CHARACTERIZATION OF METAL ORGANIC FRAMEWORK AND POLYMER
COMPOSITES AND THE METHOD OF THEIR PREPARATION
By
DHAYALAN ELANGOVAN

A THESIS
Submitted to
Michigan State University
In partial fulfillment of the requirements
For the degree of
MASTER OF SCIENCE
Packaging
2010 

ABSTRACT
CHARACTERIZATION OF METALLIC ORGANIC FRAMEWORK AND
POLYLACTIC ACID COMPOSITE AND THE METHOD OF THEIR PREPARATION
By
DHAYALAN ELANGOVAN

The research in this paper develops biodegradable functional polyester membranes based
on poly(lactic acid) (PLA) and metallic organic frameworks (MOFs). PLA without and with the
addition of 1, 3, and 5 w/w % MOF was melt compounded in a twin microextrudercompounder. Disc, rectangular and dumb-bell shaped samples were produced and their optical,
physical, thermal, mechanical, thermo-mechanical and barrier properties were evaluated. The
PLA and MOF composites showed poor interfacial adhesion between the PLA matrix and the
MOF particles, which was previously predicted by using the Hansen’s solubility parameters.
The FTIR, UV and colorimetric studies showed selective absorption at particular wavelengths
due to the presence of the MOF. The DMA results revealed that the heat deflection temperature
(HDT), storage modulus, loss modulus and Tan ∆ of the PLA/MOF composites did not change
when compared to the PLA samples. However, there was a significant decrease in the brittleness
of the PLA/MOF composite as evidenced by an increase of 15% in Izod impact strength and of
170% in elongation at break with respect to the PLA control samples. The permeability of
PLA/MOF composite films to oxygen and water did not change when compared to the neat PLA
film. However, the sorption capacity of the PLA/MOF composites films increased up to two fold
at each relative humidity to which the films were exposed. The sorption and desorption curves of
the PLA/MOF composite films showed a hysteresis phenomenon.

ACKNOWLEDGEMENTS

I am very grateful to my advisor, Dr. Rafael Auras for accepting me in to his research group and
giving me an opportunity to work on this wonderful project. Without his guidance and mentoring
this work would not be possible. I would like to thank my committee members Dr. Laurent
Matuana and Dr. Susan E. M. Selke for their kindly guidance and support throughout my project.
I am very thankful to Brain Rook and Edward Drown for training me in all the machines that I
have used for my research purpose in the Composite Material and Structure Center at MSU. I
thank Yuzay Ebru Isinay for helping in my research with the Scanning Electronic Microscopy,
and David for his help in the statistical analysis of the results. I am also thankful to April
Meersdom for ordering the materials for my research in a timely manner.
I am thankful to all my research group members, Ajay Kathuria, DongHo Kang, Hayati
Samsudin, Sukeewan Detyothin, Thitisilp (Turk) Kijchavengkul, Chaiyatas Chariyachotilert, and
Praveen Rawal for their timely assistance and sharing their invaluable expertise with me.
Last but not least, I am very thankful to my parents and brothers for their motivation and
encouragement. I would like to thank all my fellow graduate students for their help in day to day
life throughout my master program.

