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LIBRARY
Michigan State
University

This is to certify that the
thesis entitled

Development of Polylactic Acid (PLA) based blends and their
Nanocomposites for Packaging Applications

presented by

MARIAPPAN CHIDAMBARAKUMAR

has been accepted towards fulfillment
of the requirements for the

Master of Science degree in Packaging

 

 

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PLACE IN RETURN BOX to remove this ched<out from your record.
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DATE DUE

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2/05 c:/CTRC/DatoDm.indd-p15

DEVELOPMENT OF POLYLACTIC ACID (PLA) BASED BLENDS AND THEIR
NANOCOMPOSITES FOR PACKAGING APPLICATIONS

By

Mariappan Chidambarakumar

A THESIS
Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of
MASTER OF SCIENCE
School of Packaging

2005

ABSTRACT

DEVELOPMENT OF POLYLACTIC ACID (PLA) BASED BLENDS AND THEIR
NANOCOMPOSITES FOR PACKAGING APPLICATIONS

By

Mariappan Chidambarakumar

Plastics packaging is one of the worst pollution menaces today. Therefore it is
necessary that “packaging should go green’. Polylactic acid (PLA), renewable
resources based biodegradable polyester, is a viable alternative to many fossil-
fuel based plastics. However, natural poly-l-lactic acid (PLLA) is a stiff plastic,
and thus needs to be made tougher for many packaging applications.
Toughening of PLLA can be achieved by blending PLLA with tough polymers.
This research consists of two parts: (i) toughening of PLLA through blending with
selected tough bio-polymer and (ii) fabrication of nanocomposites from selected
blends and a specific organically modified montmorillonite (OMMT) clay to
achieve the stiffness-toughness balance. ‘Nanocomposite’ is one of the best
techniques to achieve the required material performances. Extrusion followed by
injection molding was adopted in fabricating various samples from blends and
nanocomposites. PLLA was melt compounded with several tough biodegradable
polymers and a specific tough plastic (poly-(butylene adipate-co-terephthalate),
PBAT) was selected for further studies. PLLA-PBAT blends of varying
compositions were reinforced with OMMT clay. The blends and nanocomposites
were characterized through thenno-physical and mechanical analyses.
Environmental scanning electron microscopy (ESEM), X-ray diffraction (XRD),
and transmission electron microscopy (TEM) were used to study the morphology
behaviors. Extrusion followed by compression molding was adopted in fabricating
films for barrier property evaluations. Finally, experimental results were

correlated with theoretical Halpin-Tsai model using pseudo-inclusion.

Copyright by
MARIAPPAN CHIDAMBARAKUMAR

2005

ACKNOWLEDGEMENTS

I would like to thank my advisor, Dr. Amar K. Mohanty, for all his support,
mentoring and guidance. His high motivations and expectations helped me to
achieve beyond my capabilities. I would also like to thank to the other committee
members: Dr. Gary Burgess and Dr. Ramani Narayan. They were all very
supportive and helpful in the completion of this work and were the source of

invaluable advice through our engaging discussions.

I am grateful to Dr. AKM’s research group especially Mr. Yashodhan Parulekar
and Dr. Hiroaki Miyagawa for their assistance and for sharing their expertise and
skills with me. I am also grateful to the faculties and staffs of School of
Packaging, MSU. I am thankful to the staffs of Composite Material & Structures
Center, MSU. I am also thankful to all my friends and fellow graduate students
who have provided me the wonderful friendly atmosphere though out my

research period.

Finally, I would also like to specially thank my parents and my eldest brother.
They are the inspiration for making me what I am and they will always be the
motivation for what I will ever be. The success of this work belongs to them as

much as anyone else.

iv

TABLE OF CONTENTS

LIST OF TABLES .............................................................................. vii
LIST OF FIGURES ............................................................................ ix
Chapter 1 INTRODUCTION .................................................................. 1
Chapter 2 BACKGROUND AND LITERATURE REVIEW .......................... 8

Chapter 3 MATERIALS AND METHODS ............................................... 45

3.1 Materials ................................................................................ 45

3.1.1 Poly-L-lacticacid (PLLA) .................................................... 45

3.1.2 Poly-(butylene adipate-co-terephthalate), (PBAT) ................... 46

3.1.3 Poly-(tetramethylene adipate-co-terephthalate), (PTAT) ........... 47

3.1.4 Polybutylene Succinate (PBS) ............................................ 47

3.1.5 Poly (e-caprolactone), (PCL) ............................................... 48

3.1.6 Polyesteramide (PEA) ....................................................... 49

3.1.7 Organically Modified Montmorillonite (OMMT) Clay ................. 49

3.2 Methods .................................................................................. 50

3.3 Equipments and Preparation ........................................................ 52

3.3.1 DSM Microcompounder ..................................................... 52

3.3.2 Compression Molding Machine ........................................... 56

3.4 Characterization ......................................................................... 57

3.4.1 Dynamic Mechanical Analyzer (DMA) ................................... 57

3.4.2 Universal Testing Machine (UTM) ....................................... 58

3.4.3 lzod Impact Tester ............................................................. 58

3.4.4 Thermal Behaviors (DSC & TGA) ........................................ 59

3.4.5 Barrier Properties (OP & WVP testers) ................................... 59

3.4.6 X-ray Diffractometer (XRD) .................................................. 60

3.4.7 Environmental Scanning Electron Microscope (ESEM) ............ 60

3.4.8 Transmission Electron Microscope (T EM) ............................... 61

Chapter 4 RESULTS AND DISCUSSION .............................................. 62

4.1 PLLA based blends with tough biodegradable polymers .................. 62

4.2 PLLA — PBAT based blends ....................................................... 64

4.3 PLLA — PBAT based blends and their Nanocomposites ...................... 67

4.3.1 Direct Method Vs Master batch Method .................................. 67

4.3.2 Thermo-physical and Mechanical Properties .......................... 69

4.3.3 Thermal Properties ........................................................... 74

4.3.4 Barrier Properties ............................................................. 76

4.3.5 Structural Analysis ............................................................. 78

4.3.6 Morphology Analysis ......................................................... 80

4.3.7 Halpin-Tsai Model Correlation of Elastic Modulus through

Pseudo-inclusion Model .................................................... 83
Chapter 5 CONCLUSIONS AND RECOMMENDATIONS .......................... 84
APPENDIX 1 ...................................................................................... 88
REFERENCES ................................................................................... 92

vi

LIST OF TABLES

Table 2.1 Physical properties of biodegradable polymers .......................

Table 2.2 Comparison of Physical Properties of High molecular weight
PLA ..............................................................................

Table 2.3 Material Properties of Ecofiex® F BX 7011 ............................

Table 2.4 Mechanical properties of Nylon 6 Nanocomposites ..................

Table 3.1 Structural information for the organically modified
montmorillonite clay .........................................................

Table 3.2 Blending compositions and process parameters used in DSM

Microcompounder for PLLA with various tough biopolymers ......

Table 3.3 Blending compositions and process parameters used in DSM
Microcompounder for PLLA/PBAT/Clay blends ......................

Table 3.4 Blending compositions and process parameters followed in
Compression molding machine for making PLLA/PBAT/Clay
blends / nanocomposites based films ...................................

Table 4.1 Storage modulus and notched izod impact strength of 50PLLA-
50Tough biopolymer (PBAT, PTAT, PBS, PCL or PEA) blends
(in wt%) ..........................................................................

Table 4.2 Thermo-physical properties viz., heat deflection temperature
(HDT) and storage modulus of PLLA-PBAT-OMMT blends /

nanocomposites based injection molded samples ...................

Table 4.3 Mechanical properties viz., notched izod impact strength and
tensile properties of PLLA-PBAT-OMMT blends I

nanocomposites based injection molded samples ....................

Table 4.4 Barrier properties viz., Oxygen Permeability and Water Vapor
Permeability of PLLA-PBAT-OMMT blends/nanocomposites
based compression molded films (in SI units) .........................

Table 4.5 Barrier properties viz., Oxygen Permeability and Water Vapor
Permeability of PLLA-PBAT-OMMT blends/nanocomposites
based compression molded films (in USA standard industry

units) ..............................................................................

vii

p.11

p.17

p.

p.

p.

p.

p.

p.

p.

p.

p.

p.

p.

21

42

50

54

55

57

63

71

72

76

77

Table 4.6 Barrier properties of conventional plastics such as LDPE,
HDPE, OPP, PS, OPET, and Oriented Nylon6 (in USA standard
industry units) .................................................................. p. 77

Table 4.7 XRD patterns of nanocomposites of 100PLLA and 60PLLA :
4OPBAT with 5wt% OMMT clay blended polymer matrix ........... p. 79

viii

LIST OF FIGURES

Figure 2.1 Life cycle of biobased biodegradable polymers - C02 balance

in the environment .......................................................... p. 8
Figure 2.2 Classification of biodegradable polymers .............................. p. 10
Figure 2.3 Polymerization routes to polylactic acid ............................... p. 13
Figure 2.4 Schematic of PLA production via prepolymer and Iactide ........ p. 15

Figure 2.5 Chemical structure of the aliphatic-aromatic copolyester (M =

modular components, eg. monomers with a branching or

chain extension effect) .................................................... p. 22
Figure 2.6 Glass transition temperature behaviors for the miscible blends.. p. 28
Figure 2.7 The phase morphology of HIPS ......................................... p. 29

Figure 2.8 The crystal structure of single nano clay platelet (2:1 layered
silicates) ........................................................................ p. 37

Figure 2.9 The surface treatment of the agglomerated nano clay platelets
(silicate layers) ............................................................... p. 38

Figure 2.10 The complete dispersion (exfoliation) of the clay platelets
(silicate layers) during the compounding operation ............... p. 39

Figure 2.11 The schematic illustration of thermodynamically achievable
polymer I layered silicate nanocomposite ........................... p. 40

Figure 3.1 Structure of Polylactic Acid (PLA) ....................................... p. 45
Figure 3.2 Structure of Poly-(butylene adipate-co-terephthalate) (PBAT). .. p. 46

Figure 3.3 Structure of Poly-(tetramethylene adipate-co-terephthalate),

(PTAT) ......................................................................... p. 47
Figure 3.4 Structure of Polybutylene Succinate (PBS) ........................... p. 47
Figure 3.5 Structure of Poly (e-caprolactone) (PCL) .............................. p. 48
Figure 3.6 Structure of Polyesteramide (PEA) ........................................ p. 49

ix

Figure 3.7 Schematic representation of this research project methodology p.

Figure 3.8 Schematic of Microcompounder Extruder unit ........................

Figure 4.1 Storage modulus and notched izod impact strength of 50PLLA-

50Tough biopolymer (PBAT, PTAT, PBS, PCL or PEA) blends p.

Figure 4.2 Themro-physical properties viz., heat deflection temperature
(HDT) and storage modulus for various PLLA-PBAT blends.....

Figure 4.3 Mechanical properties viz., tensile properties and notched izod
impact strength for various PLLA-PBAT blends ......................

Figure 4.4 Effective Process engineering for the nanocomposite
preparations: Direct Method Vs Master batch Method .............

Figure 4.5 Optimization of effective process engineering between direct
method and master batch method for the nanocomposites
preparations. A=100PLLA; B=50PLLA50PBAT; C=47.5PLLA/
47.5PBAT/5OMMT-Direct; D=47.5PLLAI47.5PBATISOMMT-
Master batch; E=100PBAT (all are in wt %) ..........................

Figure 4.6 Tensile properties of the nanocomposites of various PLLA/
PBAT blend compositions along with the respective neat
blends. A=100PLLA; B=70PLLA30PBAT; C=66.5PLLA/28.5
PBAT/SOMMT; D=60PLLAI4OPBAT; E=57PLLA/38PBAT/
5OMMT; F=50PLLAI5OPBAT; G=47.5PLLAI47.5PBATI
SOMMT; H=1OOPBAT (all are in wt %) .................................

Figure 4.7 Thermo-physical and mechanical properties of the
nanocomposites of various PLLA/PBAT blend compositions
along with the respective neat blends. A=100PLLA; B=70PLLA
30PBAT; C=66.5PLLA/28.5PBAT/50MMT; D=60PLLA/
4OPBAT; E=57PLLA/38PBAT/50MMT; F=50PLLA/50PBAT;

G=47.5PLLA/47.5PBATI50MMT; H=1OOPBAT (all are in wt %) p.

Figure 4.8 Storage modulus curve analysis for the neat PLLA, 60PLLA/
4OPBAT blend and its nanocomposite (all are in wt%) ............

Figure 4.9 Stress-strain curve analysis for 60PLLA/4OPBAT blend and its
nanocomposite (all are in wt%) ..........................................

Figure 4.10 DSC curve analysis for the neat PLLA, 60PLLA/4OPBAT
blend and its nanocomposite (all are in wt%) ........................

p.

p.

p.

p.

p.

p.

p.

p.

p.

52

62

64

65

68

69

69

73

74

75

Figure 4.11 TGA curve analysis for 60PLLA/4OPBAT blend and its
nanocomposite (all are in wt%) ......................................... p. 75

Figure 4.12 XRD patterns of nanocomposites of 100PLLA and 60PLLA!
4OPBAT with 5 wt% OMMT clay blended polymer matrix (all
compositions are in wt%) ................................................. p. 79

Figure 4.13 ESEM micrographs on the fractured surfaces of 1. 60PLLA!
4OPBAT blend; 2. Nanocomposite of 60PLLA/4OPBAT blend;
3. 7OPLLA/3OPBAT blend (all compositions are in wt%);
200 um scale bar for all images ......................................... p. 80

Figure 4.14 TEM images for the phase separation (low & high
magnifications) with the intercalated nano scale OMMT clay
agglomerates (low magnification) views in the 5 wt% OMMT
reinforced nanocomposite of 60PLLA240PBAT polymer
matrix (composition is in wt%) .......................................... p. 81

Figure 4.15 Elastic modulus data correlation between the experimental
data and theoretical calculated values of 5.0 wt% (1.62 vol.%)
clay nanocomposites using Halpin-Tsai model through
Pseudo-inclusion model ................................................... p. 83

Figure A-l A model of three phase nanocomposites with a pseudo-
inclusion ....................................................................... p. 89

xi

Chapter 1 Introduction

Plastics are widely used in packaging and most of them are conventional
petroleum based plastics that are very harmful to our environment. Due to their
technological significance, packaging is totally dominated by these synthetic
plastics like Polyethylene (PE), Polypropylene (PP), Poly (ethylene terephthalate)
(PET), Polystyrene (PS), Poly (vinyl chloride) (PVC) etc. Despite their
appreciable advantages over other types of packaging materials, they are made
from the non-renewable resources, thus are not environmentally friendly. They
are not degradable for years and even incineration emits excess of CO; to the
atmosphere. This is also one of the reasons for the global warming. The
packaging plastics wastes are growing drastically worldwide and shortage of
landfills has led the plastics packaging to become one of the worst pollution
menaces today. Therefore it is necessary that ‘packaging should go green’ and
the obvious solution to this waste management of packaging would be the usage
of biodegradable plastics in packaging. Biodegradable plastics are generally
biodegradable from few months to 2 years under the given bioactive conditions.
The growing need of the sustainable and green materials to substitute the
conventional ecologically dangerous plastics led to the innovations and research
works on the biodegradable plastics application in packaging. Biodegradable
plastics are not new to the world or for research. They have been widely used in
the biomedical applications. For example, polylactic acid (PLA) has been used in
the biomedical application since 1970s. Due to their higher cost it was not

considered into other applications where cheaper options were already available

with conventional plastics. Now the growing awareness of protecting the
environment is leading to the investment of skills and resources for the
innovations & research on biodegradable plastic applications in various fields

primarily in packaging [1 .1-1 .3].

Recently, there are many biodegradable plastics being used in the packaging
applications but struggling to compete with the conventional petroleum based
plastics due to their cost and performance factors. Of course, the volume of
usage will definitely bring down the cost however the challenges of performances
are still there from the conventional plastics. For this, there are many researches
already initiated by the government as well as nongovernmental organizations
worldwide to meet the performances and other application challenges from the
conventional petroleum based plastics. Biodegradable plastics are derived from
the renewable resources or from petroleum based nonrenewable resources or
from both renewable as well as nonrenewable resources. Many of these
biodegradable polymers such as, PLA, Polyhydroxy Butyrate (PHB), aliphatic-
aromatic polyesters like Poly-(butylene adipate-co-terephthalate) (PBAT) & poly-
(tetramethylene adipate-co-terephthalate) (PTAT), Poly (e-caprolactone) (PCL),
Polybutylene Succinate (PBS), Polyesteramide (PEA) and cellulose based
polymers are making inroads into packaging. Among these, most promising
biopolymer is PLA and it is widely applied in packaging applications in the forms
of bottles, films, therrnoform cups etc. Already many researches are undenrvay to

explore more on PLA and its applications.

