; 56.3 million tons (25% of the total MSW)
generated in Europe [2] in 2005; and 3.3 million tons (10% of the total MSW) in
Australia [3] in 2004. Currently in the USA, the most dominant method of packaging
waste disposal is landfill, followed by recycling, incineration and composting. However,

landfilling results in generation of greenhouse gases and takes up or may contaminate

land that
compostir
materials
and used
can also
compostir
Cc
soil-like s
microorga
ailinOmyc
CO2. and 1
carbon, m;
and illITOgt
priOductit
[4i A Con;
3 Clll’lng p.
Oxygen is .
damages I
d0€g 001 S
nUIIICmS a.
been Come
0XSen; if

dlgeSIion l‘

land that could be used in the future. Hence, recovery methods like recycling or
composting could be more desirable ways of packaging waste disposal. The common
materials used in packaging are steel, aluminum, glass, paper and paperboard, plastics
and wood, all of which could be efficiently recovered through recycling. Paper and wood
can also be recovered through composting; biodegradable polymers also provide
composting as a waste disposal option.

Composting is a natural process by which organic material is decomposed into a
soil-like substance, called humus, a soil conditioner. Decomposition is mainly done by
microorganisms (mesophilic and thermophilic), including bacteria, fungi and
actinomycetes. These microorganisms use organic matter as their food source, generate
C02, and produce humus as an end product. This natural process requires availability of
carbon, nitrogen, water and oxygen. Microorganisms use carbon as a source of energy
and nitrogen for building cell structures. A 30:1 carbon to nitrogen ratio (CzN) is ideal for
reproduction of thermophilic microorganisms, and makes the composting process faster
[4]. A composting process goes through two main stages, an active composting stage and
a curing period. In the first stage, the temperature rises and remains elevated, provided
oxygen is available, resulting in strong microbial activity. In the later stage, temperature
decreases but the materials continue to compost, at a slower rate. The compost process
does not stop at a particular point; rather it continues slowly until the last remaining
nutrients are consumed by the remaining microorganisms and almost all the carbon has
been converted to carbon dioxide [5]. Aerobic composting takes place in the presence of
oxygen; if oxygen is absent then the process changes to anaerobic digestion. Anaerobic

digestion is also a naturally occurring process of decomposition and decay, by which

organic
digestat
gases. 1
carbon

applicat
conditit‘

microor

apphca

'4

separatc
tons of]
I€COVen

package

Iheaciic
IS a diff:
is a Dias.
CarbOn d
kHOWn C

ThEIEfQI-l

Placed an

hence it i

organic matter breaks down into simple chemical components, producing biogas and
digestate (a relatively stable soil residue similar to compost). Biogas is a mixture of
gases, mainly methane, which can be used for production of heat and electricity, and
carbon dioxide. The digestate can be used as a soil amendment, much like humus, for
applications like farming or landscaping. The quality of compost produced in aerobic
conditions is different from that produced in anaerobic digestion conditions, as different
microorganisms are active [5].

The majority of packaging materials used for food and medical packaging
applications are disposed by landfill, in part because of contaminants that are difficult to
separate and may produce complications in recycling. In 2003, in the USA, 11.9 million
tons of plastics packaging was generated, out of which only 1.06 million tons (8.9%) was
recovered through recycling. Composting provides a viable option for recovering waste
packages by retuming them to nature.

According to ASTM, a biodegradable plastic is a plastic which degrades due to
the action of naturally occurring microorganisms such as bacteria, fungi and algae. There
is a difference between a biodegradable and a compostable plastic. A compostable plastic
is a plastic that undergoes degradation by biological processes during composting to yield
carbon dioxide, water, inorganic compounds, and biomass at a rate consistent with other
known compostable materials and leaves no visually distinguishable or toxic residues.
Therefore all compostable plastics are biodegradable, but the reverse is not true.

Biodegradation of plastics depends on both the environment in which they are
placed and the chemical nature of the polymer. Biodegradation is an enzymatic reaction;

hence it is very specific to the chemical structures and bonds of the polymer. There are

di fibre:
in Will
molccu
througl
both er
structur
carbon:
hydroly
factors ‘-

C0Wi}ll

Organiz
enrironr
ACCOIdl]
disintegy
Stale cg
SpeClfiCa
Chaiacter
Character
hem)" m
procedurc

A

have been

different mechanisms 'of polymer biodegradation. One common mechanism is hydrolysis,
in which random non-enzymatic chain scission of ester groups leads to reduction in
molecular weight. The hydrolysis process is affected by the rate of diffusion of water
through the polymer. As mentioned before, the biodegradation of plastics depends on
both environmental factors (i.e., temperature, moisture, oxygen, pH) and the chemical
structure of the polymer. Biodegradable polymers usually contain ester, amide or
carbonate hydrolyzable bonds in the polymer backbone. The presence of these
hydrolyzable functional groups increases the susceptibility to biodegradation. Other
factors that affect biodegradability are crystallinity, molecular weight, and, in the case of
copolymers, the copolymer composition [6].

Standards have been developed by ASTM and ISO (International Standards
Organization) for assessment of the biodegradability of polymers in different
environments such as composting, anaerobic digestion, and wastewater treatment.
According to ASTM standard D6400 [7], a product is compostable if it passes the tests of
disintegration, biodegradation, and terrestrial and aquatic safety in controlled laboratory
scale composting. Similarly, there is a standard developed by ISO (EN 13432) [8]
specifically for packaging, which assesses packaging compostability based on
characterization, biodegradation, disintegration, and quality of compost or ecotoxicity.
Characterization of packaging includes analysis of the composition of package materials,
heavy metals, organic carbon content, total dry solids and volatile content. Detailed
procedures and their harmony with other standards are discussed later.

A number of certification systems which provide compostable packaging labels

have been established worldwide for certification of compostable plastics. Some of these

10

 

label:
Nom'
DIN l
E.\' l.‘
and C
K6952

Comm

as con
materia
Accord
million
be bette-
con'Ugat
390.000
piaSlle_
eliminah
C
especial]:
rec.VCling
Practice I”.
life CYCIQ

labels are based on standards developed by ASTM, ISO, DIN (Deutsches Institut fur
Nonnung) and JIS (Japanese Industrial Standards). These certification systems include
DIN CERTCO based on DIN V54900, OK Compost by AIB Vincotte (Begium) based on
EN 13432[8], Compostable by the US. Composting Council based on ASTM D6400 [7],
and GreenPla certification by the Biodegradable Plastics Society (Japan) based on JIS
K6953, to mention a few. JIS K6953 is reported by the Japanese Industrial Standards
Committee to be identical to ISO 14855 [9].

Currently, biodegradable bags that are certified by the US. Composting Council
as compostable are being used in San Francisco for transportation of compostable
materials to the composting facility and composted along with other materials [10].
According to the American Forest & Paper Association (AF &PA) in America, about 6.5
million tons of postconsumer paper and paper products are produced annually that may
be better suited for composting than recycling. This includes paper yard bags, waxed
corrugated containers, milk cartons, paper plates, cups, napkins, and towels. In 1999,
300,000 to 325,000 tons of postconsumer paper was composted [11]. In the case of
plastics, non-biodegradable plastics still dominate packaging applications and hence
eliminate the option of composting.

Compostable polymers are being promoted as environmentally beneficial,
especially if they can be derived from renewable resources and recovered through organic
recycling. To evaluate the environmental performance of biobased products, a standard
practice has been developed and presented in ASTM D7075 [12] and ISO 14000 using
life cycle assessment (LCA). LCA is a cradle-to-grave analysis tool developed for

assessment of the total environmental performance of a product (or process) and the

11

 

systeni
LCA 5
energy
from st
compar
process
compo:
the \al;

further

bioplast
compos
CFC 16 ar

disposal

2.2 (‘0)

Paper 'pa
Plastic 1
COmPOSl;
during C(
TherefOrE
Compostir

Not all bl(

system used for manufacturing, use and disposal (or recovery) of that product. Currently,
LCA studies of biobased polymers generally show reduced environmental impact and
energy use when compared to petroleum based polymers. For example, PLA derived
from starch utilizes 0 GJ/ton of feedstock energy and 53 GJ/ton of processing energy, as
compared to PET which utilizes 39 GJ/ton of feedstock energy and 38 GJ/ton of
processing energy [13]. Furthermore, if PLA is disposed through composting and the
compost is used in agriculture, significant emission and energy credits can accrue due to
the value of the compost in sustainable agriculture practices, which can improve even
further the sustainability of this biobased polymer.

The objective of this paper is to explore the current status of compostability of
bioplastic packaging based on compostability mechanisms, the current status of
composting, standards relevant to the compostability of packaging materials, and life
cycle analysis of the performance of biodegradable packages based on composting as a

disposal option.

2.2 COMPOSTABLE PACKAGES

Packaging materials, as previously mentioned, can be divided into 4 groups:
paper/paperboard, plastic, metal, and glass packages. Only paper/paperboard, and some
plastic packages are biodegradable and, hence, compostable. ASTM defines a
compostable plastic as a plastic that undergoes degradation by biological processes
during composting at a rate consistent with other known compostable materials [7] .
Therefore, only materials that biodegrade in composting environments and match the
composting period of known compostable materials can be considered as “compostable.”

Not all biodegradable materials are compostable [7] .

12

 

2.2.] C

and the
paper P
microor
because
a \‘arict
tremenc
material
both C35
Organic
mm 2 c;
h}dl01_\'5
the mar
mecham

Ofbiopl‘

S
bonds ar
SPECIfiC
Confonm

Con font];

2.2.1 COMPOSTABLE MATERIALS

There are two main factors that make a material compostable: the material itself
and the microorganisms in the compost. The material must be biodegradable, such as
paper/paperboard and biodegradable polymers, which can be consumed by
microorganisms as food sources. A compost pile is a great source of microbial activity,
because it has a high moisture content and temperature, so it is a suitable environment for
a variety of microbes, such as bacteria and fungi, to live and reproduce, providing a
tremendous amount and variety of organisms able to attack and digest compostable
materials. Bacteria can be either aerobic or anaerobic, while fungi are strictly aerobic. In
both cases, the degradative reaction proceeds via production of enzymes that break down
organic substrates providing nutrients [14]. The enzymatic mechanisms can be divided
into 2 categories: enzymatic oxidation (by aerobic microorganisms only), and enzymatic
hydrolysis (by either aerobic or anaerobic microbes). The biodegradation mechanisms of
the main packaging materials differ. Therefore, in this overview, the degradation
mechanisms are described by material, and it will mainly concentrate on the degradation

of bioplastics.

2.2.2 BIODEGRADABLE POLYMERS AND DEGRADATION MECHANISMS

Since biodegradation is an enzymatic reaction, it is very specific to chemical
bonds and structures of particular functional groups. Microorganisms can attack only
specific fimctional groups at specific sites, and the polymer chain also has to be
conforrnationally flexible enough to fit into the active site of the enzyme. The meaning of

conformational flexibility is defined later. There are various types of biodegradable

13

 

p01)“ll

IIBIUI'Z

IN)
[‘0
IQ

starch.
their a
The po
transfer
acceler.
molecu

IO enzyi

POM hyt
“‘Inicrcel
bur nutn'
PHAS an
and p01)
mECham-S
POIymCr

PsuedODm

polymers, with differing degradation mechanisms, so we will separately discuss them: (1)

natural polymers, (2) carbon chain polymers, and (3) hetero chain polymers [14].

2.2.2.1 Natural Polymers

As mentioned earlier, microorganisms can directly consume natural polymers like
starch, cellulose, and polymers based on starch, since enzymatic reactions can reduce
their molecular weight in extracellular environments - outside the microorganisms’ cells.
The polymer chains are enzymatically cleaved, and the portions that are small enough are
transferred into the cells and consumed. The biodegradation rate of these polymers can be
accelerated by hydrolysis involving random chain scission, which results in rapid
molecular weight reduction. The resulting smaller molecules are much more susceptible

to enzymatic attack, making the polymer degrade much faster.

Another type of natural polymer is “bacterial polyester”,
poly(hydroxyalkanoates), or PHA. These natural polyesters are produced by bacteria as
“intercellular reserve materials” when they are fed carbon sources such as sugar or lipids
but nutrients are restricted. The polymers are then extracted from the bacterial cells [14].
PHAs are aliphatic polyesters; the most common are poly(B-hydroxybutyrate) or PHB,
and poly(hydroxybutyrate-valerate) or PHBV, see Figure 2.1. The degradation
mechanism starts with rapid enzymatic hydrolysis to cleave the ester bonds present in the
polymer structure via extracellular depolyrnerases, such as those produced from

Psuedomonas lemoignei and Alcalignesfaecalis [15].

14

 

:9
[VJ
O

I Q

Chlorit
biodeg
becaus
fomis 1
groups

“eight

2.2.2.3 .

2.2.2.2 Carbon Chain Polymers

Vinyl polymers, such as poly(ethylene), poly(propylene), and poly(vinyl
chloride), with carbon-only backbones, are normally not susceptible to hydrolysis or to
biodegradation. An exception is poly(vinyl alcohol) or PVOH, which is biodegradable
because of its high hydrolizability. The enzymatic oxidation of hydroxyl groups (-OH)
forms carbonyl groups (C=O) in the polymer backbone, and hydrolysis of two carbonyl
groups (~CO-CH2-CO-) causes polymer chain cleavage leading to a decrease in molecular

weight [14, 16]. Microbes will then consume those low molecular weight portions.

2.2.2.3 Hetero Chain Polymers

Hetero chain polymers are polymers that have atoms other than carbon, such as
oxygen and nitrogen, in their backbones. Those atoms make the polymers susceptible to
hydrolysis (i.e., in which random non-enzymatic chain scission of ester groups leads to
reduction in molecular weight), and therefore can make them susceptible to
biodegradation. Most synthetic hetero chain polymers, such as polyesters, nylons,

polycarbonates, etc., do not biodegrade to any significant extent.

Currently, the most common hetero chain biodegradable polymers are
poly(lactide) (PLA), poly(glycolic acid) (PGA), and poly(e—caprolactone) (PCL). The
bacterial polyesters such as Polyhydroxyalkanoate (PHA) also fit in this category. The
higher the rate of hydrolysis is, the more available sites there are for microbes to attack,
and hence the faster is the biodegradation. Polymer hydrolysis is controlled in part by the

rate of diffusion of water in the amorphous regions of the polymer [6]. Water diffiision

15

 

chloric
biodeg
becaus
fomis 1
groups

Weight

2.2.2.3

OXYgen
hydro];-
YEductio
biodegrz

pOII'Carh

p01” lacr
baciBria]
higher m

and hence

rare ofdi]

2.2.2.2 Carbon Chain Polymers

Vinyl polymers, such as poly(ethylene), poly(propylene), and poly(vinyl
chloride), with carbon-only backbones, are normally not susceptible to hydrolysis or to
biodegradation. An exception is poly(vinyl alcohol) or PVOH, which is biodegradable
because of its high hydrolizability. The enzymatic oxidation of hydroxyl groups (~OH)
forms carbonyl groups (C=O) in the polymer backbone, and hydrolysis of two carbonyl
groups (~CO-CH2-CO-) causes polymer chain cleavage leading to a decrease in molecular

weight [14, 16]. Microbes will then consume those low molecular weight portions.

2.2.2.3 Hetero Chain Polymers

Hetero chain polymers are polymers that have atoms other than carbon, such as
oxygen and nitrogen, in their backbones. Those atoms make the polymers susceptible to
hydrolysis (i.e., in which random non-enzymatic chain scission of ester groups leads to
reduction in molecular weight), and therefore can make them susceptible to
biodegradation. Most synthetic hetero chain polymers, such as polyesters, nylons,

polycarbonates, etc., do not biodegrade to any significant extent.

Currently, the most common hetero chain biodegradable polymers are
poly(lactide) (PLA), poly(glycolic acid) (PGA), and poly(e-caprolactone) (PCL). The
bacterial polyesters such as Polyhydroxyalkanoate (PHA) also fit in this category. The
higher the rate of hydrolysis is, the more available sites there are for microbes to attack,
and hence the faster is the biodegradation. Polymer hydrolysis is controlled in part by the

rate of diffusion of water in the amorphous regions of the polymer [6]. Water diffusion

15

 

 

throu g

\tithou

apphca
Figure

polytbu
polyestt
commo;
provide;
are con:
Pmpertit
and p0]:
baCkbon
carbondt
function.
blOdegm
1].)leth

easjh- an

T
On Iheir
applicant

releasing

through crystalline regions is negligible. Some plastics, such as PLA, will not biodegrade

without prior hydrolysis.

The biodegradable polymers that have a promising future for packaging
applications are mainly aliphatic polyesters, such as PLA, PCL, and PHA [14, 15] (see
Figure 2.1), and also include poly(tetramethylene adipate/terephthalate) (PTMAT),
poly(butylene succinate) (PBS), poly(butylene succinate adipate) (PBSA), and some
polyesteramides, since their properties are comparable to petroleum-based polymers
commonly used in the packaging industry. For example, PHBV is hydrophobic and also
provides excellent gas barrier [14, 15]. Temperature stability and processability of PLA
are comparable to those of poly(styrene); oil and grease resistance and flavor barrier
properties are comparable to PET; and sealing temperature is lower than poly(ethylene)
and poly(propylene) [17, 18]. Almost all of these polymers contain in the polymer
backbone at least one of the following hydrolyzable bonds: ether, ester, amide or
carbonate [6]. While C-C linkages increase stability, the presence of hydrolyzable
functional groups in the polymer backbone dramatically increases the susceptibility to
biodegradation [19] (see Figure 2.2), since it not only increases the vulnerable sites for
hydrolysis but also the polymer flexibility [20], so that the polymer chains can more

easily arrange themselves to fit into the active sites of the enzymes.

The performance of hydrolyzable biodegradable polymers is primarily dependent
on their erosion mechanisms, especially if they are intended for use in medical
applications, such as drug delivery agents, or in agricultural applications, such as nutrient

releasing agents in fertilizer [6].

l6

 

Figure.

Figure;

degmdatio
hi'drolysjs
the amOrph
and Compet
degradanOn'
eIOSIOn“ [6,
“SurfaCe Eros

role in determ

a drilg dell-VG

O

-Fsfii

CH3 n

Poly(lactide)
i’
‘ED—CHZ‘CHz‘CHz-Cl'lz‘CHz—C

n
Poly(caprolactone), PCL

Il
irsWWrE—

R n
Poly(hydroxyalkanoates), PHA
PHB: R= -CH 3

PHV: R= -CH 20H 3

Figure 2.1 Structures of poly(lactide), poly(caprolactone), and poly(hydroxyalkanoates)

0
II R—U—N—R' fl
R-O-R' R—C—O—R' H R-O—C—O-R’
Ether Ester Amide Carbonate

Figure 2.2 Hydrolyzable functional group commonly found in biodegradable polymers

There are two modes of erosion: surface erosion and bulk erosion. Enzymatic
degradation caused by microbes occurs only at the polymer surface, while non-enzymatic
hydrolysis can occur throughout the polymer’s bulk because water can diffuse through
the amorphous regions of the polymer. Both reactions usually happen at the same time,
and compete with each other. If water-induced hydrolysis is faster than the enzymatic
degradation, then the polymer tends to degrade throughout its cross section, in “bulk
erosion” [6, 17, 21]. On the other hand, if the enzymatic degradation is faster, then
“surface erosion” predominates [6, 17]. These erosion mechanisms play a very important

role in determining the applications of a biopolymer. For instance, if a polymer is used as

a drug delivery agent and the active ingredient is located in the polymer surface,

17

 

pOI)'l
other
suital

longc

2.2.3

condit

2.2.3.1

"trier

Water is
plentiful
Second, 1
in moistt
Chain scis
Kai-Lai e1
humidity C
weight 1033
chamber a,
Ihcrefm,’ ll

tannin/”mmS

polymers that mostly undergo surface erosion will release the compound faster; on the
other hand for a slow release drug, a polymer that undergoes bulk erosion will be more
suitable so the active ingredient contained in the polymer matrix can be released over a

longer period of time [6].

2.2.3 FACTORS AFFECTING THE RATE OF BIODEGRADATION

Factors affecting biodegradation rates can be categorized as: (l) the exposure

conditions, and (2) the polymer itself [20].

2.2.3.1 Exposure conditions

Water or moisture

Water or moisture can affect the biodegradation of polymers in two ways. First,
water is needed for microorganisms to grow and reproduce. Therefore, when moisture is
plentiful, there should be more microbial activity, and polymers should degrade faster.
Second, since hydrolysis plays a fundamental role in biodegradation for some polymers,
in moisture-rich environments hydrolysis reactions should increase, producing more
chain scission reactions and increasing the available sites for microorganisms to attack.
Kai-Lai et al [22] found that degradation rates increased tremendously as the relative
humidity of the exposure conditions increased. They determined that the molecular
weight loss of PLA films exposed to 10%, 50%, and 100% RH in an environmental
chamber at 55°C was 3,972, 61,947, and 121,836 Daltons per week, respectively.
Therefore, it can be expected that polymers will biodegrade faster in moisture-rich

environments than in dry conditions.

18

 

pH

pll.si
the h)
acidic
lachc
aflect

Tempe

boutlr

h0\\'€\’(

For hydrolyzable polymers, the rate of hydrolysis reactions can also be altered by
pH, since reactions can be either acid or base catalyzed. For instance, it was found that
the hydrolysis rate of PLA capsules was slowest at a pH of 5.0 and increased in more
acidic and more alkaline solutions [17, 21]. Degradation products, such as water-soluble
lactic acid from PLA, can change the pH of the exposure environment. Changes in pH
affect not only the rate of hydrolysis, but also the growth of microorganisms.

Temperature

Temperature is a significant factor in controlling polymer biodegradation since
both hydrolysis reaction rates and microbial activity increase as temperature increases;
however, if temperatures are too high, microbial activity decreases or even stops. Kai-Lai
et al [22, 23] reported that the average degradation rate of PLA films at 25, 40, and 55°C
and 100% RH in an environmental chamber was 4,691, 40,634, and 91,892 Daltons per
week, respectively. Therefore, moderately increasing the exposure temperatures
enhances the degradation rate of PLA, at least in part due to increasing the rate of
hydrolysis. A study done by Cargill Dow LLC also showed that the hydrolysis rate of
PLA increased dramatically above the glass transition temperature (T3) [21]. Further,
different microorganisms can grow and reproduce at their best at different temperatures.
In general, the rate of biodegradation increases with temperature, as long as it is not high

enough to kill the microorganisms.

19

.4 en

from ‘
releas
ifa hi.
ai'ailat
metabc
anaerol
and rel.
carbon
aerobic
eXample
10 biodel

ASTM D
5713} 7119

Di
more ab 16
‘fipflglllu.
demed fit
"10aners

depoii‘men',

Aerobic or anaerobic conditions

In aerobic biodegradation, the microorganisms use oxygen and consume carbon
from the polymer as a food source; as a result carbon dioxide and water are produced and
released. This corresponds to enzymatic biological oxidation. This reaction predominates
if a high oxygen concentration (not less than 6%, as described in ASTM D 5338 [24]) is
available. If the oxygen supply is depleted, aerobic microorganisms will change their
metabolism rate, causing a reduction of the biodegradation rate. On the other hand, in
anaerobic biodegradation, anaerobic microorganisms consume carbon from the polymer
and release methane and carbon dioxide. Each kind of microorganism may consume
carbon from polymers at a different pace; therefore, biodegradation of polymers in
aerobic conditions may be totally different than that in anaerobic conditions. For
example, as reported by Gartiser et a1 [25], PCL did not biodegrade, and PLA was found
to biodegrade at a minor level (less than 10%) under anaerobic conditions based on

ASTM D 5511 [26] and ISO 14853 [27] test methods.

Enzyme specific

Different enzymes may have differently shaped active sites and therefore are
more able to biodegrade certain polymers. For example, the fungi Aspergillus niger and
Aspergillus flavus produce enzymes that more readily degrade aliphatic polyesters
derived from diacid monomers with 6-12 carbon atoms than those derived from other
monomers [14]. It was found that extracellular PHB depolymerases - enzymes that

depolymerize PHB - degrade PHB by different mechanisms depending on the specific

20

bacteria

specific
2.2.3.2 l

Polt'mt

I
much en
closer to
flexible,
easily fit
rate. T“
gIOUpS th;

Sit
P013] glycc
because [h
Inhibits Ch;

ihe pOIETTie:

Doubt

adjaCem Sing}

bacteria producing those enzymes [15]. Therefore, different microorganisms consume

specific polymers at different rates.

2.2.3.2 Polymer factors

Polymer structure and chain flexibility

The “flexibility” (conformational flexibility) of a polymer chain indicates how
much energy it takes to rotate molecules around bonds and how easy it is to move atoms
closer to or further away from others. If a polymer chain is more conforrnationally
flexible, more sites will be accessible to water for hydrolysis, and the polymer will more
easily fit into the active sites of enzymes; both of these will increase the biodegradation
rate. Two factors that affect the polymer’s conformational flexibility are bulky side

groups that limit chain movement and certain types of linkages in the polymer backbone.

Side groups increase the energy required for chain rotation. For example,
poly(glycolic acid), Figure 2.3 (left), degrades faster than poly(lactide), Figure 2.3 (right),
because the poly(lactide) chain is less flexible due to the methyl (-CH3) side group that
inhibits chain movement [20]. The methyl side group reduces the water accessibility of

the polymer chain as well as the biodegradation rate.

(,3 i3
“EC-CH2“ 3L {O-CH-C
n c

H3n

Figure 2.3 (Left) Poly(Glycolic acid), (Right) Poly(Lactide)

Double bonds in the backbone increase flexibility by easing rotation around

adjacent single bonds, as illustrated by the fact that the rotational barrier (energy required

21

for rota
only 2.
llexibili
2.7 kcal
chain rc
polyleth

ent'ironr

Cljl'SfrIl

Water dil
diffuse th
amOrphOL
CD'SIallint
erosion d
biodegrad;
pollmer cf
different C'
effeCi 0n ll.
degrade mu

laCilde) m0]

for rotation around the bond) of CH3-CH3 is 3.0 kcal/mol while that of CH2=CH-CH3 is
only 2.1 kcal/mol. The presence in the backbone of oxygen or nitrogen also increases
flexibility by lowering the rotation energy barrier; CH3-OCH3 has a rotational barrier of
2.7 kcal/mol. A ring structure, on the other hand, decreases flexibility because it hinders
chain rotation[20]. For example, the aromatic ring structure that provides rigidity for
poly(ethylene terephthalate) (PET) hinders water and enzyme access, making PET more

environmental stable than aliphatic polyesters.

Crystallinity

As mentioned earlier, hydrolytic reactions are controlled in part by the rate of
water diffusion into the polymer bulk in the amorphous regions, since water cannot
diffirse through crystalline regions and amorphous regions are more flexible. Therefore,
amorphous regions are more susceptible to both hydrolysis and biodegradation than
crystalline regions [6]. For polymers like PHB, biodegradation occurs mainly via surface
erosion due to enzymatic hydrolysis, and the main factors that control the rate of
biodegradation were found to be the degree of crystallinity [15] and accessibility of the
polymer chain to microorganisms. PLA with different degrees of crystallinity, due to
different contents of L-lactide and D-lactide, has different degradation rates, due to the
effect on the rate of hydrolysis [17, 28]. PLA polymers with higher contents of D-lactide
degrade much faster since D-lactide induces twists in the otherwise very regular poly(L-

lactide) molecular architecture, reducing crystallinity.

22

lilo/ecu.

G
high (e. g
their entr
molecular
metaboliti
attack the
the natura
outside th.
by microc
molecules
or pholodc
differs by

20~0U0 D3]

Tht‘
ways, As
Wilmer g]
has a lcngc
order to re,

“fight bIOd

Molecular weight

Generally, plastics are immune to microbial attack if their molecular weights are
high (e.g., for PLA, MW 220,000 Daltons) because their molecules are too large to allow
their entrance into the microorganisms’ cells. Microorganisms can degrade only low
molecular weight portions, which are taken into the cells and then converted into
metabolites [14]. For natural polymers, such as starch and cellulose, microorganisms can
attack the molecules directly since they can produce enzymes to cleave, or depolymerize,
the natural polymer backbones, and consequently molecular weight reduction can happen
outside the microbial cells [14]. For other biodegradable polymers, before being utilized
by microorganisms, the molecular weights have to be reduced to a point at which the
molecules can enter the microbial cells by other means of degradation, such as hydrolysis
or photodegradation. The upper limit of molecular weight that microbes can metabolize
differs by polymer; for example, a critical molecular weight (Mw) for PLA is 10,000-

20,000 Daltons [17, 21], and for PHB is approximately 13,000 Daltons [14].

The molecular weight of a polymer affects the biodegradation rate in two different
ways. As the molecular weight increases, the polymer’s Tg also increases, making the
polymer glassier and less flexible. Furthermore, a higher molecular weight polymer also
has a longer chain length, which means that there are more bonds that must be cleaved in
order to release the water soluble oligomers or monomers that are small enough to be
consumed by microorganisms [6]. Consequently, a polymer with a higher molecular

weight biodegrades more slowly than the same polymer with a lower molecular weight.

23

C opal ‘

polymer
increase
[6]. If
increase
groups I
cOpoljm
C hiel l ini
found to

mineraliz.