iii

TABLE OF CONTENTS

LIST OF TABLES ......................................................................................................................... vi
LIST OF FIGURES ..................................................................................................................... viii
1. INTRODUCTION ...................................................................................................................... 1
REFERENCES ............................................................................................................................... 4
2. LITERATURE REVIEW ........................................................................................................... 6
REFERENCES ............................................................................................................................. 32
3. MATERIALS AND METHODS .............................................................................................. 39
3.1. Materials ............................................................................................................................. 39
3.2 Equipments and Preparation................................................................................................ 39
3.2.1. Twin Screw Extruder ................................................................................................... 39
3.2.2. Metal Organic Framework Quantification .................................................................. 40
3.2.3. Film Preparation .......................................................................................................... 41
3.2.4. Surface Area of MOF .................................................................................................. 41
3.2.5. Molecular Weight ........................................................................................................ 43
3.2.6. Contact Angle .............................................................................................................. 44
3.2.7. Hansen’s Solubility Parameters ................................................................................... 45
3.2.8. Scanning Electron Microscopy (SEM) ........................................................................ 47
3.2.9. FTIR Spectrophotometer ............................................................................................. 48
3.2.10. Ultraviolet/Visible Spectroscopy............................................................................... 48
3.2.11. Colorimetry................................................................................................................ 48
3.2.12. Dynamic Mechanical Analyzer (DMA) .................................................................... 49
3.2.13. Izod Impact Tester ..................................................................................................... 50
3.2.14. Tensile Test................................................................................................................ 50
3.2.15. Differential Scanning Calorimetry (DSC) ................................................................. 50
3.2.16. Barrier Properties ....................................................................................................... 51
iv

3.2.17. Isotherm ..................................................................................................................... 52
3.2.18. Statistical Analysis .................................................................................................... 52
REFERENCES ............................................................................................................................. 53
4. RESULTS AND DISCUSSION ............................................................................................... 55
4.1. DSM Samples..................................................................................................................... 55
4.2. Compression Molding ........................................................................................................ 57
4.3. Quantification of MOF ....................................................................................................... 58
4.4. Contact Angle ..................................................................................................................... 59
4.5. Solubility Parameters ......................................................................................................... 66
4.6. Molecular Weight ............................................................................................................... 70
4.7. Surface Area ....................................................................................................................... 71
4.8. Scanning Electron Microscopy (SEM) .............................................................................. 74
4.9. FTIR Spectrophotometer .................................................................................................... 76
4.10. Ultraviolet/Visible Spectroscopy ..................................................................................... 78
4.11. Colorimeter....................................................................................................................... 79
4.12. Dynamic Mechanical Analyzer (DMA) ........................................................................... 80
4.13. Differential Scanning Calorimetry ................................................................................... 83
4.14. Thermal Gravimetric Analysis ......................................................................................... 88
4.15. Izod Impact Testing Machine ........................................................................................... 90
4.16. Tensile Test ...................................................................................................................... 91
4.17. Barrier Properties ............................................................................................................. 94
4.18. Sorption ............................................................................................................................ 95
4.19. Desorption ........................................................................................................................ 97
REFERENCES ............................................................................................................................. 99
5. CONCLUSION ....................................................................................................................... 103

v

LIST OF TABLES
Table 2.1

Physical properties of PLA ..................................................................................... 19

Table 2.2

MOF performance Comparison .............................................................................. 24

Table 2.3

Common ligands (linkers) in MOFs ....................................................................... 26

Table 2.4

MOFs used for hydrogen storage ............................................................................ 30

Table 2.5

Surface area of different industrial MOFs .............................................................. 31

Table 3.1

Optimized Parameters of DSM Micro Extruder ..................................................... 40

Table 3.2

Scoring scale for Hansen’s Solubility Parameters .................................................. 46

Table 3.3

Solvents used for determining Hansen’s Solubility Parameters ............................. 47

Table 4.1

Quantification of MOF content in the extruded samples ........................................ 58

Table 4.2

Theories and equation of contact angle (Young, Geometric mean, Wu-harmonic
mean, -base, Equation of state) ............................................................................... 60

Table 4.3

Surface tension, dispersive and polar component of test liquids ............................ 61

Table 4.4

Contact angle and surface energy parameters of PLA and MOF ........................... 62

Table 4.5

Interfacial tension and spreading coefficient of PLA and MOF ............................. 63

Table 4.6

Scoring of PLA and MOF on various solvents ....................................................... 66

Table 4.7

Dispersion, polar, and hydrogen parameters for PLA and MOF ............................ 69

Table 4.8

Number average molecular weight (Mn), weight average molecular weight (Mw),
and molecular weight distribution (PDI) of PLA resin and PLA/MOF composite. 71

Table 4.9

BET surface area, micropore volume, and pore diameter of MOF ........................ 72