PLA is made from the 100% renewable resources and it was the first bio polymer
made from these resources. It requires very less energy to produce unlike the
conventional polymers [1.1, 1.4]. Cargill Dow is the leading company who is
pioneer in PLA technology and its applications. Thus, Cargill Dow has already
started its way to prevent pollution, substitute the petroleum based feedstock with
green polymers and to eliminate the use of solvents and hazardous materials.
PLA is an intrinsically rigid and stiff bio-polymer whose properties depend on the
% of D-Lactide contents presents in the polymer. lt behaves like PET and PS in
many ways and has better performances than PP and so has an ample scope of
applications in packaging. Although PLA is the stiff and rigid polymer due to its
high crystallinity and higher glass transition temperature (T 9) value, its brittle
nature would reduce the scope of applications in packaging. So, it is very much
necessary to make stiff PLA as tough just like making plasticized PVC or High
impact polystyrene, and this will provide more chances for PLA to go for many
applications including packaging. Toughening of PLLA can be achieved through
plasticization, incorporation of its own isomers during polymerization, or blending
PLA with tough polymers. Many researches are also undenivay in improving the
toughness of Poly-l-Iactic acid (PLLA) that is naturally produced in which almost

100% L-lactide monomers exists [1 .1, 1.3, 1.4].

Based on these studies and researches to improve the toughness of the PLLA, it
was decided to blend with a tough biodegradable polymer in optimum
composition so as to improve it toughness to a required level. There are many

tough biodegradable polymers like PBAT, PTAT, PBS, PCL, PEA etc already

available in the market. A number of researches have already been done on
these kinds of blends too. This leads us to select the suitable tough
biodegradable polymer and blend in the right composition with PLLA to improve

the toughness of PLLA with out adding any plasticizers.

Presently, ‘Nanotechnology’ is one of the hot research areas in which ‘Polymer
Nanocomposite’ has plenty of scopes in many applications including packaging.
Nanotechnology is defined as “Technology development at the atomic,
molecular, or macromolecular range of approximately 1-100 nanometers to
create and use structures, devices, and systems that have novel properties”
[1.5]. Nanocor defined ‘Nanocomposite Technology” as “the materials and
processes required to disperse nano-scale particles in plastics, metals, or
ceramics” and also defined ‘Polymer Nanocomposites’ as “new class of plastics
derived from a highly refined form of nanoclay that disperses in plastic matrix”.
So, polymer nanocomposites are the polymers that are reinforced with natural
nano clay platelets (in the range of 2% to 5%) that are about 100 nm in length
and 1 nm in thickness. Various natural nano scale clays are available for this
nanocomposite purpose and montmorillonite is one of the most widely used ones

among all.

Three kinds of polymer/clay nanocomposites can be achieved based on the clay
structure and morphology in the polymer matrix and they are intercalated,
intercalated and flocculated and exfoliated nanocomposites. In intercalated

nanocomposites, the clay platelets got separated further each other within its

agglomerate by the incorporation of polymer chains between the nano clay
platelets (each single clay plate is about 1 nm in thickness) when compare to the
natural or modified clay platelets. Where as, in the exfoliated nanocomposite, the
nano clay platelets are well separated from each other and well dispersed across
the polymer matrix uniformly in various angles. Here, surface area of clays due to
the high aspect ratios will be more and so more interaction between the polymer
and clay and so improvement in properties. Barrier properties are also improved
due to the tortuousity created by these exfoliated clay particles across the
polymer matrix. Nanocomposites can be prepared through many ways like melt
compounding, in-situ polymerization, solvent casting method etc. However, melt
compounding is claimed to be the better method to exfoliate the clay particles in
the polymer matrix since the shear force helps in the separating the clay platelets
effectively. Still, the exfoliation is not always possible to achieve and mostly
intercalation of clays take place. It also depends on the hydrophilic and
hydrophobic balance between the surface of the clay and that of the polymer.
The nanocomposite gives better performances in terms of thermo-physical
properties, mechanical properties, barrier properties etc [1.6]. Due to the
exfoliation of the clay particles within the polymer matrix, it tends to increase the
heat defection temperature (HDT) and coefficient of linear thermal expansion
(CLTE) and also creates the tortuous path for gas I vapor molecules to pass
through the polymer matrix across its thickness and so giving better barrier
performances. Barrier is one of the important parameters in food and medical

packaging applications. Nylon-6 was the first plastic to be used for its

nanocomposites that leads the way to other plastic and various other polymers
were tried for the nanocomposites [1.7]. However, few biodegradable polymers
were prepared for their nanocomposites and many researches were already
done with PLA based nanocomposites. Mohanty et al has already provisionally
applied for a US patent on “Biodegradable Polymeric Nanocomposite Packaging

Materials and Production Methods” [1.8].

PLLA is yet to compete with the conventional plastic due to its higher cost and its
moderate performance. PLLA is blended with a tough biopolymer to improve its
toughness while there may be some reduction in the strength and modulus.
However, to maintain the stiffness-toughness balance, nanocomposite method is
used; since incorporation of nano-clay will improve the strength and modulus
while improving the barrier properties provided the right exfoliation takes place in
the polymer matrix. To achieve this, we decided to use specific organically
modified montmorillonite (OMMT) nano-clay with more hydrophobicity since
PLLA resins are hydrophilic in nature and also that will maintain the hydrophilic-
hydrophobic balance in the polymer blended matrix. This OMMT clay is
organophilic and so better chances of mixing with the polymer like PLLA that is
also organophilic in nature. Not many researches are done with any biopolymer
blend based nanocomposite. Hence, from the above finalized right blend
composition, the nanocomposite for the same would be prepared through the

melt compounding process to achieve the required performances.

Thus, the objectives are derived as:
“To develop a passive bio-degradable packaging material by utilizing nano
composite technology with optimized Poly L- Lactic Acid (PLLA) based blend with

a suitable flexible/tough biodegradable polymer without using any compatibilizer. ”

This objective will be achieved in the three phases of activities. In the first phase,
PLLA will be melt compounded with the tough biodegradable polymers such as,
PBAT, PTAT, PBS, PCL and PEA in 50:50 (wt %) compositions and will be
evaluated for their thermo-physical and mechanical behaviors to choose the

suitable tough biodegradable polymer.

In the second phase, with the above selected tough biodegradable polymer blend
partner, different blend compositions would be melt compounded and optimized
for the right compositions based on their mechanical and thermo—physical
properties. Hence the significance of the blending here is to improve the

toughness of the stiff biopolymer that is PLLA.

In this third phase, from the above selected blend compositions, nanocomposites
of the same will be prepared with specific OMMT clay and evaluated for the
mechanical, thermo-physical and barrier properties. Then the optimized
nanocomposite formulation will be evaluated for the structural and morphology
analyses. Hence, the significance of the nanocomposite here is to maintain the

stiffness-toughness balance as well as to improve the barrier properties.

Chapter 2 Background and Literature Review

Plastics are widely used in many different applications including in medicines due
to their versatile properties. Today it's almost impossible to live without plastics in
our daily life in this modern society. It is not surprising to see that plastics are
dominant materials for packaging. However, most of them are conventional
petroleum based plastics that may have many advantages but at the cost of
environment and landfill spaces. These conventional nonrenewable plastics do
not degrade for years and also not all the plastics are recyclable either due to
their nature or their applications. Incineration also emits hazardous gases and

C02. In contrast, the biodegradable plastics can be collected and disposed in

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PROCESSING

Figure 2.1 Life cycle of biobased biodegradable polymers - C 02 balance in the
environment [2. 2]

bioactive environments and can be either degraded by microorganisms like
bacteria, fungi and algae through enzymatic actions or by nonenzymatic process
through chemical synthesis. Then biodegradable polymers will be degraded into
C02, methane, water, biomass, humic matter, and other natural substances and
thus these biodegradable polymers are naturally recycled by biological processes

(Figure 2.1). [2.1, 2.2]

Hence, a feasible solution to protect the environment will be to substitute the
conventional plastics with the degradable plastics. In this turn of 21‘it century,
recent developments and innovations leads to the naturally derived resources
based materials that will dominate and contribute in many applications. Also
present researches efficiently bringing the success to the developments and
technologies to cut down the costs and to match the performances of the
biodegradable plastics to the conventional plastics. This research project also
has the similar kinds of objectives. There is difference between the terms
‘biobased’ and ‘biodegradable’ which are often wrongly used. In simple terms,
biobased can be biodegradable where as not necessarily the other way. There
are biodegradable materials that are actually derived from the nonrenewable
resources like petroleum. So we can say the materials (plastics) derived from
renewable resources such as corn (e.g. PLA), are biobased materials that can be

degradable in the above said manners. [2.3]

Biodegradable polymers can be classified in three ways as schematically

explained in the Figure 2.2 [2.4].

 

I Biodegradable Polymers: Classification
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Figure 2.2 Classification of biodegradable polymers [2. 4]

We can classify three major kinds of biodegradable polymers based on the way
they were derived viz., from renewable resources, from nonrenewable resources
and from both renewable and nonrenewable resources (mix). Various kinds of
biodegradable polymers such as starch and cellulose based, polyesters based
are available and some are water soluble too. However, the focus would be more
on the polyesters based ones here. This polyesters family contains both
renewable-resource based ones like PLA, PHB etc, as well as nonrenewable-

resource based biodegradable plastics like, PBAT, PTAT, PBS, PCL, PEA etc.

10

The physical properties for few of the biodegradable polyesters have been

reported as shown in the following Table 2.1 [2.1].

Table 2.1 Physical properties of biodegradable polymers [2.1]

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Tensile
m... mg, sggggkat treat" .1332; 337:3”
(Mpa, (A) (We)

PHB (Blopol) 177 40 6 4000 1 .25
PHB-V (Blopol) 135 25 25 1000 1.25
PCL (Tone 787) 60 4 800—1000 386 1 .145

PLA (Ecopia) 177-180 45 3 2800 1.21
PAS (Bionolle) 1 14 60 800 500 1.2

PEA (BAK 1095) 125 25 400 180 1.07
Ecoflex 1 10—1 15 36 820 80 1 .25
Eastar Bio 108 22 700 100 1.22

 

Among these biopolymers, some are stiff and some are tough in nature. For
example, PLA, PHB are the examples of the stiff bio polyesters where as PBAT,
PEA, PBS, PCL are few of the tough biodegradable polyesters. There are
different kinds of polyesters viz., aliphatic polyesters (eg: PLA, PCL), aromatic
polyesters and aliphatic-aromatic polyesters (eg: PBAT). Most of these polymers
are similar in performance and behaviors to some conventional polymers such as
LDPE, PS, PP and PET. Among all, PLA is the most widely used bioplastic
commercially even in packaging and the behaviors of PLA are comparable with
that of PS, PP and PET [2.1, 2.2, 2.5]. The focus here would be mainly on the
PLA, stiff biodegradable aliphatic polyester made from the renewable resources

like corn. Few of the tough biodegradable polymers such as PBAT, PTAT, PCL,
PBS and PEA would also be discussed.

11

PLA comes under the biobased plastics and is made from 100% annually
renewable resources like corn & sugar beets and has highest potential for the
commercial large-scale production and applications in packaging materials. It is
stiff, rigid thermoplastic and can have totally amorphous or semi crystalline
nature depends on the stereochemistry of the polymer backbone, however, Poly
L-lactic acid (2-hydroxy propionic acid) is the common form of this polymer. D-
lactic acid monomers are incorporated to modify the crystallization behavior to
have certain properties and applications. These modified flexible PLA can be
used to make sheets, films, blow molded articles and thermoforrned articles. PLA
can be used in the conventional processing machines and equipments to make
required articles or finished products. PLA is not a new material, because it was
produced from lactic acid in 1932 by Carothers and then later on further
developments done by Dupont and Ethicon. However, it has been used only in
the bio-medical applications in commercial form and has not been used in other
applications due to their high cost until late 19805. Technological innovations and
cost reduction made PLA available for the non-medical applications in larger
scale. Still, it achieved little success and was yet to compete and replace the
conventional plastics, due the higher cost and relatively lower performances so
far. Cargill Dow LLC took appreciable efforts to reduce its cost of production and
made PLA as large scale produced plastic by innovations and business mergers
of 2 larger companies and thus Cargill Dow LLC is the largest producer and

supplier of PLA based polymers in the world now. Unique thing about PLA is that

12

it is degraded primarily by the simple hydrolysis and does not require the

microbial attacks to do the hydrolysis [2.1, 2.2, 2.6, 2.7].

PLA can be produced with high molecular weight ranges with different
techniques. For example, Cargill Dow uses the solvent free continuous process
followed by the novel distillation method where as Mitsui Toatsu uses the solvent
based process with azeotropic distillation to convert the lactic acid into high
molecular weight PLA [2.1]. It has been reported that PLA is prepared with two
kinds of methods viz., direct condensation of lactic acid and ring opening

polymerization of the cyclic Iactide dimer (Figure 2.3) [2.7]

 

 

 

| H 20 ¥
H O <1 r
o H
H c H 3 L-PLA
L-Lactic Acid ‘\\‘ o /
H 20
o — - CH3
CHy- o
L-Lactide

Figure 2.3 Polymerization routes to polylactic acid [2. 7]

13

However, most of the productions are based on the later method ie., ring opening
polymerization, although as Mitsui Toatsu patented the solvent based process
with azeotropic distillation to remove the water in the direct etherification process.
Cargill Dow developed and patented the low-cost continuous process that is
based on the melt method rather than the solution one and so solvent free with
However, most of the productions are based on the later method ie., ring opening
polymerization, although as Mitsui Toatsu patented the solvent based process
with azeotropic distillation to remove the water in the direct etherification process.
Cargill Dow developed and patented the low-cost continuous process that is
based on the melt method rather than the solution one and so solvent free with
substantial economic and environmental benefits. In this process, prepolymer of
low molecular weight PLA is produced first by the continuous condensation
process of aqueous lactic acid. Then to increase the rate and selectivity of the
intramolecular crystallization reaction, using the tin catalyst, that prepolymer is
depolymerized into a mixture of Iactide stereo isomers which is then purified by
the vacuum distillation. At last, the high molecular weight PLA is produced
through the ring opening polymerization of those lactides in the melt form using
the tin catalyst again and thus avoiding the use of the costly and non—eco—friendly
solvents. The unreacted monomers will be removed under vacuum and recycled

back to the beginning of this process (Figure 2.4) [2.7]

14

o
H CH3
.. r:
HO H n OH

 

 

H CH3
0 High Molecular Weight PLA
Lactic Acid
Ring Opening Polymerization
H20
Condensation
O
O
H C
1” 3 °
< H
H n OH >
H CH3 Depolymen'zation HO H
CH3
Prepolymer Mn - 5000
0

Figure 2.4 Schematic of PLA production via prepolymer and Iactide [2. 7]

There are many other ways to polymerize the Iactide monomers though tin
catalyst based one is the predominant in practice. Other catalysts systems used
are complexes of aluminum, Ianthanides, zinc and some strong bases like metal
alkoxides. Stereochemistry of PLA is also an important part that results in the
final polymer’s thermal behaviors and so their mechanical and thermo
mechanical performances. It has 3 kinds of stereo isomers viz., L-lactide, D-
Iactide and meso-lactide. PLA has its highest melting point (T m) of 180°C with an
enthalpy of 40-50 Jlg, however for the semi crystalline PLA, depending on the
structure, the range would be from 130 - 230°C and would have glass transition
point (T g) of about 58°C. An enthalpy of fusion of about 93.1 Jlg (ie., AH°m = 93.1

J/g) can be used for the 100% crystalline PLLA or PDLLA homopolymers that

15

would have infinite crystal thickness and the following equation—2.1 can be used

to calculate the % crystallinity:
% of crystallinity = [AHm - AHc]*100 / 93.1 (2.1)

Where, AHm is the heat of fusion measured and AHc is the heat of crystallization.
The pure crystalline PLLA has estimated density range of 1.37 — 1.49 g/cc
however, the solid amorphous PLA has the density of about 1.25 g/cc. The
incorporation of other monomers in this predominantly produced natural P(L)LA
will affect its stereo chemistry, crystallization and so their properties although T9
will have little effects. It is also possible to derive the purely amorphous PLA by
incorporating about 15% of meso-Iactide monomers. It’s been reported that the

optimized crystallization temperature (Tc) in the range of 105 — 115°C [2.1, 2.7].