SIZE and

Th
biodegradt
lower Ones
With moist
ASTM [ 7]

(lilting bled.

materials Sucl

called compo

Copolymer composition

Introducing comonomers into a polymer structure will increase irregularity of the
polymer chains, which generally will reduce the polymer’s crystallinity and thus may
increase biodegradability. However, the effect also depends on the type of comonomer
[6]. If the comonomer contains hydrolyzable groups, the biodegradability should be
increased. On the other hand, if the comonomer contains aromatic structures, or other
groups that provide rigidity to the polymer chain, and no hydrolyzable groups, the
copolymer will generally have lower biodegradability or may not even biodegrade at all.
Chiellini and Corti [29] reported that graft copolymerization of lignin with PCL was
found to increase the biodegradability from 10% mineralization with pure lignin to 60%

mineralization during a 100 day incubation period in mature compost at 5 5°C.

Size and Shape

The size and shape of the exposed polymer also play an important role in
biodegradation. Polymers with higher surface areas will degrade faster than those with
lower ones, other factors being equal, since a larger fraction of the polymer is in contact
with moisture and microorganisms for hydrolysis and enzymatic degradation. Both
ASTM [7] and ISO [9] standards for biodegradability require control of size and shape

during biodegradation testing.

2.3 COMPOSTING

Composting is a biological process in which microorganisms convert organic
materials such as manure, sludge, leaves, paper and food waste into a soil-like substance

called compost. Composting is an aerobic process (in the presence of oxygen) as

24

discuss
mechar
compo:

compos
2.3.] \\

2.3.l.l ‘

mainten;
Clippings
IO nitrogt
shrub rm
C0mposte
and mam]
generated
In

Sites. Pub]
their ,V'ard i
lip Yard flit
be COmPOSl
Envimnmer
c0mpOSiing

In Ca

Willi [82 faC

discussed earlier. Compost can be produced by commercial techniques involving turning
mechanisms, sorting and shredding on a large scale; and also in small scale backyard
composting. Commercial composting is typically a much faster process than backyard

composting, as it is managed more intensively and optimal conditions are maintained.

2.3.1 WASTE MATERIALS

2.3.1.1 Yard waste

Yard waste can be defined as the vegetative waste resulting from the care and
maintenance of landscaped areas, lawns and gardens. It may include leaves, grass
clippings, garden wastes, tree trunks and prunings from trees or shrubs. The C:N (carbon
to nitrogen) ratio of yard waste ranges from 9 to 80 (grass clippings 9-25, leaves 40-80,
shrub trimmings about 53, tree trimmings about 16) [5]. Sometimes, yard wastes are
composted in passive piles (a method of composting in which there is little management
and manipulation of the materials after they are mixed and piled). Yard waste is mostly
generated from municipalities and landscapers.

In the USA, yard waste is commonly collected at curbside or via public drop-off
sites. Public drop-off sites are specified locations where residents and businesses can take
their yard trimmings. In curbside collection, the municipality or concerned agency picks
up yard trimmings that residents have placed outside of their homes [30]. Yard waste can
be composted in either Commercial composting facilities or by backyard composting.
Environmental Protection Agency (EPA) of United States estimates that 3,800 yard waste
composting facilities were in operation in 2000 in USA [31].

In Canada, leaf and yard trimmings are the most common materials composted,

with 182 facilities in operation. Collection methods range from drop-off by private

25

haulei

the va

includ
rec-yell
metric

organii

and 6V1
New 2
compos

about 6

PFOduci
million
due to

mUnlCir
2.3.1.2 1

re“Ilene
Cafelel‘ia
ranges fr

Of [God I

haulers and residents (135 facilities) to curbside residential programs (77 facilities, with
the vast majority being either source-separated or wet-dry programs) [32].

In 2003 in Europe, 1800 composting plants were in operation, 40% of which only
included yard waste [33]. Victoria, Australia has contracts with composting companies to
recycle green organic materials from yards and gardens with a capacity of over 100,000
metric tons per year. New South Wales diverts over 300,000 metric tons per year of
organic materials with an estimate of 800,000 metric tons still to be diverted [34].

New Zealand has undertaken a zero waste initiative with the goal of minimizing
and eventually eliminating waste. There are growing numbers of composting facilities in
New Zealand, and in 1999 approximately 23,000 cubic meters of material was
composted. In Christchurch, New Zealand, 70% of households recycle each week and
about 60% compost at home or take green waste to the council’s composting plant [34].

According to the Japan Organics Recycling Association (J ORA) the annual
production of wood residuals such as bark, sawdust and wood chips was about 5.34
million tons in 2001; about 95% of these residuals were utilized effectively. Yard waste
due to pruning trees or trimming grass represented 6% (2.47 million tons) of total

municipal solid waste in 2001 [35].

2.3.1.2 Food waste

Food wastes mostly consist of uneaten food and food preparation wastes from
residences, commercial establishments like restaurants, institutional sources like school
cafeterias, and industrial sources like factory lunchrooms. The C:N ratio of food wastes
ranges from 14 to 80 (garbage food waste 14-16, and refuse 34-80) [5]. The main source

of food waste is usually garbage and refuse (mixed food and packaging) that results from

26

mixed
will cc
sorting
comes
out. int
generat
noncon
prepara

homes (

nomiall}
Waste is
quantitie

cOmPOSt:

mixed MSW. MSW is extremely heterogeneous in size, moisture and nutrient content and
will contain varying degrees of non-compostable and possibly hazardous wastes. Hence,
sorting of MSW, using mechanical or manual techniques, plays an important role when it
comes to composting of food waste. While some composting of mixed MSW is carried
out, increasingly composting of food waste is dependent on source separation — the waste
generator separating food (perhaps along with other compostable wastes) from
noncompostables. The food wastes may be pro—consumer, such as food processing or
preparation wastes from institutional or industrial sources, or post-consumer, wastes from
homes or from restaurant or institutional meals [36].

Food waste has a high moisture content and little physical structure; hence
normally it is mixed with a bulking agent such as yard waste for composting. Also, food
waste is very susceptible to odor production (ammonia) and tends to generate large
quantities of leachate. Hence, normally a well aerated pile is recommended for
composting food scraps [36].

In 2005, in the USA there were16 mixed MSW composting facilities in operation
and 11 more that compost residential source separated food wastes were in operation [3 7,
38]. In Canada, there are 54 facilities composting food residues from the residential
sector [32]. Around 39% of the total 200 million tons MSW generated in Europe in 2000
was food scraps or food waste [33]. In Australia, food residuals comprise up to 41% of
the domestic waste stream and 17% of the commercial/industrial stream. A food residuals
processing facility was set up in the Melbourne metropolitan area that composts food
scraps. EcoRecycle Victoria provided almost $1.2 million to support infrastructure

development for green organics and food residuals collection and processing [34]. JORA

27

has e
Minis
dema
2001

landti

2.3.l.£

may cc
classifi
normal}
and or r
the amp
material;
Commer
home‘bac
In 1998.
COmPOStir
Productioi
29 million
“’35 reg-Ck.

”76 total am

3003,

has estimated an annual production of food residuals based on the supply basis by the
Ministry of Agriculture, Forestry and Fisheries and food intake calculated on nutrition
demand basis on the Ministry of Health and Welfare which was 18 million tons in June
2001 out of which only 0.1 percent was used for composting and majority was either

landfilled or incinerated [35].

2.3.1.3 Manure waste

Manure is the fecal and urinary excretion of livestock and poultry. Manure waste
may contain bedding, spilled feed, water, and soil as well as livestock excreta. It can be
classified as liquid, semi-solid, slurry or solid. Manure waste used in composting
normally involves broiler litter, cattle manure, horse manure, laying hens, sheep, swine
and/or turkey litter or a combination of these. The C:N ratio ranges from 3 to 56. Most of
the animal manures are rich in nitrogen content and hence are normally mixed with
materials with higher carbon content to achieve an optimized C:N ratio for composting.
Commercial composting is a more suitable way for handling manure waste than
home/backyard composting [5]. In Canada, 39 facilities compost manure or animal waste.
In 1998, finished compost production was around 845,400 tonnes, which included
composting of manure waste, food waste and yard waste [32]. In Japan, annual
production of animal waste was around 94 million tonnes: 65 million tonnes of feces and
29 million tonnes of urine. According to JORA, in 2001 94% of total animal excretion
was recycled to farmland and grassland after drying or composting [35]. Table 2.1 shows
the total amount of yard and food waste generated and composted in the USA. during

2003.

28

 

and pap.
cannot b
of the P3.
l5 normal
Paperboai
Li}

have stan
ComPOStin
COmPOSIah
et1$ier {0”
the MaSsat
COmllosting
“ya-Rid Card
Recl'Cling ,\
commerciaj
major gen era

Stare generati

Table 2.1 Food and yard waste generated during 2003 in the USA

 

 

Waste Generated Composted
Food, million tons 25.1 0.7
Yard, million tons 26 14.6

Total 51.1 15.3

 

2.3.1.4 Packaging waste

Packaging waste is generated due to disposal of packaging materials such as paper
and paperboard, plastics, steel, aluminum, glass and wood. Steel, aluminum and glass
cannot be composted and must be separated prior to composting. A substantial amount
of the paper and plastics in MSW come from packaging of food and consumer goods and
is normally recycled, landfilled, or incinerated. In the USA, in 2003, 56.4% of paper and
paperboard packaging was recycled while only 9% of plastics packaging was recycled.

Upon introduction and certification of compostable plastics, composting plants
have started accepting compostable liner bags. For example in San Francisco, the
composting facility accepts “compostable liner bags” containing food scraps. The
compostable liner bags (commercially available and produced from corn starch) make it
easier for residents to separate food scraps for compost collection [39]. In Massachusetts,
the Massachusetts Department of Environmental Protection (MADEP) is encouraging
composting of items such as spoiled fruits and vegetables, floral and deli wastes, and
waxed cardboard from supermarkets through the Massachusetts Supermarket Organics
Recycling Network. The main goal of this program is to divert to compost facilities the
commercial food waste generated by supermarkets. MADEP identified supermarkets as a
major generator of waste organics. They estimated that there are 400 supermarkets in the

state generating around 90,600 tons of organics per year. Compostable liner bags that

29

biodegrade quickly and safely are being used in this program to transport the materials
from collection containers to the commercial composting facility [40, 41]. Some
commercial compostable bag brands are Bio-Bag (Canada), Cereplast (CA, USA) and
EcoFilm and EcoWorks by Cortec Corporation (MN, USA).

Currently, researchers are demonstrating that compostable packages can be
composted in facilities handling yard waste and manure as well as in those handling food
wastes. Therefore, more options to compost biopolymers could be available if
compostable biopolymers used in packaging applications were accepted by these compost
facilities. Figures 2.4 and 5 show the degradation of PLA bottles and EcoflexTM films
under compost conditions (58°C, 60%RH) after 30 days and 60 days, respectively [42-

45].

 

Figure 2.4. Pictorial view of PLA bottles exposed at 30 day of compost conditions

30

 

th

St:
f0:
Ste
pm

me

big
llle
for

and

 

Figure 2.5. Pictorial view of Ecoflex films exposed at 60 day of compost conditions.

As market incentives are created for green and environmental friendly polymers,
there is also interest in developing new compostable materials from petroleum resources
[46]. As previously defined, a compostable material must completely biodegrade under
standard compost conditions. Currently, some manufacturers are claiming compostability
for polyolefin plastics containing additive technologies that are reported to work in a two-
step process that accelerates oxidation and then biodegrades. The manufacturers claim the
prodegradant additives control these processes in a highly predictable and manageable
manner in all conditions with a source of oxygen and naturally occurring microorganisms
(air, soil, landfill, compost, litter). The process is commonly referred to as “oxo-
biodegradation”. The main market for these polymers is biodegradable mulch film, but
these need'to be collected after the harvesting season if composting is the intended option
for their disposal. According to manufacturers, these polymers are engineered to degrade

and totally fragment in 90 to 120 days. After that they will 60% mineralize/biodegrade in

31

a further 12 to 24 months when disposed of in a commercial compost facility and in
subsequent soil application [46]. Figure 2.6 shows commercially available LDPE film
with the oxo-biodegradation additive exposed to composting conditions for 60 days at
48°C i 5°C and 52 d: 16% RH. After 60 days in the compost pile, no visual fragmentation

was observed. Therefore, further study of these polymers is necessary to determine

whether the compostability claims can be substantiated.

 

Figure 2.6. Pictorial view of LDPE with oxo-additive exposed at 60 day of compost

conditions (48°C:t:5°C, 52i16%RH).

32

 

2.3.2 l

genera
compo

paramc

mixing
materia
Sorting
0Plional
tree stur
(rotary c
mixing S
or Vegge]
bucket lc
F:
initial mi.
fOITned it
loaders p
plletwindr
ingredientf

Step by de3

2.3.2 COMPOSTING TECHNIQUES

2.3.2.1 Commercial Composting

Commercial or municipal composting is a large scale composting operation which
generally employs turning and active aeration, except static pile and some in-vessel
composting systems. Since waste materials have different characteristics, operational
parameters such as moving, mixing and manipulation differ.

Composting begins with collection of suitable organic materials, followed by
mixing to achieve the desired C:N ratio, moisture content and pore space. Usually one
material is primary and then one or more amendments are added [5]. Raw material
sorting is essential, especially if it is a mixed waste stream. Shredding or grinding is
optionally employed if the raw materials include newspaper, corrugated cardboard, brush,
tree stumps or other large yard wastes. Grinding or shredding may use shear shredders
(rotary or belt), hammer mills or tub grinders [5]. In some of the in—vessel methods, the
mixing step is built into the system. The material needs to be loaded into the silo, hopper
or vessel using conventional materials handling equipment such as conveyors, angers or
bucket loaders. Subsequent turning mixes the materials more thoroughly.

Frequent turning improves consistency and diminishes the importance of the
initial mixing in windrow systems, relative to a static-pile system, where organic waste is
formed into rows of long piles and aerated by turning the pile periodically. Bucket
loaders play a very versatile role in composting operations by allowing mixing and
pile/windrow formations. Mixing can be simply done by repeatedly bucketing the
ingredients together. Windrows and passive piles can be mixed and formed in a single

step by depositing the raw materials on the composting site in layers, forming a crude

33

pile. The loaders then mix the materials together and work them into the desired shape

until the materials are well mixed. Other equipment used in mixing includes batch mixers

in which amendments are placed in the mixer and then the manure added on top. The

rrrixture can be discharged through the side delivery elevator directly into the windrow, or

onto an aerated pile as the mixer is pulled forward parallel to the air distribution pipe.

After the active composting phase, compost requires a curing period of at least

one month to finish the process and allow the compost to develop the desired

characteristics for its intended use.

i l‘l‘ll‘tll ‘ '
Pile Formation

Grinding or Sorting
Shredding (Optional)

Amendments

Aeration, Turning,
Monitoring, Odor
Control

Active Composting Curing

 

Landscaping
Turf grasses
Soil nutrient
Soil amendment
Reducing erosion
End use

I

Compost Storage Screening or Shredding

 

Figure 2.7 Commercial composting system and operations

34

 

shapt
quali
tromr

auger

typica

2.3.2.2

Canada
level 1,
States 0

sorting

San Fm
COHsists

SOUI'Ce 5'
diversion
ColleCIIOr
consumer:
EUIOpe, C(

or Separatc

After curing, screening of compost separates materials of different sizes and/or
shapes. Screening is nearly always performed after curing either to improve compost
quality or recover bulking agents. Different type of screens are available, including
trommel screens, shaker screens, vibrating screens, flexing belt screens, disc screens,
auger and trough screens and rotary (spinning disc) screens [5].

Drying follows after screening to lower the moisture content of the compost. It
typically involves extra aeration or an extended composting period.

Figure 2.7 shows a flowchart of a complete commercial composting process.

2.3.2.2 Advances in composting techniques

Currently source separated composting has gained lot of attention in USA,
Canada and Europe in which the waste is separated by the consumers at the residential
level. In the USA, 11 residential source separated composting projects were active in the
states of California, Michigan, Minnesota and Washington in 2003 [38]. The residential
sorting and collection methods differ based on the composting facility; for example in
San Francisco, CA, residential 3 source separation cart collection is employed which
consists of organics, single stream recyclables, and trash [38]. Similarly in Canada,
source separating MSW into wet and dry streams is a popular way to achieve waste
diversion objectives, as it offers great flexibility in classification of waste streams,
collection methods, collection frequency and waste processing. About 98% of the
consumers in Guelph, Canada, participate in the wet-dry 2 stream program [47]. In
Europe, composting of mixed MSW is becoming rare due to growing recognition of the
benefits of source separated MSW composting. In 1998, around 85% of home composted

or separately collected MSW was being recovered in Austria, Belgium, Denmark,

35

 

Germ;
policic

rates [1

tjpical
the ore
inapprc
from tl‘
at diffe
as the l
IlerUgh
[0 an a]
Sorting:
knll‘es 1
Water is
Aeration
The V655
II is SCTeg
g
Separaijo
Waste mt
malen‘ajs

Cflmed 0U

Germany and Netherlands [48]. Those five nations have finalized their organic waste
policies based on source separated MSW diversion and have achieved better recovery
rates [48].

In the case of mixed MSW, sorting is necessary. Goldstein [38] explained a
typical composting process for a mixed MSW stream. Initially MSW is sorted to remove
the oversized items and then passed by conveyor through a manual sorting step to remove
inappropriate materials for composting. A bag breaker machine is used to remove wastes
from the bags. This automated system consists of different diameter drums which rotate
at different speeds. They are equipped with hooks which grab the bags and elongate them
as the drums spin to spill out the contents from the bags. Next the waste is screened
through a debris (disk) roll screen. The waste material obtained through the screen goes
to an anger mixer, and the remaining material on the screen is moved to an optional
sorting station where more recyclables can be removed. The mixer auger is equipped with
knives which help in reducing the particle size without shredding or grinding. Later,
water is added to the mixture in vessels to improve the moisture content. The vessels’
aeration system is designed to minimize evaporation and maintain temperature levels.
The vessels are later unloaded to form the aerated static piles. After the compost is ready,
it is screened to remove any foreign materials contained in the final product.

Savage et al [52] provide an overview of screening and introduction to air
separation based on material density. Air separation uses an air current to classify the
waste materials; a typical air classification system consists of introduction of MSW
materials through a chute into an upward flowing stream of air. The lighter materials are

carried out with the air and the heavier materials fall onto a conveyor or into a bin. The

36

 

lighter
functio

separat

temper:

compos

power :

mechan

trapezoi
by Diaz
ability ti
and Iran
for lilrge
regardins
I

(PM) (Ur
[51]cOm
a ball SCr

F“) gaV‘c

lighter particles next enter into an air cyclone where they settle out. Air separation is a
function of density, shape and size of the particles and can be efficiently used in
separation of plastic particles and film from the compost [52].

Turning equipment is used for the mechanical agitation of piles to manage the
temperature and oxygen levels. The Windrow turners commonly used in commercial
composting can be categorized by turning mechanisms, orientation to the windrow,
power source and mode of travel [49, 50]. Some categories of turners based on their
mechanical agitation are straddle type, auger equipped turner, elevating face and
trapezoid turners [49, 50]. Some improvements in recently produced turners (as reviewed
by Diaz et.al. [49, 50]) include better efficiency, increased durability, less maintenance,
ability to accommodate large or different sizes of Windrows, and increased ease of travel
and transportation. Turner manufacturers are stressing improving the turning equipment
for larger windrow sizes which will help in larger production of compost. More details
regarding turning equipment and the turning process can be found elsewhere [49, 50].

The last step after the compost is produced is screening to remove foreign matter
(FM) (undesirable materials such as plastic, metal or glass). A recent study by Page et.al.
[51] compared three different screening methods for finished compost. One pass through
a ball screen (resulting in 0.26% FM) and two passes through a trammel screen (0.53%

FM) gave the best results.

2.3.2.3 Home composting (back yard)

Home composting is handled on a small scale using small piles or composting
bins. Turning is usually done manually unless the bins are equipped with rotating drums.

Home composting usually involves lower temperatures than commercial composting,

37

with n
Yard \
inanag
aniniai
take u;
Comni
revolvi
there h
man}: i
compo:
BOkash
Process
increasi
Within t
50mg sy
“'llll Stir,
househoj
”“9 of 2:
approxjm

dll'emng

2'33 PLA

3)]

and hence

with much of the decomposition taking place at mesophilic temperatures (10°C to 46°C).
Yard waste and food waste normally go into home composting systems [5], but improper
management of food scraps can cause odors and also might attract unwanted insects or
animals [31]. In back yard composting, conversion of organic matter to compost may
take up to two years, but manual turning can decrease this time to 3 to 6 months [31].
Commercial backyard composting bins are typically either open or closed cylinders,
revolving drums, or orbs that can be rolled along the ground to turn the pile. Recently
there have been many developments in commercial indoor and outdoor composing bins,
many of which are specifically designed to compost food scraps. An indoor kitchen
composter developed in Japan anaerobically ferments food scraps using the patented
Bokashi method [53] of beneficial microbial inoculation which speeds up the microbial
process. Some other systems have bins containing three compartments which allow
increasing or decreasing the volume and classifying fresh and mature compost or humus
within the same bin. Also, as ventilation is important to maintain the aerobic process,
some systems continuously circulate air throughout the bin. Some bins are also equipped
with stirrers and screens which turn and screen the compost [53]. In Seattle, Washington,
households doing back yard composting of yard waste had an annual household recovery
rate of 254 kgs and those who composted food waste recovered 131 kgs [53]. In Canada,
approximately 27% of homeowners in Edmonton are composting in their back yards,

diverting 10,224 tonnes of organic waste from landfill each year [32].

2.3.3 PLASTICS IN COMPOST

Synthetic plastic waste or particles in compost is a major contamination problem

and hence plastic separation in compost is an important factor for both the compost

38

feeds

separ

L'SA
plasti
foreig
in the
air kn

bulkir

and Oil
repeatc
COmpc:
of l m
Contami
study-cO
found si
COmiiOst
D.
poll'lilers
mall’sisq
“imposing

Sl’Slem I‘nc

feedstock and the compost end product. As mentioned above, different screening and
separation mechanisms can be used to separate plastics fi'om compost.

A case study on plastic-wrapped industrial food residuals was done in California,
USA in 2005 [38]. The composting facility received industrial food waste contained in
plastics packaging which was then ground with the green feedstock, composted, and
foreign matter was subsequently screened out through a trammel screen. Plastics present
in the compost floated through the trammel and were ejected over a belt equipped with an
air knife. The plastic particles were sucked up through the air knife, leaving behind the
bulking agents, which could be used again in the composting process.

Rynk [54] reported case studies about contamination of compost due to plastics
and other foreign particles. In one study, samples of MSW compost were inspected after
repeated sieving, drying and weighing; it was found that plastics (average 1.9% of
compost dry weight) remained in the compost even after repeated sieving with seive sizes
of 1 mm to 4 mm. For larger compost size ranges (4 mm to <25 m) the plastics
contamination percentage ranged from 3.5 to 6.6 % of compost dry weight [54]. Another
study comparing the presence of plastics contamination in sieved and non-sieved samples
found similar results for plastics contamination in sieved (1.875 mm) and non-sieved
compost [54].

De Baere [54] evaluated the replacement of biodegradable with synthetic
polymers and their composting in commercial composting facilities, including cost
analysis. The first case study was for a 50,000 ton/year Belgium-based source separated
composting facility which had 80% of its organic waste delivered in plastic bags. The

system included prescreening to remove the plastic material to avoid plastics

39

ccnta
use 0
woult

doesr

2.3.4 I

C ompt
dlSEZiSt
applies
embanl
hydron
more p:
the abil:
during C
f0r [€th
Such IUl
reSlSlanC
CO"illost
mUlch CO
by Comic

"trough er

contamination in the composting process and end product. According to De Baere [54],
use of 500 tons of compostable biopolymer per year rather than non-compostable plastics
would eliminate 2000 tons/year of overs for pre-screening since biodegradable plastic

does not need this step.

2.3.4 USES OF COMPOST

Compost is a very valuable soil amendment which improves plant growth.
Compost-enriched soil can also reduce erosion, alleviate soil compaction and help control
disease and pest infestation in plants. In addition to common agricultural and horticultural
applications, compost is used in some building and construction projects. On steep
embankments along roads and highways, compost can be more effective than traditional
hydromulch at reducing erosion and establishing turf because compost forms a thicker,
more permanent growth due to its ability to improve the infrastructure of the soil. Due to
the ability of compost to retain moisture, it also helps protect soil fiom wind erosion and
during droughts. Compost is also used to remediate turf grasses that are extensively used
for recreational activities such as golf, football, soccer, etc. Often the wear and tear on
such turf results in disease, pests and soil compaction. Use of compost increases
resistance to grth of turf diseases, such as snow mold, brown patch and dollar spot.
Compost is an effective landscape mulch; when placed over the roots of plants, compost
mulch conserves water and stabilizes soil temperatures. It also helps keep plants healthy
by controlling weeds, providing a slow release of nutrients, and preventing soil loss

through erosion [55, 56].

40

 

2.3.5 E

Leaclm

extracts
water i
leachat:

Hence.

SlOpe f.
C0mp05
the ma:

“'lndrm

2.3.5 ENVIRONMENTAL IMPACTS OF THE COMPOSTING PROCESS

Leachate

Leachate is the liquid that results when water comes in contact with a solid and
extracts material, either dissolved or suspended, from it [5]. Leachate differs from other
water that may accumulate on a compost site due to precipitation or flooding since
leachate may contain a combination of nutrients, soluble chemicals, and organic matter.
Hence, good drainage at composting sites is necessary.

Leachate management can be achieved in different ways, including by providing a
slope for easy run off, maintaining sufficient and recommended distances between
compost and ground water facilities, maintaining the moisture content of compost below
the maximum recommended level, and encouraging effective drainage by orienting
Windrows with the slope of the compost pad rather than across it.

In Canada, leachate is either disposed through local waste water systems, released
to engineered wetlands to purify it, or released through natural purification systems [57].
In Europe, leachate is used for watering the composting mass or is discharged [58]. In
Australia, containment of leachate within the composting area is required. It can be used
for irrigation of piles, disposed of in existing slurry lagoons, or be treated adequately
before discharge. The drainage and collection system has to be able to handle heavy

rainfall [59].

2.4 STANDARDS

In order to determine whether certain packaging materials, i.e. plastics and papers,

are compostable, standards organizations, such as ASTM and ISO, have published their

41

 

mm SC
differen'
definitic
interpret

ISO star

2.4.] A5

biodegra
(1) com}
Table 2.

OVEFVieu

(see Fig

blOdC’gja

own series of standards for compostability and/or biodegradability of materials in
different exposure environments. In general, these standards describe terminology and
definitions, testing guidelines, procedures, conditions, significance, limits, and results
interpretation. In this overview, the standards are separated into two groups, ASTM and

ISO standards, as these are the two main standards organizations.

2.4.1 ASTM STANDARDS

The current ASTM standards involving materials compostability and
biodegradability can be categorized into three groups based on exposure environments:
(1) composting, (2) anaerobic digestion and wastewater treatment, and (3) others (see
Table 2.2). Only standards involving composting of plastics will be included in this
overview and the discussion mainly will focus on standards for compostable plastics.

According to ASTM D 6400 [7], to claim that a certain material is compostable
(see Figure 2.8), it must meet requirements that include satisfactory disintegration,
biodegradation, and terrestrial and aquatic safety in a controlled laboratory scale
composting test. In this test, described in guide D 6002 (Tier 2) [60] and test method D
5338 [24], the test materials are exposed to the compost mixture in closed vessels. At
least 12 vessels must be used: 3 blanks, 3 negative controls such as LDPE, 3 positive
controls such as cellulose, and 3 for the test material. COz—free humidified air is supplied
for a test period of no less than 45 or more than 180 days, at a constant 58°C temperature
(thermophilic phase), or using a desired temperature profile (e.g., 35°C for 1 day, 58°C

for 4 days, 50°C for 23 days, and 2 days for 35°C).

42

Table 2.2 List of current ASTM Standards sorted by category

 

Composting Environment

 

D 6400 “Standard Specification for Compostable Plastics”
D 6002 “Standard Guide for Assessing the compostability of Environmentally
Degradable Plastics”

0 D 5338 “Standard Test Method for Determining Aerobic Biodegradation of
Plastic Materials Under Controlled Composting Conditions”

0 D 5988 “Standard Test Method for Determining Aerobic Biodegradation in Soil
of Plastic Materials or Residual Plastic Materials Afier composting”

o D 5929 “Standard Test Method for Determining Biodegradability of Materials
Exposed to Municipal Solid Waste Composting Conditions by Respirometry”

o D 6954 “Standard Guide for Exposing and Testing Plastics that Degrade in the
Environment by a Combination of Oxidation and Biodegradation”

o D 6340 “Standard Test Methods for Determining Aerobic Biodegradation of
Radiolabeled Plastic Materials in an Aqueous or Compost Environment”

 

Anaerobic Digestion and Wastewater Treatment

 

o D 5210 “Standard Test Method for Determining the Anaerobic Biodegradation of
Plastic Materials in Presence of Municipal Sewage sludge

o D5271 “Standard Test Method for Determining the Aerobic Biodegradation of
Plastic Materials in an Activated-Sludge-Wastewater—treatment system”

0 D 5526 Standard for Determining Anaerobic Biodegradation of Plastic Materials
Under Accelerated Landfill Conditions

0 D 5511 Standard Test Method for Determining Anaerobic Biodegradation of
Plastic Materials Under High-Solids Anaerobic-Digestion Conditions

 

Other Standards

 

 

o D 5951 “Standard Practice for Preparing Residual Solids Obtained After
Biodegradability Standard Methods for Plastics in Solid Waste for Toxicity and
Compost Quality Testing”

0 D 5975 “Standard Test Method for Determining the Stability of Compost by
Measuring Oxygen Consumption”

 

The amount of carbon dioxide gas evolved is measured using either a cumulative
method (titration method), or direct measurement from the exhaust air, using an infrared
(IR) detector or gas chromatography (GC). Figure 2.9 (a) and (b) shows systems for

biodegradation evaluation by the cumulative method and by direct measurement,

43

 

respective

weight is

 

material 5

"<1C
Wetgl

respectively [61]. At the end of the test period, if no more than 10% of the original dry
weight is found to remain after sieving the final compost with a 2 mm sieve, then the test

material shows satisfactory disintegration.