Table 4.10

FTIR absorption bands of PLA/MOF composite films .......................................... 78

Table 4.11

CIE L*a*b* Values of for PLA and MOF samples ................................................ 80

Table 4.12

HDT and Tg by Tan delta results of PLA, PLA + 1% MOF, PLA + 3% MOF, and
PLA + 5% MOF samples ........................................................................................ 81

Table 4.13

Thermal Properties of PLA/MOF Composites (films) ........................................... 86
vi

Table 4.14

Thermal Properties of PLA/MOF Composites (extruded disc samples) ................ 86

Table 4.15

TGA analysis of PLA and PLA/MOF Composites................................................. 88

Table 4.16

Impact strength of PLA and PLA/MOF composites............................................... 91

Table 4.17

Mechanical Properties of PLA/MOF Composite .................................................... 92

Table 4.18

Barrier properties of PLA/MOF Composites .......................................................... 94

Table 4.19

Weight change of PLA and PLA/MOF composite between 0 and 90% RH .......... 96

vii

LIST OF FIGURES
Figure 2.1

Classification of the biodegradable polymers ......................................................... 10

Figure 2.2

Polymerization routes to polylactic acid ................................................................. 12

Figure 2.3

Schematic of PLA via prepolymer and lactide ....................................................... 13

Figure 2.4

Nonsolvent process to prepare polylactic acid........................................................ 13

Figure 2.5

MJ/Kg of energy required to produce various polymers ........................................ 15

Figure 2.6

CO2 emissions (kg/ton) resulting from production of various polymers ................ 16

Figure 2.7

Cradle-to-polymer-factory-gate greenhouse gas emissions for PLA year 5 (PLA 5),
PLA year 6 (PLA 6) and PLA long term (PLA NA) .............................................. 16

Figure 2.8

Cradle-to-polymer-factory-gate gross energy use for PLA year 5 (PLA 5), PLA
year 6 (PLA 6) and PLA long term (PLA NA)....................................................... 17

Figure 2.9

Simplified flow diagram of industrial metal-organic framework synthesis
procedures via solvothermal (Mg –MOF) and electrochemical (Cu-MOF) routes 28

Figure 4.1

DSM specimens (A) disc; (B) rectangular; and (C) dumb-bell samples ................ 56

Figure 4.2

Compression molded film samples: (1) PLA, (2) PLA + 1%MOF, (3) PLA + 3%
MOF, and (4) PLA + 5%MOF................................................................................ 57

Figure 4.3

Sessile drop images of MOF on diiodomethane, water, ethylene glycol and
formamide ............................................................................................................... 65

Figure 4.4

Sessile drop images of PLA on diiodomethane, ethylene glycol, formamide, and
water. ....................................................................................................................... 65

Figure 4.5

Dissolution of PLA in THF, tetrachloroethane, dichloromethane, and chloroform 67

Figure 4.6

Dispersion of MOF particles in various solvents .................................................... 68

Figure 4.7

MOF particles in various solvents after 2 days of storage ...................................... 68

Figure 4.8

Nitrogen adsorption isotherm ................................................................................. 72

Figure 4.9

Nitrogen desorption isotherm ................................................................................. 73

Figure 4.10 SEM images of MOF powders ............................................................................... 74
viii

Figure 4.11 SEM images of PLA and PLA composites with 5 wt% MOF fabricated using 2 and
5 min mixing time in the micro-compounder ......................................................... 75
Figure 4.12 IR Spectra of PLA, PLA + 1% MOF, PLA + 3% MOF, and PLA + 5% MOF ..... 77
Figure 4.13 UV spectra of PLA, PLA + 1% MOF, PLA + 3% MOF, and PLA + 5% MOF .... 79
Figure 4.14 DMA Curve for Storage Modulus of PLA, PLA+1%MOF, PLA+ 3%MOF and
PLA+5%MOF ......................................................................................................... 82
Figure 4.15 DMA Curve for Loss Modulus of PLA, PLA+1%MOF, PLA+ 3%MOF and
PLA+5%MOF ......................................................................................................... 83
Figure 4.16 Thermograph of PLA and PLA films plus 1, 3, and 5% wt/wt MOF composites .. 87
Figure 4.17 TGA curves of PLA and PLA/MOF composites .................................................... 88
Figure 4.18 TGA curve of MOF activated at 200°C in vacuum ................................................ 89
Figure 4.19 Sorption of PLA/MOF composite at 23°C and 40% RH ........................................ 96
Figure 4.20 Desoprtion isotherm of PLA with 5% MOF ........................................................... 98