Based on the above PLA behaviors it is possible to make various kinds of PLA
resins (Nature works PLA) that can be made into blown films, cast films, biaxially
oriented films, injection molded and blow molded articles, fiber spinning etc by
controlling the certain process parameters at the molecular levels like,
branching, MWD, D-isomer contents and branching introduction and also by
incorporating the L-, D- and meso Iactide isomers at various levels in the PLA
back bone allows PLA for specific applications [2.8]. PLA has some distinct
properties even compare to the regular plastics. It has excellent oil & grease
barrier, very good barrier for aroma and flavor, low temperature sealability, good
crease retention and crimp properties and these all make an excellent choice for

many applications especially in packaging. PLA has very good modulus, even

16

the solid state amorphous PLA has the modulus in the range of 2 - 3 GPa where
as the semi crystalline PLA has the modulus in the range of 3 — 4 GPa. A review
paper has reported mechanical properties of oriented PLA as well as of non

oriented PLA as shown in the following Table 2.2 [2.1, 2.6, 2.7].

Table 2.2 Comparison of Physical Properties of High molecular weight PLA [2.6]

 

 

 

 

 

 

 

 

 

Property Unoriented Oriented“
Ultimate Tensile Strength (psi x 6.9-7.7, 47.6—
103,MP a) 531 69—24, 476—166
Tensile Yield Strength (psi x 6.6-8.9, 45.5- N IA
103.MPa) 61.4
Tensile Modulus (psi x 103,MPa) 50044800603447” 564—600, 3889-4137
Notched Izod Impact (ft-lblin) 0.3—0.4 N/A
Elongation at break (%) 3.1—5.8 15—160
Rockwell hardness 82—88 82—88
Specific Gravity (g/cc) 1.25 1.25
Glass Trans???) temperature 57—60 57-60

 

 

 

 

 

' Results depend on the degree of orientation and isomer content

 

PLA possesses good water vapor barrier and relatively good oxygen barrier and
this makes PLA as one of the favorable food packaging materials among the
biodegradable plastics. The physical and barrier properties for the biobased
materials such as Polylactate, PLA, polyhydroxybutyrate, PHB, wheat starch and
corn starch were investigated. PLA and PHB have the 02:00; permeability ratio
in the range of 1:7 to 1:12 that makes these materials suitable for packaging of
food with high respiration. The mechanical properties were comparable to the

conventional polymers like PE and PS and they had relatively good barrier

17

properties, however the starch based materials required many improvements to
be used as food packaging materials [2.9]. Comparison of barrier and physical
properties between the PLA, PS and PET has been reported. PLA showed better
barrier performances than PS but little lower than the PET where as PLA showed
similar physical behaviors with that of PS but much less than that of PET. PLA
has very good aroma barrier that makes it to be co extruded with conventional
polymers like LDPE according to the requirement in the multiplayer packaging

materials [2.3, 2.5].

Properties of Plasticized PLA were investigated in which tributyl citrate and other
plasticizers were used to improve the flexibility of PLA to overcome its brittleness
however, it reduces the T9 and resulted in the unstable system due to the
morphological changes that was caused by the cold crystallization. So there was
a requirement of optimum PLA-Plasticizer composition prior to achieve the
balance of required properties while maintaining the minimum required flexibility
and morphological behaviors [2.10]. This discussion so far has been on the
toughening of PLA either by the incorporation of other isomers of PLA or by

some other plasticizers.

There is another possibility of improving the flexibility and toughness for the stiff
polymers like PLA through blending technique with some other tough polymers
just like toughening the conventional plastics (e.g. High Impact Poly Styrene
(HIPS) — by blending and co polymerization). Its been reported that PCL

improved the plasticity of the PHB biopolymer through a reactive blending

18

method and showed improved toughness compare to PHB and improved
strength compare to PCL and could achieve optimized properties [2.11]. Another
study reported that blending of PLLA-CL with PLLA and PCL was miscible and
improves the tensile modulus and break elongation of the blended films [2.12].
Thermal and physical properties of PLLA-PEO blends have been reported. In the
amorphous phase, one T9 was found that indicates the miscibility of the blend in
this phase however, Tm of PLLA decreases with increasing the PEO. It was
reported that less than 10% of PEO in the blend does not affect the mechanical
properties significantly and it is improving the flexibility while maintaining the
required expected strength however more the quantity of PEO better will be the
elongation. Also, PEO presence increases the crystallinity of the blend than the

neat PLLA at high undercooling where as other way at low undercooling [2.13].

Another interesting research reported on the PLA polymeric blends with PDLLA
and PCL with and without surfactants in which the purpose of the study was to
improve the toughness of the hard and brittle PLLA without sacrificing much with
the original strengths. This study followed the solution blending method to
prepare the blending samples and blending proportions from 20 wt% to 80 wt%
were followed and it was found that PCL and PDLLA improved the toughness at
the cost of its strength. However, PDLLA with 2 wt% surfactant improved the
toughness while keeping the strength especially 40PLLA/60PDLLA provide better

toughness and hardness than the neat PLLA [2.14].

19

PLLA, one of the stiff and rigid thermoplastic polyesters in the biodegradable
polymers like PHA & PHB, has been discussed so far. There are flexible
biodegradable polymers like PBAT, PTAT, PBS, PCL, PEA etc also being used
and these are thermoplastic polyesters or co-polyesters category. Since these
are also used for providing the flexibility and toughening the stiff polymers and
act like a plasticizers as we just discussed above. Many researches and
investigations have also been carried out on these tough biodegradable polymers

and their blends with any stiff polymers.

Poly-(butylene adipate-co-terephthalate) (PBAT), is a thermoplastic aliphatic-
aromatic co-polyester, produced by condensing the 1,4-butanediol with 1,4-
benzenedicarboxylic acid (terephthalic acid) and hexanedioic acid (adipic acid). It
is an important biodegradable flexible polymer, which has also been used in

established blown-film applications [2.15].

PBAT has the properties similar to the LDPE due to their long chain branched
molecular structure. BASF is the leading supplier for this polymer under the
brand name of ‘Ecoflex’. It can be biodegraded by the microorganisms and the
process of biodegradation depends on the specific environment includes soil
quality, population of microorganisms and the climate. It has very good
compatibility with other biopolymers like PLA (dry blend), other bio polyesters
and starch. As per BASF, this material can replace many conventional film
applications as well as in packaging applications. It is very much biodegradable

however made from non-renewable resources. It is hydrophobic and relatively

20

has good water vapor barrier that make this used for hydrophobic applications
and it is approved for the food contact applications that make an opportunity for
this to be used as very good packaging material. Blown films can be made in
conventional equipments and typical applications include packaging, agricultural
films and compost bags. This can be transparent to translucent in nature, and
has semi-crystalline structure with melting point in the range 110 - 120 °C with

the density range of 1.25-1.27 g/cc.

Table 2.3 Material Properties of Ecoflex® F BX 7011 [2.16]

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Property Unit Test Method Ecofl;;<l®lF BX Lupolip 2420
Mass density glcc ISO 1183 1.25 - 1.27 0.922 — 0.925
Melt flow rate MFR .
190°C, 2.16 kg gl10min ISO 1133 2.7 — 4.9 0.6 — 0.9
Melting point °C DSC 110 - 120 1 1 1
Viscat VST A150 °C ISO 306 80 96
For the blown film, 50pm
ASTM
Transparency % D1 003 82 89
Tensile Strength N/mm2 ISO 527 35/44 26 I 20
U't‘maie % ISO 527 560 I710 300 I600
Elongation
Fai'ure Energy Jlmm DIN 53373 24 5 5
(Dyna-Test) '
Oxygen cc I
Permeation rate (m2.d.bar) DIN 53380 1400 2900
$53223:th g / (m2.d) DIN 53122 170 1.7

 

 

 

 

 

21

 

PBAT possesses high ultimate break elongation (560 % to 710%) and high
failure energy (24J/mm). It has good therrnostablity up to 230°C and can blown
film processed in the conventional blown lines. The film can be down gauged up
to 10 um and it can be heat sealable and printable. The BASF has reported a
comparison chart of PBAT with LDPE as shown in the following the Table 2.3
[2.16]. PBAT is also widely used in polymer blending for various purposes. It has
been reported that PBAT was used as a plasticizer for making the starch foams.
This study discussed about the maleated PBAT (MA-g-PBAT) used as a
compatibilizer between starch and PBAT prior to improve the resilience and
hydrophobic nature of the Starch and so lower weight gains and better
dimensional stability on the moisture sorption with reduction in the density that
give more yield of the finished products. It also reported that maleated PBAT
(MA-g-PBAT) is acting better as a compatibilizer between the Starch and PBAT

than as a blending component with starch [2.15].

Aliphatic-aromatic polyester was investigated for their degradation behaviors and
ecotoxicological impacts of the degradation intermediates by U. Vlfitt et al. The
chemical structure was analyzed for the monomers and branching chains and

their effects in the degradations (Figure 2.5) [2.17]. The C-NMR analysis of the

O O C“)

II II .
/— (CH2)4—O —c": — (CH2),——c—o—/m— (CH2)4—o——-c 00—0— _ i _

Figure 2.5 Chemical structure of the aliphatic-aromatic copolyester (M = modular
components, e. g. monomers with a branching or chain extension eflect) [2.1 7]

22

neat polymer composition reported for the content of the diol and diacids
(butanediol—50 mol%, adipic acid-27.8 mol%, terephthalic acid-22.2 mol%). It
was reported that almost 99.9 % of the polymer has been depolymerized after
the 22 days of degradation and no significant toxicological effect was observed
neither from the intermediates of the monomers nor from that of the oligomers
and so concluded that no environmental risk and can be fully biodegradable

[2.17].

US Patent (US 6573340 B) reported the investigation on the blending of hard
polymers with tough polymers to achieve the optimized properties and
performances. The polymer blends were targeted for the applications of
laminates, a wraps and coatings and other packaging materials made from the at
least one hard biopolymer having Tg>10°C and at least one soft biopolymer
having Tg<0°C. The biodegradable polymers involved in the study were
thennoplastics of polyesters, polyesteramides and starch based ones. Certain
blends of hard and soft polymers possessed synergistic properties that are
superior to those concerned neat hard or soft polymers by themselves. Water

Vapor Permeability Coefficient was also analyzed for the laminated films [2.18].

There is another kind of useful flexible (soft) tough biodegradable aliphatic-
aromatic thennoplastics co-polyester, Poly-(tetramethylene adipate-co-
terephthalate), (PTAT), having linear structure unlike the above PBAT. It is
marketed in the name of “Eastarbio” by Eastman Chemical Co. The chemical

composition of this polymer is 1,4-benzenedicarboxylic acid polymer with 1,4-

23

butanediol and hexanedioic acid. It is a co-polyester of buthylene glycol and
adipic and terephthalic acids. It has density of 1.22 glcc and the melting
temperature in the range of (Tm) of 109°C - 111°C with glass transition
temperature (T9) of about -30°C. As per this company, these co-polyesters are
completely biodegradable and tough, resilient, liquid impermeable, fully
compostable and ecologically safe while meeting the FDA and EU requirements
for the food contact and so for the food packaging applications. It can be used in
various applications including packaging, agricultural films, fabrics, nonwovens,
medical disposals, fast food service wares. Its unique chemistry was designed to
provide the combined effect of physical strength, extended shelf life and
processability with complete biodegradable in nature. It has tensile properties
similar to that of LDPE and its structure is highly linear in nature. It can be
processed in the conventional processing equipments. It becomes invisible to the
unaided eyes within 12 weeks and is completely biodegradable within 6 months
under the active microbial environment like in a commercial composting site. It
was found in a study that it has a crystallization temperature (T c) of 29°C and the

decomposition starts at 354°C [2.19, 2.20].

Polybutylene Succinate (PBS) is another one of the flexible biodegradable
plastics available today. This is marketed by few companies and Show
Highpolymer Co. Ltd., Tokyo, Japan, sells this under the trade name of ‘bionolle’.
It is a synthetic aliphatic polyester of buthylene glycol and succinic acid. It has
density of 1.26 glcc and the melting temperature (Tm) of 114°C with glass

transition temperature (T9) of -32°C. It has melt flow index (MFI) of 3 - 10

24

(g/10min) was reported on the crystallization temperature (Tc) in the range of 80
— 100°C [2.20]. PBS is commercially available, aliphatic thermoplastic polyester
that has many interesting properties including melt processability, thermal and
chemical resistance and biodegradability. Due to its excellent processability, it
can be processed into melt blow, multifllament, monofilament, nonwoven, flat,
and split yarn in the field of textiles and also into injection-molded plastics
products and thus being a promising polymer for various potential applications
including packaging. However, certain other properties of PBS, such as barrier
properties, softness, and melt viscosity for further processing etc. are often not

sufficient for various end-use applications [2.21].

Park et al investigated the morphological changes during heating PLLA/PBS
blend systems as studied by differential scanning calorimetry (DSC) and
synchrotron wide-angle (WAXS) and small-angle (SAXS) X-ray scattering
techniques at a heating rate of 10 °C/min. Two distinct melting peaks from DSC
analysis indicated the semicrystalIine-semicrystalline blends over entire
composition range of these blends systems. Depression of the melting point of
the PLA component via blending was also observed. WAXS results revealed that
there was no co-crystallization or crystal modification via blending. The SAXS
data showed that well-defined double-scattering peaks during crystallization,

indicating that this system possessed dual lamellar stacks [2.22].

Poly (e-caprolactone) (PCL) is another example of tough/flexible biodegradable

polymer. PCL is commercially sold under the trade name of ‘TONE’ by Union

25

Carbide Corporation. It is a homopolymer made by ring opening polymerization
of e-Caprolactone, a seven member ring compound. It has density of 1.145 glcc.
It is a semi crystalline polymer with low sharp melting temperature (Tm) of 60°C
and has the glass transition temperature (T9) range of —65 to —60°C. It has melt
flow index (MFI) of 0.5 -— 4 (gl10min) and has structure similar to that of PE. PCL
has desirable thennogravimetric and electrical properties and also has the strong
light stability unlike many conventional plastics. It can be processed in the
conventional processing equipments. Various grades of PCL are available to
make sheet extrusions, fibers, blown films, cast films as well as injection molded
articles. It is nontoxic and truly biodegradable in nature when composted. It has
better miscibility and mechanical compatibility with many polymers and also gives
excellent adhesion to many substrates. It has FDA clearances for food contact

[2.11, 2.23].

Polyesteramide (PEA) is also one of the tough/flexible biodegradable polymers
commercially available. PEA is sold under the trade name of ‘BAK’ by Bayer AG,
Germany. It is a thermoplastic with semi crystalline in nature. It is a co-polymer of
poly amide and aliphatic polyester and in specific it is based on butanediol,
caprolactam and adipic acid. It has density of 1.14 g/cc and the melting
temperature (T m) of 137°C with molecular weight (Mw) of 37,000 g/mol. It has
melt volume rate (MVR) of 8.8 (cc/10min) at 2.16 Kg & 200°C. It is claimed to be
biodegradable according to the DIN V 54900 and ecofriendly since it is free from

halogens, solvents and heavy metals etc. It is also easy to process and

26

recyclable and mechanical properties and thermal properties of PEA are similar

to that of polyethylene [2.24-2.26].

Polymer blends are one of the rapidly expanding research areas to achieve the
required properties and take advantage of the cost reductions. The resultant
physico-mehanical behaviors depend on the ability to control the interfacial
tension that produce a small phase size and strong interfacial adhesion to
transmit applied force effectively between the component phases [2.27]. There
are three types of polymers blends can be found based on their miscible
behaviors and they are completely miscible, partially miscible and completely
immiscible. However, based on the crystalline/amorphous nature these blend can
also be divided as amorphous/amorphous, amorphous/crystalline and
crystalline/crystalline polymer blends though, the later one is rarely found unless
the specific requirement and technological interests. Otherwise the former two
types of blends viz., amorphous/amorphous, amorphous/crystalline are found in

general in most of the polymer blends [2.28].