Test Materials

J

ASTM D 6400

 

 

 

 

 

L i

Disintegration Biodegradation Safety 3 criteria

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Controlled Laboratory Scale Composting Test
(ASTM D 5338)

 

 

 

 

 

 
 

  

 

    

 

 

 

     
 

 

 

 

 

 

 

 

Sample
<10% dry Preparation
eight foun (ASTM D 5152,
5951)
>60% or 90% carbon
conversion E 1440
Toxicity Test OECD 207
' OECD 208

 

 

 

Yes

Yes ¢

t i ‘2“

Identify as compostable materials

 

 

 

 

Figure 2.8 Compostable materials identification flowchart

44

 

D'<J Needle Valve

I I"
® F W ‘ E 002 Trap

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I

     
  
  

Biore

Is 002 Trap

Air Inlet

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

    
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Humidified CO2 free Air Bioreactor
/ / / 2 002 Trap
4N 4N 4N Bioreactor
Water
H SO NaOH H SO
2 ‘ 2 ‘ Total of 6 Bloreactors
(a)
Inside
Environmental T

___________Ch_am_beL__ vent N-DAQ

I 7 w use-6501

I , 9

I a Carbon dioxide g

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l .

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|

I Water

I

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| I - _ . c,

l 4' Emma—— PC
Dl<t Needle Valve
® Flowmeter

 

 

 

(b)
Figure 2.9 a & b. Accumulative and direct method to measure biodegradation [61]

45

car?
val?
(ho

cup

11161

the

Bra

bier

To achieve satisfactory biodegradation, the cumulative percentage of organic
carbon converted to carbon dioxide gas, or mineralization, compared to the theoretical
value for the test polymer must be at least 60% for a material containing a single polymer
(homopolymer or random copolymer), and 90% for a material containing a block
copolymer, segmented copolymer, blend, or low molecular weight additives.

For determination of terrestrial and aquatic safety, the concentration of heavy
metal in plastic must be lower than 50% of the amount listed in 40CFR§503.13 [62], and
the final compost must pass the toxicity test, including aquatic toxicity test with rotifer
Brachionus (Guide E 1440) [63], the plant germination with cress seed test, the plant
grth test (OECD Guideline 208) [64], and the earthworm test (OECD Guideline 207)
[27]. In order to pass the toxicity test, the results from the compost containing the test
materials must have no significant differences compared to the blank compost. Prior to
the toxicity test, the final compost from the controlled laboratory scale composting test
must be prepared in accordance with test method D 5951 [65].

ASTM D 6400 also defines biodegradable plastic as a degradable plastic in which
the degradation results from the actions of microorganisms such as bacteria, fungi and
algae [7]. Therefore, based on this definition, for example, PLA, a commonly used
biopolymer, would not qualify as a biodegradable material since the main degradation
mechanism is hydrolysis. Another definition needing more explanation is compostable
plastic. D 6400 defines this term without including the types of compost the plastic will
be exposed to, or the time limit required for material to become fully degraded. This

vague definition gives room for materials to claim they are compostable even if they will

46

not com;
paper.

T
Tier 1. c:
sample a
desiccatc
Stored in
carbon d:
or 9000
Wilmer
biodegrm
negative

T?
that are r
IESI met}
blOdegI-ac
detenmnc
leaner {O
by dll'id“
Ihemettca
compare a
combined

C(”1113081 u,

not compost as fast as natural materials such as yard trimmings, food wastes, and krafi
paper.

Test method D 5988 [66] or the “soil contact test”, as described in guide D 6002
Tier 1, can be used as a rapid screening test prior to test method D 5338. In this test, the
sample and reference materials are mixed with a soil mixture in air sealed vessels, such as
desiccators, with each vessel containing only one test material. The test vessels are
stored in the dark at 21°C (mesophilic phase) for 30-60 days. The amount of evolved
carbon dioxide is quantified by titration. A positive result, which means more than 60%
or 90% of the total organic carbon converted to carbon dioxide (depending on the
polymer composition as described above), indicates that the test material will also
biodegrade in the composting environment, which has a higher temperature. However a
negative result should be confirmed by test method D 5338.

There are some standards involving exposing materials to a compost environment
that are not listed in specification D 6400 for compostable materials identification, e.g.
test method D 5929 [67], and guide D 6954. In test method D 5929 [67], the
biodegradability of the test material exposed to the MSW composting condition (40°C) is
determined by measuring the oxygen uptake and carbon dioxide production from each
reactor for a test period of 45 days. Then, the percentage of biodegradation is calculated
by dividing the total cumulative oxygen uptake and carbon dioxide production by the
theoretical value. Guide D 6954 [68] is a tier based framework, similarly to D 6002, to
compare and rank the degree of degradation of polymers by thermal- and photo-oxidation
combined with biodegradation in disposal environments such as soil, landfill, and

compost with other tested polymers chosen for that application. Tier 1 involves exposing

47

the test
apphcan
such as
dnposal
6Mbam
tothm g

Which at

ZHLZ El

compos'
EFJ 13;
P3Ckagi
instead
standarc
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three Ct:

COmPOS
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examplr
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Values 1;

the test material to the thermal- or photo—oxidation conditions, based on its intended
application. In tier 2, the residual fragments from tier 1 are subjected to a “biometer test”
such as D 5338 or D 5988, to measure the carbon dioxide evolution in the simulated
disposal environment; soil (20-30°C), landfill (20-35°C), or compost (30-65°C). The
60% and 90% organic carbon conversion described in specification D 6400 also applies
to this guide. In tier 3, the residue from the biometer test is subjected to toxicity tests

which are similar to those listed in guide D 6002 tier 2.

2.4.2 EUROPEAN AND [SO STANDARDS

There are only a few European and ISO standards involving packaging and
composting environments. The specification, test scheme, and guidelines are detailed in
EN 13432 [8]. Unlike the ASTM standards, this standard can be applied to any
packaging or packaging component, and is not limited to plastic materials. Moreover,
instead of three criteria for plastic compostability, there are four criteria in the EN 13432
standard: (1) characterization, (2) biodegradability, (3) disintegration, and (4) compost
quality or ecotoxicity. However, these four criteria cover the same scope as ASTM’s
three criteria.

In characterization, the packaging materials are analyzed to determine the
composition, the presence of hazardous substances (e. g. heavy metals), organic carbon
content, and total dry and volatile solids. To pass this criterion, the packaging material
must have those values within specifications listed in Annex A.l of EN 13432. For
example, packaging, packaging materials, and packaging components should contain at
least 50% of volatile solids, and the concentration of heavy metals should not exceed the

values listed in Table 2.3. The volatile solids mean the materials that become volatile at

48

TC

St

pit
co]
Cor
Cn't

CO}:

high temperatures; a temperature of 550i50°C is used for an ignition test as described by
ASTM D 5338 [24] and the American Public Health Association (APHA) standards 2540
E [69].

Table 2.3 Maximum heavy metal content of packaging material and whole packaging
from EN 13432 Annex Al [8].

 

 

Element mg/kg on dry Element mg/kg on dry
substance substance

Zn 150 Cr 50

Cu 50 Mo 1

Ni 25.0 Se 0.75

Cd 0.5 As 5

Pb 50 F 100

Hg 0.5

 

 

The biodegradation test is described in ISO 14855 [9], and is similar to the test
method in ASTM D 5338, with a few differences. First, the ISO test method does not
require the negative control vessels; therefore, only 9 vessels are required instead of 12.
Second, ISO 14855 also includes the determination of percentage of biodegradation
based on weight loss as an optional result to support the value determined from carbon
dioxide evolution. Third, the acceptance level of percentage of biodegradation of the test
material is at least 90% in total or 90% of the maximum degradation of the reference
material after a plateau stage for both reference and test materials has been reached. For
disintegration, the European and ISO standard suggest testing the materials in controlled
pilot-scale and fiill-scale tests, as described in ISO 16929 [70], instead of using the
controlled laboratory-scale test in ASTM D 6400. But the rest is similar, i.e. the final
compost is screened with a 2 mm screen, and the material needs to pass the disintegration
criterion (i.e. no more than 10% of the original dry weight is recovered after 12 weeks of

composting).

49

such
to sh
quah
EFQ l
comp
dean]
Ehili
as “cc
tnetho
such a
passing
Conunr
Percent
and Slit
(POnU\
“Tullhf
andln0(
accordin
the mmF

COuld DOt

For the compost quality or ecotoxicity test, physical and chemical parameters
such as density, total dry and volatile solids, salt content, and pH, have to be determined
to show that the test packaging does or does not have negative effects on the compost
quality. Only the plant grth test, based on OECD guideline 208 [64], is included in
EN 13432 for ecotoxicity. The results (germination numbers and plant biomass) of the
compost with test material and the blank compost are compared. Figure 2.10 shows a
detailed flowchart of the evaluation of organic recoverability of packaging according to
EN 13432. As shown in Figures 2.9 and 2.10, the procedure to have any package certified
as “compostable” is very elaborate. It involves not only the package passing the test
method ASTM 5338 [24] or ISO 14855 [9], but also meeting various other requirements,
such as passing the disintegration test, having levels of heavy metals within limits, and
passing the plant grth test by having no significant difference between the compost
containing test material and the blank compost. For example, Figure 2.11 shows the
percentage of mineralization of the PLA bottles previously tested in the compost facility
and shown in Figure 2.5, compared with PET bottles (negative control) and corn starch
(positive control), according to ASTM D 5338 and ISO 14855 [61]. This test will comply
with the first and second requirements of ASTM D6400 and EN 13432, characterization
and biodegradability. However, this test does not certify that the material is compostable
according to these standards. Further studies assessing the complete disintegration and
the compost quality or ecotoxicity of the bottles are required. Therefore, the PLA bottle

could not be labeled as compostable just by passing ASTM D5338 and ISO 14855.

50

 

 

[ Packaging

 

 

 
  

Each material shall
Nov comply with the
requirement

   

Is it a mono-material
packaging?

 

 

 

 

Yes
1

 

For each single packaging
Material

 

 

 

 

 

 

 

Measure thickness or mass/
surface

 

 

 

  

as the material been
evaluated before?

   

 

  
 
  

Yes

      

Accepted using a
sample with a higher
thickness or mass/
surface?

 

No further test is
NOW required

   

 

 

 
 

 

Yes
L

 

Only assessment of
disintegrability. Go to a. and
stop at c.

 

 

 

 

 

 

 

 

Measure heavy metals

 

 

  
  

  

Are heavy

metals within limits? ”0* Not accepted

 

 

   

 

Yes
Y

 

 

 

Measure volatile Solids

Figure 2.10 Flowchart of evaluation of organic recoverability of packaging

 

51

Fi‘

  
 

 

ls volatile
solids content >50%?

  

Yes
V

 

Identification of constituents
of packaging material

 

 

 

   

Are they known of
expected to become
harmful to the
environment?

NO

  
  

  
  

Is the packaging

material of natural
origin and chemically
unmodified?

No

V

 
       
 
   
 

 

Assessment of
biodegradability

 

No Not accepted

 

 

 

 

Yes v Not accepted

 

 

 

 

No biodegradation
test is required.
Go to a.

Yes,

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Yes

 

 

 

  
  
   
   
     

  
  

v
Applied on packaging Applied on organic
FT material packaging constituents
1 For each
No biodegradation test Constituent:
is required. Check the (No is concentration>1% and
next constituent the total content of
constittents >5°/o

 

     
 

ls biodegradability
>90%?

Figure 2.10 Flowchart of evaluation of organic recoverability of packaging

52

 

Not accepted

No+I

 

 

 

a. Assessment of
disintegrability in pilot or full
scale test

9

b. Sieving after composting
anf retrieval of test material
residues

 

 

 

 

 

 

 

 

     
 

c. Is the fraction
with size >2mm higher
than 10%

Yesbl Not accepted

 

 

 

  

 

No

m

’egative effects on the

 

    

Yesbl Not accepted

    
   
 

composting
rocess?

 

 

 

No
I

 

,___

Quality determination of final
compost

v

Test physical-chemical
parameters using a sample
obtained from a.

 

 

 

 

 

  
 

  

Do they
fulfil national or
European
equirements

 

 
   

No fl Not accepted

 

 

 
 

 

 
 

Yes
!

 

Test biological parameters
using a sample from b. and
a control sample

 

 

 

 

   
    

Is there any
significant difference
between the test
compost ?

 

   

No > Not accepted

 

 

    

 

Yes
V

 

Accepted

 

 

 

Figure 2.10 Flowchart of evaluation of organic recoverability of packaging

53

70

60

%Mlneralizatlon
8 8

N
O

.5
O

CEnifiCa.

certifiCat

 

so H————«

(BS
60 -

%Mineralization

20 -

ioI

 

 

"~—-—-—‘-—_--————_———-—---—-—--——
’
’

0 10 20 3O 40 50 60 70
Time, days
Figure 2.1] Percentage of mineralization of PLA and PET bottles and corn starch

measured according ASTM D 5338 [24] and ISO 14855 [9].

2.5 LABELING AND CERTIFICATION

Currently, there is confusion about conventional plastics and biodegradable and
compostable plastics throughout the US, since they are hardly physically distinguishable
[71]. To succeed in recovering these materials and properly composting them, there must
be a labeling system that separates them from conventional materials. Organizations
such as the Biodegradable Products Institute (BPI) located in New York City; the US.
Composting Council (USCC), located in Holbrook, NY; and DIN CERTCO, the
certification organization of DIN, the German Institute for Standardization, offer

certification programs that award a compostable logo to approved products.

54

Ir
there she
are com;
due to di
temperat
considen
certificat

products

Which c:
that cenj
t0 haVe
recOgniz
With the
Specific
COmPOs
produCIS
approve
“'ebSite
Cei'tifies
Ifists Of
and the

In order to claim or label a product or package as compostable, or biodegradable,
there should be reliable scientific evidence supporting this claim [72, 73]. Packages that
are compostable in institutional facilities may not be compostable in home composting,
due to different composting conditions, such as the waste mixture, moisture content, and
temperature. Therefore, the claim must be clarified enough to avoid deception, especially
considering the limited availability of compost facilities [72]. These are reasons for
certification; therefore concrete evidence must be submitted to organizations to have any
products certified.

Packaging manufacturers can have their products certified as “compostable”,
which can be used as a marketing advantage. Also, composting facilities can be ensured
that certified products are definitely compostable. Therefore, certification is the first step
to have compostable packages accepted by composting facilities. Two of the most
recognized certification organizations are BPI and DINCERTCO. BPI, in cooperation
with the USCC, uses the ASTM specifications D6400 [7] and D6868 [74] “Standard
Specification for Biodegradable Plastics Used as Coatings on Paper and Other
Compostable Substrates” [8]. The compostable logo, see Figure 2.12(a), is given to
products that are compliant with ASTM specifications based on testing results from any
approved laboratory. A list of the approved laboratories can be found online at the BPI
website: http://bpiworld.org/BPI-Public/Prograrn/Labs.html. Similarly, DINCERTCO
certifies compostable products made from biodegradable materials based on laboratory
tests of either ASTM specification D 6400 [7], or the European standard EN 13432 [8],
and the “compostable” logo, see Figure 2.12(b), is awarded to products that meet one of

these standards [75]. Many other organizations also certify compostable materials based

55

onASTN
mmgm
award cet
nandards
biodegrat‘

C.
composta
microwat

from BA:

Fig“ re

on ASTM D 6400 [7], EN 13432 [8], or both. For example, AIB Vincotte (AV), located
in Belgium, awards the “OK compost” logo, see Figure 2.12(c). Other certification bodies
award certificates (not compostable labels) to products that meet ASTM, ISO, or CEN
standards, similar to the ISO 9000 series certification. For example, SGS offers
biodegradability and ecotoxicity testing based on ISO standards.

Currently, approved BPI and DIN CERTCO compostable products include
compostable bags and films; packaging, such as water bottles, ovenable and
microwavable trays; dishes and bowls; disposable utensils; and resins, such as EcoflexTM

from BASF, PLA from NatureWorks® LLC, and Mater-Bi from Novarnont [8, 75].

 

 

 
 

 

COMPOSTABLE
Q Elhita’t'iintl‘i I usesrrsam
(a)
§
K compost -
:12;-

   

(b) (c)
Figure 2.12 (a) BPI compostable logo, (b) DIN CERTCO compostable logo, (c) AV OK

compost logo

56

beverag
plastic

“compo
existing
ASTM

with. fo
packagi
errone01
marketit

scientifi

2.6 LIF

Pertbrm
CORSEqu
D7075 [
8021] Se
defines
intentm
material
asSOCiar.
int-emor

In 2006, Assembly Bill No. 2147 “Solid waste: Compostable plastic food and
beverage containers” was introduced by Harman in California. This bill prohibits selling
plastic food and beverage containers labeled “degradable”, “biodegradable”, or
“compostable” unless the containers meet current ASTM standards [76], in contrast to the
existing law which applies only to plastic bags. However, the bill does not specify the
ASTM standards, and it does not address which standards the packages have to comply
with, for example D5338 or D6400. The purpose of the bill is to stop food and beverage
packaging manufacturers or distributors from using mislabeling, because there have been
erroneous uses of the words “degradable”, “biodegradable”, and “compostable” in
marketing. Therefore, there must be a system to label the packages that is reliable and

scientifically based.

2.6 LIFE CYCLE ANALYSIS

As discussed earlier, LCA is an evaluation technique which compares the
performance of alternative systems and products; and quantifies the environmental
consequences of a product, system or process over its entire life. As delineated in ASTM
D7075 [12], the LCA methodology for biobased products involves distinct stages such as
goal setting, inventory analysis, impact assessment and interpretation. Goal setting
defines the reasons for and scope of the study, including its breadth and depth. The
inventory analysis identifies and quantifies the environmental inputs (water, energy, raw
material, land and other resources) and outputs (releases to air, land, and water)
associated with the product over its entire life cycle. Impact assessment characterizes the
inventory input-output flows in relation to a set of environmental impacts (such as

resource depletion, global warming, ozone depletion, human toxicity, ecotoxicity,

57

phOlOCht
landscap
describe:
The prac

used in I

compost
importar
biobased
land app
Vflueof
Studies 0

15
Sh0uld i,
c.V'Cle of
(3) the e
material;
“59d to 1
BOhhliar
biodegra
have be:

photochemical oxidant, acidification, eutrophication and degradation of ecosystems and
landscapes). The final interpretation step combines the environmental impacts and
describes the results in a manner and in accordance with the goals of the LCA study [13].
The practice stated in ASTM D7075 is in accordance with the terminology and concepts
used in ISO Standards 14040 — 14043 [77-80].

The waste management stage for the compostable packages may include
composting, combustion, landfilling or recycling. The final disposal system has an
important role in the overall ecobalance, especially for biodegradable materials. If
biobased materials are disposed through composting, and the compost is further used in
land application, then significant emission and energy credits can accrue, because of the
value of the compost to sustainable agriculture. Impact factors emphasized in earlier LCA
studies of biodegradable packaging include eutrophication, ecotoxicity, and land use [81].

According to EPA, evaluating greenhouse gas emissions of a polymer system
should include analysis of three factors: (1) greenhouse gas emissions throughout the life
cycle of the polymer, including utility emissions and emissions from the disposal option;
(2) the extent to which carbon sinks are affected by manufacturing and disposing of the
material; and (3) the extent to which the management option recovers energy that can be
used to replace electricity, thus reducing utility greenhouse gas emissions. According to
Bohlmann [81], there is considerable uncertainty in estimating the impact of
biodegradable polymers such as PLA on emissions of greenhouse gases, and few studies
have been published that address greenhouse gas emissions and carbon sequestration

associated with landfilling.

58

Wales. .1
the total
reductior
conditior
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A
managem
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benefits 0
and uses
could n01
fertilizer u
P€SllClde
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pIOdUCIIOn
EXpen'memE
considers If
that the Odor

the total Cap

LCA studies have been done on composting at the University of New South
Wales, Australia. However, they reported some limitations of LCA as a tool to evaluate
the total environmental impact assessment of a compost operation, since a number of
reductions in agricultural inputs (such as fertilizers and water) and improvement in soil
conditions could not be evaluated due to the unavailability of required characterization or
equivalency factors [82].

Another LCA study evaluated the environmental impacts of solid waste
management alternatives, concluding that if organic waste is diverted from landfills to
composting, there is reduction in the energy recovery and greenhouse gas emissions
benefits of the waste management system. The composting process increases emissions
and uses energy. Again, in this study; the environmental consequences of composting
could not be characterized completely due to lack of data. Offsets could include reduced
fertilizer use, conservation of nutrients in compost-amended soil, less irrigation, reduced
pesticide application, avoided harvest and transportation of peat, or avoided
manufacturing of erosion control products [83].

Komilis and Ham developed a life cycle inventory (LCI) model for municipal
solid waste composting and yard waste facilities [84]. Their model considers the
production of compost as a high and low value product, and was based on laboratory
experiments to determine selected emissions which were not available. The model
considers three organic streams: food waste, mixed paper, and yard waste. They found
that the odor control system and the building were the largest capital cost (around 77% of
the total capital cost) for these types of operation. In addition, they reported that more

than 90% of the emitted C02 was due to solid waste decomposition. Further research

59

charactl

RECESSJ

2.7 CO.

and pol
consumt
is an at;
these blt
reneu‘abl
refinery l
COmposti
materials
Therefore
Elddithn~
Claims.
Alt
many Of [1
requ11’6mcn
Sj'Slem in F
ETEen mark]
is That it e h
packaging S(

characterizing the emissions and determined that indicators for composting facilities are

necessary in order to systematically evaluate and compare composting facilities.

2.7 CONCLUSION

As new biopolymers obtained from renewable resources such as poly(lactide),
and poly(hydroxybutyrate) are increasingly becoming available for food, medical and
consumer goods packaging applications, disposal of these polymers through composting
is an available alternative. However, until now the main focus of companies promoting
these biomaterials is the claim that they are obtained from environmentally-fiiendly
renewable resources and reduce petroleum consumption (even though only about 5% of
refinery production goes to chemical products, including polymers). Since recycling and
composting programs for these materials are generally not available, these “green”
materials mostly end up in landfill, along with many other packaging materials.
Therefore, a better approach to the disposal of these new biomaterials is needed. In
addition, state or federal regulations are necessary to avoid improper compostability
claims.

Although recycling could be energetically more favorable than composting for
many of these new biopolymers, it may not be practical due to sorting and cleaning
requirements. A viable alternative is composting. However, since at present there is no
system in place for collection and composting these materials, their main benefit is just
green marketing based on pseudo environmental benefits. The risky point of these claims
is that we have really created a new packaging waste problem, rather than a sustainable
packaging solution. Compostable packages can be a valuable alternative if we are willing

to formally address the challenge of clearly understanding the cradle-to-grave life of

60

these n1
compost
countne

adopting

these materials. Including compostable polymers in existing food, manure, or yard waste
composting facilities is a promising approach. Canada and Germany are among the
countries in the forefront of this initiative, positioning them to take full advantage of

adopting these new materials.

61

I9

\1

AS]
Per;
Niall

Nara

QSSQ

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lS<
bit.

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71

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67

CHAPTER THREE
Gaurav Kale, Rafael Auras, Sher Paul Singh. (2006). Degradation of Commercial

Biodegradable Packages under Real Composting and Ambient Exposure Conditions.
Journal of Polymers and the Environment. 14: 317-344

68

CHAP?
PA(

SL'MM:
T

applicati:

foodstuff

impractic
biodegrar
based pac
sorting a.
C0mposta
energy in‘
more fine:
commerci
real COmp.
chromatoé
“0"61 tech
rate undEr
for 30 day:
l5 and 30

PLA Packg

the Liam- d

CHAPTER THREE - DEGRADATION OF COMMERCIAL BIODEGRADABLE
PACKAGES UNDER REAL COMPOSTING AND AMBIENT EXPOSURE
CONDITIONS

SUMMARY

The use of long-lasting polymers as packaging materials for short lived
applications is not entirely justified. Plastic packaging materials are often soiled due to
foodstuffs and other biological substances, making physical recycling of these materials
impractical and normally unwanted. Hence, there is an increasing demand for
biodegradable packaging materials, which could be easily renewable. Use of biopolymer
based packaging materials allows consideration of eliminating issues such as landfilling,
sorting and reprocessing through taking advantage their unique functionality, that is
compostability. Composting allows disposal of biodegradable packages and is not as
energy intensive compared to sorting and reprocessing for recycling, although it requires
more energy than landfilling. The aim of this work was to study the degradation of three
commercially available biodegradable packages made of poly( LD-lactide) (PLA) under
real compost conditions and under ambient exposure by visual inspection, gel permeation
chromatography, differential scanning calorimetry, and thermal gravimetric analysis. A
novel technique to study the degradability of these packages and to track the degradation
rate under real compost conditions was used. The packages were subjected to composting
for 30 days, and the degradation of the physical properties was measured at 1, 2, 4, 6, 9,
15 and 30 days. PLA packages made of 96% L-lactide exhibited lower degradation than
PLA packages made of 94% L-lactide, mainly due to their highly ordered structure,
therefore, higher crystallinity. The degradation rate changed as the initial crystallinity and

the L-lactide content of the packages varied. Temperature, relative humidity, and pH of

69

the com
order dr

three pa

3.1 INT

material
are ofter
recycling
increasir
renewab
renewal);
COHSldCr;
Walling '
biodegra,
reIJTOC‘c‘ss
inSIanCe,
expensin

C.
humus, a
21180 earth
111 cOmpO:
mlCrQOrga

organlSmS

the compost pile played an important role in the total degradation of the packages. A first
order degradation of the molecular weight as a function of time was observed for the

three packages.

3.1 INTRODUCTION

It is increasingly being realized that the use of long-lasting polymers as packaging
materials for short lived applications is not entirely justified. Plastics packaging materials
are often soiled due to foodstuff and other biological substance contents, making physical
recycling of these materials impractical and normally unwanted. Hence, there is an
increasing demand for biodegradable packaging materials which could be easily
renewable. To date, production of packaging plastics to a large extent is based on non-
renewable packaging materials. Use of biopolymer based packaging materials allows
consideration of eliminating issues such as landfilling, sorting and reprocessing through
availing their unique functionality, that is compostability. Composting allows disposal of
biodegradable packages and is not as energy intensive compared to sorting and
reprocessing for recycling, although it requires more energy than landfilling. For
instance, in countries like the USA where landfilling is predominant, composting is more
expensive [1].

Composting is a natural process by which organic material is decomposed into
humus, a soil like substance. Decomposition is principally done by microorganisms, but
also earthworms, small insects, and other soil inhabiting organisms play an important role
in composting at lower temperatures. The major groups of mesophilic and thermophilic
microorganisms involved in composting are bacteria, fungi, and actinomycetes. These

organisms decompose the organic matter as their food source. The process requires

70

carbon. nit]
carbon as 2
nitrogen ra
compost pi
stage. In th
strong mic
(140°F) \Vl
temperatur
to compost
cOmpost c
continues
microorgal
C 01
by biologi.
and bioma
Visible, dis
Collditions
a cOmPOSI
degradatiol
the mated;
mechaniSn,
SinCe bloc

backbone

carbon, nitrogen, water, oxygen, and heat. Organisms that decompose organic matter use
carbon as a source of energy and nitrogen for building cell structures. A 30:1 carbon to
nitrogen ratio is ideal for reproduction of thermophilic microorganisms [2]. Normally, a
compost pile goes through two stages: an active composting stage and a curing period
stage. In the first stage, the temperature raises as long as oxygen is available producing a
strong microbial activity. During this stage, the temperature can rise well above 60°C
(140°F) when many microorganisms begin to die or become dormant, and after that the
temperature starts to stabilize or may even fall. In the curing stage, the materials continue
to compost but at a much slower rate. The rate of oxygen consumption decreases, and the
compost can be piled without turning or forced aeration. The composting process
continues until the last remaining nutrients are consumed by the remaining
microorganisms and until almost all the carbon is converted to carbon dioxide.
Compostability of compostable plastic (i.e., “ a plastic that undergoes degradation
by biological processes during composting to yield C02, water, inorganic compounds,
and biomass at a rate consistent with other known compostable materials and leave no

” 6) are commonly evaluated in simulated compost

visible, distinguishable or toxic residue
conditions and by assessing the final quality of the compost. Degradation of polymers in
a compost environment occurs mainly through mechanical, thermal, and chemical
degradation. Photodegradation is only present on the surface of the compost pile where
the material is exposed to ultraviolet (UV) and gamma radiation. Of all the degradation
mechanisms, chemical degradation is the most important for biodegradable polymers.