ix

CHAPTER 1. INTRODUCTION
The concerns related to environmental pollution caused by non-biodegradable polymers
are increasing. As a consequence, researchers are developing polymers with a lower
environmental footprint from biobased resources for potential use in packaging. Among the
various commercially available biobased and/or biodegradable polymers such as
poly(hydroxybutyrate) (PHB), poly(butylene adipate-co-terephthalate) (PBAT),
poly(tetramethylene adipate-co-terephthalate) (PTAT), and poly(ε-caprolactone) (PCL),
poly(lactic acid) (PLA) is one of the most used and promising biopolymers that has drawn
commercial attention in recent years due to its compostability, high mechanical strength, high
transparency, good processability, and water solubility resistance [1, 2].
PLA has been used in a number of biomedical applications and drug delivery devices.
Some of these applications include implants, sutures, and drug encapsulation [3]. It has been
approved as GRAS (generally regarded as safe) for use in contact with food [4], and it is
currently used for packaging fresh produce, bottled water, juices, yogurt, and disposable
tableware in Japanese, European and North American markets [5]. In the form of fibers and nonwoven textiles, PLA also has many potential uses, for example as upholstery, disposable
garments, awnings, feminine hygiene products, and diapers [6].
The use of PLA containers for food and medical packaging has increased. It is necessary
for the container/package to protect the product by functioning actively throughout the product
shelf life by providing, for example, active or selective barrier properties. In the packaging
industry, several means of regulating the exposure of product to gases have already been
developed, including modified atmosphere packaging (MAP) and active packaging. In the case
of active packaging, the inclusion of scavengers in the form of sachets within the cavity or

1 
 

interior of the package is one of the most common and accepted practices. One disadvantage of
sachets is the need for additional packaging operations to add the sachet to each package, and the
end disposal of the system. A further disadvantage arising from the use of some sachets is that
certain atmospheric conditions (e.g., high humidity, low CO2 level) in the package are required
in order for scavenging to occur at an adequate rate.
Another means of limiting the exposure of product to gases involves incorporating a
functional membrane into the packaging structure itself. By incorporating the scavenging
material in the package itself, a more uniform scavenging effect throughout the package can be
achieved. In addition, such incorporation can provide a means to restrict and scavenge gases and
moisture as they pass through the walls of the package (referred to as an "active” or “functional”
barrier), thereby maintaining the lowest possible gas and moisture level throughout the package
[7]. Adsorbents are the materials used to modify the packaging material in order for the package
to function actively by adsorbing gases and moisture.
The most commonly used adsorbents are zeolites, activated carbon, silica gel, and
alumina [8, 9]. These materials are being used to modify polymer properties in order to increase
the absorbent capacity for water and other compounds such as gases, vapor, and liquids to permit
its use as a functional membrane in industrial applications. The surface area of these added
compounds largely determines the absorbent capacity of the particular material when it is
combined with the polymers. The main disadvantage of these materials is their limited surface
area, resulting in reduced absorbent capacity. Moreover, it is not possible to tailor their structures
based upon the requirements for particular applications, and it is impossible to increase the
surface of these materials, without altering the dead volume of the adsorbant.