Making new polymer by mixing 2 or more polymer together called blending.
Polymer blends are mixtures of at least two macromolecular species, polymers
and/or copolymers. Depending on the sign of the free energy of mixing, blends
are either miscible or immiscible. Total polymer/polymer miscibility does not exist
- observed miscibility is always limited to a "miscibility window,“ a range of
independent variables, viz., composition, molecular parameters (viz., molecular

conformation and configuration, molecular weight, molecular weight distribution,

27

etc.), temperature, pressure, and others. In spite of a vast number of such
“windows” being identified, immiscibility is dominant in polymer blend technology.
However, it is not necessary that those polymers are miscible or compatible in
nature. If it is so, we may get a behavior which is similar to a homopolymer’s
such as single melting point and glass transition point. They are called miscible
blends. For examples, polystyrene (PS) with poly(phenylene oxide) gives
miscible blend though PS generally don’t mix with most of the polymers. Likewise
other examples are PET with PET and PMMA with PVDF give miscible blends.
When polymer-A mixes with polymer-B in miscible nature then we can observe
the two kinds of behaviors in the glass transition temperatures (Figure 2.6) of the

resulting polymer depend on the nature and proportions of each polymer in the

 

 

 

 

 

 

 

 

 

 

blend [2.29].
T of
To <-_Foly‘iner B T,I <— Te °f
/— Polymer B
T 0f TO Of a
PolyinerT) Polymer A
% Polymer 8 v % Polymer A V

Figure 2.6 Glass transition temperature behaviors for the miscible blends [2.29]

Otherwise we get a phase separated or immiscible or incompatible blends. Often
these immiscible blends do give the useful required properties. The best example

for this, PS can be blended with small amount of poly butadiene (P80) and gives

28

required properties like toughness and flexibility to the stiff and brittle

polystyrene. If we look at the following morphology (Figure 2.7), the small PBD

Polystyrene Polybutadiene

m... \e .1 . :/ ......

Figure 2. 7 The phase morphology of HIPS [ 2. 29]

spheres are dispersed in the PS matrix and the stress is applied these spheres
provide the rubbery nature and absorb the energy and so giving better toughness

to the blended polymer [2.29].

This blend is also called High Impact Polystyrene (HIPS) which is already
commercially available. These blend morphology plays an important role in
deciding the properties especially in the immiscible blends [2.29]. There was a
study on PLLA-PHB blend in which miscibility, crystallization and melting
behaviors were investigated. It was found that low molecular weight PLLA/PHB
blend showed better miscible over all the composition where as high molecular
weight PLLA-PHB blend did not show any miscibility as expected on the basis of
thermodynamics and the investigation was based on their spherulitic structure,
growth rates and melting behaviors [2.30]. In another study on miscibility,

crystallization and morphology behaviors of the PHB-PLA blends showed that

29

both are immiscible when the blend was prepared by solvent casting method
where as it showed few evidences of better miscibility when it was made from
high temperature melt process. The crystallinity of PHB was affected by the
presence of PLA contents and vice versa. However, the blend showed certain

improved propertied when compared to plain PHB [2.31].

In any immiscible blend, the sphere size of the polymer which is less in
proportions, does affect the properties. For constant volume, smaller the sphere,
then more number of spheres and larger the total surface areas and vice versa
for these immiscible blends. It is interesting to note that when stretching applied
on these blends like in blown film or blow molding process where stretching is
applied either uni-axially or bi-axially. During this, the spheres are stretched in
plate or rod shaped phases that give another advantage in deciding their
physico—mechanical properties. Sometimes these rods acts like reinforced fibers
in composites. We can also make these immiscible blends to give stronger
properties by using a suitable compatibilizer often a block copolymer, in case of
conventional polymers. For example, copolymer of PS and PBD can be used
successfully as a compatibilizer for this immiscible blend to enhance its
properties further. Only few polymers can be blended effectively irrespective of
their similarity in natures. For example, PE can not be blended effectively with PP
even though both belong to polyolefin family and hydrophobic in nature. Apart
from “like dissolves like” concept, the effective blending is also depending on the
‘Entropy’. When polymer is blended, the polymer blend gets more disorder than

that of the individual polymer. So, when the polymer is blended, its amorphous

3O

state already has more disorder and will not gain any more entropy due to the
disorder gained from the blend and so they do not give the effective blends.
However, few polymers behave in a different manner. In certain compositions
two polymers may give a miscible blend where as in the rest of the compositions
they may give immiscible blends and it also depends on the process parameters

too. [2.29].

The purposes behind the blending of different polymers in different proportions
have been discussed so far. Many studies have been done on the stiff/tough
biodegradable polymer blends and their significances. Biodegradable polymers
including PHB, PHBV, PBS, PES and PCL were investigated for their structure
and properties that were significantly influenced by the miscibility, morphology,
crystallization and melting behaviors. This study found different blend behaviors
including the miscible crystalline/crystalline, immiscible crystalline/crystalline and
miscible amorphous/crystalline blends for various polymer blends. It reported that
binary blends of crystalline polymers including PES with PEO and PBS with PEO
showed the miscible crystalline/crystalline behavior. It was also studied that the
binary immiscible blends of crystalline polymers including PHB/PBS, PEO/PCL,
PHBVIPCL and PBS/PCL and the crystallinity of one polymer had effective
significant on that of the other polymer. PBS/PVPh binary blend was reported for
their miscible amorphous/crystalline behavior based on their thermal,

crystallization and morphological behaviors [2.28].

31

Takagi et al investigated and reported the morphologies and mechanical
properties of the blends of PLA! medium chain length PHA and PLA/chemically
modified PHA (ePHA). It was found that both kinds of PHA improved the impact
toughness of the PLA blends while decrease in the tensile strength and
maintaining their biodegradability with more accessible to hydrolysis and
microbial attack resulting better weight losses when compare to the neat PLA
[2.32]. Terada et al patented a biodegradable film developed based on the
investigation of the melt compounded blend of PLA with aliphatic biodegradable
polyester (here PBS) other than PLA in the weight ratio range from 70:30 to
20:80. The objective was to develop a bio degradable film having high flexibility
and transparency while degrade in the natural environment. It was found that by
blending the PLA with aliphatic tough bio polyester (PBS) providing the
biodegradable film possessing the tensile modulus of maximum of about 2.5 GPa

with at least 65% transparency [2.33].

In another US patent, PLA based blends (with aliphatic polyester like PBS, PBSA
and PES) including a compatibilizer were investigated in the weight ratio ranges
of 9:1 to 1:9. Various mechanical properties such as stress, strain & %elongation,
modulus and toughness were analyzed and reported. It was found that the brittle
PLA based blends showed improved toughness and elongation while maintaining
the significant strength even after few days of aging and also had the better
degradation rates in comparison to PLA [2.34]. Sheth et al investigated the
biodegradable polymer blends of PLA and PEG in the ratios of 100/0, 90/10,

70/30, 50/50, 30l70. These melt blended compound was analyzed at DSC and

32

DMA resulting that some blends are miscible where as some are partially
miscible depend on the composition. Until 50% of PEG in the blend PEG
plasticize the PLA and reduce modulus while increase the % elongation where as
above 50% of PEG resulting in higher crystallinity of PEG and yielding higher
modulus with lower break elongation. However, tensile strength decrease in
linear manner with increase in % PEG contents and all the blends showed better
enzymatic degradation than the pure PLA especially for less than 30% PEG
content in the blend for the rest dissolution of PEG predominated in the

degradation process [2.35].

Bastioli et al patented a research study in which they investigated ternary mixture
of biodegradable polyesters that includes aliphatic-aromatic polyester (PBAT),
aliphatic polyester (PBS) and PLA in various weight ratios and targeting food
packaging and other applications. Tear strength, tensile properties with modulus
and transparency behaviors were evaluated and claimed for the blended and
extruded films in both directions [2.36]. There was an interesting investigation on
the blend of PLA with PHA based copolymers (Nodax) that has lower crystallinity
and melting point due to the incorporation of the 3HA units with medium chain
length side groups just like in the LLDPE. This reduced crystallinity provides
ductility and better toughness for many plastics applications and so when they
incorporated little amount (below 20%) of these co polyesters with better
dispersion in the PLA matrix providing extra ordinary results due to lower
interfacial energy between these highly compatible PLA and PHA copolymer.

This blend improved the toughness without compromising the optical clarity of

33

the brittle PLA until 20% of the PHA in the PLA matrix in a manner similar to
HIPS. However rest of the blending proportions (more than 20% of PHA) did not
give any appreciable results due to the crystallinity behavior of the PHA in the
PLA matrix [2.37]. Averous et al investigated the blends of thermoplastic starch
with polyesteramide (up to 40%) in the presence of a compatibilizer prior to
develop a starch based to biodegradable plastics. The blended samples were
analyzed and reported for mechanical and thermo mechanical properties with
thermal behaviors. It was reported that certain compatibility in the blend systems
and PEA presence in the Starch matrix improved the hydorphobicity and
mechanical properties while restricting the shrinkage during the injection process

even at 10% of PEA in the blend [2.38].

The biodegradable polymers, their blends with their significance have been
discussed so far. Just like biodegradable polymers, there is relatively new
technology called ‘Nanocomposite Technology” which is, “the materials and
processes required to disperse nanoscale particles in plastics, metals, or
ceramics” defined by NANOCOR. The materials derived from this technology are
also called ‘Nanocomposites’ that is defined again by NANOCOR as “new class
of plastics derived from a highly refined form of nanoclay that disperses in plastic
matrix” [2.39]. In recent years, the synergistic effect of this technology with
polymer/its blends providing enhanced properties with cost effective when
compare to the conventional micro composites. This gives an ample scope for
this technology to many applications including packaging and automotive. 2

million lb of nanocomposites were nanoclay-based nylon products produced by

34

Unitika and Ube Industries in Japan for automotive and packaging applications,
respectively, out of the total of 3 million lb market. The rest of the 1 million lb was
carbon nanotube—filled PPO/nylon nanocomposites made in North America for
automotive body parts applications. It is expected that there will be strong growth
over the next 10 years and Principia Partners Estimated that more than 1 billion
lb of nanocomposites will be in demand worldwide for Nanocomposites out of
which 160 million lb is carbon nanotube-filled products by 2009 [2.40]. The
biodegradable polymers are still struggling to compete with the conventional
polymers in many applications due to their cost and the performances. Cost can
be brought down by having the more volume however performances can only
brought up using these kinds of innovations and technology. So the synergistic
effects of this nanocomposite technology with biodegradable polymer/blends
would give the required polymer properties and performances so as to replace
the petroleum based conventional polymers in many applications primarily in
packaging. To discuss this nanocomposite further, it is required to understand

the nano particles especially nano clay chemistry and its properties.

Nanoclay is a naturally occurring inorganic raw material originated from the
volcanic ash. These volcanic ashes were deposited in the earth or in the sea
and/or sea beds during the volcanic eruption about 85 — 125 million years back.
Over the years the ash beds deposited inside the sea become accessible in the
land form now due to the geographical changes in the earth. There are many
different kinds of clay minerals are available such as montmorillonite, hectorite,

saponite, betonite, smectite based. However the montmorillonite based nano

35

clays will be discussed here. An individual clay particle is plate like structure
however these clay platelets exists in the agglomerate stacks form. Each clay
platelet is about one nanometer in thickness with 50 to 600 nm ranges of surface
dimensions that gives the high aspect ratio (ranges from 100 to 1000) for the clay
particles. As for its structure and chemistry, silica is the dominant constituent
which is tetrahedral while alumina exists in the octahedral form that is also
essential too. Each clay particle has sheet structure consisting of 2 types of
layers which are silica tetrahedral and alumina octahedral layers. The silica layer
has SiO4 groups that are bonded together to give a hexagonal network of the
repeating units of composition Si4O1o. Where as, in alumina layer the aluminum
atoms that coordinates the octahedral structure, are embedded in between the
two sheets of closely packed oxygens or hydroxyls in such a way that aluminum
atoms are equidistant from six oxygens or hydroxyls. The cross section of the
single clay sheet can be seen the sandwich structure meaning the alumina
octahedral layer is sandwiched in between the 2 tetrahedral silica layers (Figure
2.8) which shares their apex oxygen with the octahedral alumina layer. Thus,
they are also called layered silicates. In this kind of structure, the negative charge
is located on the surface of the tetrahedral silica layers and thus can readily
interact with the polymer matrices. However this single clay platelet is bonded
(van der waal’s bond) through the exchangeable cations like sodium, potassium
etc., with other clay platelets in the agglomerate stack forms as shown in Figure

2.8 [2.39, 2.41, 2.42].

36

 

.
C
.0
.

 

   

“Ci etrah ed ral sh eet

(SiO4)
I.

Stacked clay (1 nm)

platelets
— /
_

Figure 2.8 The crystal structure of single nano clay platelet (2:1 layered silicates)
Source: Modified by Dr. AKM’s group after referred from NANOCOR [2.39]

It is also important to understand how this clay (montmorillonite based) is going
to be effectively used in the polymer nanocomposite especially. The
agglomerated clay platelets need to be separated prior to disperse in the polymer
matrix and so giving the better properties and performances. This natural
montmorillonite (MMT) clay is hydrophilic in nature due to the hydroxyl groups in
the structure, where as the most of the polymers are organophilic in nature and
so these clays can not be dispersed in the polymer matrix effectively. For this
purpose, the MMT is organically modified prior to be more compatible and can
disperse easily in the polymer matrix. Generally the platelets or silicate layers are

agglomerated within a distance between the adjoining layers of 0.35 nm and so

37

surface treatment reduces the particle-particle attractions and increase the space
between layers more than 2 nm (Figure 2.9). Various modifications techniques
are in practice. In general, this is done by the ion-exchange reactions with

cationic surfactants including the primary, secondary, tertiary and quaternary

surface
treatment

If

 

Figure 2.9 The surface treatment of the agglomerated nano clay platelets (silicate
layers) [2.39]
alkyl ammonium or alkyl phosponium cations which lowers the surface energy
and improves the wetting ability of the clay in the polymer matrix and results in
the larger interlayer spacing of the platelets. This surface modified MMT is also
called organically modified montmorillonite (OMMT). Spacing varies depend on

the packing mode and the chain length of the polymer inserted [2.39, 2.42].

In general up to 5% of clay (OMMT) would be dispersed in the polymer matrix
prior to achieve the effective nanocomposites. It can be done through various
ways of polymerization or polymer processing such as in-situ polymerization,
solvent casting and also though melt process. However the focus here would be
mainly on the melt process. It is expected that melt process gives better results
since the shear rate plays an important role in separating the clays further within
the polymer matrix so as to get the exfoliation of the clay in the polymer matrix.

When there is a complete dispersion of the clay platelets or the layered silicates

38

with in the polymer matrix after the compounding operation then it is called

exfoliated clay in the polymer (Figure 2.10) [2.39].

/,/

 

/

/
/ // /
00/ / / I /

. melt
+ /./ comounder I / / /
/ 0’
Figure 2.10 The complete dispersion (exfoliation) of the clay platelets (silicate layers)
during the compounding operation [ 2. 3 9]

Depending on the interaction between the polymer and the clay surfaces, three
different kinds of nanocomposites can be formed viz., intercalated, flocculated
and exfoliated nanocomposites. lntercalated nanocomposites are commonly
found in which, insertion of polymer chains between the clay platelets to provide
more spacing in a crystallographically regular fashion, regardless of polymer to
OMMT ratio, with a repeat distance of few nanometers. Flocculated is
conceptually same as above however silicate layers are flocculated sometimes
due to the hydroxylated edge-edge interaction of the silicate layers. Exfoliated is
usually very difficult to achieve in which each clay platelets are separated and

dispersed in an average distance with in the polymer matrix. Usually, it is

39

possible to achieve the mixed behaviors of the nanocomposites discussed
above. In the exfoliated nanocomposites, we can see three kinds of form factors
that are LLs, DLs and §Ls where, LLs and 0.3 are the length and thickness of the
exfoliated clay platelet and its is the average distance between any two clay
platelets in the polymer matrix of exfoliated nanocomposite. These factors can be
derived from the TEM images and can be used to derive models for the barrier

properties correlations (Figure 2.11) [2.43].