Since biodegradable polymers have hydrolysable functional groups in the polymer

backbone, the polymer chains first become susceptible to water attack and chemical

71

degradation
due to the it
for compos
Materials (.1
Committee
polymeric n'
04 [5]. D('
subcommittc
evaluation 0
[9], and ISO
based on I
degradation.
Standardizat
c011113051 qua
the COmpost
entire PaCka
feveclstock m.
Worst Case
COmPOSting.
be drawn as

The a
packaging a]

Commercial 1'

degradation initiates polymer erosion (i.e., the reduction of mass of the polymer matrix
due to the loss of monomers and oligomers or non-degraded polymer pieces). Standards
for compostability have been developed by the American Society for Testing and
Materials (ASTM), the International Standards Organization (ISO) and the European
Committee for Standardization for evaluation of the compostability of biobased
polymeric materials. ASTM standards (i.e., ASTM D5338-98 [3], D6003-96 [4], D6954-
04 [5], D6400-99e1 [6], & D 6002-96 (Reapproved 2002)81 [7]) developed by
subcommittee 20.96 for assessing compostability are laboratory scale and limited to
evaluation of plastic materials. [4-7] Similarly ISO standards ISO 14851 [8], ISO 14852
[9], and ISO 14855 [10] allow evaluation of materials under laboratory conditions and are
based on measuring the carbon dioxide evolution and oxygen demand during
degradation. The EN 1343222000 [11] standard developed by European Committee for
Standardization addresses compostability referring to ISO standards and evaluates the
compost quality and toxicity. As such and until now, no standard or study has focused on
the compostability of complete packages under real conditions. Degradation time of an
entire package as encountered in the case of full-scale facilities that do not grind
feedstock may be much longer than when the polymer pieces are grinded, representing a
worst case scenario for compostability. Moreover, poor representation of actual
composting conditions is a major negative aspect since mistaken conclusions could easily
be drawn as biodegradation mechanisms vary among substrates.

The applications of biopolymers are growing in areas of food and consumer goods
packaging and hence the first concern that needs to be addressed is environmental.

Commercially available biopolymers that are biodegradable (i.e., polymers that are

72

engineere
PLA dev
million pt
and Gaml
line of pc
polymers
plastics a
(Hartlepo
used in l;-
DuPont l
POIyethyl

both over

engineered to completely biodegrade in a microbial environment) include NatureworksTM
PLA developed by Cargill Dow LLC (Blair, NB). NatureworksTM is producing three
million pounds of PLA annually for a variety of packaging and fiber applications. Proctor
and Gamble Co. (P&G) (Cincinnati, OH) have produced an aliphatic copolyester (Nodax)
line of polymers that are biodegradable in aerobic and anaerobic conditions. The Nodax
polymers are produced by microorganisms through a fermentation process, and the
plastics are extracted from the biomass. Similar to Nodax, Eastman Chemical Company
(Hartlepool, England), has developed Eastar Bio aliphatic copolyester, which is being
used in lawn and garden bags, food packaging and horticultural applications worldwide.
DuPont has a 200 million lb/year production facility in Tennessee for its Biomax
polyethylene terephthalate copolymer hydro/biodegradable polyester, which is available
both overseas and in the United States [12].

Poly (lactide) polymer (PLA) derived from starch is the main biopolymer which is
commercialized as a biodegradable packaging material. PLA is fabricated by
polymerizing lactic acid (LA) monomer, which is mostly produced by carbohydrate
fermentation of corn dextrose. The fermentation of dextrose produces two optically active
enantiomers, namely D (-) and L (+) lactic acids. Three methods are adopted to produce
high molecular mass PLA of about 100,000 Daltons: a) direct condensation —
polymerization, b) azeotropic dehydrative condensation currently used by Mitsui Toatsu
[13], and c) polymerization through lactide formation, which was developed by Cargill
Inc. in 1992 [13]. The properties of PLA such as melting point, mechanical strength and
crystallinity are determined by the polymer architecture (determined by different

proportions of L, D or meso-lactide) and molecular mass. The glass transition

73

temperature (Tg) ranges from 50°C to 80°C while the melting temperature (Tm) ranges
from 130°C to 180°C. PLA can be processed by injection molding, sheet extrusion, blow
molding, therrnoforming, and film forming. PLA is approved by the Food and Drug
Administration for its intended use in fabricating articles in contact with food[13].
Currently, PLA is being commercialized and being used as a food packaging polymer for
short shelf life products with common applications such as containers, drinking cups,
sundae and salad cups, overvvrap and lamination films, and blister packages. As PLA is a
growing alternative as a green food packaging material, new applications have been
claimed in the arena of fresh products, where thermoformed PLA containers are used in
retail markets for fruit and vegetables. In the coming years, PLA production and package
consumption are expected to increase. Therefore, there is a need to address the
compostability of these packages under real composting conditions. In 2003 in the USA
[1], 15 full-scale solid waste composting facilities (i.e., “one that includes the residential
waste stream that arrives at the plant as mixed waste or source separated fractions [1]”)
were in operation. Therefore, for biodegradable polymers to be an attractive alternative, a
wide range of composting facilities need to be created, or PLA will need to be composted
with general yard waste.

As mentioned before, the standards mainly focus on providing information about
compostability of biodegradable polymeric materials in simulated composting conditions.
Simulated and real composting conditions vary due to several factors such as temperature
and relative humidity, and in general simulated conditions only poorly represent real
composting conditions. [14-16] Also while most of the commercialized biopolymer

materials meet the standards of being biodegradable, these standards do not address

74

compostabili
longer than:
Therefore. I
commercial?
correlate thc
we also se
composting
conditions
permeation

gr avimetric

3.2 MATE
3-2-1 Pack
rue hUnd
brands of .
The bOttle
dimension
= 0.24 m.
obtained f

contaiRErs

compostability of a complete package in real composting conditions, which may take
longer than a simple piece of polymer (i.e., worst case scenario for degradation) [14, 15].
Therefore, the aim of this paper is to provide information about compostability of
commercially available biodegradable packages in real composting conditions, and to
correlate the degradation process with their physical properties’ breakdown. In addition,
we also seek to introduce a method to assess compostability of packages in real
composting conditions. Three poly (LD-lactide) packages were exposed to compost
conditions and their properties’ breakdown were monitored by visual inspection, gel
permeation chromatography (GPC), differential scanning calorimetry (DSC), and thermal

gravimetric analysis (TGA).

3.2 MATERIALS AND METHODS

3.2.1 Packages

Five hundred milliliter poly (lactide) spring water bottles commercialized by Biota
brands of America (Telluride, CO) were obtained from NatureWorksTM PLA (Blair, NE).
The bottles were made of 96% L-lactide and 4% D-lactide with bluetone additive and
dimensions of height = 0.2 m and base diameter = 0.065 m. Poly (lactide) trays (diameter
= 0.24 m, height: 0.046 m) and deli containers (0.195 m x 0.17 m x 0.04 m) were
obtained from Wilkinson Manufacturing Company (Fort Calhoun, NE). The tray and deli
containers both were made of 94% L-lactide and 6% D-lactide. Figure 3.1 a, b & c show

pictures of the containers.

75

s‘
N
"h-
n‘
.
m.
1.4..
gm 1
, ..
".J
u"

L"
.y"
\‘.

1"-
,,

 

Figure 3.1. PLA containers a) bottle; b) tray; c) deli

76

3.2.2 Compost pil-

A compost
(East Lansing. M
commercial tumer
tow manure and '.

with waste feed (i

 

of 2:1. The mixtm
which \V as turned
heated up at arou
of mixture is ex;
After that. the m
on an asphalt p:
63 i 5%. and i
distribution ins
3.33 Box
Woode
Packages into t
31) image of a
rust and stain p

rom the COmpo

3.2.2 Compost pile

A compost pile prepared at the Michigan State University Composting facility
(East Lansing, MI) was used for the study. The compost pile was produced in a
commercial turner manufactured by Global Earth (Ontario, Canada). Initially, 11.6 m3 of
cow manure and 7.8 m3 of wood shaving were mixed. After that, this mix was combined
with waste feed (i.e., the feed that the cows do not eat between feedings) in a proportion
of 2:1. The mixture was allowed to stay in a rectangular bay of 3.6 m x 36.5 m x 1.8 m,
which was turned every 3 days per week during 3 weeks. During this time the mixture
heated up at around 60°C, and it is turned up to ensure aeration and that the total volume
of mixture is exposed to temperatures above 60°C to kill the weed seeds and pathogens.
After that, the mix was pulled out of the bay, and a pile of 6 x 24 x 3 meters was built up
on an asphalt pad. The initial pile temperature, relative humidity, and pH was 65 i 5°C,
63 :t: 5%, and 8.5 i 0.5 respectively. Figure 3.2 shows a 2-D graph of the temperature
distribution inside the compost pile at the beginning of the testing.
3.3.3 Box

Wooden boxes having dimensions of 0.6 x 0.3 x 0.10 m were used to insert
packages into the compost pile and to facilitate the actual identification of the package. A
3D image of a box is shown in Figure 3.3. The bottom of the box was 0.011 mesh gauge,
rust and stain proof. This allows a portion of the compost and the package to be removed

from the compost pile for evaluation.

77

Height of pile, m

 

Width of pile, m

Figure 3.2: Temperature distribution inside the compost pile at the beginning of the

testing

 

Figure 3.3: 3D view of Box

78

3.3.4 Placement of Packages

Composting exposure: The packages were placed in duplicate sets in the compost pile
with the help of the boxes, as mentioned above, at approximately 1.2 meters above the
ground and 1 meter inside the compost pile where a uniform composting temperature was
obtained during the experiment. Compost was placed over the mesh in the box and the
package was placed on this compost followed by the addition of more compost. In this
manner, the packages were buried in the compost pile. The handle on the box facilitated
identification of the exact location of the boxes in the pile. The packages were subjected
to composting for l, 2, 4, 6, 9, 15 and 30 days. Each package was labeled for easy
identification.

Ambient exposure: The packages were placed in open foldable reusable plastic containers
obtained from CHEP (Orlando, FL) of dimensions 0.6 x 0.4 x 0.4 meters, and they were

exposed to ambient conditions. Two packages were evaluated at each condition.

3.3.5 Compost property testing

Temperature: Continuous pile compost temperatures were recorded using HOBO® brand
battery operated data loggers obtained from Onset Computers (Pocasset, MA) for 6 hours
intervals for the complete 30 days. Additional readings of the temperatures around the
compost surrounding the packages were taken by a stainless steel thermometer (21:1°C)
obtained from Reotemp (San Diego, CA).

Moisture Content: The wet weight moisture content of compost was measured using a
modified version of ASTM D4643-00 [17] (previously validated using a traditional

vacuum oven) [18]. A sample of the compost mix was taken out every time along with

79

packages and checked immediately for the moisture content. The wet weight of compost
was recorded and then it was subjected to microwave heating for 3 minutes. The weight
drop in compost due to evaporation of moisture was recorded, and again it was subjected
to microwave heating for 1 minute. The cycle of recording the weight and heating for 1
minute was continued until constant weight was obtained. The percentage wet weight
moisture content is determined by the ratio of the difference between the weight of the
moist and oven dried specimens to the total weight of the moist specimen.

pH: The protocol for measuring pH of compost was originally obtained from Cornell
Composting [18]. The compost was dried through the microwave heating process and 5 g
of specimen was weighed in a small container. 25 m1 of deionized water was added and it
was allowed to mix for 5 minutes. The pH of the solution was recorded using calibrated

pH paper obtained from Micro Essential Laboratory Inc (Brooklyn, NY).

3.3.6 Ambient Conditions

Hourly data for ambient parameters such as temperature, relative humidity and
solar radiation were obtained from the Michigan Automated Weather Network (East
Lansing, MI) located at 42.6734 degree latitude, -84.4870 degree longitude and 264 m
elevation for the complete 30 day period. The air temperature measurements were taken
above 1.5 meters above ground level. Figure 3.4 a) shows the maximum and minimum
ambient temperatures, Figure 3.4 b) shows the maximum and minimum relative humidity
during the 30 day testing period, and Figure 3.4 c) shows the average daily solar radiation

during the same period.

80

 

Temperature, °C

 

 

RH, °%

 

 

 

 

 

Solar Radiation x 103, kJ/m2

 

 

 

 

0 5 10 15 20 25 30
Time, days

Figure 3.4: a) 30 days maximum and minimum temperature data; b) 30 days maximum

and minimum relative humidity data; c) 30 days average total solar radiation

81

3.3.7 Visual Inspection

The packages were inspected every time they were removed from the compost
and plastic containers. A Sony Cybershot DSC-P150 7.2 MegaPixel digital camera was
used to take pictures. The packages were inspected for color, texture, shape, and changes
in dimensions.
3.3.8 Physical Properties
Thickness: The thickness of packages was determined using a Magna Mike 8000
thickness gauge manufactured by Panametrics (Japan) according to ASTM D4166-
99(2004)°“. [19]
Molecular Weight: The molecular weight was determined using a standard Gel
Permeation Chromatography (GPC) technique. A Waters 600 Multisolvent delivery
system equipped with Waters 717 autosampler and Waters 2410 R1 detector from Waters
(Milford, MA) was used to determine the molecular weight of samples after extraction.
Inhibitor free tetrahydrofuran (THF) solution obtained from Sigma Aldrich (Milwaukee,
USA) was transferred to 2 ml vials containing 2 mg of specimen. The vials with the
specimens were manually shaken for 2 minutes. The dissolved samples were filtered with
0.2 pm pore size, 13 mm disposable PTFE (Polytetrafluroethylene) filters obtained from
Whatrnan (Florham Park, NJ). Diluted solution was transferred to the 1 ml clear glass
shell vials used in the autosampler and capped using polyethylene snap caps; both
obtained from Waters (Milford, MA). Two PLgel 10pm MIXED-B 300*7.5mm columns
from Polymer Laboratories (Amherst, MA) in series were used, giving a detection range of
1000 to 10,000,000 Daltons. Polystyrene obtained fi'om Sigma Aldrich (Milwaukee,

USA) was used as a standard for calibration purposes. Experiments were run at 35°C.

82

Sample concentrations for polystyrene and PLA samples were 1 mg/ml with a flow rate
of 1 ml/min.

Glass Transition and Melting Temperature, Enthalpy of Fusion and Crystallinity: The
glass transition temperature, melting temperature and crystallinity were determined using
a Differential Scanning Calorimeter (DSC) Q-100 made by TA Instruments (New Castle,
DE) in accordance with ASTM D 3418-97. [20] The DSC standard calibration
procedures was performed according to ASTM E967-03 [21] and ASTM E968-02 [22].
Analyses of the results were done with a TA Instruments Universal Analysis 2000
(Version 3.9A). The percent of crystallinity was determined according to ASTM D3417-
97 [23] and equation 1.

AH

M

where AHc is the enthalpy of cold crystallization, AHm is the enthalpy of fusion, AH; is

the heating of melting of purely crystalline poly (lactide) PLA, 135 J/ g [24, 25].
Decomposition Temperature: The decomposition temperature was obtained using a
Thermogravimetric Analysis instrument (TGA) TA 2950 made by TA Instruments (New
Castle, DB) in accordance with ASTM E1131-03 [26]. The specimens were heated at the
rate of 20°C from 23°C up to 500°C in presence of inert gas (N 2) and oxidative gas (02)
both above 90 psi. The results were analyzed with Universal Analysis 2000 (Version
3.9A).

Statistical Analysis: All treatments were conducted in replicates of two. Statistical
analyses were carried out using the General Linear Models procedure in JMP software

(SAS Institute Inc. SAS Campus Drive, Cary, NC 27513).

83

3.4 RESULTS AND DISCUSSION

Poly(lactide) bottles, trays, and deli containers were introduced into the compost
pile described above and composted for a period of 30 days. Table 3.1 shows the initial
physical properties of these commercial packaging containers. PLA bottles, since they are
made of 96% L-lactide, are a more highly ordered structure, which results in a higher
crystallinity than PLA trays and deli containers. The deli containers had a higher
molecular weight than the bottles and trays.

Table 3.1. Physical properties of the poly(lactide) bottles, trays, and deli containers

 

 

Properties Bottle Tray Deli
L-Lactide, % 96 94 94
Molecular weight 209,324 176,779 215,466
PDI 1.72 2.00 1.70
Tg, °C 60.6 i 0.3 61.3 i 0.6 62.1i3.4
Tm, °C 151.0i0.1 149.0i2.9 149.1103
Crystallinity, %’ 12.2:l:1.4 9.2i9.7 2.7il.8

 

a- The percent of crystallinity was calculated according to equation 1.

The containers were introduced and located in the compost pile as described
above. The temperature, relative humidity, and the pH at which the three packages were
exposed during the composting conditions are shown in Figure 3.5 a & b, respectively.
pH is one of the most important factors of hydrolytic polymer degradation since pH
variations can change hydrolysis rates by few order of magnitude[27-30]. In this work,
there was a slight alkalization of the pile after the second day of testing, although this
difference was not statistically significant at 0t=0.05, P=0.91 during the 30 days of

composting.

84

 

70 V f I I I U V 1 00

60

 

 

 

 

 

RH,%

50

 

 

Temperature, °C

 

 

 

 

 

 

pH

 

 

‘ U
n 4 1 a i

10 15 20 25 30

 

 

. IL- I

H

 

°rr
O
UI

Time, days

Figure 3.5. a) Temperature and relative humidity of the compost pile at time of package
removal, b) pH of the compost pile at time of package removal

3. 4.1 Visual Inspection

Pictures showing the degradation process of the bottles, trays, and deli containers
are presented in Figures 3.6, 3.7, & 3.8. Figure 3.6 shows degradation of the PLA bottles
over the 30 days. Initially the bottles decreased in size and became tough. This
phenomenon is attributed to the hydrolysis process that takes place in polylactide

polymers. A similar degradation pathway can be seen in Figures 3.7 and 3.8 for the trays

85

and deli containers. However, the decrease in thickness and increase in fragility of the
tray and deli containers was much faster than for the bottles. From the first day,
degradation in all packages was observed correlated to their change in shape. The
dimensions of the containers before and after composting until the bottles, trays, and deli
containers started to fragment were calculated by measuring the variation on width,
length, height and thickness of the containers. Bottles dimensions reduced to 90%, trays
to 22.4% and deli to 38%. Color changes were observed in the tray and deli containers;
both were significantly white at the bottom. On the fth day, the bottle structures
seemed almost the same as in the first day, but with shorter dimensions by approximately
63.4% of the original volume whereas trays started breaking apart and had same opaque
characteristics at the creases and less dense areas. The deli container showed increased
degradation on the fourth day. On the sixth day, bottle breakdown at the neck was
observed and cap liners were already separated. Color change and brittleness were also
observed. Trays and deli containers showed ahnost the same rate of degradation with deli
containers having almost 70% breakdown. On the ninth day, the bottle color showed
white, blue and yellow shades, a powdery texture, and was more brittle. Most of the parts
of the trays were already part of compost and approximately 98% of the deli containers
were composted. Fifteenth day, the bottle walls and necks were almost degraded except
the cap liners and bottom parts still had some residues, whereas the trays and deli
containers were already degraded and became part of compost. Some residuals from
bottles were still observed on day 30. The residuals were mostly part of cap liners and in
the form of string-like structures of very little strength. All other packages were degraded

by the thirtieth day.

86

law
'I a
,
I:
".
...

 

Day Day9 Day 15 ‘ Day 30
Figure 3.6. Pictorial View of the PLA bottles exposed at 30 day of compost conditions.

 

Day 15 ' Dy 30
Figure 3.7. Pictorial view of the PLA trays exposed at 30 day of compost conditions.

87

 

Day 15

Figure 3.8. Pictorial view of the PLA deli exposed at 30 day of compost conditions.

Although a major difference between the molecular weight of the trays and deli
container was measured at time zero, this difference was not a reason for the longer
degradation time of the deli containers. These will be expanded later in the paper.

An immediate increase in thickness of all three packages was observed after the
first day in the compost pile (not shown). A doubling of the PLA wall and neck
thicknesses was found in the bottles, although near the cap this variation was smaller (not
shown). This increase in thickness is attributed mainly to the distortion of the containers
due to high temperature levels, and the increased presence of a porous structure due to

hydrolysis of the polymer.

88

342Ph
Molecul
ambient
meghtt
inbnnm
hating -
groups (5

P
hi niolec
tonperau
WMta r
molecula
nucroorg;
degradatit
baCkbOne
Pr0cess fl
reduced 0
“fight oh

and Water,

3. 4. 2 Physical properties

Molecular weight: The molecular weight of bottles, trays, and deli containers exposed to
ambient exposure and to composting conditions were monitored by GPC. Molecular
weight variations are an indication of the degradation rate of the polymers and give
information about when the main fragmentation occurs in a polymer. PLA polymers, by
having —C-O- ester linkages in the polymer backbone which are hydrolysable functional
groups (see Scheme 3.1), are susceptible to hydrolysis.

First, randon non-enzymatic chain scission of the ester groups leads to a reduction
in molecular weight. This step is accelerated by acids or bases and is affected by
temperature and moisture levels[13]. Embrittlement of the polymers occurs in this step
with a reduction of the molecular weight to around 50,000 Daltons. Second, low
molecular weight PLA (Mn<10,000) can diffuse out of the bulk polymer and be used by
microorganisms, yielding carbon dioxide, water, and humus. In the first step, PLA
degradation is driven by the hydrolysis and cleavage of the ester linkages in the polymer
backbone, autocatalyzed by the carboxylic acid end groups (Scheme 3.1). This part of the
process follows first order kinetics[31]. In the second step, the molecular weight is
reduced by the diffusion of the bulk polymer, and the lactic acid and low molecular
weight oligomers are naturally metabolized by microorganisms to yield carbon dioxide

and water.

89

Mai
group and
PIOCeSs in l
accessibilit)
Percemage,
dlSlIibUll‘On‘
1101},aner deg
60°C) Will c
bottle, trayg‘

gH3 O 9H3 9H3
' E \ 5 Opoly
3

Scheme 3.1. PLA hydrolysis and molecular weight loss

Mainly, the polymer degradation rate is determined by the nature of the functional
group and the polymer reactivity with water and catalysts. Although the degradation
process in PLA is a simple hydrolysis, any factor which affects the reactivity and the
accessibility such as particle size and shape, temperature, moisture, crystallinity, isomer
percentage, residual lactic acid concentration, molecular weight, molecular weight
distribution, water diffusion, and metal impurities from the catalyst, will affect the
polymer degradation rate[13, 32, 33]. In general, high temperature and humidity (50°C to
60°C) will cause PLA to degrade rapidly[34]. The molecular weight variation of the
bottle, trays, and deli containers exposed to ambient and composting conditions for a

period of 30 days can be seen in Figure 3.9 a to f. PLA bottles show a small increase of

90

molecular
these var
lower nu
statistical
first 15 d
variation
(P>0.01).
significan
to ambien
the contait
cleavage 2
increase it
P01}'(lactid
deterioratic
in the mole
glass lransi
degradation
Figu
were eXPOSc
Weight Val’Ia
the PLA tray

9, While [he I

Was not POssi

molecular weight due to the exposure to ambient conditions (Figure 3.9-a); however,
these variations were not significant at the or=0.05 level (P>0.01), mainly due to the
lower number of samples tested (six). In the case of the trays (Figure 3.9—b), a
statistically significant increase in the molecular weight of ~28% was observed during the
first 15 days (P<0.01). In the case of the deli containers (Figure 3.9-c), no significant
variation of the molecular weight as a function of time was found at the or=0.05 level
(P>0.01). However, the variation of the polydispersity index (PDI) was statistically
significant at the or=0.05 level (P<0.01). The increase of the MW for the sample exposed
to ambient conditions could be due to recombination which occurs during the exposure of
the containers to UV or gamma radiation. The electromagnetic radiation produces chain
cleavage and subsequent recombination, which can result in crosslinking and hence an
increase in the MW. Kai- Lai and Pometto, (1999) showed that the exposure of
poly(lactide) fihns to ultraviolet light (UV) enhances the degradation rate and the
deterioration of the mechanical properties of these polymers [35]. However, the increase
in the molecular weight, in case of the bottles and the trays, produces an increase in the
glass transition temperature (shown later in Figure 3.11 a, b, &c) and leads to slower
degradation since glassy polymers degrade more slowly than rubbery ones.

Figures 3.9 d, e, and f show the molecular weight change of the packages that
were exposed to compost conditions for 30 days. Figure 3.9 (I) shows that the molecular
weight variation of the PLA bottles in the first 15 days of composting is much lower than
the PLA trays and deli containers. Major fragmentation of the bottles was observed at day
9, while the trays and deli containers showed similar fragmentation at day 6. At day 30, it

was not possible to locate any pieces of the tray and the deli container for analysis. The

91

 

PLA bot
after bei
attribute:
degradat
followin
molecule
degradat‘

kinetic p.

Table 3.2
level of s
(the pres

dffgradatic

PLA bottles and trays (Figure 3.9 d & e) show a small increase in the molecular weight
after being exposed to the compost pile for 1 day. This MW increase could mainly be
attributed to crosslinking or recombination reactions. In the case of PLA, the slow
degradation rate produces a loss of molecular weight over the polymer cross-section
following first order kinetics[31]. Therefore, by fitting the data of the variation of the
molecular weight as a function of time (equation 2), we can observe that the Mw
degradation of the bottles, trays, and deli containers correlated well with a first order

kinetic process as described by equation 2.

Mw = a * exp _b*t (2)
Table 3.2 shows the estimate of “a” and “b” values from equation (2) and their statistical
level of significance for the PLA bottles, trays, and deli containers. Higher “b” values

(the pre-exponential factor of equation 2) shown in Table 3.2 are an indication of faster

degradation process, shown in Figure 3.9 e and f for the deli containers and the trays.

92

 

150_

100(

O:

u- i

0 00 m M

258 L.-
zoo

25.—IA- .no — {$2

”1

Figure 3.9

(PL

 

 

 

 

  
 

'é
a .
N
.
.
..
.
..
N

 

 

 

 

 

 

 

 

 

m E
g 42.0 2 2-0
a 150 . I31 I-
a 9 "' ‘3 1:
0~ arr" a:
"éa 7' °
— ’ >1 1.5
100 "‘1 t
F; 1.5 3
E
E
50
1.0
==1.0 ==
258 v 2.5 258 ‘ 4 ' l . 25
(f)
‘ 2.0
4 1.5
‘ 1.0
. . . . . (m
0 5 10 15 20 25 30 0 5 10 15 20 25 30

Time, days Time, days
Figure 3.9. Comparison of the variation of the molecular weight and polydispersity index
(PDI) as a function of time for a) bottles, b) trays, c) deli containers exposed to
the ambient for 30 days; and d) bottles, 6) trays, f) deli containers exposed to
composting conditions for 30 days.

93

Tab

 

Pmpr

 

Bot

Tr.

De

 

0 P,&
depe
an as

. Adj]
aCCOI

° The‘

Th
reduction
COmpost it
alkaline m
Crl’stallinit
researChers
randomly. 1
Therefore‘ 1
Place, and ;
ProduCes dr

mOHOmers.

Table 3.2. First order equation (Mw x 103: a*exp (-b*t)) of the degradation process

of poly(lactide) bottles, trays, and deli containers

 

 

Properties L- x, a P, b Pb Adj
Lactide, qur
%
Bottle 96 12.2i1.4 229.7:t28.4 0.0002 0.1865:t 0.85
0.0533 0.0128
Tray 94 9.2:t9.7 204.8:t21.5 0.0002 0.1953 0.0088 0.88
0.0470
Deli 94 2.7i1.8 195.0i42.0 0.0056 0.24013: 0.0911 0.64
0.1 149

 

0 Pa & Pb are the probability of being wrong in concluding that there is an association between the
dependent and independent variables. The smaller the Pvalue, the greater the probability that there is
an association. For this paper or=0.05.

0 Adj qur is the R2 which measures the proportion of the variation in the dependent variable
accounting for the number of explanatory variables.

0 The “a” and “b” values are shown with their 95% confidence levels.

The lower adjusted R values for the deli container is mainly due to a smaller
reduction in the Mw of the samples extracted at day 4, credited mainly to the lower
compost temperature in this part of the compost pile. So, PLA polymers in a slightly
alkaline medium follow a first order hydrolysis process mainly affected by the initial
crystallinity, thickness, and the shape of the samples as previously demonstrated by other
researchers[27]. Figures 3.9 d, e, and f also show the change of the PDI values of the
bottles, trays and deli containers. Since the hydrolysis of poly(LD-lactide) occurs
randomly, longer PLA chains are more susceptible to cleavage than the shorter ones.
Therefore, an initial rise of the PDI after day 4 and after that for a few more days took
place, and it can be correlated with an increase in the fragmentation process, which
produces decomposition of the macromolecules into shorter oligomer chains and
monomers. Afterwards, polymer fragmentation took place and a narrowing of the

molecular weight distribution occurred with a decrease in PDI until total degradation

94

 

where thr
Similart
reach fin
Glass trc
temperat
shown ir
increase
a total N
conditior
molecular
rate in tl
degradati
amorphor
degradatir
Other regc
increased
Shown] E
hEating CI
of the San:
and Trn OI‘
Shown in F
when the P]

the recombir

where the PDI tends to 1.00. At this point, only oligomers of the PLA chains are present.
Similar trends are observed for the three containers although PLA tray and deli containers
reach final degradation much faster.

Glass transition and melting temperature: Examples of the glass transition and melting
temperature variation of PLA bottles exposed to composting conditions for 30 days are
shown in the DSC plot of Figure 3.10. During the first four days of composting, a slight
increase of Tg is observed which is due to the short-span increment of the MW. After that,
a total reduction of T8 to around 30°C is observed for the bottles exposed to compost
conditions for 30 days. This reduction in TS is associated with the reduction of the
molecular weight of the bottles. Since the hydrolysis of PLA polymers occur at a higher
rate in the amorphous region, the overall crystallinity of the containers increased as
degradation of the polymer chains took place. By the preferential degradation of
amorphous areas, an increase in total crystallinity was also observed during the
degradation process of the partially crystalline polymers in aqueous media also noted by
other researches[36]. For example, the initial crystallinity of the bottles xc = 12.2i1.4
increased to values of around 16% until the last degradation day (First run of the DSC not
shown). During the second run, the crystallinity of the samples decreased because the
heating of the samples over the melting temperature erased all the previous thermal story
of the samples, and the cooling cycle did not allow crystallization. The variation of Tg
and Tm of the packages exposed to ambient and composting conditions for 30 days are
shown in Figures 3.11 a, b, c, d, e, and f. The T8 of the bottles and the trays slightly rose
when the PLA containers were exposed to ambient conditions for 30 days mainly due to

the recombination process which increases the molecular weight and the Tg,

95

->

- Endo Exo -

 

Figu r.

Th

fOllows a 1

Vaers

Where “T121 1

the T‘g as 3

0'970003 V
container at

Table 33 Silt

 

 

 

 

 

 

 

 

, ~—-~-—-~——--——--...,_- ___P.ez:t-
E, ~-—--—~—-—-‘_,_._.____/—*“":--.. Day 5
a F— T
[a ‘h'_'—'—"'""“‘~.—-—-__-_- _._-—-—-—-._ \‘V’ Day 9
, __ \ ',_._.._._--
V" f\ “Nu—d
_______ / \.
"“- ——————— -" xx . Day 15
\U\ f ——————
T
fig \/ Day 30

 

 

 

 

r 20 40 5'0 8'0 100 1:30 140 160 is 0
Temperature

Figure 3.10. 2nd run of DSC showing the glass transition and melting temperature
variation of the PLA bottle exposed to composting conditions for 30 days
The reduction of the Tg for the PLA packages subjected to compost conditions
follows a linear trend. Table 3.3 shows the results of fitting equation 3 to Figure 3.11’s
values
Tg= Tgwy+d*t (3)
where “Tm,” is the glass transition temperature at time zero, and “d” is the reduction of
the Tg as a function of time. Table 3.3 and Figure 3.11 d) show that a reduction of Tg=
O.97°C/day took place in the bottles exposed to composting. For the trays and the deli
container a reduction of Tg= O.70°C/day and Tg= 0.53°C/day were observed, respectively.

Table 3.3 shows that a good fit to equation 3 is found for the PLA bottles and trays.

96

 

60r

40

3Q;
70

1”

it )1

l

60

St.)

1.2. "C

40 .

3T :3
mL .

60' 0\
St)

40

 

30:]:
0

 

 

70

(a)

 

70‘

60

50

Tg, °C

40

3Q:

160

:100

 

70

60

40'

160

140

120

 

’(t

 

 

15

20

Time, days

25

160

 

70

 

(d)'

2100

 

160

 

 

 

 

 

 

3&1: *************** 12100
70 ‘ ‘ 160
(0
‘ 140
- 120
40 -

30:: ::100
0 ' ‘ ‘ ‘ ‘ ‘ ' O
0 5 10 15 20 25 30
Time, days

Figure 3.11. Glass transition and melting temperature variation of a) bottles b) trays c)
deli containers exposed to the ambient conditions for 30 days; d) bottles e) trays f)
deli containers exposed to composting conditions for 30 days

97

 

ln

 

 

agreemer
I

Propc
Bot

Tr:

De

. PTgll
depe

an 85

. Adjl
accor

° The‘
If t

(Mn), “he
the “it (If:
decreases_
Ta:

Where “Tat:
results of fl.
the best fit
bOIIles haw
containerS sf

and d6“ COnt.

or being in if.

In the case of the deli containers the fitting of equation 3 does not show a good
agreement (Adsqu= 0.67).

Table 3.3. Variation of glass transition Tg= Tg(0)+d*t as a firnction of time for

poly(lactide) bottles, trays, and deli containers

 

 

Properties L- x, Tgm, PTgm) d Pd Adj
Lactide, qur
%

Bottle 96 12.2:t 60.86:t1.01 <0.0001 -0.97:t <0.0001 0.95
1.4 0.08

Tray 94 9.2i 59.87i0.95 <0.0001 -0.70:t 0.0031 0.82
9.7 0.13

Deli 94 2.7i 59.15i1.04 <0.0001 -0.53:1: 0.0143 0.67
1.8 ' 0.14

 

0 PTg(0) & Pd are the probability of being wrong in concluding that there is an association between the
dependent and independent variables. The smaller the Pvalue, the greater the probability that there is
an association. For this paper or=0.05.

o Adj qur is the R2 which measures the proportion of the variation in the dependent variable
accounting for the number of explanatory variables.

0 The “Two,” and “d” values are shown with their 95% confidence levels.

If we plot the reduction of Tg as function of the number average molecular weight
(Mn), where M": Mw/ PDI (Figure 3.12 a, b, and c), we can observe that Tg decreases as
the Mn decreases, which translate into a reduction of PLA degradation rate when Mn
decreases. The influence of Mn on Tg can be expressed by an equation of the type:

Tg= Tg,...) — A/Mn (4)
where “Tg(o,)” is the Tg for very high Mn , and “A” is a constant term. Table 3.4 shows the
results of fitting equation 4 to the data of Figure 3.12. There is a slight difference between
the best fit of equation 4 for the bottles, the trays, and the deli containers. The PLA
bottles have a better fit to equation 4 (Adj-qur=0.95). However, the trays and the deli
containers show a poor correlation. This lack of correlation of T8 against Mn for the trays
and deli containers is mainly because it was not possible to analyze samples after 15 days

of being in the compost (i.e., lower Mn), and due to the variation in temperature at day

98

four for

relation:

 

i conditio

Tab

1 mole

 

Pro

I

\

0 Ply
the (1

there

- Adj 1
accor

0 The .r
Decompos
by melt hv.
COHdensatir
room temp,-
depolirnen;
re(111011.011 in
degradathn

m mOiecular

it'aler at reialj

four for the trays. The variation of Tm as a function of time does not follow a linear
relationship. A slight increase of Trn is found for the samples submitted to compost
conditions at the beginning of the composting process.

Table 3.4. Variation of glass transition Tg= Tg,») — A/Mn as a function of average

molecular weight number for poly(lactide) bottles, trays, and deli containers

 

 

Properties L- x, Tgm PT gm A PA Adj
Lactide, qur
°/o
Bottle 96 12.2i 60.423: <0.0001 -112,972:1: <0.0001 0.95
1.4 0.94 8,968
Tray 94 9.2:t 58.833: <0.0001 -44,435:t: 0.0147 0.67
9.7 1.14 12,166 '
Deli 94 2.721: 58.662t <0.0001 -32,643:l: 0.0289 0.58
1.8 1.12 10,750

 

o PTg(°°) & P A are the probability of being wrong in concluding that there is an association between
the dependent and independent variables. The smaller the Pvalue, the greater the probability that
there is an association. For this paper or=0.05.

o Adj qur is the R2 which measures the proportion of the variation in the dependent variable
accounting for the number of explanatory variables.

0 The “Ta 0,,” and “A” values are shown with their 95% confidence levels.
Decomposition temperature: PLA polymers in an open system such as the TGA degrade
by melt hydrolysis or thermal degradation. Melt hydrolysis is the reverse of the
condensation esterification of lactic acid which is important for articles stored in air at
room temperature and composting conditions. Thermal decomposition occurs by
depolymerization and random degradation. Depolymerization is characterized by a rapid
reduction in polymer mass with a slow reduction in molecular weight, while random
degradation is characterized by a slow loss of polymer mass with an exponential decrease
in molecular weight. These two processes are important during resin processing without

water at relatively high temperature.

99

 

 

 

 

 

 

 

 

 

 

 

. ((8)
60b F44
t
50 w .. 1 i
40 , 4
l
3132“ g =3
l (b)
I
60 T a t
I .
. I
U 50
O
a?)
E"
40'
3 ' S:
0 L l
(c) g o
60‘ " _ ‘__“
F i
so‘
40‘
0‘1“. . . . r. . .» T
0 20 40 60 80 100 120 140

M3103
Figure 3.12. Tg vs Mn of the a) bottles b) trays, and c) deli containers exposed to compost
conditions for 30 days

100

 

Day 0
Day 1
Day 2
Day 4
Day 6
Day 9
Day 15
Day 30

 

Weight (%)

 

 

 

 

 

 

-20...,...,...,-..,...,...
0 100 200 300 400 500 600

Temperature (°C)
Figure 3.13. a) Weight percent reduction vs temperature

A TGA plot of the variation of weight as temperature increased for the bottles
exposed at different composting times is shown in Figures 3.13 a & b. It is possible to
observe that the major change in variation of the decomposition temperature (TD)
happened between days 15 and 30 when the Mw of the bottles decreased from around
11,000 to 4,000 Daltons.

The variation of TD as a function of time for the packages exposed to ambient and
composting conditions is shown in Figure 3.14. Figures 3.14 a, b, & c show the variation
of TD versus time for PLA bottles, trays, and deli containers exposed to ambient
conditions and to composting conditions, respectively. As shown in Figure 3.14, no

variation of the TD as a function of time was observed for the samples exposed to ambient

101

conditions. However, a reduction of TD was observed for all the samples exposed to
compost conditions.
The variation of TD with time is a linear variation. Table 3.5 shows the values obtained
from fitting equation 6 to the data shown in Figure 3.20:

TD: Tm + e*t (6)
where “T90” is the decomposition temperature at t=0 day, and “e” is the variation of TD
as a function of time. Table 3.5 also shows the variation of TD vs Mn for equation 7:

TD: TD(oo) — B/Mn (7)
where “TD(°°)” is the TD for very high Mn , and “B” is a constant term. The variation of TD
vs time and the correlation with the number average molecular weight show that PLA
bottles presented a lower reduction of TD as they were exposed to compost conditions

than the trays and the deli.

102

 

420 T 77 I I I T I

400 ‘

380"

360 .

340 :

 

320 ‘

300 : .
420 . t t : t t t

j}

#1

 

400 r
380 a

360 ‘

TD, °C

340 .

320 :

 

I)

 

300 ~i

H
L

400 ‘

380 r

360 r

340 r

320 ..,

 

I

 

 

..... . d ‘

300 J
0 l J l l l l l
o 5 10 15 20 25 30

 

Time, days
Figure 3.14. Decomposition temperature a) bottles b) trays c) deli containers exposed to
(D) ambient and (') composting conditions for 30 days

103

Table 3.5 shows that a good adjustment of equation 6 & 7 are obtained for the
bottles, trays, and deli containers (see Adj qur values).
Table 3.5. Variation of decomposition temperature TD: Too + e*t as a function of time

(equation 6) and Molecular number for poly(lactide) bottles, trays, and deli containers.
Variation of decomposition temperature TD: Top») — B/Mn as a function of Mn

 

Equation 6: TD: TDO + e*t

 

 

Properties L- 1, Too PT DO e Pe Adj
Lactide,% qur

Bottle 96 12.2d:1.4 403.4i2.7 <0.0001 -2.8i0.2 <0.0001 0.95
Tray 94 9.23:9.7 403.5i3.9 <0.0001 -5. 1:1:0.5 0.0003 0.93
Deli 94 2.7i1.8 398.4i9.5 <0.0001 -6.2i1.3 0.0057 0.77

 

guation 7: TD: Tom) — B/Mn

 

 

Properties L- x, Tom P T1)(oo) B P3 Adj

Lactide,% qur

Bottle 96 12.2:t1.4 402.2123 <0.0001 -327,501:t <0.0001 0.97
21,647

Tray 94 9.2i9.7 397.8:t3.3 <0.0001 -342,941d: 0.0002 0.94
35,267

Deli 94 2.7i1.8 395.8i6.9 <0.0001 -417,296i 0.0015 0.86
66,225

 

0 PTDO, PC, Tm on), & P3 are the probability of being wrong in concluding that there is an association
between the dependent and independent variables. The smaller the Pvalue, the greater the probability
that there is an association. For this paper or=0.05.

0 Adj qur is the R2 which measures the proportion of the variation in the dependent variable
accounting for the number of explanatory variables.

0 The “Tm,” TDW, and “B” values are shown with their 95% confidence levels.

In summary, PLA polymers absorb water resulting in the hydrolysis of the ester
linkages, which produces the breakdown of the long macromolecular chains. PLA 94%
L-lactide packages degraded faster than those of 96% L-lactide. The rate of degradation
is mainly affected by the L-lactide content and the crystallinity of PLA, and the
temperature, relative humidity, and pH of the pile. The change of the degradation rate
with respect to the initial crystallinity of the containers should be considered when

samples are introduced in compost piles; however, the three packages did not take more

104

than a month to completely degrade even though the packages were not ground (worst
case scenario) before they were introduced to the compost pile. Similar compost studies,
but with PLA samples and not complete packages, were carried out by Weber [37] by
storing PLA samples in biodegradation chambers. As a result, they recommended that a
maximum of 10% PLA be used in compost piles to prevent pH reduction of the pile. In
this study, this concern was not a problem due to the ratio of polymer to compost. Some
comparisons between laboratory and field exposure degradation have been carried out by
Pometto and collaborators [34, 35, 38-40]. They exposed PLA films in banana fields in
Costa Rica, and found that these PLA plastic films lost their mechanical properties faster
than during exposure in simulated conditions in the laboratory [39]. They also found that
degradation of PLA is enhanced by an increase in temperature and relative humidity [34].
However, no comparison or methods of assessing the degradation of complete packages
were carried out.

Thus, the present work addressed the degradation time of the physical properties
of three commercially available PLA packages and gives information on the
compostability and the reduction of the physical properties under real compost as well as
ambient exposure conditions. Further studies are being carried out to simulate the real
degradation process in simulated conditions in order to establish reliable tests to evaluate
degradation under real compost conditions. This work found that the degradation time of
PLA trays and deli containers in a commercial facility was not more than 30 days, and in
the case of the bottle was not more than 45 days. Packages made of PLA will compost in
municipal/industrial facilities, but they may be difficult to completely compost in

backyard composting since PLA degradation is driven by hydrolysis which needs higher

105

temperatures to take place. Further research is necessary to find methods and techniques
that can assess the degradability of biodegradable packages under real composting

conditions before they are degraded in commercial composting operations.

3.5 CONCLUSIONS

Three PLA packages, a bottle, a tray, and a deli container, were used to determine
the degradation process under ambient exposure and under compost conditions. A novel
method was used to identify and keep track of the degradation of the PLA packages on a
real compost facility. The degradation of the PLA containers was monitored by visual
inspection, GPC, DSC, and TGA. PLA trays and deli containers degraded before 30 days
under composting conditions (T>55 °C, >65%RH, ph~7.5). First order degradation
kinetics was observed for the bottle and tray. A Tg reduction of 1°C/day was found for
PLA containers with 96%L-lactide, and a Tg average reduction of around 0.6 °C/day was
found for PLA containers with 94% L-lactide. A method to study the compostability of
biodegradable packages under real compost conditions has been outlined. Further studies
are being carried out to address the compostability of biodegradable packages under
simulated conditions, and to establish a standard that can address the compostability of

biodegradable packages under real and simulated compost conditions.

106

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110

CHAPTER FOUR
Gaurav Kale, Rafael Auras, Sher Paul Singh. (2007) Comparison of Degradability of

Poly (lactide) Packages in Composting and Ambient Exposure Conditions. Packaging
Technology and Science. 20(1): 49-70

111

CHAPTER FOUR - COMPARISON OF THE DEGRADABILITY OF POLY
(LACTIDE) PACKAGES IN COMPOSTING AND AMBIENT EXPOSURE

CONDITIONS

ABSTRACT

The adoption of biodegradable polymeric materials is increasing in food and
consumer goods packaging applications, due to concerns about the disposal of petroleum-
based polymers and the increasing cost of petroleum-based polymer resins. Currently,
poly(lactide) (PLA) polymers are the biggest commercially available bio-based
polymeric packaging materials. As the main motivation for adopting biopolymers is
environmental, there is a need to address the degradability and environmental
performance of biodegradable packages. The aim of this study was to investigate and
compare the degradation of two commercially available biodegradable packages made of
PLA under real compost conditions and under ambient exposure, using visual inspection,
gel permeation chromatography, differential scanning calorimetry and thermal
gravimetric analysis. A novel technique to study and track the degradability of these
packages under real compost conditions was used. Both packages were subjected to
composting and ambient exposure conditions for 30 days, and the degradation of the
physical properties was measured at l, 2, 4, 6, 9, 15 and 30 days. PLA bottles made of
96% L-lactide exhibited lower degradation than PLA delicatessen ('deli') containers made
of 94% L-lactide, mainly due to their highly ordered structure and, therefore, their higher
crystallinity. The degradation rate changed as the initial crystallinity and the L-lactide

content of the packages varied. Temperature, relative humidity and pH of the compost

112

pile played an important role in the rate of degradation of the packages. First-order
degradation kinetics and linear degradation trends were observed for both packages

subjected to composting conditions.

4.1 INTRODUCTION

There is an increasing demand for biopolymer-based packaging materials that are
easily renewable, providing enhanced environmental performance. Until recently the
majority of the production of packaging plastics was based on non-renewable materials.
Plastic packaging materials are often landfilled due to their content of foodstuffs and
other biological substances, making physical recycling of these materials impractical. Use
of biOpolymer-based packaging materials reduces concerns such as landfilling, sorting
and reprocessing by taking advantage of their unique functionality, i.e. compostability.
Hence, compostability has been the main focus of applications of biobased packaging
materials, which is the natural outcome for a vast amount of food and pharmaceutical
packaging materials and waste. Composting permits disposal of biodegradable packages
and is not as energy intensive as sorting and reprocessing for recycling, although it
requires more energy than landfilling. For example, in countries like the USA, where
landfilling is predominant, composting at this time is more expensive.l

Composting is the controlled and natural decomposition of organic materials by
microorganisms. The organic materials are decomposed into a soil-like substance called
humus. The major groups of microorganisms involved in composting are fungi, bacteria
and actinomycetes. Microorganisms need food in the form of carbon, nitrogen, oxygen

and water. Organisms decompose the organic matter by utilizing carbon as a source of

113

energy and nitrogen for building cells. A 30:1 carbonznitrogen ratio is an ideal proportion
for the reproduction of thermophilic microorganisms.2 A compost pile goes through two
composting stages. In the first stage, the temperature rises up to around 60°C, so long as
oxygen, carbon and nitrogen are available in the ideal proportions, and promotes strong
microbial activity. In the second 'curing' stage, the decomposition continues at a slower
rate and the last remaining nutrients are consumed by microorganisms and until almost
all the carbon has been converted to carbon dioxide.

The compostability of a compostable plastic (i.e. 'a plastic that undergoes
degradation by biological processes during composting to yield CO2, water, inorganic
compounds, and biomass at a rate consistent with other known compostable materials and
leaves no visible, distinguishable or toxic residue'3) is commonly evaluated in simulated
compost conditions and by assessing the final quality of the compost. While evaluating
the compostability, plastics are subjected to mechanical, thermal and chemical
degradation, of which chemical degradation is the most important. Biodegradable
polymers first become susceptible to water attack and chemical degradation initiates the
polymer erosion as a result of hydrolysable functional groups in the polymer backbone.
Standards have been developed for evaluating the degradation and compostability of a
biopolymer by the American Society for Testing and Materials (ASTM), the International
Standards Organization (ISO) and the European Committee for Standardization. The
ASTM standards (i.e. ASTM D5338-98,4 D6003-96,5 D6954-04,° D6400-99,3 and D
6002-96 (reapproved 2002)°],7) developed by subcommittee 20.96 for assessing
compostability, are laboratory-scale and limited to the evaluation of plastic materials.”—7

Similarly ISO standards, such as ISO 14851,8 148529 and 14855,10 allow evaluation of

114

materials under laboratory conditions and are based on measuring the carbon dioxide
evolution and oxygen demand during degradation. The EN 1343222000ll standard
developed by the European Committee for Standardization addresses compostability
referring to ISO standards and evaluates the compost quality and toxicity. The above-
mentioned standards mainly focus on addressing the compostability of a polymer or a
material, but not that of a package in real conditions. The degradation time of an entire
package as encountered in the case of full-scale facilities that do not grind feedstock may
be much longer than when the polymer pieces are ground, representing a worst-case
scenario for compostability. Moreover, poor representation of actual composting
conditions is a major negative aspect, since mistaken conclusions could easily be drawn
as biodegradation mechanisms vary among substrates.

The adoption of biodegradable polymeric materials is increasing in food and
consumer goods packaging applications, due to concern about the disposal of petroleum-
based polymers. Currently, poly(lactide) (PLA) polymer developed by Cargill Dow LLC
(Blair, NE) and at this time under the name of NatureWorks® LLC, is the biggest
commercially available bio-based polymeric packaging material. NatureWorks® LLC is
producing 300 million 1b PLA annually for a variety of packaging and fibre applications.
Eastman Chemical Company (Hartlepool, UK), has developed Eastar Bio aliphatic co-
polyester, which is being used in lawn and garden bags, food packaging and horticultural
applications worldwide. Similar to Eastar, Proctor and Gamble Co. (P&G) (Cincinnati,
OH) has produced an aliphatic co-polyester (Nodax) line of polymers that are
biodegradable in aerobic and anaerobic conditions. The Nodax polymers are produced by

microorganisms through a fermentation process, and the plastics are extracted from the

115

biomass. DuPont has a 200 million lb/year production facility in Tennessee for its
Biomax polyethylene terephthalate co-polymer hydro/biodegradable polyester, which is
available both overseas and in the USA.'2

PLA polymer, the predominant biopolymer in the market for packaging
applications, can be manufactured by carbohydrate fermentation or chemical synthesis.
Lactic acid (2-hydroxypropionic acid) is the simplest hydroxyl acid with an asymmetric
carbon atom, and it exists in two optically active configurations, the L(+) and D(—)
isomers. The majority of lactic acid is made by bacterial fermentation of carbohydrates.
The fermentation processes to obtain lactic acid can be classified according to the type of
bacteria used. High molecular weight PLA can be obtained using different methods: (a)

13 (b) azeotropic dehydrative condensation

direct condensation polymerization;
polymerization, currently used by Mitsui Toatsu;13 and (c) polymerization through lactide
formation, developed by Cargill Inc. in 1992.13 The properties of high molecular weight
PLA are determined by the polymer architecture (i.e. the stereochemical make-up of the
backbone) and the molecular mass, which is controlled by addition hydroxylic
compounds.13 The ability to control the stereochemical architecture permits precise
control over the speed of crystallization and finally the degree of crystallinity, the
mechanical properties and the processing temperature of the material.'3 In addition, the
degradation behaviour strongly depends on the crystallinity of the PLA.13 The glass
transition temperature (T g) is in the range 50—80°C, while the melting temperature (T m) is
in the range 130—180°C. PLA can be processed by injection moulding, sheet extrusion,

blow moulding, thermoforming and film forming. PLA is approved by the Food and

Drug Administration for its intended use in fabricating articles in contact with food.13

116

Life-cycle assessment (LCA) and economic studies indicated that PLA polymers are

“H7 which is mainly because PLA

more energy-efficient than PP and PS polymers,
consumes almost no feedstock energy.

Currently, PLA is being commercialized and used as a food packaging polymer
for short shelf-life products with common applications, such as containers,18 drinking
cups, sundae and salad cups, overwrap and lamination films, blister packages, and
bottles. As the PLA consumption is increasing, there is a need to address its
compostability in real composting conditions and its potential recyclability. In 2003 in
the USA,1 15 full-scale solid waste composting facilities (i.e. 'ones that include the
residential waste stream that arrives at the plant as mixed waste or source separated
fractions”) were in operation. Hence for PLA to be considered as an alternative to
conventional polymers, a wide range of composting facilities needs to be developed, or
PLA will need to be composted with general yard waste. Looking at PLA's potential
recyclability, NatureWorks® LLC instituted a large volume 'buy-back' programme in
North America for post-consumer treatment of PLA bottles in mixed plastic waste
recycling streams.19 PLA can be sorted from other plastics using near-infrared
technology. However, as already mentioned, recyclability is not an alternative for
containers with foodstuff contents.

As previously described, the standards developed so far mainly address the
compostability of plastic in simulated conditions and correlated to evolution of CO2.
There are several parameters which differentiate the real and simulated or controlled

composting conditions. According to ASTM D 6002-96(2002),7 and the Federal Trade

Commission (FTC),20 'compostable claims would be appropriate on products or packages

117

that will break down, or become part of usable compost, in safe and timely manner in
home compost piles',20 where 'timely manner' means the time necessary for leaves, grass
and foodstuffs to compost. Some of the commercially available 'biopolymer materials'
comply with the standards of compostability, but generally packages or containers made
from these materials were not evaluated. According to ASTM D 6400-04,3 'products and
finished articles should be tested in the same form as they are intended to be used'.
Therefore, if the packages show different chemical composition or structure, it is
necessary to test them to evaluate their compostability.

The aim of this paper is to provide information about the comparison of
degradability of two commercially available biodegradable packages in real composting
and ambient environments, further correlating and comparing their degradation through
visual inspection and analysis of physical properties. The physical properties analysed
were: molecular weight, using gel permeation chromatography (GPC); glass transition
(T g) and melting temperature (T m), using differential scanning calorimetry (DSC); and

decomposition temperature (T D), using a therrnogravimetric analysis (TGA).

4.2 MATERIALS AND METHODS
4.2.1 Packages

Poly(lactide) bottles were obtained from NatureWorks® LLC (Blair, NE) and
commercialized by Biota brands of America (Telluride, CO) with 96% L-lactide and
bluetone additive, height = 0.2 m and base diameter = 0.0065 m (volume = 500 ml).

Delicatessen ('deli') containers were obtained from Wilkinson Manufacturing Company

118

(Fort Calhoun, NE) with 94% L—lactide; height = 0.07 m and base diameter = 0.09 m

(volume = 600 m1). Figure 4.1a, b shows these containers.

 

Figure 4.1. PLA containers a) bottle & b) deli container

4.2.2 Compost pile

A compost pile used for this study was composed of cow manure and wood
shavings prepared at the Michigan State University Composting Facility (East Lansing,
MI) and was used for the study. Initially, 11.6 m3 cow manure and 7.8 m3 wood shavings

were mixed. This mixture was combined with waste feed (i.e. the feed that the cows do

119

not eat between feedings) in a proportion of 2:1. The mixture allowed a carbonznitrogen
ratio of 30:1. The mixture was kept in a rectangular bay of 36.5 x 3.6 x 1.8 m, which was
turned using a Marvel model of a commercial turner manufactured by Global Earth
(Ontario, Canada) 3 days/week for 3 weeks. Due to turning, the mixture was heated to
60°C in the presence of aeration. This temperature was enough to kill weed seeds and
pathogens. Later, the mixture was pulled out of the bay, and a pile of 24 x 6 x 3 m was
built up on an asphalt pad. Initially the compost parameters, such as temperature,
moisture and pH, were measured and determined. A temperature of 65 :b 5°C, moisture of
63 i 5% and pH of 8.5 i 0.5 was observed. Figure 4.2 shows a two-dimensional graph of

the temperature distribution inside the compost pile at the beginning of the testing.

Height ofpile. m

it.

‘ H 1(1.‘ .. .
trim,tttir1t;i=,tr.(t_(t‘;t i 111 ,( t‘
t titttt‘tttt = t itttthhttttttt
11111111111111“ m (“11111 ' At

t "

 

Width of pile, m
Figure 4.2: Temperature distribution inside the compost pile at the beginning of the

testing

120

4.2.3 Box

Wooden boxes of dimensions 0.6 x 0.3 x 0.1 m were manufactured using treated
wood and were used for subjecting packages into the compost pile. Those boxes
facilitated the exact location and identification of the package in the compost pile; and
also the removal of the package and portion of compost for analysis. A mesh of 0.011

gauge was fitted at the bottom of the boxes. A three-dimensional image of a wooden box

is shown in Figure 4.3.

0.609 m

0.304 m

m101'0

 

Figure 4.3: 3D view of Box
4.2.4 Plastic containers

Foldable reusable plastic containers obtained from CHEP-USA (Orlando, FL) of
dimensions 0.6 x 0.4 x 0.4 m were used to contain and expose the packages to ambient

conditions.