 

 

 

«EA/L
TEX/4% %XT/
ea~vwv

 

 

 

 

 

lntercalated and flocculted Exfoliated

 

 

 

 

Form factors of dispersed layered silicates

Figure 2.11 The schematic illustration of thermodynamically achievable polymer /
layered silicate nanocomposite [2.43]

These clay behavior and morphology in the nanocomposite can be analyzed
through transmission electron microscopy (TEM) and X-ray diffraction (XRD)
analysis and can be found what kind of nanocomposite is achieved. All the
polymers are not compatible with all the clays. It also depends on the hydrophilic-
hydrophobic balance of the Clay-Polymer matrix. These nanocomposites results
In better barrier, flame resistance, structural, dimensional stability, and thermal
properties with improved mechanical and thermo mechanical properties yet
without significant loss in impact or clarity. These exfoliated clay that is one nm in
size generally does not affect the transparency and also creates the tortuous
path for the movement of the molecules that pass through the polymer system
and so providing better barrier properties. These leads to the applications such
as food packaging, non food films and rigid containers. These light weight plastic
nanocomposite having better impact and scratch resistant with higher HDT
performances makes it possible to apply in many automotive applications as well

[2.39, 2.42].

Nylon-6 was the first polymer made into nanocomposite through in-situ
polymerization. After that, various conventional polymers have been tried to be
made into nanocomposites. It has been reported in a NANOCOR technical paper
that up to 8 wt% of nanoclay incorporation through in-situ process in the Nylon6,
improved the Nylon6 properties viz., 110% improvement in fiexural and tensile
moduli and 175% improvement in HDT (Table 2.4). Normalized Oxygen

transmission rate evaluated at 65% RH, is reduced to one fifth (ie., from 35 to

41

about 7 cc.mil/m2.d) after 8wt% of nanoclay incorporation in the nylon 6 polymer

matrix. This makes an appropriate choice for many packaging applications [2.44].

Table 2.4 Mechanical properties of Nylon 6 Nanocomposites [2.44]

 

 

 

 

 

 

 

Nanoclay Flexural Tensile
ADA-MONT Modulus Modulus HDT (”C)
(wt. %) (MP3!) (MP1!)
0% 2836 2961 56
2% 4326 4403 1 25
4% 4578 4897 131
6% 5388 5875 1 36
8% 61 27 6370 1 54

 

 

 

 

The synthetic roots and materials properties of the PP-MMT nanocomposites
were reviewed in a review paper. It discussed about the 2 ways of making
nanocomposites viz., functionalized PP with OMMT and neat PP with semi
fluorinated OMMT and the resulted polymer nanocomposites made through melt
process were characterized and found to be having bother intercalated and
exfoliated behaviors. Also it has been reported about the improvement in the
tensile properties, HDT, barrier, scratch resistant and flame resistant while
retaining the optical clarity for the nanocomposites containing up to 6% of clay
[2.45]. In another study, Ethylene co-vinyl alcohol (EVOH) nanocomposites with
3% OMMT were examined. Nanocomposites were prepared through melt
compounding and later extruded into blown film. It has reported the morphology,

mechanical and thermal properties. lntercalation was evident from the

42

 

morphology analysis with a higher degree of dispersion and alignment in the
blown film in contrast to compounded material. There was an improvement in the
thermal stability with the addition of MMT and also found improved modulus in
the nanocomposite film [2.46]. So far, the polymer nanocomposite in a single
polymer matrix has been discussed. There were some nanocomposites prepared
from the polymer blends and nano-clay. There was a study on a polymer blend
nanocomposite in which PPIEPDM blends based nanocomposites with OMMT
were prepared by direct melt intercalation in an internal mixer. The
nanoreiforcement is constrained to exist either in continuous matrix or in the
dispersed phase or in both phases of this thermoplastic and thus not only
affected the interaction like In the single polymer system but also the degree of
blending that in turn will affect the micro scale morphology and nanoscale
dispersion. This kind of selective reinforcement strongly affected the morphology
and mechanical properties of the blended nanocomposite. However mechanical
properties strongly further dependent on the blend composition as well. XRD
and TEM were used to analyze the morphology behavior of both blending and

nanocomposites [2.47].

The nanocomposites of the conventional polymers have been discussed. Many
researches have been reported on the polymer-clay nanocomposites [2.48-2.68].
Recently, many studies have been done with biodegradable polymers based
nanocomposites especially with PLA based nanocomposites [2.21, 2.24, 2.25,

2.58-2.68]. Few researches have also been done on the polymer blends based

43

nanocomposite [2.47]. However almost no study on the nanocomposites of PLA

based blends.

Polymer blends including the biopolymer blends and nanocomposites in a single
polymer phase as well as blended phase have been discussed. PLLA is a very
stiff thermoplastic aliphatic polyester which can have more opportunity to be used
in many applications if we can overcome few of its draw backs such as barrier, its
brittleness but not at the cost of its existing properties like modulus and strength.
So, by combining all the above discussed techniques, we can come up with a
need for the development of the sustainable green polymer which can equally
compete with conventional polymers. Being a widely used biopolymer today, PLA
has the ample scope of applications; we can apply the above said convergence
that gives the synergistic effects to achieve the target. Thus, PLA can be blended
with one of the best suitable tough/flexible biodegradable polymers and then
nanocomposites can be prepared with the specific OMMT with out using any
compatibilizer. PLA would tend to have lower strength while improving the
toughness after the blending with that tough biodegradable polymer. However
that will be either compensated or improved by maintaining the stiffness-
toughness balance after the effective nano-clay reinforcement. Thus we reached
our objective to develop the PLA based blends and nanocomposites that can go

for packaging applications.

44

Chapter 3 Materials and Methods

3. 1 Materials

3.1.1 Poly-L-lacticacid (PLLA), Aliphatic Polyester

0

T

H -——O C C OH
L l... _ .
Figure 3.1 Structure of Polylactic Acid (PLA)

 

 

 

Poly-L-lacticacid, PLLA pellets were supplied by Biomer, Germany under the
trade name of Biomer® L9000. PLLA has a density of 1.25 glcc with the melting
temperature (T...) range of 168 - 172°C and the glass transition temperature (T 9)
range of 50 - 60°C. It has melt flow index (MFI) of 3 —- 6 (g/10min). It is
transparent, odorless, and an inert solid that can thermal decompose at about
250°C. It is'biodegradable and can be disposed off by composting, incinerating or
depositing in landfills. The pellets were dried in the vacuum oven at 40°C for 4
hours prior to process and then packed in air tight zipper bags since it is sensitive
to humidity. It does not contain any additives like plasticizer and it is catalyst free.
PLA is one of the leading biopolymers used in many applications especially in

packaging.

45

3. L2 Poly-(butylene adipate-co-terephthalate), (PBA T), Aliphatic-Aromatic

C o Jolvester

_ f O— —— — — 1) W—
-—o—<|:—©>——fl c (CHzm—o—ci—(CHzlr—G-—

i.— —l——. ——-I

 

 

 

 

 

 

 

Figure 3.2 Structure of Poly-(butylene adipate-co-terephthalate) (PBAT)

Poly-(butylene adipate-co-terephthalate) (PBAT), film grade pellets were supplied
by BASF AG, Germany under the trade name of Ecoflex® F (BX7011). PBAT is
made by the condensation reaction of 1,4-butanediol with 1,4-
benzenedicarboxylic acid (terephthalic acid) and hexanedioic acid (adipic acid). It
has density range of 1.25 — 1.27 g/cc with the melting temperature range (T...) of
110 - 120°C with good thermal stability up to 230°C. It has melt flow index (MFI)
of 2.7 — 4.9 (g/10min). It is transparent to translucent with semi crystalline
structure. It is compostable and biodegradable with non-hazardous in nature
since it can be degraded by microorganisms. As pre the supplier’s
recommendation, no need of predrying the pellets prior to process. It has
properties similar to LDPE due to its higher molecular weight and longer chain
branched molecular structure. It complies with the European food stuff legislation
for food contact. It has wide opportunity for the flexible packaging applications

through blown films.

46

3.1.3 Poly-(tetramethylene adipate-co-terephthalate), (PTA T), Aliphatic-

Aromatic Co polyester

I"—

II l l i
C ©C—O— (CHzlt—O—C—(CHzis—‘C C

Figure 3.3 Structure of Poly-(tetramethylene adipate-co-terephthalate), (PTAT) [3.1]

 

 

 

 

L... 4"

[1 ,4-benzenedicarboxylic acid, polymer with 1,4-butanediol and hexanedioic acid]

Poly-(tetramethylene adipate-co-terephthalate), (PTAT), general purpose grade
pellets were supplied by Eastman Chemical Co., TN, USA, under the trade name
of ‘Eastarbio’ GP co polyester. It is a copolymer of terephthalic and adipic acid
and butanediol. It has density of 1.22 g/cc and the melting temperature (T m) of
108°C with glass transition temperature (T g) of -30°C. It has melt flow index
(MFI) of 28 (g/10min). The pellets were dried in the vacuum oven at 65°C for 6

hours prior to process.

3.1.4 Polybutylene Succinate (PBS), Aliphatic polyester

/\/\/o
0

Figure 3.4 Structure of Polybutylene Succinate (PBS)

47

Polybutylene Succinate (PBS), pellets were supplied by Show Highpolymer Co.
Ltd., Tokyo, Japan, under the trade name of bionolle(1020). It is aliphatic
thermoplastic polyester that is chemically synthesized by polycondensation of
1,4-butanediol with succinic acid. It has density of 1.26 glcc and the melting
temperature (T...) of 114°C with glass transition temperature (I'g) of —32°C. It has
melt flow index (MFI) of 3 — 10 (gl10min). The pellets were dried in the vacuum

oven at 70°C for 2 hours prior to process.

3.1.5 Poly (e-caprolactone), (PCL)LAliphatic polyester

 

 

 

 

Figure 3.5 Structure of Poly ( e-caprolactone) (PCL)

Poly (e-caprolactone) (PCL), pellets were supplied by Union Carbide corporation,
under the trade name of TONE (P-787). It is a homopolymer made by ring
opening polymerization of a-Caprolactone, a seven member ring compound. It
has density of 1.145 glcc. It is a semi crystalline polymer with low sharp melting
temperature (T m) of 60°C and has the glass transition temperature (T 9) range of -
65 to -60°C. It has melt flow index (MFI) of 0.5 - 4 (g/10min). The pellets were
sufficiently dried in the vacuum oven prior to process. It is nontoxic and
biodegradable in nature when composted. It has FDA clearances for food

contact.

48

3. 1.6 Polyesteramide (PEA)

— _— fl

0—

 

(CHzis—N——

 

——c——(CH2I4 .. 0 (“2’4 °

 

 

 

 

Figure 3.6 Structure of Polyesteramide (PEA) [ 3. 3, 3. 4]

Polyesteramide (PEA), pellets were supplied by Bayer AG, Germany, under the
trade name of LP BAK 404 004. It is a co-polymer of poly amide and aliphatic
polyester and in specific it is copolymer of butanediol, caprolactam and adipic
acid. It has density of 1.14 g/cc and the melting temperature (T...) of 137°C with
molecular weight (M...) of 37,000 g/mol. It has melt volume rate (MVR) of 8.8
(cc/10min) at 2.16 Kg & 200°C. It is claimed to be biodegradable according to the
DIN V 54900 and ecofriendly since it is free from halogens, solvents and heavy
metals etc. It is also easy to process and recyclable and mechanical properties
and thermal properties of PEA are similar to polyethylene. The pellets were dried

in the vacuum oven at 80°C for 3 hours prior to process [3.2-3.4].

3.1. 7 Organically Modified Montmorillonite (OMMT) Clay

Organically modified montmorillonite (OMMT) clay in the powder form was
supplied by Southern Clay Products Inc., under the trade name of Cloisite®25A.
This clay is natural montmorillonite clay modified with (Dimethyl, hydrogenated

tallow, 2-ethylhexyl quaternary ammonium), a quaternary ammonium salt. Table

49

3.1 shows the relative structure information, XRD patterns and specific gravity for

this clay. Clay was predried at 60°C for about 4-6 hours in oven prior to process.

Table 3.1 Structural information for the organically modified montmorillonite clay
[3.5]

 

XRD - Extent of S ecific
OMMT S Bascal Modification p .
tructure . Gravrty
clay spacing (001) [meq/100g (g/cc)
- d001 (nm) clay]
on,

 

 

Cloisite‘”

I.
25A agar—orgasm 1.86 95 1.87
HT

 

 

 

 

 

 

Where ‘HT’ is Hydrogenated Tallow (~65% C18; ~30% C16; ~5% C14) with
methyl sulfate anion [3. 5]

3.2 Methods

This research project methodology is given the following schematic (Figure 3.7).
This has got three phases. In the first phase, stiff biopolymer (PLLA) was melt
compounded with tough bio polymers such as PBAT, PTAT, PBS, PCL and PEA
in certain (50/50 in wt%) composition. Based on their mechanical and therrno-
physical properties, suitable tough bio polymer was selected. In the second
phase, PLLA was melt compounded with that selected tough biopolymer (PBAT)
in various compositions. These samples were evaluated for their mechanical and
thermo-physical properties based on which the optimized compositions were
selected for making nanocomposites. Thus far, the significance of the blending is
to improve the toughness. In the third phase, above selected compositions of

PLLA-PBAT blends were reinforced with the specific OMMT of 5 wt%. These

50

samples were then analyzed for their mechanical, thermo-physical and barrier
properties. Based on these properties, the suitable nanocomposite composition
was chosen for further studies such as morphological studies to understand the
structural-property correlation in order to understand the chemistry behind the
nanocomposite and their behaviors. Here the significance of the nanocomposite

is to maintain the stiffness-toughness balance and to improve the barrier.

 

PLLA + PBAT/PTATIPBSIPCLIPEA

LA
V

 

Melt compounding and analysis of
Blend Simificance mechanical 8. thermo-physical behaviors
To improve the

 

 

PLLAIPBAT blends with various compositions
V

 

 

Select the suitable blend compositions based
on the mechanical 8. thermo-physical
behaviors

 

 

selected PLLAIPBAT blend compositions + specific

 

 

 

 

OIIIMT
Nanocomposite for
the 0mm“? blend Select the best nanocomposite composition
W "'3 based on the mechanical, memo-physical
. and barrier properties
Nanocogpggte
Significance V
7° maim‘" the Analyze the morphological behaviors for the
$1; In' 'cee sea-3%”: ”Eves selected nanocomposite to understand the
the barrier K structural-property correlation

 

 

Figure 3. 7 Schematic representation of this research project methodology

5]

3. 3. Equipments and Preparation
3. 3. 1 DSM Microcompounder

The polymers with or without clay were melt compounded at the DSM Micro 150C
extruder-compounder (DSM Research, The Netherlands) having vertical conical
co-rotating twin screw extruding unit with screw length of 150 mm, UD of 18 and
barrel volume of 15 cc. The schematic diagram of the microcompounder is

shown in the following figure 3.8. From the melt compounds of the extruder,

 

 

 

 

  
  

 

 

 

 

\\\\\\\\\\\‘

 

 

 

 

._ — c- _
|\\“‘

   

 

 

 

 

 

 

I_

Figure 3.8 Schematic of Microcompounder Extruder unit [3. 6]

52

strands were extruded out from this pellets were prepared using a palletizer prior
to make master batches as well as to make compression molded films. The
various kinds of samples such as DMA bars, izod bars, tensile and flexural
specimens and discs, were also prepared by taking molten polymers in a
preheated cylinder from the extruder and then injected into a preheated mold that
is placed in an injection molding unit where we can us maximum injection

pressure of 160 psi.

In this research experiments, all the blend compositions or nanocomposite
compositions are taken in weight percentages (wt %). PLLA was melt
compounded with different tough polymers in the 50l50 (in wt%) composition to
find the suitable tough polymer that would give the required optimized properties
so as to prepare the nanocomposite for the same. For this purpose, PLLA was
blended with Poly-(butylene adipate—co-terephthalate) (PBAT), Poly-
(tetramethylene adipate-co-terephthalate), (PTAT), Polybutylene Succinate
(PBS), Poly (a—caprolactone) (PCL) and Polyesteramide (PEA) in the 50/50 (in
wt%) composition and the parameters used in the DSM are given in the Table

3.2.