121

4.2.5 Placement of Packages

Composting exposure: Both bottles and deli containers were placed in duplicate sets in
the compost pile with the help of boxes, as mentioned above, at approximately 1.2 m
above the ground and 1 m inside the compost pile, where a uniform composting
temperature was obtained during the experiment. Initially, the compost was placed over
the mesh in the box; later, a package was placed with the addition of compost completely
over the box. The handle on the box facilitated identification of the exact location of the
boxes in the pile.

Ambient exposure: The packages were placed in the plastic containers mentioned above
in duplicate sets, as in case of composting exposure. The packages were taken out at 1, 2,
4, 6, 9, 15 and 30 days from both the compost pile and plastic containers.

4.2.6 Compost parameters

Temperature: Temperatures were recorded every time the packages were removed from
the compost pile, using a A60FR fast response windrow stainless steel thermometer (i
1°C) obtained from Reotemp (San Diego, CA). Temperatures were continuously recorded
using H12 Type I HOBO® brand battery-operated data loggers obtained from Onset
Computers (Pocasset, MA) at 6 h intervals for the duration of the study.

Moisture content:. The wet weight moisture content of the compost was measured using
a modified version of ASTM D4643-002| (previously validated using a traditional
vacuum oven).22 A sample of compost was obtained whenever packages were taken out
of the compost pile and checked immediately for the moisture content. Initially the wet
weight of compost was recorded and then heated in a 600 W microwave, Model

MW8625W, obtained from Emerson Radio Corporation (Parisppany, NJ) for 3 min. The

122

weight reduction in the compost due to evaporation of moisture was recorded, and the
sample was again subjected to microwave heating for 1 min. The cycle of recording the
weight and heating for 1 min was continued until constant weight was obtained. The
percentage wet weight moisture content was determined by the ratio of the difference
between the weight of the moist and oven-dried specimens to the total weight of the
moist specimen.

pH: The protocol for measuring pH of compost was originally obtained from Cornell
Composting.22 After the compost was dried through the microwave heating process, 5 g
of the specimen was added to 25 ml deionized water. This mixture was stabilized for 5
min before the pH of the solution was recorded using a calibrated pH paper (150AB
pHydrion paper dispenser), obtained from Micro Essential Laboratory Inc. (Brooklyn,
NY).

4.2.7 Ambient parameters

Hourly data for ambient parameters such as temperature, relative hmnidity and solar
radiation were obtained from the Michigan Automated Weather Network (East Lansing,
MI) located at 42.6734° latitude, —84.4870° longitude and 264 m elevation, for the
complete duration of the study. The air temperature measurements were taken 1.5 m
above ground level. Figure 4.4a shows the maximum and minimum ambient
temperatures; Figure 4.4b shows the maximum and minimum relative humidity during
the 30 day testing period; and Figure 4.4c shows the average daily solar radiation during

the same period.

123

 

Temperature, °C

 

RH, °°/o

 

 

 

‘ t
-—I— Max . ,
-0— Min

 

(C)
25 - 2

20'

15'

 

10'

 

 

 

Solar Radiation x 103, kJ/m2

 

 

 

 

0 5 10 15 20 25 30

Time, days
Figure 4.4: a) 30 days maximum and minimum temperature data; b) 30 days maximum
and minimum relative humidity data; c) 30 days average total solar radiation

124

4.2.8 Visual inspection

Every time that the packages were removed from the compost and ambient
exposure conditions they were visually inspected by the authors. A Sony Cybershot DSC-
P150 7.2 MegaPixel digital camera was used to take pictures. The packages were
inspected for colour, texture, shape and changes in dimensions.
4.2.9 Physical properties
Thickness. The thickness of the packages was determined using a Magna Mike 8000
thickness gauge, which utilizes a magnetic method manufactured by Panametrics (Japan)
according to ASTM D4166-99 (2004).23
Molecular weight. The molecular weight was determined using a standard GPC
technique. A 600 Multisolvent delivery system equipped with 717 autosampler and 2410
R1 detector from Waters (Milford, MA) was used to determine the molecular weight of
samples after extraction. Inhibitor-free tetrahydrofuran (THF) solution obtained from
Sigma Aldrich (Milwaukee, WI) was transferred to 2 ml vials containing 2 mg of
specimen. The vials with the specimens were manually shaken for 2 min. The dissolved
samples were filtered with 0.2 pm pore size, 13 mm disposable PTFE
(polytetrafluoroethylene) filters obtained from Whatrnan (F lorham Park, NJ). Diluted
solution was transferred to the 1 m1 clear glass shell vials used in the autosampler and
capped using polyethylene snap caps; both obtained from Waters (Milford, MA). Two PL
gel 10 um MIXED-B 300 x 7.5 mm id. columns from Polymer Laboratories (Amherst,
MA) in series were used, giving a detection range of 1000—10 000 000 Da. Polystyrene

obtained from Sigma Aldrich (Milwaukee, WI) was used as a standard for calibration

125

purposes. Experiments were run at 35°C. Sample concentrations for polystyrene and PLA
samples were 1 mg/ml at a flow rate of 1 ml/min.
Glass transition and melting temperature, enthalpy of fusion and cnrstallinity. The
glass transition temperature, melting temperature and crystallinity were determined using
a DSC Q-100 made by TA Instruments (Newcastle, DE) in accordance with ASTM D
3418-03.24 The DSC standard calibration procedure was performed according to ASTM
E967-0325 and ASTM E968-02.26 Analyses of the results were made using Universal
analysis software (version 3.9A). The percentage crystallinity was determined according
to ASTM D3417-9927 and equation 1:

AH + AHm

x (%)=100x C
C AHC
m

(1)

 

where AHC is the enthalpy of cold crystallization, AH”, is the enthalpy of fusion, and

AH ‘ is the heating of melting of purely crystalline PLA, 135 J/g.28’29

Decomposition temperature. The decomposition temperature was obtained using a TGA
TA 2950 made by TA Instruments (Newcastle, DE) in accordance with ASTM E1131-
03.30 The specimens were heated at a rate of 20°C/min from 23°C to 500°C in the
presence of inert gas (N2) and oxidative gas (02), both > 90 psi. The results were
analysed using Universal analysis software (version 3.9A).
4.2.10 Statistical analysis

All treatments were conducted in duplicate. Statistical analyses were carried out
using the General Linear Models procedure in JMP software (SAS Institute Inc., SAS

Campus Drive, Cary, NC).

126

4.3 RESULTS AND DISCUSSION

Poly(lactide) bottles and deli containers were subjected to composting and
ambient exposure conditions for a period of 30 days. Table 4.1 shows the initial physical
properties of these packages. The PLA bottles, made of 96% L-lactide, are a more highly
ordered structure, resulting in a higher crystallinity than the deli containers, with 94% L-
lactide. PLA derived from > 93% L-lactic acid can be semi-crystalline.13’31 Meso- and D-
lactide induce twists in the otherwise very regular poly(L-lactide) molecular architecture.
Molecular imperfections are responsible for the decrease in both the rate and extent of
poly(L-lactide) crystallization. In this study, the deli container had a higher molecular
weight than the bottle and a lower initial polydispersity index (PDI).

Table 4.1. Physical properties of the poly(lactide) bottles and deli containers

 

 

Properties Bottle Deli
L-Lactide (%) 96 94
Molecular weight (kDa) 209.3 :I: 1.06 222.7 d: 9.20
PDI 1.72 1.66

Tg (°C) 60.6 a 0.3 62.6 :1: 4.3
Tm (°C) 151.0i0.1 149.0i1.l
Crystallinity (%)a 12.2 i 1.4 1.4 :1: 0.3

 

“Percentage crystallinity was calculated according to equation 1.

The containers were introduced and located in the compost pile as described
above. The temperature, relative humidity and pH to which the three packages were

exposed during the composting conditions are shown in Figure 4.5a, b.

127

Temperature, °C

70

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

a %.

6 [i

0:“ i l i i t :—
0 5 10 15 20 25 30

Time, days

i r I I f 100
1 (a)
60 — - 80
< T °\°
50 t-'~ ~' - +- 60
i __ ‘ I >
I ‘ l
.' q
4 Es . - ~~240
0 i i i i i i 9u 0
* -- ‘(br -

 

Figure 4.5. a) Temperature and relative humidity of the compost pile at time of package
removal, b) pH of the compost pile at time of package removal

pH is one of the most important factors of hydrolytic polymer degradation, since

pH variations can change hydrolysis rates by a few orders of magrritude.3’2’35 In this

128

study, there was a slight alkalization of the pile afier the second day of testing, although
this difference was not statistically significant at the or = 0.05 level (p = 0.91) during the
30 days of composting.
4.3.1 Visual inspection

Pictures showing the degradation process of the bottles and deli containers in the
compost pile are presented in Figures 4.6, 4.8. Figure 4.6 shows the degradation of the
PLA bottles over the 30 days. Initially the bottles decreased in size. The change in shape

is because of distortion due to the higher temperatures in the compost pile.

 

      

Day 15 Day 30 i 1
Figure 4.6. Pictorial view of the PLA bottles exposed at 30 day of compost conditions.

129

 

Day 4

      

Day 6 Day 9 Day 15 Day 30
Figure 4.7. Pictorial view of the PLA bottles exposed for 30 days under ambient
conditions

A similar degradation process can be seen in Figure 4.8 for deli containers. From
the first day of being in the compost pile, shape changes were observed in both packages.
The dimensions of the containers before and after composting until the bottles and deli
containers started to fragment were calculated by measuring the variations in width,
length, height and thickness of the containers. Variation in thicknesses and shapes were
observed on both packages from day 1, when the bottle dimensions reduced to 90% and
those of the deli container reduced to 22.22% of their original volumes. Colour changes
were observed in the deli containers, which became white at the bottom. On day 4, the
bottle structures seemed the same as on the first day, but with shorter dimensions by
approximately 63.4% of the original volume, whereas the deli containers showed
toughness in the material. On day 6, bottle breakdown at the neck was observed and

bottle threads were already separated.

130

V, ‘
. r"

. . , a
Ti“, ,’. , .ri' ”i
1“ . .l ' . tl“ 1

t , .
. 31.1171‘1'1211 '1

 

Day 15 y
Figure 4.8. Pictorial view of the PLA deli container exposed at 30 day of compost
conditions.

 

Day 6 Day 9 Day 15 Day 30

Figure 4.9. Pictorial view of the PLA deli containers exposed for 30 days under ambient

conditions

131

Colour change and brittleness were also observed. The deli containers showed a
similar rate of degradation. On day 9, the bottle colour showed white, blue and yellow
shades and a powdery and more brittle texture; the deli containers started breaking apart,
had powdered structure, and were very brittle. By day 15, the bottle walls and necks were
almost degraded except for the parts of the bottle threads and bottom that still had some
residues, whereas the deli containers showed some residues in the form of a yellowish
film, although it could not be identified whether the residue was from the walls or bottom
of the containers. Some residuals from the bottles were still observed on day 30. The
residuals were mostly part of bottle threads and in the form of string-like structures.
Bottles and deli containers exposed to ambient conditions were also examined by visual
inspection. Figures 4.7, 4.9 show the degradation process of the bottles and deli
containers in ambient environments. The packages faced different atmospheric conditions
such as solar radiation, rain, snow, wind and variable atmospheric pressures (Figure 4.4a—
c). No visible difference was observed in either of the packages exposed to ambient

exposure conditions for the duration of the study.

4.3.2 Physical properties
4.3.2.1 Molecular weight

The molecular weight was monitored using the standard GPC technique, as
previously described. The molecular weight degradation gives information about the
main fragmentation which occurs in a polymer. PLA polymers, by having —C—-O— ester
linkages in the polymer backbone that are hydrolysable functional groups (see Scheme

1), are susceptible to hydrolysis.

132

= 0 CH
CH3 3
PVC?
H
O 9H3 O

O CH
CH3 - 3 -
- O E 0‘ Opoly
CH3 n 0

Scheme 4.]. PLA hydrolysis and molecular weight loss

Initially, random non-enzymatic chain scission of the ester groups leads to a
reduction in molecular weight and is accelerated by acids or bases, affected by
temperature and moisture levels.13 Embrittlement of polymers occurs with reduction of
molecular weight to around 50 000 Da. The PLA degradation is driven by the hydrolysis
and cleavage of the ester linkages in the polymer backbone, autocatalysed by the
carboxylic acid end-groups. This part of the process follows first-order kinetics.

Secondly, low molecular weight PLA (M, < 10 000) or low molecular weight
oligomers are metabolized by microorganisms to yield carbon dioxide and water. In
general, high temperature and humidity (SO—60°C and RH > 60%) will cause PLA to
degrade rapidly.36 Mainly, the polymer degradation rate is determined by the nature of

the functional group and the polymer reactivity with water and catalysts. Although the

133

degradation process in PLA is a simple hydrolysis, any factor that affects the reactivity
and accessibility, such as particle size and shape, temperature, moisture, crystallinity,
isomer percentage, residual lactic acid concentration, molecular weight, molecular weight
distribution, water diffusion and metal impurities fiom the catalyst, will affect the PLA
degradation rate.'3"37’3’8 The variation in molecular weight of bottles and deli containers is
shown in Figure 4.10. PLA bottles and deli containers exposed to ambient conditions for
30 days did not show significant MW variation as a function of time at the or = 0.05 level
(p > 0.01) (Figure 4.10a, c). Also, the variations of PDI for the bottles and deli containers
were not statistically significant at the or = 0.05 level (p > 0.01 for the bottle and deli
containers). Kai-Lai and Pometto (1999) showed that the exposure of poly(lactide) films
to ultraviolet light (UV) for 8 weeks enhances the degradation rate and the deterioration
of the mechanical properties of these polymers.39 In this study, the bottles and deli
containers were exposed for 4 weeks to ambient conditions and compared with the time
taken by the packages to degrade in the compost environment.

Figure 4.10a, c, shows the molecular weight change of the packages that were
exposed to compost conditions for 30 days. Figure 4.10a shows that the molecular weight
variation of the PLA bottles at the first 15 days of composting is much lower than the

PLA deli containers, as shown in Figure 4.10c._

134

 

 

 

 

 

 

 

 

 

   

 

 

 

 

 

 

300 300
(C)
$250 2 ‘2‘; 250 .
TU. «2 i
"5.200 2 g“ 200 .
"é a
5,150 2 150
in :50
g 100 . ‘2‘; 100
£3 E
E 50 . g 50 »
O '5
2 0 , 2 0
25 L 2 25 l -
(b) ' (d)
2.0
—!
9.1.5 »
1.0 -
V: :2 v: JL
00 . r 4. + + . . 00 J i i i , .
0 5 10 15 20 25 30 0 5 10 15 20 25 30

Time, day Time, day

Figure 4.10. Variation of the molecular weight and polydispersity index (PDI) as a
function of time for a) and b) bottles exposed to composting (D) and ambient (0)
conditions for 30 days and (c) and (d) deli containers exposed to composting (Cl) and
ambient (0) conditions for 30 days. ((—'—) dot line in Figure 4.10 0 indicates the fitting

of equation 2 without considering the Mw values at day 4 and 6)

Both high molecular weight polymers are reduced to low molecular weight
polymer by a combination of chain scission and removal of repeat units from the chain
ends of the polymer. This leads to fragmentation or dissolution of the polymer. Major

fragmentation with MW < 10000 of bottles and deli were observed at day 15. At day 30 it

135

was not possible to locate any residues of the deli containers. Further enzymatic action
yields oligomeric fragments and simple organic compounds that are intermediates of the
biodegradation process. The PLA bottles (Figure 4.10a) show a small increase in the
molecular weight after being exposed to the compost pile for 1 day. This increase in
molecular weight could mainly be attributed to cross-linking or recombination reactions.
In the case of PLA, the slow degradation rate produces a loss of molecular weight over
the polymer cross-section, following first-order kinetics.40 Therefore, by fitting the data
of the variation of the molecular weight as a fimction of time (equation 2), we can
observe that the MW degradation of the bottles and deli containers correlated well with a
first-order kinetic process:
Mw = a * exp—baht (2)

Table 4.2 shows the estimate of a and b values from equation (2) and their
statistical level of significance for the PLA bottles and deli containers. The b (the pre-
exponential factor of equation 2) values indicate the degradation rate. Higher b values
denote higher degradation rates. We can observe that PLA bottles have a higher b value
(b = 0.18 i 0.05) than deli containers (b = 0.15 i 0.04) (solid line in Figure 4.10c).
However, if the M,,. values for the deli containers at days 4 and 6 are not taken in
consideration when fitting equation 2, the degradation rate of the deli containers (b = 0.29
:1: 0.04) is higher than that of the bottles (b = 0.18 at: 0.05). Also, a higher adjusted R value
is obtained in the second case for the deli containers (Adj RSqueri = 0.991). The higher
MW values obtained at days 4 and 6 for the deli containers could be mainly attributed to
the temperature variations on those days in the position that the deli containers were

located, and to local variations in the compost pile. PLA polymers in a slightly alkaline

136

medium follow a first-order hydrolysis process mainly affected by the initial crystallinity,

thickness and the shape of the samples, as previously demonstrated by other

researchers.”

Table 4.2. First-order equation [M,,, x 103 = a*exp(—b*t)] of the degradation
process of poly(lactide) bottles and deli containers

 

 

Properties Xc a3 pa1 bT p2,I Adj
qur2

Bottle 12.2 a: 1.4 229.7 :t 28.4 0.0002 0.18 :t 0.05 0.01 0.867

Deli 1.4 :t 0.3 209.6 1 27.8 0.0010 0.15 i 0.04 0.03 0.823

Deli (-'-)4 1.4 :t 0.3 221.2 i 11.7 0.0003 0.29 :t 0.04 0.008 0.991

 

‘pa and p, are the probability of being wrong in concluding that there is an association between the
dependent and independent variables. The smaller the p value, the greater the probability that there is
an association. For this study, or = 0.05.

2Adj qur is the R2 which measures the proportion of the variation in the dependent variable accounting
for the number of explanatory variables.

3a and b values refer to equation 2. These values are shown with their 95% confidence levels.

4Second line fitted in Figure 4.10c.

Figure 4.10b, (1, shows the variation in PDI for both bottles and deli containers
subjected to composting and ambient conditions. Longer PLA chains are more
susceptible to cleavage than the shorter ones, as the hydrolysis of PLA occurs randomly.
Hence, an initial rise in PDI for both packages subjected to compositing conditions was
observed on day 4, which could be correlated to the fragmentation process, which
produces decomposition of the macromolecules into shorter oligomer chains and
monomers. After day 15, narrowing of the molecular weight distribution was observed
with decrease in PDI until complete degradation. At this point, only oligomers of the

PLA chains are present. When both packages were subjected to ambient conditions, no

significant changes of MW at the a = 0.05 level (p > 0.01) were observed.

137

4.3.2.2 Glass transition and melting temperature

The second run DSC plots for PLA bottles and deli containers exposed to
composting conditions are shown in Figure 4.11. A decrease of 28°C was observed in
bottles on day 30, whereas it was 8°C for deli containers on day 15. Initially, a short
increase of T g is observed, which can be attributed to the short span increment of the
molecular weight. The later reduction in T g is associated with the reduction of the
molecular weight for both packages. Since the hydrolysis of PLA polymers occurs at a
higher rate in the amorphous region, the overall crystallinity of the containers increased
as degradation of the polymer chains took place. By the preferential degradation of
amorphous areas, an increase in total crystallinity was observed during the degradation
process of the crystalline PLA polymers in aqueous media by other researchers.41 In this
study, the initial crystallinity of the bottles (Xe = 12.2 :t 1.4) increased to values of 16%
until the last degradation day, and in the case of the deli containers xc = 1.40 i 0.3 it was
observed to increase to 27% higher (first run of the DSC, not shown). During the second
run, the crystallinity of the samples decreased because the heating of the samples over the
melting temperature erased all the previous thermal history of the samples and the

cooling cycle did not allow recrystallization.

138

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Tg Day 0
_________________ \“_____'_'______h_ Day 1
H ........... fix ,— _ T Da-yTZ
”t a. -------------- k _ D934
a ---—-—~aa___3/--\a Au:
8
.5 _.._._-__-L. ~__ ____________ ___~ \_\,l Day9
\j ——————— /f\\\ \‘H:
\ ——————— I \~.\ Day15
T T 1" _—m-
m3 ‘ Day 30
W
t 2'0 40 6'0 8'0 100 120 140 trio 1! 0
Temperature
(3)
-——_—\T§——’/_\\/_Pio‘
_ _________________ Da 1
x — “rural...
,, — —— — ----- '\ _____________ .- -—--. .222-
t - /
Lg __ -------------- \, " \:.. Pay—fis
E "—“rr—x ______ .-/'\ .92:
v L‘ _________ ‘N.____-_-_—-— / \. \f’ Day9
.\‘ .....
~__ ______ Tg /~\ \pJ Day 15
\\A fr V
\l
c 2'0 4'0 6'0 8'0 ' 100 120 11in 160 1r 0
Temperature
00

Figure 4.11. 2nd run of DSC showing the glass transition and melting temperature
variation of the PLA (a) bottle and (b) deli container exposed to composting conditions

for 30 days

139

The variation in T g and T m for packages subjected to both composting and
ambient environments is shown in Figure 4.12. Figure 4.12a, b, shows the T g and T m
variations, respectively, for bottles and Figure 4.120, (1, shows T8 and Tm variations,

respectively, for deli containers.

 

 

 

 

 

 

 

 

0 , . .
160 . . . . 1 . . 168 . . . . . a .
1 i (d)
140 ‘ 140 .
5,) o
{—8 HE
120 ~ 120 »

 

 

 

((
ll

 

 

loaf . JR 10 a
0 r I 1 J r T

o 5 10 15 20 25 30 o 3 i0 is 2'0 25 3'0
Time, day Time, day

 

Figure 4.12. Variation of the glass transition and melting temperature as a function of
time for a) and b) bottles exposed to composting (1:1) and ambient (O) conditions
for 30 days and (c) and (d) deli containers exposed to composting (C1) and ambient

(0) conditions for 30 days

140

A slight increase in T g for both bottles and deli containers was observed for the
samples exposed to composting, which can be correlated to the increase in molecular
weight in the early stages, due to recombination reactions. A linear degradation trend in
case of PLA packages subjected to composting conditions was observed. Values in
Figure 4.13 for equation 3 are shown in Table 4.3:

Te 2 TgtO) + 91"" (3)
where T gm) is the glass transition temperature at time zero, and d is the reduction of the T g
as a function of time. Table 4.3 and Figure 4.13a show that a reduction of Tg =
0.97°C/day took place in the bottles exposed to composting. For the deli containers, a
reduction of T g = 0.46°C/day was observed, but a good correlation was not obtained (Adj
qur = 0.47). Higher adjustment R values were observed for bottles than for deli

containers.

Table 4.3. Variation of glass transition T g = Tm) + d*t as a function of time for
poly(lactide) bottles and deli containers

 

 

Properties Xe T gm)3 Prg(0)' d3 pd' Adj
qur2
Bottle 12.2 :1: 1.4 60.86 i < 0.0001 —0.97 i < 0.0001 0.954
1.01 0.08
Deli 1.4 i 0.3 59.90 i: < 0.0001 -0.46 :t 0.0516 0.477
1.30 0.18

 

'prgw, and pd are the probability of being wrong in concluding that there is an association between the
dependent and independent variables. The smaller the p value, the greater the probability that there is
an association. For this study, or = 0.05.

2Adj qur is the R2 which measures the proportion of the variation in the dependent variable accounting
for the number of explanatory variables.

3 T540) and d values refer to equation 3. These values are shown with their 95% confidence levels.

141

No significant changes in T g and T,,, were observed in case of both packages
subjected to ambient conditions at or = 0.05 level (p > 0.01). However, a slight reduction
of the T g values is graphically observed (Figure 4.12c).
4.3.2.3 Decomposition temperature

The variation of T D as a function of time for both package and for both
environments is shown in Figure 4.13 a, b.

A linear variation was observed for packages subjected to compositing conditions,
whereas no significant changes were observed for the packages subjected to ambient
conditions at or = 0.05 level (p > 0.01).

Table 4.5 shows the values obtained from fitting equation 4 to the data shown in
Figure 4.14:

T D = T DO + e*t (4)
where T DO is the decomposition temperature at day t = 0, and e is the variation of T D as a
function of time. Table 4.5 also shows the variation of T D vs. Mn, number average
molecular weight for equation 5:

TD = Twp) — B/Mn (5)
where T mm) is the T D for very high Mn, and B is a constant term. The R2 values obtained
for fitting equation 5 to both packages are shown in Table 4.4. An inverse decay (as
shown in equation 5) was observed in correlation of T D with the number average

molecular weight for both the packages.

142

 

 

 

 

 

 

420 fi-- W4 -+ +---
400 ~ '
i
380 ~ 0
g) 360 -
,9
340 .
320 »
300:: ga
428 ' AAAAAAAAAAAAAA e
400 ~- '
{N
330 J .
%J
. 360 .
Q
[—
340 >
320 .
300w 9L
0T1 1 l 1 1 1 1T
0 5 10 15 20 25 30
Time, day

Figure 4.13. Variation in decomposition temperature as a function of time for a) bottles
exposed to composting (a) and ambient (0) conditions for 30 days and (b) deli containers

exposed to composting (Cl) and ambient (0) conditions for 30 days

A graphical decrease in T D was observed in case of both packages subjected to
ambient conditions. T D for bottles decreased from 395°C to 378°C; however, no statistical
significance was observed at the a = 0.05 level (p = 0.0130). Similarly the decrease in
case of deli containers was from 396°C to 378°C and no statistical significance was

observed at the or = 0.05 level (p = 0.0118).

143

Table 4.4. Variation of decomposition temperature TD = T 00 + e*t as a function of
time (equation 4) and molecular number for poly(lactide) bottles and deli
containers. Variation of decomposition temperature T p = Tom - B/M, as a function

 

 

 

 

 

 

of Mn
Equation 4: TD = T120 + e*t
Properties Xc T1203 pmo' e3 pe' Adj
qur2
Bottle 12.2 i 1.4 403.4 i 2.7 < 0.0001 —2.8 i 0.2 < 0.0001 0.960
Deli 1.4 d: 0.3 404.1 i 4.8 < 0.0001 —5.6 :t 0.6 < 0.0001 0.918
Equation 5: T D = T m a.) — B/Mn
Properties X0 TD(oo)3 pTD(oo)' B3 p3] Ad].
qurz
Bottle 12.2 i 1.4 402.2 i 2.3 < 0.0001 -—327 501.0 < 0.0001 0.97
:1: 21 647.0
Deli 1.4 :t 0.3 394.0 i 2.5 < 0.0001 —403 956.8 < 0.0001 0.97
:t 30 589.1

 

'pmo, pa, T0,...) and p3 are the probability of being wrong in concluding that there is an association between
the dependent and independent variables. The smaller the p value, the greater the probability that there is an
association. For this study, or = 0.05.

2Adj qur is the R2 which measures the proportion of the variation in the dependent variable accounting for
the number of explanatory variables.

3 T DO refers to equation 4; and T as.) and B refer to equation 5. These values are shown with their 95%
confidence levels.

In summary, PLA polymers break down due to the absorption of water, resulting
in hydrolysis of the ester linkages. The rate of degradation is highly affected due to the
temperature, moisture and pH conditions of the compost. Considering the PLA package,
the rate of degradation was affected by the initial crystallinity and the percentage L-
lactide content. The 94% L-lactide content packages disappear more rapidly from the
compost than the 96% L-lactide packages. Hence, the initial crystallinity and L-lactide
content of the PLA packages should be considered for estimation of the time required for
decomposition in the composting environment. Similar compost studies, but with PLA

samples and incomplete packages, were carried out by Weber42 by storing PLA samples

144

in biodegradation chambers. Weber42 recommended that a maximum of 10% PLA be
used in compost piles to prevent pH reduction of the pile. In this study, this concern was
not a problem, due to the ratio of polymer to compost. Some comparisons between
laboratory and field exposure degradation have been carried out in various studies.36’39’43‘
45 They exposed PLA films in banana fields in Costa Rica, and found that these PLA
plastic films lost mechanical properties and degraded faster in composting conditions
than during exposure in soil conditions (3 weeks and 6 months, respectively).44 These
studies also found that degradation of PLA is enhanced by an increase in temperature and
relative humidity.36 Previous studies have been based on assessing the degradability of
plastic samples and not complete packages. This study has assessed and addressed the
degradation time, physical properties and comparison of two commercially available
PLA packages. It also gives information about the compostability and reduction of the
physical properties under real compost as well as ambient exposure conditions. Packages
made of PLA will compost in municipal/industrial facilities, but they may be difficult to
completely compost in backyard composting, since PLA degradation is driven by
hydrolysis, which needs higher temperatures in order to take place (T > 50°C). Further
research is being carried out to simulate the real degradation process in simulated or
controlled conditions in order to establish a standard laboratory-scale test for the
evaluation of packages under real compost conditions. Furthermore, future research is
necessary to find methods and techniques that can assess the degradability of

biodegradable packages under real composting conditions before they are introduced and

degraded in commercial composting operations.

145

4.4 CONCLUSIONS

Two PLA packages, a bottle and a deli container, were used to determine the
degradation process under ambient exposure and compost conditions. A novel method
was used to identify and track of the degradation of the PLA packages in a real compost
facility. The degradation of the PLA containers was monitored by visual inspection,
GPC, DSC and TGA. PLA deli containers degraded in < 30 days under composting
conditions (T > 60°C, RH > 65%, pH z 7.5). First-order degradation kinetics were
observed for the bottles. A T 8 reduction of 1°C/day was found for PLA bottles with 96%
L-lactide. A method to study the compostability of biodegradable packages under real
compost conditions has been outlined. Further studies will aid in the development of a
reliable laboratory test that can address the compostability of biodegradable packages

resembling real conditions.

146

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150

CHAPTER 5 - BIODEGRADABILITY OF POLYLACTIDE BOTTLES IN REAL
AND SIMULATED COMPOSTIN G CONDITIONS
5.1 INTRODUCTION

According to the ASTM, a biodegradable plastic is “a plastic that degrades
because of the action of naturally occurring microorganisms such as bacteria, fungi, and
algae,” and a compostable plastic is “a plastic that undergoes degradation by biological
processes during composting to yield carbon dioxide, water, inorganic compounds and
biomass at a rate consistent with other known compostable materials and leaves no
visually distinguishable or toxic residues [1].” Standards developed by ASTM and ISO
are used to assess the biodegradability of biodegradable plastics in different environments
such as composting (ASTM D5338), anaerobic digestion (ASTM D5511 and D5526),
and wastewater treatment (ASTM D5210 and D5271) [2]. In order to justify a cradle to
cradle approach, one of the most attractive alternatives would have biodegradable plastics
be composted at the end. of their useful life and later used in sustainable agricultural
practices; hence, in this scenario addressing the efficiency of the plastic’s
biodegradability process becomes essential [2, 3].

ASTM D6400 [1] addresses the compostability of plastic materials, and standard
specifications and terminologies for biodegradable plastics as well as guidelines using
test method ASTM D5338 [4]. ASTM D5338 is a method used to assess biodegradability
of biodegradable plastics under simulated or controlled composting conditions which
correlates biodegradability to the total mineralization of organic carbon (CO2 evolved) in
the polymer. A 60% or higher mineralization value for a material containing a single

polymer (homopolymer and random copolymer) certifies that the material is

151

biodegradable and further ecotoxicity tests are carried out in accordance with ASTM
D6400 to certify that it is compostable. ISO 14855-1 [5, 6] gives similar guidelines to
that of ASTM D5338 except that the mineralization of an unknown biodegradable
material should be 90% of the value obtained for a reference material to prove its
biodegradability. In both methods, the amount of CO2 evolved due to biodegradation can
be measured using acid-base titration, or by using a direct measurement such as infrared
or gas chromatography as suggested in the references [4-6].

ASTM and ISO standards guidelines are limited to the biodegradability evaluation
of plastic material or a plastic material from a package; however, the European
Committee for Standardization (CEN) has developed a standard EN 13432 [7], which
provides detailed guidelines for evaluation of packaging and packaging components’
biodegradability and compostability based on their characterization, biodegradability,
disintegration and compost quality/ecotoxicity. The biodegradability test methods are
mainly based on the ISO 14855-1 and somewhat similar to the ASTM D5338 standard
[2].

ISO has a standard under development, ISO 14855-2, which measures
mineralization of a polymer by a gravimetric method. ISO 14855-2 [8] is similar to
14855-1 except for the method of CO2 measurement and the amount of compost and
sample used. In addition, inert materials such as sea sand or vermiculite can be used with
the compost for providing better aeration and retention of moisture content. Also the
mixture of compost and sea sand or vermiculite is periodically taken out from the closed

system to turn or agitate to prevent channeling of air in the biodegradation vessel.

152

Biodegradation of biodegradable packages in real composting conditions have
been reported and correlated to visual changes and variation in physical properties of the
materials [9, 10]. Real composting studies give clear representation of the
biodegradability nature of the whole package configuration and the time required for the
disintegration in different compost recipes and composting processes. This information
can further provide a basis for deciding packaging compostable materials and the
planning of composting processes. Real composting conditions are governed by the outer
atmosphere, the type of compost, and the compost parameters such as temperature,
moisture and pH; and hence they may differ from the controlled composting conditions
as proposed by ASTM and ISO standards for materials and whole packages.

As new standards for assessment of biodegradability of materials are becoming
available and usage of biodegradable plastic packages increases, there is a need to find a
reliable method which would give a clear understanding of the biodegradability of a
package with respect to the time required for disintegration and the efficiency of disposal
to justify its compostability. To the best of the authors’ knowledge, there has not been
any study done which compares biodegradability in real and simulated conditions. This
paper investigates and compares the biodegradability of PLA bottles under different
testing methods of existing standards, standards under development and a novel method
of evaluating biodegradability of biodegradable materials under real composting
conditions.

5.2 MATERIALS AND METHODS

5. 2. 1 Samples

153

PLA bottles (500 mL) used for packaging of spring water and commercialized by
Biota brands of America (Telluride, CO) were obtained from NatureWorksTM PLA (Blair,
NE). The PLA bottles were composed of 96% L-lactide with bluetone additive and
dimensions of 0.2 m height and 0.065 m in base diameter. The organic carbon content of
the PLA bottle was 49.5% which was determined by elemental analysis (Organic
Elemental Analysis, PerkinElmer, Shelton, CT) A picture of the PLA bottle is shown in

figure 5.1.

 

Figure 5.1 PLA Bottle

5.2.2 Real composting conditions

A compost pile made of cow manure, wood shaving and waste feed (i.e., the feed
that the cows do not eat between feedings) was prepared at Michigan State University
composting facility (East Lansing, MI) and used for assessing the biodegradability of the
PLA bottles. The biodegradation study was carried out for 30 days. The dimension of the

pile was 6 meters in width, 24 meters long, and 3 meters in height, and it was built up on

154

asphalt pad. The initial temperature, relative humidity and pH of pile were 65 i 5°C, 63 :1:
5%, and 8.5 :t 0.5, respectively, and it was monitored throughout the duration of the
biodegradation study with a thermocouple type I attached to a datalogger from Onset
Computer Corporation (Boume, MA). External atmosphere parameters such as
temperature, relative humidity and solar radiation which may affect the performance of
composting process were recorded through the Michigan Automated Weather Network
(East Lansing, M1) for the entire period of the study [9, 10]. A novel method was
developed to track and trace the PLA bottles in the compost pile. A wooden box of
dimensions 0.6 x 0.3 x 0.1 meters was built with a mesh attached at its bottom to retain
and easily identify the samples and the surrounding compost for further analysis. Initially,
compost was added on the bottom of the mesh, and later the PLA bottle was placed on it
and completely covered with compost. The box was placed at approximately 1.2 meters
above the ground and 1 meter inside the compost pile where a uniform composting
temperature of 65°C was obtained. For a detail description of the system, the readers can
refer to references [9, 10]. Figure 5.2 shows how the packages were located in the
compost pile. After the packages were covered with compost soil, the pile was closed and
the temperature of the pile reached normal composting temperature.

The PLA bottles were taken out periodically from the compost pile for analysis of
variation in its molecular weight. In addition, the bottles were visually inspected, and

pictures were taken for visual evaluation of its biodegradation trend.

155

 

Figure 5.2 Placement of packages in compost pile

5. 2.3 Molecular weight analysis

Molecular weight analysis was conducted using a standard Gel Permeation
Chromatography (GPC) technique. A Waters 600 multisolvent delivery system with a
Waters 717 autosampler and Waters 2410 refractive index detector was used; all
manufactured by Waters Corporation (Milford, MA). Inhibitor fi'ee Tetrahydrofuran
(THF) obtained from Sigma Aldrich (Milwaukee, WI) was used as a solvent for diluting
and preparing the PLA bottle samples [9, 10].
5. 2.4 Cumulative Measurement Respirometric (CMR) System

A CMR system based on ASTM D5338 [4] and ISO 14855-1 [6] was built. This
system was designed to yield the percentage of carbon dioxide from the organic carbon
content of the sample. Three month old mature compost obtained from Michigan State

University composting facility was used for biodegradation purpose. The preparation of

156

the compost was previously discussed. The compost was sieved through a 5 mm sieve
and inert materials such as glass, stones and metal were removed. Fine particle of
vermiculite grade number 4 soil conditioner manufactured by Thenn-O-Rock (New
Eagle, PA) was used for mixing with compost to provide better aeration and retain of
moisture. Dry compost (400 grams) was mixed with 100 grams of dry weight
vermiculite, and the moisture level was adjusted so that the mixture retains moisture of its
90% water holding capacity [11]. PLA bottles were cut into 0.01 m x 0.01 m pieces,
except the part of neck and cap threads. These cut PLA bottle samples were used as a
sample for biodegradability evaluation. Cellulose powder obtained from Sigma Aldrich
(Milwaukee, WI) was used as the known reference material (i.e., positive control). The
organic carbon content of the cellulose was 42.5% determined by elemental analysis.
Currently, ASTM D5338 recommends using a negative control such as polyethylene and
should be in same form as of the same material. This is planned to be removed in the new
version of D5338, and since ISO 14855-1 does not recommends using a negative control
for this experiment, a negative control was neglected in this study. The current system
comprised of 9 bioreactors; 3 blanks, 3 positive control (cellulose) and 3 samples (PLA
bottles) placed in a temperature controlled system. An enviromental controlled room
manufactured by Lab-Line Instruments Inc (Melrose Park, IL) was used to place the
bioreactors in the temperature controlled environment. A schematic of CMR system is

shown in Figure 5.3.

157

Dry air

   
 

Compost
+ Vermiculite

CO2 Trap
0.25 N NaOH
solution

/' K' g i Set of 9 Bioreactors

Deionized
10 N 10 N
Water (:02 Trap

NaOH NaOH 0.25 N NaOH

Humidified air solution
generation

Air Inlet

 

 

 

 

 

 

meter fl

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Biomctor9
Figure 5.3 Schematic of CMR system

Initially pressurized air of 2 psi was passed through 10N sodium hydroxide
(NaOH) solution to remove the CO2 present in the air. Later the air was passed through
deionized water to humidify and maintain uniform moisture level during the experiment
between 50 and 60%. The moisture was controlled by mixture of dry and humidified air
and was monitored by an RH meter produced by Hygrodynamics (Jessup, MD). The air
was divided and passed through flowmeters for each bioreactor at a flow rate of 60
mL/min. Two mounted 2 mm screen at the bottom of bioreactor and above the air inlet
were introduced to equally distribute the air in the compost and avoid channeling, as
previously proposed by Kijchavengkul et.al [12]. A solution with 200 mL 0.25N NaOH
was used for trapping the CO2 from the bioreactors and the amount of CO2 content in
solution was calculated through acid-base titration. NaOH solution was changed every
time that CO2 was calculated. Ten mL aliquots were removed from the 200 mL trapping
NaOH solution and titrated with 0.186N hydrochloric acid (HCl) solution to obtain the
value of CO2 in solution. The CO2 content in the 10 mL solution was correlated to the
200 mL solution and actual CO2 amount was determined. The CO2 trapping reaction was

done in a two step reaction as described in ASTM D5338 and mentioned below:

158

NaOH + CO2 ———> NaHCO3 (1), then

NaHCO3 + NaOH ———> Na2co3 + H20 (2)

Similarly, during titration CO2 is removed through the following reactions:

Na,co, + HCI —> Nch0, + NaCl (3), then

NaHCO3 + HCl —+ NaCl + H20 + C02 (4)

Initially, few drops of phenolphthalein indicator were added to the 10 mL NaOH
aliquot and further titrated till it turned from pink to colorless. At this point, the Na2CO3
is converted into NaHCO3 and NaCl. Further, few drops of methyl orange indicator were
added and titrated till the solution turned from orange to red. The NaHCO3 reacted with
HCl to form NaCl, H20 and CO2. Hence, the amount of HCl consumed in the second
reaction could be used to find CO2 concentration in solution according to the following
formula:

V.C.44
CO = — 5
g 2 1000 ( )

where gCO2 is the amount of evolved carbon dioxide in grams; V is the volume of HCl
consumed in the second reaction (4); C is the concentration of HCl solution. The
percentage mineralization was further calculated by comparing the amount of carbon

dioxide in the positive control and the sample with the blank by the following equation:

gCO2 — gCOzb
%C E

 

%Mineralization = X 100 (6)

material

g material . 1 00 1 2

159

where gCO2 is the amount of evolved carbon dioxide in grams in the sample and the
positive control; gCO2b is the amount of evolved carbon dioxide in grams in blank;
gnmen-ai is the mass of the bottle or sample; %Cmaien-ai is the percentage organic carbon
content of the bottle/sample.
Gravimetric Measurement Respirometric (GMR) System

The GMR system construction is based on ISO 14855-2 [8] which is an standard.
under development phase and differs from ISO 14855-1 and ASTM D5338. Some of the
differences are; a) the amount of compost/vermiculite mixture and sample used; b) the
number of blanks; c) the positive control; d) the sample bioreactors; and e) the method of
CO2 measurement. ISO 14855-2 recommends using 2 blanks, 2 positive reference
material and 2 samples to be analyzed for the biodegradation measurement. ASTM
D5338 and ISO 14855-1 recommends to use compost and sample in a ratio of 6:1 and
commonly used quantity is 600 grams of compost to 100 grams sample, whereas in ISO
14855-2 one tenth of compost/sample ratio is used. A GMR system according to some of
these specifications has been built by Hissan Trading Co. Ltd. (Japan), and it is
commercialized under the name of Microbial Oxidative Degradation Analyzer (MODA).
A MODA system was provided by Saida UMS Inc. (Tokyo, Japan) for part of the test
presented in this work. The MODA system consists of 4 bioreactors, one for blank, one
for positive control (cellulose) and two for samples. Similar to the CMR, in the MODA
system pressurized air is passed through a column containing soda lime fi'om Fluka
(Steinheim, Germany) with CO2 absorption indicator from Sigma Aldrich) to make it CO2
fiee. Later, the air is bubbled through a flask containing deionized water to maintain the

humidity in the compost mixture and in the reaction column constant. The reaction

160

column consists of a column covered with a heating jacket and a thermosensor to
maintain the temperature at 58°C. Further, air is passed through each bioreactor and later
through an ammonia eliminator, moisture remover and finally to a C02 trap column. A
schematic of the MODA system with a single bioreactor and column connections is
shown in Figure 5.4.

Thennal Jacket

Temperature probe Calcium

Chloride

 

   

Soda lime 50%
Sodium Hydroxide 50%

Calcium Chloride 80%

Soda Silica Gel 20%

Lime

Silica Gel

Deionized water Bioreactor 1M H2304
Compressed Air

Mixture of Compost (50%)
& Venniculite (50%)

Fig 5.4 Schematic of MODA system
The standard test soil for the MODA system is a mixture of mature compost (60 grams
dry weight) and vermiculite (60 grams dry weight) and initially the moisture is adjusted
up to 90% of its water holding capacity. Mature compost (three months old) was obtained
from Michigan State University composting facility and vermiculite grade number 4 fine
particle soil conditioner was obtained from Therrn-O-Rock (New Eagle, PA). Vermiculite
(18 grams dry weight) was also added at the bottom of reaction column to absorb the
water drips from the compost and also provide equal aeration to the compost mixture.
The vermiculite and compost mixture were separated by sponge disks and stainless disk

net as shown in Figure 5.5.

161

Reaction column

Compost mixture

Stainless steel net
Spacer

Wet vermiculite
Sponge disk

 

Humdified air supply

Figure 5.5 Schematic of the reaction column for MODA system
Initially, a sponge disk was placed at the bottom of reaction column followed by wet
vermiculite (18 grams dry weight) and again sponge disk on top of it. A 1 mm ring was
introduced above the sponge disk to provide spacing between it and the stainless steel
disk (with 1 mm holes) as shown in Figure 5. The compost mixture was added on top of
the stainless steel disk and finally the reaction column was closed with a lid attached with
the thermosensor which stayed all the time in contact with the compost mixture. The
reaction column was covered with a thermal jacket at a temperature of 58°C which was
continuously controlling the compost mixture. In addition to the carbon dioxide;
ammonia and water was also generated from the reaction column which was eliminated
by passed the output of the reactors through 2 N sulfirric acid (H2S04) in the ammonia
absorption flask, and the neutralization of H2S04 by ammonia was monitored by methyl
red. Later the air was passed through moisture removal column 1 and 2 as shown in

figure 4. Silica gel (type 3) obtained from Sigma Aldrich (St. Louis, MO) was used for

162

moisture removal column 1; when the silica gel was saturated due to moisture it changed
color from dark blue to colorless. Moisture removal column 2 consisted of 20% silica gel
and 80% of calcium chloride (93% granular, anhydrous) obtained from Sigma Aldrich
(St. Louis, MO) which completely removes moisture fiom the air. Column 3 was a
carbon dioxide absorption column and contains a mixture of soda lime (cica reagent)
obtained from Kanto Chemical Co (Chuo-Ku, Tokyo) and Sodium Hydroxide (1.6 mm —
3 mm pellets) obtained from Merck KGaA (Darmstadt, Germany). Both soda lime and
sodium hydroxide were mixed in 1:1 ratio. This chemical reaction generated water and
hence column 4 containing calcium chloride collected the remaining water from the
reaction. The carbon dioxide generated by biodegradation in the reaction column was
measured by the weight gain seen in column 3 and column 4. The MODA system is a
closed system; however, the compost mixture was taken out twice a week for manual
turning to ensure proper mixing of compost and sample, and also to improve aeration and
maintain accurate moisture in the mixture. While turning the entire mixture was collected
in an aluminum bowl, except the divider sponge and stainless steel disks. The reaction
column was immersed in water to completely wet the vermiculite at the bottom. Compost
mixture was turned properly manually and appropriate amount of water was added to
adjust moisture upto 90% water holding capacity of mixture.
5.3 RESULTS AND DISCUSSION
5. 3.1 Real composting conditions

PLA bottles were first visually inspected in the compost pile for changes in their
shape, texture and color. Right from the first day, changes in color and shape were

observed [9, 10]. The biodegradation trend is shown in Figure 5.6.

163

in

0:11

Utmflflr

Day is

 

Figure 5.6 Biodegradation of PLA bottles in real composting conditions

The shape changes on the first day could be attributed to distortion due to higher
temperatures (65 :t 5°C) in the compost pile and also because the glass transition
temperature (Tg) of PLA bottle was 60.6 i 03°C [9, 10]. On fourth day, the bottles
seemed tough as compared to its original configuration. On the sixth and ninth days, a
powdery texture was observed on the bottle surface and also the top part of bottle became
brittle and started breaking apart. On the fifteenth day, the bottle was already in pieces
and mostly consisted parts from cap threads, neck and bottle (bottle parts having higher

thickness). On the thirtieth day, only few pieces of bottle were observed and were

164

majority from cap threads. After that, no bottle residuals could be located through visual
inspection.

In case of PLA, the presence of -C=O- in the ester linkages in the polymer
backbone makes it susceptible to hydrolysis. Initially, random non-enzymatic chain
scission of ester groups results in reduction of molecular weight, and then lower
molecular weight PLA was consumed by microorganisms which yields CO2 and humus
[13, 14]. Apart from hydrolysis, there are certain parameters which govern the
biodegradation rate of PLA, for example higher temperatures and humidity results in
rapid biodegradation of PLA [15]. Other factors which can govern the degradation rate
are size and surface area of polymer/package, crystallinity, isomer percentage, residual
lactic acid concentration, molecular weight, number average molecular weight and water
diffusion [13, 14, 16]. As mentioned before, the temperature, relative humidity and pH of
compost surrounding the containers were monitored every time the PLA bottles were
taken out from the compost pile. Along with that, the atmospheric conditions such as
temperature, relative humidity and solar radiation were also monitored for the duration of
the study [9, 10]. The compost parameters may change with atmospheric changes which
can affect the biodegradation. During the duration of study, atmospheric temperature
varied from -4.2°C to 27°C; and atmospheric relative humidity from 20.3% to 98.9%
which might have affected the composting process [9, 10].

Variation in physical properties of PLA bottles such as molecular weight was also
analyzed. Molecular weight gives representation of the fi'agmentation process in PLA and
also their degradation trend. Figure 5.7 shows the variation in molecular weight for PLA

bottles for a period of 30 days.

165

 

 

 

 

25o . . . 2.5
200 ~ i 2.0
M
S:
X
g 150 ~ ~ 1.5
72
Q r—d
a E
g 100 - . 1.0
E
:3
8
O
E 50 — - 0.5
o _ ‘1 - 0.0
1 i i r i i _L

 

 

0 1 0 20 3O 40 50 60 70
Time, days

Figure 5.7 Variation in molecular weight (I) and PDI (D) for PLA bottles in real

composting conditions; (-) solid line indicated fitting of equation 7.

Small increase in molecular weight (+11,400 Daltons) was observed on first day
and it can be attributed to cross-linking or recombination reactions [9, 10]. Major
fragmentation, which produces decomposition of the polymer chain into shorter oligomer
chains and monomers, was observed on the fifteenth day when molecular weight was
reduced from 210,600 to 11,000 Daltons. On the ninth day, large difference in the
molecular weight was observed (42,000 d: 26,000 Daltons), and this could be attributed to
the differences in the compost parameters and/or the atmospheric conditions. PLA

degradation starts by a hydrolysis reaction which follows a first order kinetics as shown

166

by Kale et. al. [9, 10], which fitted the variation of molecular weight as a function of time
to a first order kinetic process as expressed by equation (7).
Mw = a "‘ exp—[fl (7)

where “a” and “b” are constants and equal to a= 229.7i28.4 kDaltons, and
b=0.1865:t0.0533 s"; t is the time in days. According to this equation, molecular weight
values below 5 Daltons could be obtained on 57 days as shown in Figure 7. Figure 7 also
shows the variation in PDI on the right axis; PDI was reduced from 1.84 to 1.04 mainly
because of narrowing of the molecular weight distribution due to polymer fragmentation.
Initial rise in PDI could be attributed to the increase in the fragmentation process [9, 10].
For a detail study of the correlation between molecular weight and glass transition,
melting and decomposition temperatures for PLA bottles in real composting conditions
the readers can refer to references [9, 10]
5.3.2 Cumulative Measurement Respirometric System

Figure 8 shows the biodegradation of cellulose powder and PLA bottles in the
CMR system at controlled temperature conditions of 58°C. Mineralization value of 60%
(requirement of ASTM D533 8) was obtained on 30th day for cellulose and on 39th day for
PLA bottle. At the end of 58th day, cellulose reached 86% mineralization and PLA bottle
was 84%. Initial slower mineralization action in PLA is due to the fact that it first
undergoes hydrolysis which is a non-enzymatic reaction decreasing the molecular weight
(as shown in figure 7) and later low molecular weight oligomers are consumed by
microorganisms to evolve carbon dioxide. A similar study was done by Kijchavengkul
et.al. [12] on the same type of PLA bottles, but in a direct measurement respirometric

(DMR) system and with yard waste compost showed that PLA bottles reached 60%

167

mineralization value on around 55th day. However, the size of PLA bottle sample used
was lesser (18.86 grams) as compared to the 25 grams used in CMR system. The amount
of compost used was 300 grams wet weight as compared to 400 grams dry weight
compost used in this study. The higher is the quantity or surface area of compost
regarding the sample the more is the chance to have enough microorganisms to
biodegrade the samples. Also, the nature of the compost used as in this case yard waste
compost will play an important role in the rate of the biodegradation since different

amount of microorganism will be present.

 

100

301 ' _._.. ‘. ,. ,.

I

40

I
‘ C

% Mineralization

I

20'

 

 

1 l 1 l 1 l 1 1 L l L

1
051015202530354045505560

 

Time, Days
Figure 5.8. Percentage mineralization as a function of time for cellulose (O) and PLA

bottles (CI) in CMR system.

Gravimetric Measurement Respirometric (GMR) System

168

Figure 5.9 shows the biodegradation results of cellulose and PLA bottles in the
GMR system. In this case, cellulose reached 70% biodegradation value on 55th day. ISO
14855-2 recommends that this test is valid only if cellulose or positive reference control
reached 70% mineralization value before 45 days. However, ISO 14855-2 also
recommends using two positive controls in the test, and it is only valid if the difference
between two positive controls mineralization value is less than 20%. In our case, the

system only had one positive control due to limitation of the commercial equipment.

 

 

 

 

 

 

100
80-' ~ w ”-3,--
‘ ‘ . i .'/
. 1 1’ j
1.. a,
.2 ..
a '1 w
.s
g 40-
.a .
E
g
20 e -
O '- Ettl IIIJ! 1
x xx x xx x xxx xx x
0 10 2o 30 4o 50 60

Time, Days
Figure 5.9. Percentage mineralization as a function of time for cellulose (O) and average

of PLA bottles (E1) in MODA. Turning days are represented by (x).

169

One of the PLA bottles showed negative biodegradation in the beginning which
could be due to few reasons; (a) as discussed in case of CMR system, PLA bottles first
undergo hydrolysis which is non-enzymatic reaction and (b) PLA bottles consisted of a
bluetone additive and also a label adhesive which may have affected the microbial
activity; c) the homogeneity of the compost, which make the compost generate different
background of CO2. However, after 12 days, the lag phase for the PLA bottle was over
and the average mineralization for two PLA bottle samples was 0.33% (23% in case of
cellulose). On 52nd day, one of the PLA bottles reached more than 70% of the average
mineralization value which can conclude that PLA bottles are biodegradable according to
the ISO 14855-2, but only if all the ISO 14855-2 conditions of number of samples and
validity criteria are met (which is not true in this case with MODA system). At the end of
67th day, the average mineralization of both PLA bottles was 80.9% with a large variation
of 21:10.3%; which is very large as compared to the CMR data. The compost mixture in all
reaction columns was turned twice a week; each time during turning moisture was
adjusted to sustain microbial activity. The turning activity is also shown in Figure 9. On
the 25th day, 15 grams (dry weight) fresh compost was added to all reaction columns to
improve the microbial activity, and an increase in mineralization value can be observed in
the graph. A similar test was carried out by Kunioka et.al [17] on PLA and the
mineralization value reached more than 80% in just 50 days; however, the difference was
that PLA powder (size of 92.5 um) was used, whereas PLA bottle pieces of 0.01 x 0.01 m
was used in this case. PLA powder provides more surface area in the reaction column and
can be more uniformly distributed with the compost than the PLA bottle pieces (mainly

because of the label adhesive which tends pieces to adhere to each other).

170

 

Comparison of all three methods

PLA bottles were tested for biodegradability in real and simulated composting
conditions as previously described. The biodegradation trends for both conditions are
shown in Figure 5.10. The left y-axis measures the % mineralization for the CMR and the

GMR systems and the right y-axis measures the variation in molecular weight in real

 

 

 

 

 

 

conditions.
100 w . 250
80 e - 200
m
S
X
8
g 60 - i 150 ,3
a 8
'2 40 - j 100 ’3’
as 33.
5
U
Q)
'25
20 ~ - 50
0 ~ ‘ 0
70

 

Time, days
Figure 5.10. Comparison of variation in molecular weight (El) due to biodegradation and
% mineralization values for PLA bottles in CMR (o) and MODA (O) systems
On the 15"” day, the MW of the samples exposed under real composting conditions
was reduced to 15,000 Daltons. If we compare this with the samples tested under

laboratory simulated conditions, we can observe a very slow percentage of mineralization

171

increase during this period. After that, when the MW of the samples is reduced enough to
allow the microorganisms to use them as carbon source, a sudden increase in the
evolution of CO2 takes place. This correlates well with the non-enzymatic hydrolysis and
enzymatic reactions in the case of PLA as mentioned in previous research [9, 10, 13-15]
and described by equation 7.

For both simulated conditions, CMR and GMR, the % mineralization value did
not reach 100% at the 58th day when the test was stopped. However, the Mw of the
samples in the compost pile, extrapolated according to equation 7, indicates that the
samples would have reached zero Daltons at the 58th day. Variation in the degradation
time frame between the simulated and real composting conditions can be attributed to
many factors such as size of the polymer sample, sample/compost ratio and the nature of
the compost material.

In real composting conditions, the entire bottle as shown in Figure l was tested,
whereas in the CMR system the whole bottle (25 grams) was tested but cut into 0.01 x
0.01m pieces. Therefore, the higher surface area of the samples introduced in the CMR
system should reduce the overall degradation period; however, since the relation compost
/ sample were larger in the real composting conditions, a faster degradation process of the
bottles was observed. In the case of the MODA system where these two factors (i.e.,
sample size and compost/sample ratio) were lower than the real composting conditions an
even slower degradation process was observed. Kunioka et al. conducted a
biodegradation test on PLA powders in a GMR system and also found that the size of
PLA powder particles affected the biodegradation rate (i.e., smaller size samples will

degrade faster due to higher surface area exposure to microorganisms attack) [17]. Hence,

172

if a whole bottle, rather than its small pieces is introduced in the simulated conditions, we
should expect longer times to breakdown. On the other hand, it is a common practice in
industrial compost facilities to shred the materials before introducing them to the mixture
so that an even shorter degradation time should be expected for the bottle pieces in real
conditions.