53

Table 3.2 Blending compositions and process parameters used in DSM
Microcompounder for PLLA with various tough biopolymers

 

 

 

 

 

 

 

 

 

 

 

 

 

Blend Screw Cycle Temperature Mold Injection
Composition Speed Time (T op—Center—Bottom) Temperature Pressure
(in Wt %) (EPm) (min) (°C) 0’9 (PSiL
100PLLA 100 5 185— 185-185 55 120
50PLLA /
50PBAT 100 5 185-185-185 53 120
1OOPBAT 100 5 150 - 150 - 150 50 90
50PLLA /
50PTAT 100 5 185-185-185 53 100
100PTAT 100 5 150 - 150 - 150 50 80
100PBS 100 5 150 - 150 - 150 50 80
50PLLA I
50PBS 100 5 185 - 185 - 185 53 90
100PCL 100 4 150 - 150 - 150 45 80
50PLLA / '
50PCL 100 5 185 - 185 - 185 52 120
100PEA 100 4 160 - 160 — 160 50 90
50PLLA /
50PEA 100 5 185-185-185 52 100

 

 

 

 

 

 

From the above blended combinations, the PLLA/PBAT blend combination was
finalized for further studies and their nanocomposites based on their mechanical
and thermo-physical behaviors. The four different PLLAIPBAT (in wt%) blending
compositions were prepared for the characterizations with the neat polymers viz.,
100/0, 70l30, 60/40, 50/50, 30l70, 0/100 From these, nanocomposites of 100m,

70l30, 60l40, 50I50 and 0/100 blends with 5 wt% of OMMT were also prepared.

54

 

The different parameters are used for different blend compositions and materials

as given in the Table 3.3.

Table 3.3 Blending compositions and process parameters used in DSM
Microcompounder for PLLAIPBAT/Clay blends

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

(Am, 3:3: tit: 8.723333%...) .3332... 8:222:
(rpm) (min) (°C) (°C) (psi)

100mm 100 5 185—185-185 55 120
70/3010 100 5 185—185—185 54 120
60l40/0 100 5 185-185-185 53 120
50150/0 100 5 185-185-185 53 120
30/70/0 100 5 185-185-185 52 100
or1ooro 100 5 150—150-150 50 90
95/0/5 150 8 185—185—185 55 120
0/95/5 100 6 150—150—150 50 120
47.5/475/5" 150 8 185—185—185 55 120
0180/20“ 150 4 150-150—150
68.5/285/5W 150 6 185—185-185 54 120
57/38/51" 150 6 185-185-185 53 120
47.5/475/5‘“ 150 6 185—185—185 52 120

 

 

 

 

 

 

" directly blend in one shot
1" for the master batch preparation
m from the master batch

Note: Processing parameters were followed and fine tuned based on their
thermal behaviors (derived by DSC & TGA) and their suppliers’ guidelines.

55

 

Direct as well as master batch methods were used in order to choose the
efficient process engineering for the nanocomposites preparation. This would be
discussed in detail in the following chapter. Master batch method was giving
better results in terms of mechanical and thermo-physical properties and so
decided to carry only master batch method for the rest of the nanocomposite
preparations. In direct way, we blend all the materials such as, polymers and clay
melt compounded in one shot where as in the master batch method, we prepared
the melt compound of 80% PBAT with 20% of the Clay, as a master batch pellets
using the micro compounder as well as the pelletizer. Then these pellets were
again melt compounded with appropriate proportions of neat polymers viz., PLLA
and PBAT so as to get the required blend combination like the 5%

nanocomposites of 50/50, 60/40 and 70l30 blends.

3. L2 Compression Molding Machine

Compression molding machine (Model - M, Carver Laboratory Press, USA) was
used to prepare films from pre-blended pellets that was in turn prepared from the
above said microcompounder twin screw extruder. These films were prepared for
the barrier properties measurements. This is one of the simple processes to
make the films by just compressing the pellets in between the two hot platens.
The blending compositions and the process parameters followed to prepare the
films as shown in the following Table 3.4. Teflon sheets were used for the
preparation of the films prior to avoid the stickiness of the molten plastic to the

metal plates or molds.

56

Table 3.4 Blending compositions and process parameters followed in

Compression molding machine for making PLLAIPBAT/Clay
blends/nanocomposites based films

 

 

 

 

 

 

 

 

PLLA/PBAT/cla Sam I Re'iiilence M°ld C°mpr°35i°n

(in wt %) y Sizep(ge)s (mihlirlteegz Temperature Pressure
(x + y) (°C) (ps1)

100mm 4 2+3 190 185—210
70/30/0 4 1+3 190 185-210
60/40/0 4 1+3 190 185-210
0/100/0 4 0+3 150 185—210

66.5/285/5" 3.5 1+ 3 190 148- 173
57/3815“ 3.5 1+3 190 148—173

 

 

 

 

 

 

" these pellets were prepared through the master batch method using DSM

” Residence time includes the time involved in softening (x = preheating with out
any pressure in between the molds) and the compression time (y) i. e., (x + y)
minutes.

3. 4. Characterization

3. 4. 1 Qynamic Mechanical Analyzer (DMA)

Dynamic Mechanical Analyzer (DMA 0800 - TA Instruments, USA) was used to
measure the thermo-physical behaviors such as storage modulus, tan delta, loss
modulus and HDT. DSM molded rectangular specimens were used for the
experiments. Dual cantilever bending mode was used at an oscillating frequency
of 1.0 Hz to measure the behaviors except for Heat Deflection Temperature
(HDT) for which 3-point bending mode was used. Testing was carried out at dual

cantilever using multi frequency strain mode at amplitude of 15 um while heating

57

from 29°C to 100°C at the scanning rate of 3°C/min. In the 3-point bending, using
controlled force mode according to ASTM D648 standard, HDT was measured at
0.195% strain and amplitude of 20 pm while heating from ambient temperature to
80°C at the scanning rate of 2°C/min under constant load of ‘P’ where P = [26t2w
/ 3|] in which, stress (6) is 66 psi (455 KN/mz), t = thickness, w = width, l = length

(50mm). At least 3 specimens were tested for any of the above experiments.

3. 4. 2 Universal Testing Machine ( U TM)

Universal Testing Machine (UTS, USA, model: SFM-20) was used to measure
the tensile properties as well as flexural properties such as, % Elongation at
break, tensile strength, flexural strength and their relative modulus. The tensile
testing was done as per the ASTM D638 standard except the sample size and
the gauge length, since the DSM made tensile samples are smaller in size unlike
the standard size. So the gauge length of 1 inch was followed instead of the
standard 2 inch gauge length. Grip separation speed of 1 in/min was used for
almost all the samples except for neat PBAT samples for which the speed of 10
in/min was used. At least five specimens were used for each sample and a load

cell of 1000 lb was used for all the experiments.

3. 4.3 Izod Impact Tester

Monitor Izod Impact tester (Testing Machines Inc., USA, Model TMI® 43-02-01)
was used with 5-lb pendulum to measure the notched Izod Impact strength of

samples at ambient conditions according to the ASTM D256 standard. TMI

58

notching cutter (model-22-05) was used to notch the samples as per that
standard. The notched samples were conditioned for at least 48 hours at 23°C

and 50% RH. At least five specimens were used for any sample.

3. 4.4 Thermal Behaviors (DSC & TGA)

Thermal properties of the polymers, clay and their blends & nanocomposites
were analyzed using Differential Scanning Calorimetry (DSC — TA 0100, TA
Instruments, USA) and Thermo Gravimetric Analysis (T GA — moel-2950, TA
Instruments, USA). In DSC, experiment was carried out at scanning rate of
10°C/min in the temperature range of - 50°C to 200°C with Heat-Cool-Heat cycle
prior to measure the thermal properties such as melting temperature (T m). glass
transition temperature (T9), crystallization temperature (T c) etc. In TGA, the
experiment was done at the scanning rate of 25°C/min in the presence of inert
nitrogen atmosphere prior to process the pellets and also to analyze the

degradation behavior of the biopolymers and their nano composites.

3. 4. 5 Barrier Properties (0P & WVP testers)

Oxygen Permeability was measured by the Oxygen Permeation tester (MOCON
OX-TRAN® 2/21). At least 5 cm2 area exposures of samples with aluminum mask
were used for testing any specimen. The film samples were tested at 23°C, 0%
RH. and 740 mmHg. Water Vapor Permeability was measured by the Water
Vapor Permeation tester (MOCON PERMATRAN-W® 3l33) and the samples

were tested at 378°C, 85% RH. and 740 mmHg.

59

3. 4.6 X-ray Diffractometer (XRD)

X-ray diffraction (Rigaku 200B XRD diffractometer with 45kV, 100mA) studies
were carried out for the nanocomposites of neat PLA and 60PLLA/4OPBAT
blended injection molded samples. XRD studies were done with CuKa radiation
(=0.1516 nm) and a curved graphic crystal monochromator at a scanning rate of
0.5 °lmin. Wide angle measurements and d-spacing in the nanocomposites were
derived prior to analyze the intercalation and/or exfoliation behaviors of the clay
in the bio polymer matrix and correlate with the mechanical, thermo-physical and

morphological behaviors.

3. 4. 7 Environmental Scanning Electron Microscope (ESEM

ESEM was used to analyze the morphology of the both neat polymer blends
as well as the blend based nanocomposites. The fractured surfaces of the
samples were analyzed for this purpose using ESEM (Phillips Electroscan 2020)
with 4.0 torr water vapor and field emission filament (current set at 1.83A). An
accelerating voltage of 15 W was used to collect the ESEM images for these
samples which were angled perpendicular to the fractured surface prior to view
and record the images. Prior to view the same, a gold and platinum coating was

applied on those fractured surfaces by Denton Desk ll XLS sputter coater.

60

3. 4.8 Transmission Electron Microscope 1T EM

The morphological behaviors of the nanoclay platelets in the nanocomposites of
the 60PLLA/4OPBAT blended polymer matrix were observed in the Transmission
Electron Microscopy (TEM). Cryogenically microtomed ultra thin film specimens
of the nanocomposites with the thickness of about 100 nm were used for the
TEM observations. The microtoming was carried out at —120°C using the
ultramicrotomy with a cryogenic attachment and diamond knife having an
included angle of 4 deg. A Joel 100 CX TEM with LaB6 filament in 100kV
accelerating voltage was used to collect bright field TEM images of these

nanocomposites.

61

Chapter 4 Results and Discussion
4. I PLLA based blends with tough biodegradable polymers

Stiffness and toughness are the critical properties that will decide the
performance of the plastics and their applications. Storage modulus and notched
izod impact strength were evaluated to finalize the suitable tough biopolymer that
would give the required performances once blended with PLLA. Storage modulus
and notched izod impact strength are related to the stiffness and toughness
respectively. So, thermo-physical properties like storage modulus and
mechanical properties like notched izod impact strength were used to choose the
suitable tough polymer to blend with PLLA. In the first phase, PLLA was blended
with selected biodegradable tough polymers such as PBAT, PTAT, PBS, PCL

and PEA in the 50/50 (in wt%) composition to finalize the tough polymer.

 

 

 

 

 

 

 

400 I :3lzodlmpactStrength(Jlm) I 4
A T +Storage Modulusg 30°C (GPa)
5 ’ 1 a:
ti. .‘ ..
c j 2
4 a
1% 200 ‘I‘ 2 '3
'5 E
N l q,
°- or
U l
o w
.5 I m I
o 9 I I 1 p m t 1 F“_.l A- . o

 

 

 

 

 

50PLLA50PBS 50PLLA50PCL 50PLLA50PEA

PLLA I Tough Biopolymer (In wt%)

100PLLA 50PLLA50PBAT 50PLLA50PTAT

Figure 4.1 Storage modulus and notched izod impact strength of 5 OPLLA -5 0Tough
biopolymer (PBAT, PTAT, PBS, PCL or PEA) blends

62

Injection molded samples were prepared from the DSM and then they were
tested and evaluated at DMA and Izod impact tester to derive the above
mentioned properties. Storage modulus data as well as notched izod impact data

for the above said compositions are given the following Table 4.1 and Figure 4.1.

Table 4.1 Storage modulus and notched izod impact strength of 50PLLA-50Tough
biopolymer (PBAT, PTAT, PBS, PCL or PEA) blends (in wt%)

 

 

 

 

 

 

 

 

PLLA-Tough Izod Impact Std. Storage Modulus Std.

Biopolymer (in wt. %) Strength (J/m) Dev. @ 30°C (MPa) Dev.
100PLLA 28 2 3331 22
50PLLA l 50PBAT 327 36 1 139 14

50PLLA / 50PTAT 47 5 692 2

50PLLA / 50PBS 49 12 1592 32
50PLLA l 50PCL 199 94 1343 64
50PLLA I 50PEA 1 1 1 867 39

 

 

 

 

 

 

From the above results, it was evident that 50PLLA/50PBAT blend was having
better properties (storage modulus=1.139 GPa and izod impact strength = 327
J/m) although PLLA-PBS blend showed better storage modulus at the cost of the
impact strength that is very poor. PLLAIPBAT blend has got required modulus
and izod impact strength is much better than any other tough plastics based
blends here. It can be seen that more than 1000% improvement in the toughness
when compare to the neat PLLA while maintaining about one third of its modulus.
Still this modulus is comparable to that of conventional PP. As the objective is to

improve the toughness of this PLLA while maintaining the required the modulus,

63

it was decided to go for further studies for the optimization of the best blend
compositions for PLLA with PBAT from this reference blend proportion ie.,

50PLLA/50PBAT.

4.2 PLLA - PBA T based blends

In the second phase, PLLA:PBAT blend ratios (in wt%) of 100:0, 70:30, 60:40,
50:50, 30:70 blend compositions were melt compounded and injection molded
samples were prepared. Samples were evaluated at DMA, izod impact tester and
universal testing machine for the thermo-physical properties like heat deflection
temperature (HDT) and storage modulus and the mechanical properties like
notched izod impact strength, % of elongation at break and tensile strength. The
thermo physical properties for the above compositions are reported in the Table

4.2 and Figure 4.2

 

 

 

 

 

ml HeatDellectlonTerpamle 4' WWQII'C
3 1
6°“ 5 3
5 3""
-0 =0- 2 e
i- 8:9
O E O
‘0 ' e
0 ol- , . . T 9
mo mm am 5150 30170 01100 0 m m a) m 100
PUNPBNG‘HM‘IQ %thhmm

Figure 4.2 T hermo-physical properties viz., heat deflection temperature (HDT) and
storage modulus for various PLLA-PBAT blends

It was clear from the above results that the storage modulus was quite coherent
with the blend compositions ie., the storage modulus is decreasing with

increasing in the % of PBAT in the PLLA blend matrix In a coherent manner. So,

64

the blend worked well in better manner without any compatibilizer however, there
might not be any miscibility or compatibility in these blends that was derived from
the DSC results. HDT was not much affected by the PBAT presence in the PLLA
matrix irrespective of the various weight % of PLLA or PBAT. Even at the 70% of
PBAT had the HDT of 50.44°C in comparison to neat PLLA that had the HDT of
52.84°C. PLLA:PBAT blends of 50:50, 60:40 and 70:30 having the moderate
storage modulus viz., 1139 MPa, 1423 MPa and 2009 MPa when compared to
100PLLA that had about 3331 MPa.

The injection molded samples were also evaluated for the mechanical properties
such as notched izod impact strength, tensile strength and % break elongation.
These mechanical properties are also important properties that decide the

polymer selection for many applications especially in packaging. The mechanical

 

 

 

 

 

 

 

m: Sundown?!) +600 no
I ‘* +%ofBongelonatbreek .5 i ,
i ”i .33
A .8
fig... gg +3541 s
% 1mm '2- . Nil)-
° 3’“ [:1 U ‘5 3 e beak
I- s! E o . . . . .
01* h ,, *i .7 . i * 0 o 20 40 so so no
1000 mm m 5150 3000 0’10) %ofPBATlnthePLLAIPBATbIend
PLLAIPBATmM‘lo) couposition

Figure 4.3 Mechanical properties viz., tensile properties and notched izod impact
strength for various PLLA -PBA T blends

properties such as notched izod Impact strength and tensile properties are

reported in the Figure 4.3 and Table 4.3.

65

It was evident from the above data figure that the diversified performance of the
various blends of PLLA/PBAT. Neat PBAT was highly flexible that it was not
breakable in the notched izod impact strength. There was an increase in the
impact strength of PLLA blends with increase in this tough polymer (PBAT) % in
the blend matrix. The notched izod impact strengths improved for the
PLLA/PBAT blends about 210%, 460% and 1070% for the blends of 70l30, 60/40
and 5050 respectively when compared to neat PLLA. Also the % of elongation at
break had improved from 2 % for neat PLLLA to 61% (30 times), 157% (78
times) and 199% (100 times) for the blends of 70l30, 60/40 and 50/50
respectively. However, tensile strength had come down from 74 MPa for the neat
PLLA to 49 MPa, 39 MPa and 30 MPa for the blends of 70l30, 60/40 and 50/50
respectively. It was still found that larger standard deviations especially in
elongation and that showed the incompatibility and immiscibility of the blends.
The tough polymer PBAT was contributing its elongation behavior to the stiff
polymer PLLA and improves the toughness that could be seen from the
elongation and impact improvements for the blends in comparison to the neat
PLLA. This indicated that they are very much comparable with the conventional
plastics and it was decided to carry out the nanocomposite works on these
compositions viz., PLLA:PBAT = 70:30, 60:40 and 50:50 (in wt%) based on the

above performances.

66

4.3 PLLA — PBA T based blends and their Nanocomposites

In the third phase, PLLA:PBAT blend ratios (in wt%) of 70:30, 60:40 and 50:50
blend compositions were melt compounded with 5wt% of OMMT clay and
injection molded samples were prepared from the same. In this research
experiments, all the nanocomposites were prepared with 5wt% of OMMT. Now
onwards, the phrase ‘nanocomposite’ would imply that it contains 5 wt% of

OMMT in the polymer/polymer blend matrix.

4. 3. 1 Direct Method Vs Master batch Method

There were 2 methods of nanocomposite preparation were followed viz., direct
blending and master batch based blending for one composition ie., 50/50 that
was taken to choose the best method. The schematic diagram is shown in the
figure about the both methods (Figure 4.4). In the direct blending method, we mix
required ratios of the polymers and OMMT manually in a container and then this
mixer was fed into the extruder through feeder to prepare the nanocomposite
melt compounding. Where as in the other method, we prepared the master batch
in which 80 wt% of PBAT and 20 wt% of OMMT were mixed and fed into the
extruder to prepare the melt compounded strands from which the pellets were
made using a pelletizer. This master batch was mixed with PLLA and PBAT in
the required ratios and then this mix again fed into the extruder to get the final
nanocomposite melt compounding. Here we took PBAT for the master batch
preparations since it has better thermal stability than the PLLA. Both methods

were used to prepare the samples and then were evaluated for their mechanical

67

and thermo-physical properties in order to find the better method for the

nanocomposite preparations.

 

Dirgct Method Master batch Method

 

 

 

 

 

 

   
 
    

Nano
composite Nam,

composite

 

 

 

 

 

 

 

 

 

 

 

Figure 4.4 Efl'ective Process engineering for the nanocomposite preparations: Direct
Method Vs Master batch Method

The samples of master batch method showed better properties than that of direct
method (Figure 4.5). This was decided based on the thermo-mechanical and
mechanical behaviors. Although both methods show similar behaviors except in
the tensile strength where master batch method exhibited better results. Then for
the rest of the blends such as 60l40 and 70/30 of PLLAIPBAT, the master batch
method was followed to prepare the nanocomposite samples. Nanocomposites

of neat polymers viz., PLLA and PBAT were also prepared and evaluated for

68

their mechanical and thermo-physical properties so as to give the comparison

with their blends and nanocomposites.

CJSthQm'C(G’a) DTMWMI

J
I

 

 

 

 

 

 

 

 

 

 

 

34 +Il°dmwuml “'00 E 4] +%daagaiarabreak i g
g F" E 5 L ’ a
v /\‘ ‘ ”50‘ s
8 ‘1 3 '5: ‘ 4m:
'5 , 13' I: .9
'82 , Non-T ma £40] a
= ..... E 3 at
a g 2720)» "—‘J I III
/ - ~=   Ll :2
o .- +-— g— +4224» 0 o 4 . . i . . 4, , 4 “+0
A B C D E A B C D E

Figure 4.5 Optimization of effective process engineering between direct methodfld
miter batch method for the nanocomposites preparations. A =1 00PLLA;
B=5 0PLLA 5 0PBA T; C =4 7. 5PLLA/4 7. 5PBA T /5 OMMT -Direct;
D=4 7. 5PLLA/4 7. 5PBA T/50MMT-Master batch; E=100PBAT (all are in wt %)

4. 3. 2 Thermo-physical and Mechanical Properties:

From the above, the selected compositions of PLLA:PBAT blends in the ratios of
70:30, 60:40 and 50:50 were fabricated into nanocomposites with 5wt% of

OMMT through master batch method by melt blending technique. Blends showed

 

 

80 .. Tensile Properties 7 806
A l +Tenslle Strength (MPa) i a;
g - + - % of Elongation at break a
a so i a
, 400 ‘5
g 40 i :3
(D : _ g
3 I 200 5
2 20 + ' -
0 O
r- , l’ g
. +. 42.. l .

 

A B C D E F G H

Figure 4.6 Tensile properties of the nanocomposites of various PLLA/PBAT blend
compositions along with the respective neat blends. A =100PLLA;
B = 70PLLA3 0PBA T; C =66. 5PLLA/28. 5PBA T/50MMT; D=60PLLA/40PBA T;
E =5 7PLLA/38PBA T/5 OMMT; F =5 0PLLA/5 0PBA T;
G=4 7. 5PLIA/4 7. 5PBA T/50MMT; H =1 00PBA T (all are in wt %)

69

coherent results again. Storage modulus had improved about 33%, 47% and
36% for the nanocomposites of PLLA:PBAT blends of 70:30, 60:40 and 50:50
respectively when compared to the respective neat blends. However, notched

izod impact strength results were decreased viz., 35, 55, 140 Jlm for the same

 

 

4000 T +Stor'ageModulrIsQ30‘C (ma) — 400

- 4 - Izod Impact Strength (Jlm) A
A - E
a \
é 300° i Mi 3003
V ' “ a
g l , e
= w .8
“32000 I 1 200m
l H
E ' o
8 I a
£1000 + — 100-g
u i '8
”’ l . a

. ' l

0 LE ~- 7 1‘ °

 

 

A B C D E F G H

Figure 4. 7 Thermo-physical and mechanical properties of the nanocomposites of
various PLLA/PBAT blend compositions along with the respective neat blends.
A = 1 00PLLA; B = 70PLLA3 0PBA T; C =6 6. 5PLLA/28. 5PBA T/5OMMT;

D = 6 0PLLA/4 0PBA T; E =5 7PLLA/3 8PBA T/5 OMMT; F =5 0PLLA/5 0PBA T;
(i=4 7. 5Pl.l.A/47. 5PBA T/50MMT.‘ H=100PBA T (all are in wt %1

nanocomposites when compared to the respective neat blends that had 87, 157
and 327 Jlm respectively for 70l30, 60I40 and 50/50 based blends (Table 4.2,
Table 4.3 and Figure 4.7). Still tensile strength and elongation results are
retained near to that of neat blends (Table 4.3 and Figure 4.6). The mechanical
and thermo-physical properties of these nanocomposites along with neat blends’

are given in the Tables 4.2 & 4.3 and Figures 4.6 & 4.7.

70

Table 4.2 Thermo-physical properties viz., heat deflection temperature (HDT) and
storage modulus of PLLA-PBAT-OMMT blends/nanocomposites based injection
molded samples

 

 

 

 

 

 

 

 

 

 

 

 

 

 

PLLA/PBAT/OMMT Dailieeztion Std. Storage Modulus Std.
(in wt %) Temperature Dev. @ 30°C (MPa) Dev.
(°C)
100 l 0 I 0 52.84 0.15 3331 22
70 I 30 I 0 51.96 0.47 2009 22
60 I40 I 0 51.80 0.22 1423 55
50/50/0 51.89 0.16 1139 14
30 I 70 I 0 50.44 0.06 565 45
0 I 100 I 0 -- -- 92 6
95 I 0 I 5 57.17 0.10 4261 93
0/95/5 42.10 1.65 188 2
47.5 I 47.5 I 5 * 55.91 0.48 1574 45
66.5 I 28.5 I 5 ”7" 54.76 0.14 2863 30
57 I 38 I 5 1" 54.72 0.32 2088 41
47.5 I 47.5 I 5 t" 54.80 0.35 1544 86

 

 

 

 

 

 

" directly blend in one shot
1" from the Master batch

71

Table 4.3 Mechanical properties viz., notched izod impact strength and tensile
properties of PLLA-PBAT-OMMT blends/nanocomposites based injection molded
samples

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Izod . % of
PLLA/PBAT, Impact Std. Tensrle Std. Elongation Std.
OMMT S h D Strength
(in wt%) trengt ev. (MPa) Dev. at break Dev.
(Jlm) (%)
100 I 0 I 0 28 2 74 1 2 1
70 I 30 I 0 87 14 49 2 61 29
60 I 40 I 0 157 9 39 2 157 57
50 I 50 I 0 327 36 30 1 199 42
30 I 70 I 0 665 28 22 1 243 47
0 I 100 I 0 Non-break -- 20 1 516 25
95 I 0 I 5 28 1 73 1 7 2
0 l 95 / 5 Non-break --- 18 2 285 16
47'5 ’ 375 ’ 5 167 17 20 1 161 36
555/315“ 5 35 8 51 0.33 78 39
57/38/5“ 55 5 41 1 111 38
47'5 ’375 ’ 5 140 22 30 1 184 46

 

 

 

 

 

 

 

 

# directly blend in one shot
1” from the Master batch

72

It was evident from the storage modulus curve analysis that storage modulus
was improved due to the nanoclay reinforcement even better than neat PLLA

above the T9 of PLLA (Figure 4.8).

 

neat PLLA

— 60PLLA/4OPBAT
— 57PLLAI38PBATI5-GIIIIIIT

Storage Mogulus (MPa)

 

 

25 50 75 100
Temperature (°C)

Figure 4.8 Storage modulus curve analysis for the neat PLLA, 60PLLA/40PBA T
blend and its nanocomposite (all are in wt%)

Also the stress-strain curved analysis showed that area under the curve for the
nanocomposite was larger than that of the respective neat blend and this implied
that energy absorption would be more for the nanocomposite samples than that

of the respective neat blend (Figure 4.9).

73

45 - —57PLLN38PBATI5-OMMT
- - - -60PLLA-40PBAT

 

on
O
l

‘
~-
5
'5.
a...
------------------

 

Stress (MPa)
at

 

 

 

 

0 ~— _- I -——=-— 2- . . +4

0 0.4 0.8 1.2 1.6
Strain (in/in)

Figure 4. 9 Stress-strain curve analysis for 60PLLA/40PBA T blend and its
nanocomposite (all are in wt%)

4. 3. 3 Thermal Properties:

Thermal properties were evaluated using DSC and TGA. The glass transition
temperature (T g) and melting point (T m) of PLLA were not affected by the
presence of nanoclay reinforcement when compared to the neat PLLA. This was
also evident from the storage modulus curves discussed earlier. HDT showed the
similar behavior that was discussed earlier in the thermo-physical properties.
However, the DSC curves showed that the crystallization temperature (Tc) of the
nanocomposite lied in between that of the neat PLLA and that of the respective
neat blend (Figure 4.10). This implied that crystallization was affected by the
presence of the nanoclay particles in the polymer blend matrix and improved the
crystallization of the nanocomposite when compared to the respective neat
blend. TGA curves showed that nanocomposite improved the thermal

degradation temperatures when compared to the neat blend (Figure 4.11).

74

P
.5
j

 

 

 

 

neat PLLA? i
____60PLLAI40PBAT

0.2 ——95(60PLLAI4OPBAT)50MMT l
A I
i 0 ji
5 -o.2 4‘
u.
‘5
or -0.4 i
I I

 

b
0’
.—_—-_:'_

 

.b
g G
I
I

60 120 180
Temperature (°C)

Figure 4.10 DSC curve analysis for the neat PLLA, 60PLLA/4OPBAT blend and its
nanocomposite (all are in wt%)

 

 

 

 

 

 

 

105 7. —60PLLN40PBAT
] g
i 11 ——95(60PLLAI40PBAT)50M
I MT
‘ x
:\5 70 j
‘5 I
s |
.9 1
c
3 35 1
I
0 l
0 200 400 600
Temperature (°C)

Figure 4.11 TGA curve analysis for 60PLLA/4OPBAT blend and its nanocomposite
(all are in wt%)

75

4. 3. 4 Barrier Properties:

Based on the above mechanical properties only selected combinations like 60l40
and 70/30 blends and their nanocomposites along with neat PLLA and neat
PBAT were evaluated for the barrier properties. We used the compression
molded films and for blends, strands were extruded from the DSM micro
compounder and then they were pelletized prior to use in compression molding.
Barrier properties such as Oxygen Permeability and Water Vapor Permeability
data are reported in two different units in the following Tables 4.4 & 4.5. Also
barrier properties also reported (Table 4.6) for some of the conventional plastics

like PE, PP, PS, PET and Nylon that are widely used in packaging.

Table 4.4 Barrier properties viz., Oxygen Permeability and Water Vapor
Permeability of PLLA-PBAT-OMMT blends/nanocomposites based compression
molded films (in SI units)

 

 

 

 

 

 

 

 

Oxygen Water Vapor
Permeability Permeability
PLLA / PBAT / 2 2
OMMT “(PE/6351f“) Std. Dev. “(gs/63.33")” Std. Dev.
0“ Wt %) @ 23°C & 0% @ 37.8°C &
RH 85% RH
100 l 0 I 0 9.2026797632 0133520554 1 .81 1337475 021827045
70 I 30 I 0 -- --- 3.043114272 0444018386
60 I 40 I 0 9560034810 1387556138 3.508807439 0.596093638
0 I 100 l 0 23.181543925 1277135773 6.274510735 0.016147332
66.5 / 28.5 I 5 # --- -- 2.325265472 0137291689
57 I 38 / 5 # 8.323919854 1.702471714 2.755923089 0290641885

 

 

 

 

 

“I from the Master batch

76

 

Table 4.5 Barrier properties viz., Oxygen Permeability and Water Vapor
Permeability of PLLA-PBAT-OMMT blends/nanocomposites based compression
molded films (in USA standard industry units)

 

 

 

 

 

 

 

 

Oxygen Water Vapor
Permeability Permeability
PLLA / PBAT/ . . 2 . . 2
OMMT (consul/100m . Std. Dev. (g.mnI/1001n .d. Std. Dev.
(in wt %) .atm) mmHg) @
@ 23°C & 0% 37.8°C & 85%
RH RH
100 / 0 l 0 155.40 2.26 0.53 0.064
70 I 30 I 0 --- --- 0.89 0.130
60/40 I 0 161.43 23.43 1.03 0.174
0 / 100 l 0 391.45 21.57 1.84 0.005
66.5 / 28.5 / 5 t -- 0.68 0.040
57 / 38 / 5 1’ 140.56 28.75 0.81 0.085

 

 

 

 

 

 

” from the Master batch

Table 4.6 Barrier properties of conventional plastics such as LDPE, HDPE, OPP,
PS, OPET, and Oriented Nylon6 (in USA standard industry units)

 

Literature Data [4. 1]

 

 

 

 

 

 

 

 

Oxygen Permeability Water Vapor
(ee.mi11100in2.d.atm) Permegblhty
(g.mill100in .d.mmHg)
@ 23°C 8‘ 0% RH 40°C & 90% RH

LDPE 554 0.02289543
HDPE 150 0.00763181
OPP 153 0.00763181

PS 260 0.17071153
OPET 2.3 0.02410045
Oriented Nylon6 1.78 020435333

 

 

 

77

 

It was found out to be about 13% improvement of oxygen barrier and was about
22-24 % improvement of the water vapor barrier for the nanocomposite when
compared to the concerned neat blends. This implied that clay might not be fully
exfoliated and the tortuousity across the polymer matrix might not be achieved
successfully. However the tortuousity due to the intercalated and flocculated
platelets contributed certain improvements in the barrier properties of the
nanocomposites. It was also evident from the compression molded films that
have transparent spots formed due the agglomerates and this was also evident
from the morphology analysis that would be discussed later here. Oxygen barrier
of the nanocomposite was better than that of the oriented polypropylene and
polystyrene where as the oxygen barrier of neat blend molded film was
comparable to that of polyolefins. Here we didn't consider the orientation effects
since we were using the compression molded film that doesn’t give any
orientation effects. Still they are good enough to compete with those oriented
conventional polymers. This gives a scope of replacing few of the conventional

polymers at this stage it self.