As mentioned above, the compost to PLA bottle ratio was different in both real
and simulated conditions. In the case of real composting conditions the compost/sample
ratio could be considered as infinity to 1; in the case of the CMR system it was 1621 and
in the MODA system it was 6:1. The number of microorganisms in a well-managed
compost is proportional to the amount of compost and hence will affect the
biodegradation rate [2]. For example a large windrow compost pile would have more
microbial reproduction as compared to an in-vessel composting system, which tends to be
small. Therefore, biodegradability results under simulated conditions could also be
deceiving with regards to the time-frame for biodegradability if the biodegradable
packages are to be disposed in compost piles or in in—vessel composting systems.
Moreover, in the case of biodegradable materials whose byproducts can modify the
compost environment and the microbial population, the total amount of sample which is
introduced to the compost pile should be considered. In the case of PLA it was
demonstrated that no more than 10% wt/wt of sample should be introduced to the
compost environment to avoid acidification due to the lactic acid formation during the
hydrolysis process [13].

Since composting is an aerobic process, turning of the compost mixture is very

essential to provide better aeration and speed up the composting process. Hence, turning

173

 

is frequently done in commercial composting facilities. The fiequency of turning is based
on the need of aeration in the compost pile and the way of forming the compost pile (such
as windrow composting, turned windrow, static windrow or in-vessel) [2]. In the current
real conditions study, the compost pile was not turned to better locate the samples. This
could result in a slight reduction of the oxygen availability in the compost pile during the
30 day period so that a slower rate of degradation was achieved even though the bottles
degraded faster than in simulated conditions. To avoid channeling and to control aeration
in the compost mixture in the case of the CMR system, the bioreactors were manually
shaken every week. In the case of the MODA system, the compost mixture was taken out
twice a week from bioreactors and mixed properly also to provide better aeration to the
whole cross section.

The nature of the compost’s raw materials plays an important role in polymers’
degradation since different compost systems (i.e., manure, yard and food waste) will
produce different microbiological activity. In this study, manure waste was utilized for
the real and simulated conditions. A similar study done on the same PLA bottles using
yard waste compost obtained 60% mineralization value on the 53rd day while in this study
in the CMR system with manure waste compost the 60% mineralization value was
obtained on the 39th day [12]. Addition of vermiculite to compost in our study might have
also contributed to a faster biodegradation. Hence, the nature of compost raw materials
such as food, manure or yard waste could impact the biodegradation time-frame of PLA
bottles and other biodegradable packages planned for composting. Therefore, this should

be assessed and taken into consideration.

174

Real composting conditions provided a good representation of the time required
for the degradation of the PLA bottles, and in general this test would be helpful for
commercial composting facilities to get insight of their biodegradation process. However,
biodegradation in real conditions is also dependent on the compost raw materials,
ambient conditions, compost mixture turning, and volume of the compost pile and
compost parameters. Also as mentioned above, the size of the test samples and the
compost sample ratio will impact the time-frame of biodegradation. In the case of both
simulated conditions, there is a gap in the mineralization values obtained by the two
techniques which again shows that it would be deceiving to derive biodegradability time-
frames from these techniques.

Standards such as ASTM D5338 and ISO 14855-1 & 2 provide a traditional way
of testing plastics in respirometric systems such as DMR, CMR and GMR, but they are
limited to the plastic material and not to the whole package. However, they do
recommend considering the part of higher thickness from the package and evaluate its
biodegradability which can then be used to conclude if a package is biodegradable or not.
There is a standard specifically developed for packaging by the European Committee for
Standardization EN 13432 [7], which states that each component used in packaging
should be separately tested for biodegradability for the complete package to be certified
as biodegradable/compostable. These tests would give an understanding of the
biodegradability of each component; however, they would not provide the time required
for biodegradation of a complete package like a PLA bottle.

Thus, current standards mainly answer the question: is a plastic or package

biodegradable? But they do not address the final question: will the package successfully

175

biodegrade in a commercial compost facility? Consequently, tests should be carried out

to firlly understand the whole and real package degradation process.

CONCLUSION

A PLA biodegradation test was carried out in real composting and simulated
composting conditions. Real conditions which are governed by factors such as
temperature, pH, and relative humidity of the compost pile showed degradation of the
PLA bottles and variation in their molecular weight as a result of hydrolysis plus
biodegradation. The variation in molecular weight was also seen to be affected by the
composting process/operation and other parameters. When shredded packages are used in
real composting conditions as used in the CMR or the GMR systems, a faster degradation
time could be expected. However, an overall conclusion cannot be exclusively derived
based on the sample size and all the variables in real composting such as compost raw
materials, enzymes, ambient atmosphere, etc. and their interaction with the biodegradable
packages should be explored for better understanding and insight of the biodegradation
process. Current standard methodologies ASTM D5338 and ISO 14855-1 provide a
traditional way of testing plastics in respirometric systems, but they are limited to the
plastic material and not to the whole package. The new GMR system similar to the CMR
has limitations of using a small quantity of compost which might extend the period of
biodegradation. In short, standards mainly answer the question if a plastic or package
piece is biodegradable, but they are not addressing the final question if these new
biodegradable packages will successfully biodegrade in a commercial compost facility.

Therefore, it is important to test the biodegradation of the complete package under real

176

composting conditions for its efficient deployment in the existing composting processes

as demonstrated in this work.

177

 

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l.

10.

ll.

ASTM, Standard Specification for Compostable Plastics. 2002. ASTM D 6400-
99.

Gaurav Kale, Thitisilp Kijchavengkul, Rafael Auras, Maria Rubino, Susan Selke,
Sher Paul Singh, Compostability of bioplastic packaging materials: an overview.
Macromolecular Bioscience, 2007. 7: p. 255-277.

Narayan, R. Drivers and Rationale for use of biobased materials based on life
cycle assessment (LCA). in Global Plastics Environmental Conference. 2004.
Atlanta.

Standard Test Method for Determining Aerobic Biodegradation of Plastic
Materials Under Controlled Composting Conditions. 1998. ASTM D 5338-98.

Determination of the ultimate aerobic biodegradabilty and disintergration of
plastic materials under controlled composting conditions-Method by analysis of
evolved carbon dioxide. 1999. ISO 1485521999.

ISO, ISO [4855-] Determination of the ultimate aerobic biodegradabilty and
disintergration of plastic materials under controlled composting conditions-
Method by analysis of evolved carbon dioxide. Vol. ISO 14855-122005. 2005:
International Standards Organization.

Packaging-Requirements for packaging recoverable through composting and
biodegradation-T est scheme and evaluation criteria for the final acceptance of
packaging. European Standard, 2000. EN 13432.

ISO, ISO/DIS 14855-2 Determination of the ultimate aerobic biodegradability of
plastic materials under controlled composting conditions - method by analysis of

evolved carbon dioxide. Part2: Gravimetric measurement of carbon dioxide
evolved in a laboratory scale test. (under development), ed. ISO/TC61/SC5. 2006.

Gaurav Kale, Rafael Auras, Sher Paul Singh, Degradation of commercial
biodegradable packages under real composting and ambient exposure conditions.
Journal of polymers and environment, 2006. 14: p. 317-334.

Gaurav Kale, Rafael Auras, Sher Paul Singh, Comparison of the degradability of
poly (lactide) packages in composting and ambient exposure conditions.

Packaging Technology and science, 2007. 202 p. 49-70.

Horticulture, C.U.D.0.F.a.O., Vermiculite Grades,
http://www.hort.comell.edu/department/faculty/good/growon/media/inorgtbl.html

178

l2.

l3.

14.

15.

16.

17.

18.

Thitisilp Kijchavengkul, Rafael Auras, Maria Rubino, Mathieu Ngouajio, R.
Thomas Fernandez, Development of an automatic laboratory scale respirometric
system to measure polymer biodegradability. Polymer Testing, 2006. 25: p. 1006-
1016.

Rafael Auras, Bruce Harte, Susan Selke, An Overview of Polylactides as
Packaging Materials. Macromolecular Bioscience, 2004. 42 p. 835-864.

Zhang, X., et al., An Investigation of Poly(lactic acid) Degradation. Journal of
Bioactive and Compatible Polymers, 1994. 9: p. 80 - 100.

Kai-Lai, G. Ho, Pometto 111, Anthony L., Gadea-Rivas, Amoldo, Bricefio, Jorge
A., Rojas, Augusto, Degradation of Polylactic Acid (PLA) Plastic in Costa Rican
Soil and Iowa State University Compost Rows 1. Journal of Environmental
Polymer Degradation, 1999. 7(4): p. 173 - 177.

Garlotta, D., A Literature Review of Poly(Lactic Acid). Journal of Polymers and
the Environment, 2001. 9(2): p. 63 - 84.

Masao Kunioka, Fumi Ninomiya, Masahiro Funabashi, Biodegradation of poly
(lactic acid) powders proposed as the reference test material for the international
standard of biodegradation evaluation methods. Polymer Degradation and
Stability, 2006. 91: p. 1919-1928.

Rynk, R., On-farm composting handbook, ed. R. Rynk. 1992: Natural Resource,
Agriculture and Engineering Service (NRAES) Cooperative Extension.

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CHAPTER 6 - BIODEGRADABILITY OF PACKAGING FILMS IN REAL
COMPOSTIN G CONDITIONS

6.1 INTRODUCTION

In United States, almost 245.7 million tons of municipal solid waste (MSW) was
generated in 2005 with a decrease of 1.6 million tons from 2004. MSW recycled through
recycling and composting increased to 32.1 percent in 2005 from 31.4 percent in 2004
which shows growing potential of recycling in United States [1]. Out of the total MSW of
245.7 million tons, plastics packaging comprised of 13.7 million tons out of which only
1.28 million tons (9.4%) was recovered through recycling and mainly included
carbonated drink, milk and water bottles because of the bottle bill introduced in Vermont
in 1953 [1]. Plastics packaging films and other plastic containers were mostly land filled
and comprised of a huge volume due to light weight of films; for example shopping bags,
wrapping materials, etc. As a result new class of polymers are developed that could be
biodegraded and completely mineralized in microbial mediums such as in composting.
The biodegradable polymers commercially available for packaging applications are
mainly aliphatic polyesters (Polylactide (PLA), Polycaprolactone (PCL),
Polyhydroxyalconates (PHA)) and aliphatic aromatic co-polyesters such as PBAT
(Ecoflex® by BASF). Ecoflex® is based on terephthalic acid, adipic acid, 1,4-butanedi01
modular units. Certain desired packaging functionalities as well as biodegradation are
achieved by synthesis of customized molecular structures obtained through statistical
copolyester units, including 1-4 butanediol and dicarbonic acids, adipic acid and
terephthalic acid linkages. For example, biodegradation is obtained by introducing ester

units in carbon chain in the polymer structure. Common applications of Ecoflex® are

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compost bags for organic waste, mulch films, coated and laminated materials and
oriented films [2].

The monomer unit of Ecoflex® is shown in Figure 6.1. Ecoflex® polymer is built
up of incorporation of hydrophilic components of monomers with branching resulting in
higher molecular weight and chain-lengthening. The glass transition temperature (T g) of
Ecoflex® is -30°C and melting temperature (Tm) of 110-115°C. The properties of
Ecoflex® are comparable to those of LDPE such as tear resistance and flexibility.
However, Ecoflex® also has some limitations such as moderate water vapor permeability
which can be adjusted using different masterbatches or additives [2]. One of such
additive or masterbatch is antiblocking agent (i.e. fine talc) which is used to reduce
surface friction during film extrusion of Ecoflex® and in further processes such as

printing or bag making [3].

{O-i‘marng aria... a: M

Figure 6.1. Monomer unit of Ecoflex

 

 

 

 

Ecoflex® passes the test of biodegradability according to DIN EN 13432, ASTM
D6400-99 and Japanese GreenPla standard [2]. In many cases and especially for aliphatic
polyesters primary degradation step is caused due to hydrolysis, whereas pure aromatic
polyesters like polyethylene terephthalate (PET) are very resistant to any hydrolytic
degradation and microbial attack. Only under drastic chemical conditions (e.g sulfuric
acid at 150°C) hydrolysis of such polymers can be used for recycling purposes. Hence
many attempts have been made to increase hydrolytic susceptibility of those polymers by

adding aliphatic constituents to it (such as PBAT); and it was found that by varying the

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amount of aromatic constituents, the biodegradation rate is affected. More the amount of
aliphatic constituent, higher is the susceptibility of biodegradation[4].

Studies have been done till now to assess the biodegradability of PBAT in
simulated c0mposting conditions as per recommended in ASTM, DIN and J IS standards.
However as per author’s knowledge, no study has been done to evaluate its
biodegradability in real composting conditions correlating to its loss in molecular weight.
This paper investigates the biodegradability of PBAT based commercially available

copolyester Ecoflex® and Ecoflex® with antiblocking agent (tale) for a period of 60 days.

6.2 MATERIALS AND METHODS
6.2.1 Samples

PBAT (P) and PBAT with talc additive (PT) were provided by Northern
Technologies International Corporation (Circle Pines, MN) with thickness of 20pm and
27pm respectively. The films were cut into 4” x 4” pieces and were subjected in compost
pile in four replicates and hence 6 such sets for 5, 10, 18, 26, 45 and 60 days. The
molecular weight of P and PT was 66,29312041 Daltons and 90,12611649 Daltons
respectively.
6.2.2 Compost pile

A compost pile was built at Michigan State University composting facility (East
Lansing, MI). This compost pile was used to test the PBAT films biodegradability. The
composition of pile was 40-45% of cattle manure, 40-45% of horse barn shavings and 10-

20% of waste feed (that is the food that cattle’s do not consume). The dimension of the

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pile was 6 x 12 x 3 meters and the initial temperature, relative humidity and pH of the

pile was 60°C:1.1°C, 60.5%11.3% and 8.5 respectively.

6.2.3 Compost parameters

Compost parameters which plays essential role in biodegradation such as
temperature, relative humidity (%RH) and pH was recorded everytime the films were
taken out from the compost pile on 5, 10, 18, 26, 45 and 60 day. Temperature, %RH and

pH are shown in Figure 6.2 (a,b,c).

(a) Temperature: The temperature of the compost pile at the samples place was recorded
using a stainless steel thermometer (11°C) obtained from Reotemp (San Diego, CA).

(b) Relative humidity (RH): Wet weight moisture content of the compost was calculated
using microwave heating method previously used by Kale et.al. [5, 6].

(c) pH: 5 grams of compost sample was dissolved in 25 ml of deionized water and pH
was determined using calibrated pH paper obtained from Micro Essential Laboratory
Inc (Brooklyn, NY).

6.2.4 Ambient conditions

The ambient air conditions which may also affect the composting conditions were

recorded at the Michigan Automated Weather Network (East Lansing,MI). During the 60

days duration of study , the ambient air temperature varied from -13.1°C to 266°C, the

relative humidity from 20.3% to 98.8% and the total solar radiation from 2043 kJ/m2 to

25565 kJ/mz. Figure 6.2 (d,e,f) shows the ambient temperature, %RH and solar radiation

for the duration of study (60 days).

183

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Figure 6.2. (a) Temperature (O), (b) %RH (1:1) and (c) pH (A) of compost pile; and (d)
ambient maximum“) and minimum(u) temperatures, (e) ambient maximum(0) and
minimum(t:r) %RH and (1) solar radiation (A) as a function of time for 60 day period.

184

6.2.5 Placement of films in compost pile

A wooden box was built with mesh attached to its bottom to test films in
composting conditions. The box was placed in the compost pile where optimum
temperatures (i.e. 60°C+) were found. Initially compost was added on the mesh and later
films were placed in 4 replicates in one box. The films and the box were later covered
with compost over it. The position of box in the compost pile was at 1.2 m above ground
and 1 m inside compost pile from surface. For more information about the methodology,
readers can refer to references [5, 6].
6.2.6 Visual inspection

The films were visually inspected everytime each set of box was taken out from
compost pile on respective day. The films were inspected for their changes in the color,
breakdown or cracks and impact on each of 4 pieces of films due to different position in
compost pile. Digital pictures were taken by digital camera manufactured by Cannon
(Model A530).
6.2. 7 Molecular weight analysis

Molecular weight determination was carried out using gel permeation
chromatography (GPC). Multisolvent delivery system, autosampler and RI detector; all
manufactured by Waters (Milford, MA) were used for determination. Inhibitor free
Tetrahydrofuran (THF) solution was used to dissolve samples and was obtained from
Sigma Aldrich (Milwaukee, USA). PBAT biodegraded samples (15 grams each) were
dissolved in '10 ml of THF solution and later it was filtered through a PTFE
(polytetrafluroethylene) filters obtained from Whatman (Florham Park, NJ). The diluted

samples in THF were transferred to 1 ml vials obtained from Waters (Milford, MA).

185

6.3 RESULTS AND DISCUSSION
6.3.] Visual inspection

The pictorial representation of PBAT films biodegradation in real composting
conditions is shown in Figure 6.3. The samples shown in figure are one of the four
samples tested for biodegradation. On eighteenth day some breakdown in the film can be
seen in the Figure 3. The breakdown part could not be traced in the compost pile and
could be consumed by microorganisms. A similar breakdown can also be seen on the 26th
and 45th days where even more quantity of film is disintegrated on each day. All the four
samples of PBAT films on 60th day are shown in Figure 6.4. Samples A and D were
towards exterior of the pile, whereas samples B and C were more towards the interior of
the pile. Slow degradation can be seen in case of samples A and D as compared to
samples B and C. This could be due to the higher reproduction of microorganisms, and
higher temperature and humidity. One of the PBAT films (out of four) was disintegrated
in the compost pile on 60th day in this study. However this could be governed due to
many factors as well, for example there was much variability in the temperature and
relative humidity of the compost pile. Similarly PBAT with talc additives was also tested
for biodegradation for period of 60 days in real composting conditions. Pictorial

representation of the same is shown in Figure 6.5.

186

    

Day 26 Duty 45 Day 0.}

 

Figure 6.3. Visual inspection of PBAT films in real composting conditions

 

Figure 6.4. Pictorial representation of four samples of PBAT films on 60th day. Samples
B and C were more towards interior of the pile.

187

 

 

Figure 6.5. Visual inspection of PBAT + talc films in real composting conditions

PBAT with talc additive films (PT) shows similar trend as of PBAT films (P) in
the beginning, however no significant changes could be observed till 26th day. On 45‘h
day some breakdown can be seen and on 60‘h few residuals of the PT films could be seen.
This slow biodegradation in PT as compared to P could be due to its higher molecular
weight (which is almost 25,000 Daltons more) and also due to the presence of talc
(antiblocking agent) in it. As mentioned before, as per authors knowledge there has been
no study done to PBAT films in real composting conditions and hence it becomes
difficult to correlate the disintegration trend obtained in this study. The variation in
temperature and %RH in the compost pile during study period could be determining
factors in_the disintegration of PBAT films. For example the temperature was reduced
upto 37°C which could involve mesophilic microorganisms (0-40°C) in the composting
process, rather than thermophilic microorganisms (40-55°C) which are essential for
efficient composting processes. Composting piles are usually turned frequently for

providing better aeration to compost and hence speeding up the composting process. In

188

this study, the compost pile was not turned at all which might have also leaded to
decrease in temperatures and hence variability in the disintegration. However this case
scenario shows some insight of the difficulty of real composting studies.
Molecular weight

The variation in molecular weight for PBAT films is shown in Figure 6. One of
the four samples was degraded on 60th day in compost pile, hence 60th day molecular
weight data shown is an average of 3 samples; whereas others are average of four
samples. Initial rise in molecular weight on 5th and 10th day can be attributed to the cross
linking or recombination process occurred in films due to degradation. The solid line
Shown is a linear fitted line as a function of time based on the molecular weight data for
four samples for each day (Adj R square=0.72).

Also after 10th day, major variation can be seen on the 18'“, 26'“, 45th and 60th day.
It was observed that the films which were close to the interior of compost pile showed
greater decrease in molecular weight, whereas the ones near exterior showed very less
decrease in molecular weight. For example, on 60"I day, the molecular weight of three
available samples was 62,672 Daltons, 46,460 Daltons and 61687 Daltons respectively
which can be comparable to the molecular weight of PBAT films on zero day. Out of the
three, the sample for which 46,460 Daltons molecular weight was obtained was towards
the interior of the pile which might be the reason for the further decrease in molecular
weight. PBAT films has aliphatic and aromatic sequences in it and aromatic sequences
are quite resistant to microbial attack as can be seen in case of polyethylene terephthalate

(PET). Hence, unlike polylactide which is an aliphatic polyester, there is no hydrolysis

189

 

reaction occurred in PBAT which would decrease the molecular weight drastically to be

able to be consumed by microorganisms.

 

100 -

90-

I

80

70-

 

I

 

 

50 __

Molecular weight, kDaltons

40r

J(
J)
(L
)J

 

 

0 L 1 l l l L 1

O 10 20 30 40 50 60 70

Time, Days
Figure 6.6. Variation in molecular weight for PBAT films (0) and PBAT with talc
additive (:1) films in real composting conditions.
* 60th day data point shows average of 3 points for PBAT films.

 

In case of aliphatic polyesters, the degradation occurs due to the diffusion of
water into the polymer bulk. In case of PBAT, the degradation of polymer bonds is faster
than diffusion of water and hence the polymer will be consumed by hydrolysis on its
surface. This phenonmenon is known as surface erosion as the degradation occurs on the
surface. Hence, no significant changes could be observed in the physical shape of the
polymer as polymer is slowly decomposed on the surface [7, 8]. A degradation test on

PBAT powder was carried out by U.Witt et.al. [9] in the synthetic medium with

190

actinomycete strain T.fusca DSM 43793 at 55°C in shaking vessels. This test in mineral
salt medium and inoculum was carried out and 94% solubilization of polymer was
observed in 21 days. However, this is a type of simulated composting test where
microorganisms and temperature are controlled and which could give clear understanding
and idea of favorable conditions for biodegradation of PBAT. According to U.Witt et. al.
[9], test microorganism T .firsca DSM 43793 has a very good ability to depolymerize
PBAT but not able to readily metabolize monomers and oligomers formed. In our study,
the molecular weight could not been seen comparable to monomers or oligomers. The
least molecular weight obtained for P was 46,460 Daltons and for PT was 66,340 Daltons
on 60‘h day. According to Gopferich A. [8], molecular weight loss in polymers such as
poly (anhydrides) shows no change in molecular weight or physical geometry in the
course of degradation. The microorganisms involved in this study were not analyzed,
which could have given idea of how matrix of microorganisms affects the
biodegradability. However, it cannot be just concluded in one study or one replicate of it,
and more repetitions are essential for concluding the biodegradation of PBAT in real
composting conditions.

A similar biodegradation trend for PBAT with talc additives is shown in Figure
6.6. Unlike PBAT, as discussed before in visual inspection the biodegradation and
breakdown in PT can be seen after 26‘h day. Similar to PBAT, an initial rise due to
recombination reactions or crosslinking can be seen for the first two days. The molecular
weight increase is also seen till 45th day. However on 60th day, the average molecular
weight was below the molecular weight on zero day. The solid line represents the linear

fitting for molecular weight data points as a function of time (adj R square value of

191

0.45).The consecutive variability in the molecular weight could be again due to the
position of films in either interior or exterior of the pile. For example on the 60th day,
88,821, 66,340 , 73,022 and 83,514 Daltons was the respective molecular weight for four
film samples; as compared to 90,126:1,649 Daltons on zero day. Tale is commonly used
as an antiblocking agent in improving the processing of Ecoflex® film production.
Ecoflex® batch AB1 (60% fine tale) is one such antiblocking agent in film production
[10]. Hence, it is very much likely that additives such as talc would be incorporated for
efficient film production and which would eventually affect the biodegradation property.
For successful biodegradation of polymer, it is necessary to have a proper time
representation of its biodegradation in real conditions. As per Witt U et.al [11], Ecoflex®
reached 60% mineralization value in controlled composting conditions on 45th day,
however the conditions are controlled where therm0philic microorganisms are active,
unlike real conditions where characterization of microorganisms may change with change
in the compost variable parameters. To make a more clear representation of the
biodegradation mechanism in case of PBAT, Witt U et.al [11] exposed PBAT using
microorganisms (isolated from compost) in aqueous medium. After degradation, only
water soluble intermediates were found through GC/MS which showed that those isolated
microorganisms were able to degrade polymer chains into monomers. Later the
metabolism of monomers was achieved through adding a mixed culture of
microorganisms which did not show any residues in the GC analysis. These two steps of
degradation are referred as a “symbiosis process” by Witt U et.al in which “individual
organisms are able to perform only one degradation step, and other organisms the next. ”

However, it cannot be proved that the PBAT copolyester structure actually went through

192

this symbiosis process because of possibility of indigestion of soluble fragments in their
cells.

In summary, it can be concluded through visual inspection that biodegradation
can be seen by breakdown in films. This trend can’t be seen in variation of molecular
weight, mainly because of the presence of aromatic sequences which are resistant to
microbial attack and the surface erosion phenomenon. Miieller et.al. [4] showed that the
biodegradation of (1,4 butanediol, adipic acid, terephthalic acid) BTA is affected by the

increasing percentage of terephthalic acid.

CONCLUSION

It has already been proven according to the simulated conditions that aliphatic
aromatic copolyester such as Eooflex® is biodegradable. Looking at the current trend of
waste generation in United States, usages of such biodegradable films would be
beneficial in eliminating municipal solid waste. As per the author’s knowledge and
current literature, the biodegradability of PBAT powder/films is mostly reported for
testing in simulated microbial conditions where either compost parameters are controlled
or enzyme specific aqueous mediums are used. It is also essential to match this
information with the actual film testing in real microbial environments such as
composting. This study gave an understanding of how films biodegradation could get
affected due to location and environmental factor changes in the compost pile. This
variability in the exposure of film surface area and microbial medium parameters is an
important consideration in successful biodegradation of those films; otherwise it will

create another plastic waste problem. Also based on limited knowledge on enzymatic

193

attack on complex structures present in copolyesters, work has to be done to evaluate
biodegradability of those films in novel evaluation methods such as in real conditions
which would give good representation of biodegradation performance in different

environments.

194

 

REFERENCES

1. EPA. Municipal Solid Wastes (MSW) in United States: 2005 facts and figures.
2006 [cited 2006 11-20-2006]; Available from:
http:j/wwwepa.goflgarbage/pubs/ex-sumOS.pdf

2. Motonori Yamamoto, U.W., Gabriel Skupin, Dieter Beimbom, Rolf-Joachim
Muller, Biodegradable Aliphatic-Aromatic Polyesters: "Ecoflex® ". Biopolyrners,
ed. A. Steinbiichel. Vol. 4. 2004. 301-312.

3. BASF. Product Information-Ecoflex - Antiblocking agents for Ecoflex F BX 701 I
- The biodegradable polyester for compostable film. 2004 [cited 02-11-2007].

4. Rolf-Joachim Muller, I.K., Wolf-Dieter Deckwer, Biodegradation of polyesters
containing aromatic constituents. Journal of Biotechnology, 2001. 86: p. 87-95.

5. Gaurav Kale, R.A., Paul Singh, Comparison of Degradability of Poly (lactide)
Packages in Composting and Ambient Exposure Conditions. Packaging
Technology and Science, 2006. 19.

6. Gaurav Kale, R.A., Paul Singh, Degradation of commercial biodegradable
packages under real composting and ambient exposure conditions. Journal of
Polymers and the Environment, 2006. 14(3).

7. Friederike Von Burkersroda, L.S., Achirn GOpferich, Why degradable polymers
undergo surface erosion or bulk erosion. Biomaterials, 2002. 23: p. 4221-4231.

8. Gopferich, A., Mechanisms of polymer degradation and erosion. Biomaterials,
1996. 17: p. 103-114.

9. U. Witt, T.E., M. Yamamoto, I. Kleeberg, W. Deckwer, R.-J. Mueller,
Biodegradation of aliphatic-aromatic copolyesters: evaluation of the final

biodegradability and ecotoxicological impact of degradation intermediates.
Chemosphere, 2001. 44: p. 289-299.

10. BASF. E coflex Biodegradable Plastics Brochure. 02-11-07 [cited; Available
from:
http://www2.basf.de/basf2/html/plastics/images/pdfs/engl/polymere/Ecoflex_Bio_

e.gdf.

11. Uwe Witt, M.Y., Ursula Seeliger, Rolf-Joachim Muller, Volker Warzelhan,
Biodegradable polymeric materials - not the origin but the chemical structure
determines biodegradability. Angewandte Chemie International Edition, 1999.
38(10): p. 1438-1442.

195

 

CHAPTER 7 - FUTURE RESEARCH RECOMMENDATIONS

The following topics are recommended for future research work:

1. Variability’s in the biodegradation of packages in real composting conditions

should be investigated through more replicates of the study.

. Commonly used compostable materials such as food, manure and yard waste
in composting processes and their interaction with biodegradable packages
should be studied.

. Accurate correlation between the biodegradation performance of packages in
simulated and real composting conditions should be established. A more
detailed information and timely representation can provide better guidelines in
biodegradation processes such as composting.

. Study on microorganisms involved in composting (depending on the
compostable materials used) and its interaction with packages would be
helpful in determining the degree of biodegradation efficiency with respective
microorganisms.

. For biodegradable packaging, a focus on biodegradation testing of a whole
package should be made to have the idea of how packaging components and
its association with the main package might affect the biodegradability.

. As per the results obtained in PBAT study, the location of films in compost
pile makes difference to its biodegradability. A study on location of

package/film in compost and its biodegradability should be investigated.

196

 

7. A pilot scale study on waste management of biodegradable packages and its
composting at commercial level would be helpful in determining the

probability of packages getting disintegrated in it.

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