4. 3. 5 Structural Analysis:

XRD was used to analyze the clay behaviors in the polymer matrix as shown in
the following Figure 4.12 and Table 4.7. As per the supplier’s data, the neat
treated clay (OMMT clay) has the d-spacing of 18.6 A° where as, the
nanocomposites of neat PLLA and the 60PLLA:4OPBAT blended with 5wt%

OMMT clay, was observed at 29=2.75° and 29=2.65° showed the d-spacing of

78

intensity (cps)

—95(60PLLN40PBAT)50MMT
" ' '95PLLA-50MMT

 

 

 

 

 

i \-
o 4 7
2 3 4 5 6
2 Theta (degrees)

Figure 4.12 XRD patterns of nanocomposites of 1 00PLLA and 60PLLA/4OPBAT with
5 wt% OMMT clay blended polymer matrix (all compositions are in wt%)

31.55 A° and 33.34 A° respectively. This implied that the interaction of clay

platelets was existed in the nanocomposite polymer matrix. This was also evident

from the following TEM image discussion. It was also found that the clay

intercalation behavior is almost similar in both the neat PLLA nanocomposite and

blended polymer nanocomposite though blended one has little higher value than

the neat PLLA’s d-spacing.

Table 4.7 XRD patterns of nanocomposites of 100PLLA and 60PLLA:4OPBAT

with 5wt% OMMT clay blended polymer matrix

 

 

 

 

 

 

 

 

 

29 (°) 9 (°) Sine d (A°)

OMMT (supplier’s data) -- 18.5
100PLLA with 5%OMMT 2.8 0.024435 0.024432 31.55343
60PLLA4OPBAT with 5%OMMT 2.55 0.023125 0.023124 33.33913

 

79

 

4. 3. 6 Morghologz Analysis:

Morphological analyses were also done by the ESEM on the izod impact tested

fracture surfaces of both the neat polymer blend and their nanocomposite

 

Figure 4.13 ESEM micrographs on the fractured surfaces of I . 60PLLA/4OPBAT
blend,“ 2. Nanocomposite of 60PLLA/4 0PBAT blend; 3. 70PLLA/30PBAT blend (all
compositions are in wt%); 200 gm scale bar [or all images

especially for 60l40 and 70l30 blends and their nanocomposites. The ESEM
images were taken in the magnification of 200p scale bar to understand the
morphology between the blend and the nanocomposite in the following figure
(Figure 4.13). The phase separation is very much evident from all the blend
images where as, the phase separation is reduced in the presence of OMMT
cay. This implies that the clay acting as bridge between the 2 phases of PLLA
and PBAT in the polymer matrix. However, the crystallization is affected by the
presence of OMMT cay and its nucleation effects that can be seen in the
nanocomposite based images where the spherulite sizes are reduced compare
to the neat blend sample images. So it was expected to get the better impact and
elongation based in the effect of the clay coupling between the phases however

that was compensated by the crystallization behavior that again reduced the

80

impact or elongation. This was evident from earlier discussed mechanical
behaviors. Still this will give better barrier due to the crystallization as well as clay
platelets presence, meaning more small no of spherulites with clay platelets give
more tortuous path for the permeating molecules like oxygen or water vapor. It
could be seen that 60/40 neat blend image showed the rougher surface than that
of 70/30 neat blend and nanocomposite of 60/40 blend. This also indicated the
fracture nature of the samples and more the PBAT present more the fracture
resistance and also presence of clay particles reduce the same and so lesser

resistance to fracture. These were coherent with the izod data derived earlier.

Morphological behaviors were analyzed by the TEM analysis for the
nanocomposite of 60PLLA:4OPBAT blend. The TEM images showed the phase

separation in the blended polymer matrix as well as intercalated behaviors of the

 

Figure 4.14 TEM images for the phase separation (low & high magnifications) with
the intercalated nano scale OMMT clay agglomerates (low magnification) views in
the 5 wt% OMMT reinforced nanocomposite of 60PLLA :40PBA T polymer matrix
(composition is in wt%)

81

nanoscale OMMT agglomerates (Figure 4.14). The immiscible nature of the
blend was evident from both low and high magnification TEM images in which it
can be clearly seen that the white circular batches (high magnification) and
whitish continuous batches (low magnification) indicated the PBAT component in
the PLLA matrix. This immiscible nature was also evident from the DSC
behaviors of these blends and nanocomposites. The lntercalation of the clay
platelets was also evident from the agglomerates (darkish batches) in the high
magnification TEM images. It was also supported from the transparent spots
found in the compression molded films. It is assumed that due to the
agglomeration of the intercalated clay platelets that stretch the near by the
polymer chains and so created those transparent spots in the films that can be
seen even by the plain eyes. Due to this intercalation behavior, the barrier
properties improved for both nanocomposite films due to the tortuous bath
created by these nano scale OMMT agglomerates in comparison to the neat
blends and for oxygen barrier even compare to the neat PLLA. This could also
evident for the improvement of storage modulus while retaining the tensile

strengths for these nanocomposites.

82

4. 3. 7 Halpin-Tsai Model Correlation of Elastic Modulus through Pseudo-
inclusion Model

The elastic modulus values were correlated with theoretical values calculated
using the Halpin-Tsai equation through Pseudo-Inclusion model [4.2]. The
models are explained in the Appendix 1. Since the TEM and XRD analyses
showed the intercalated morphology, Halpin-Tsai was used through the Pseudo-
lnclusion model. In the blend matrix, uniform dispersion of intercalated clay
nanoplatelets was assumed. Additionally, it was also assumed that the PBAT
secondary phase was uniformly dispersed in the PLLA primary matrix. Since the
nanocomposite specimens were prepared by injection molding, the longitudinal
property was taken for the calculation. It was found that the calculated elastic
modulus curve of the nanocomposites was closely fit with values of the

experimental nanocomposites (Figure 4.15).

4.5

Halpin-Tsai Model Correltion

 
 
    

——Theory Curve-Nanocomposites

g 0 Exp. data-Nanocomposites
Q 3 ‘ Exp. data -Indlvidual Neat Polymer
in I
2 a
a
1:
O
E
33’ 1.5 .
in
E
I.l.l
o -1.

 

 

0 25 50 75 100
Vol. % of PBAT in the PLLAIPBAT nanocomposite matrix

Figure 4.15 Elastic modulus data correlation between the experimental data and
theoretical calculated values of 5. 0 wt. % (1.62 vol. %) clay nanocomposites using
Halpin-Tsai model through Pseudo-inclusion model

83

Chapter 5 Conclusions and Recommendations

We have discussed the melt compounding of PLLA based blends with various
tough biodegradable polymers such as PBAT, PTAT, PBS, PCL and PEA in the
absence of any compatibilizer in 50:50 (weight basis) ratio as the reference
composition. Based on their mechanical and thermo mechanical properties,
PBAT (impact - 327 Jlm and modulus — 1.14 GPA) was finalized for further
studies. In the second phase, PLLA:PBAT blend of 70:30, 60:40, 50:50, 30:70
melt compounded samples were prepared and evaluated for the mechanical and
thermo mechanical behaviors. Based on the over all behaviors and performances
of these blends, it was then decided to go for the preparation of nanocomposites
for the 50:50, 60:40 and 70:30 blend of PLLA:PBAT composition since all these 3
showed the performances which are in the range of expected optimum scale
while keeping at least 50 wt % of PLLA. In the third phase, the above finalized
blends were made into nanocomposites prepared with 5 wt% of the specific
commercially available OMMT (natural MMT clay modified with dimethyl,
hydrogenated tallow, 2-ethylhexyl quaternary ammonium — a quaternary
ammonium salt). These nanocomposite samples were further analyzed for their
mechanical and thermo physical properties. It was found that PLLA:PBAT blend
of 60:40 and 70:30 compositions showed optimum results in their mechanical
and thermo-physical properties. These 2 nanocomposites were further studied
for the barrier properties especially for water vapor barrier by using the
compression molded films and compared with that of respective neat polymer

blended films. However nanocomposite of the 60PLLA:4OPBAT showed

84

impressive optimum properties viz., _ tensile strength - 41 MPa, % break
elongation - 111%, izod impact - 55 Jlm and modulus - 2.01 GPa with
improved barrier performances. These behaviors still are very much comparable
to many conventional polymers like OPP. Here it was finalized to go for the
60PLLA:4OPBAT based nanocomposite along with its neat polymer blends and
individual polymer for further investigations like oxygen permeability, XRD, SEM

and TEM analysis. In conclusion,

a. PLLA was giving required performances with PBAT with out any
compatibilizer though it was an immiscible blend in comparison to other tough

biodegradable polymers like, PTAT, PBS, PCL and PEA.

b. In the neat polymer blends, 60:40 and 70:30 blends of PLLA:PBAT providing

the required optimum performances with improved toughness.

c. The nanocomposites of the above 2 blends were showing the expected
behaviors. However, it was decided to go for 60PLLA:4OPBAT blend since
this has relatively better impact when compare to the nanocomposite of
70PLLA:30PBAT and rest of the properties like, tensile strength, % break
elongation, modulus, barrier are as expected with linear coherency with the
blend proportions in both nanocomposites. Thus the 60/40 nanocomposite
provided the required stiffness-toughness balance with improved barrier

properties

d. Improved thermal behaviors were observed for the nanocomposites when

compared to the respective PLLA/PBAT blend

85

. The nanocomposite of 60PLLA:4OPBAT were analyzed for the Oxygen
barrier, XRD, SEM and TEM. It showed both intercalated behavior in the
morphological analysis. It was also visible in the compression molded films
showing some transparent spots that indicates the agglomerations of the
intercalated clays. These all also evident from the barrier results in which
nanocomposites showed improved barrier in comparison to the neat blends.
Oxygen barrier for this nanocomposite was better than its neat blend (60:40)
that in turn was better than that of the neat PLA even. Othenivise the

enhanced modulus was found in all the nanocomposites.

Another interesting finding was that nanocomposites retaining the tensile
strength comparable to the concerned neat polymer blend while keeping the

optimum impact as well as % break elongation.

. However, most of the samples showed larger standard deviation especially in
tensile properties and that also obvious that these blends are immiscible in
nature that was already confirmed from the morphology analysis and DSC

study.

. Since one of the objectives for this present study was not to use any
compatibilizer and examine the possibility of the blends, significant results
have been achieved in improving the toughness for the PLLA while

maintaining the stiffnesjs-toughness balance without using any compatibilizer

These final results indicate that this nanocomposite still can compete with

many conventional plastics being used today.

86

Based on the above conclusions, it would also be recommended for the future
works that a well suited compatibilizer can be tried to achieve further

requirements if any as a continuation this work.

. While trying with any compatibilizer, it would also make sense to try for other
combinations having lesser PBAT contents such as 90PLLA210PBAT,
80PLLA:20PBAT etc.

Try another suitable nano-clay with effective process engineering in order to

achieve the effective exfoliation in the PLLA

87

APPENDIX 1

The storage modulus can be calculated using the Halpin-Tsai (HT) equation
[A.1]. HT equation is useful to predict the change of the elastic modulus of two-
phase materials, such as composite materials. The following equations were

used for the calculation of the elastic modulus in longitudinal direction [A.2]. :

 

 

EL = Em (A1)
1 "' 77L Vc
where,
m = (A2)
(Ec/ Em) + f
E and V 9 the elastic modulus and volume fraction, respectively
L 9 the longitudinal property
m, c 9 matrix property, clay property,
§ 9 if=2ac/3=2Ic/3tc (A.3)
where,

ac, IC, and tc 9 aspect ratio, length, and thickness of individual clay nano-

platelets.

88

Since the TEM and XRD results showed the intercalated clay morphology in the
nanocomposites, this HT equation was utilized with the pseudo-inclusion model.
This pseudo-inclusion model [A.2] was used to analyze polymer-intercalated clay
matrix assuming that intercalated clay nanoplatelets were dispersed uniformly in
polymer (PLLA or PBAT) matrix. With the pseudo-inclusion model, it was
considered that ‘individual clay nanoplatelets’ in the original HT equation were
assumed to be ‘the intercalated clay nanoplatelets’. As a result of the above
assumptions, the modulus, aspect ratio, and the volume fractions of the pseudo-
inclusion were calculated according to the rule of mixtures that lead to the

following modified equations.

 

 

 

K rm
lnterca'ated = Wm”
Clay platelets_ '~ \ \ ‘ I 5.

{53 " ~ 83 2,... ,
* EClay platelets lntercalated / e I _ \F j

Pseudo

inclusion ~~ . \ _ \ /

 

 

 

 

 

 

 

Figure A-l A model of three phase nanocomposites with a pseudo-inclusion [A.1]
Courtgz: Dr. A. K. Mohanty ’s Research group, 2005

E, = ch 1 I + E... (1-1/N’)s/t\L (A4)

LI+(1-1/N)s/l‘j 1+(1-1/N)s/tj

ac
up = (A5)
N’[1 + (1 -1/N’)s/tQ]

 

89

where,

5
II

Vc[1+(1—1/N’)s/iq] (A.6)

N!

N+{(1-N)(S/tc)(Vc/(1-Vc))} (A-7)
where,
q 9 the aspect ratio
N 9 the number of intercalated clay platelets
N’ 9 the modified number of intercalated clay platelets
s 9 the spacing between platelets
tc 9 the thickness of clay platelets (1 nm)
V 9 the volume fraction
E 9 the elastic modulus
p, c, and m 9 pseudo-inclusion, clay platelet, and polymer matrix respectively.
The following values were used:
Elastic modulus of clay: EOMMT = 170 GPa
Based on the TEM images:
Average length of the intercalated clay platelets: Ic = 500 nm
Average thickness of the intercalated clay (N=20 clay stacks) = 50 nm
Based on the experimental data:
Neat PLLA elastic modulus = 3.331 GPa
Neat PBAT elastic modulus = 0.092 GPa
It was also possible to predict the change of the elastic modulus with increasing

the content of second rubbery phase using the HT equation. In other words, the

90

change of the storage modulus of PLLA/PBAT blend could be predicted using HT
equation, when the PBAT was separated from the main PLLA matrix as the
second phase. It was also assumed that PBAT secondary phases were
uniformly dispersed in the PLLA primary matrix. When clay/PLLAIPBAT
nanocomposites were processed, the same phase separation was still observed
by TEM as shown in Fig. 4.14. The aspect ratio of PBAT is considered to be 1,

due to the circular shape.

Figure A-1 shows a model describing that the secondary PBAT rubbery
phase is dispersed in the PLLA primary matrix, where intercalated clay
nanoplatelets were dispersed in both PLLA and PBAT phases. For this
nanocomposite study, it is necessary to separately calculate the elastic modulus
of the PLLA primary phase including intercalated clay nanoplatelets and that of
the second phase consisting of PBAT and intercalated clay nanocomposites
using HT equation. In this calculation, it is assumed that clay content in vol. % is
the same in both PLLA and PBAT phases. After obtaining the reinforced elastic
modulus of both PLLA and PBAT phases after the addition of intercalated clay
nanoplatelets, the elastic modulus of such three phase nanocomposites is finally
calculated using HT equation. Since, the injection molded samples having
tendency of longitudinally aligned dispersion of clay nanoplatelets were used for
the experiments, elastic modulus of such nanocomposites was derived from
longitudinal equation. The above pseudo-inclusion equations (A-4 to A-7) were

used for the three-phase nanocomposites.

91

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2.28

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2.32

2.33
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Appendix]

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materials”, Air Force Technical Report AFML-TR, 1967, 67 — 423, Wright
Aeronautical Labs, Dayton, OH

A.2 H. Miyagawa, M. J. Rich and L. T. Drzal, “Amine-cured Epoxy/Clay

Nanocomposites. II. The Effect of Nanoclay Aspect Ratio”, Journal of
Polymer Science: Part B: Polymer Physics, 42, 2004, 4391 — 4400

99

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