2 
 

To overcome the defects of the current adsorbent materials, researchers have developed
novel compounds named metal organic framework (MOF) materials, which are crystalline
compounds consisting of metal ions (copper, zinc, aluminum, etc.) or clusters coordinated to
rigid organic molecules to form one-, two-, or three-dimensional structures that can be porous.
2

MOFs have a surface area between 1000 and 3000 m /g or more, which is equivalent to a
football field. This surface area is close to one order of magnitude higher than that of zeolites and
activated carbon [10, 11]. Besides the increased surface, they also have open internal structures
and long-range crystallinity. Their distinctive pore sizes can accommodate different types of
gases such as CO2, O2, N2, CH4 and other small volatile organic compounds (VOCs).
To make use of the distinctive properties of MOFs and the versatile nature of PLA, the
main goal of this research is to compound poly(L lactic acid) (PLLA) with MOF particles to
produce functional polymeric membranes. The new PLLA/MOF functional membranes are
expected to have novel properties that cannot be obtained when modified with other adsorbent
materials. Thus, the main objectives of this thesis are to:


Characterize PLLA for its solubility parameters, contact angle and its molecular
weight;



Characterize the surface area, density and pore size of MOF;



Develop PLLA/MOF composite sample films by melt compounding using a twin
screw extruder;



Evaluate PLLA/MOF composite samples for their optical, physical, mechanical,
thermo-mechanical, and barrier properties, and their sorption to water and organic
compounds.

3 
 

REFERENCES

4 
 

REFERENCES
1. V. Siracusa, P. Rocculi, S. Romani. M.D. Rosa, “Biodegradable polymers for food
packaging: a review”, Trend in Food Science and Technology, 19(12), 2008, pp. 634643.
2. J. Ahmed, S.K. Varshney, J.X. Zhang, H.S. Ramaswamy, “Effect of high pressure
treatment on thermal properties of polylactides”, Journal of Food Engineering 93(3),
2009, pp.308-312.
3. L. Avérous “Polylactic acid: synthesis, properties and applications” In “Monomers,
Polymers and Composites from renewable resources”, Eds: Belgacem N. et Gandini A.,
Elsevier Limited Publication. Chap. 21, 2008, pp. 433-450.
4. T. Jin, H. Zhang, “Biodegradable polylactic acid polymer with nisin for use in
antimicrobial food packaging”, Journal of Food Science, 73(3), 2008, pp. M127–M134.
5. Mutsuga, M., Kawamura, Y., Tanamoto, K., “Migration of lactic acid, lactide and
oligomers from polylactide food-contact materials”, Food Additives and Contaminants
25(10), 2008, pp. 1283–1290.
6. Ke, T., Sun, X.S., “Thermal and mechanical properties of poly(lactic acid)/
starch/methylenediphenyl diisocyanate blending with triethyl citrate”. Journal of Applied
Polymer Science 88(13), 2003 pp. 2947–2955.
7. T.Y. Ching “Oxygen Scavenging ribbons and articles employing the same”, US Patent
No.5744246, 1998.
8. R.T. Yang, “Adsorbents: Fundamentals and Applications”, John Wiley and Sons, May
2003.
9. I.E. Yuzay, R. Auras, S. Selke, “Poly(lactic acid)/Aluminum Oxide Composites Faricated
by Sol-Gel and Melt Compounding Process” Macromolecular Materials and Engineering,
295(3), 2009, pp.283-292.
10. The BASF chemical company, “BASOLITE metallic organic framework data sheet”,
June 2008. Available at
"http://www.catalysts.basf.com/Main/adsorbents/basf_adsorbent_technologies/metal_org
anic_frameworks".
11. Mueller et al. “Metal–organic frameworks—prospective industrial applications”, Journal
of Materials Chemistry, 16, 2006, 626-636.
 
 

5 
 

CHAPTER 2. LITERATURE REVIEW
Plastics are widely used in packaging due to their distinct features such as softness,
lightness and transparency [1]. According to Kolybaba et al. [2] three classes of polymeric
materials are currently studied for their applications in packaging and other related fields: 1)
conventional, 2) partially degradable, and 3) completely biodegradable polymers.
Most of the conventional plastics are not biodegradable [3]. Microorganisms present in
the soil or other natural environments are not able to consume portions of the plastic and that
makes them non-biodegradable. This group of materials contains an impenetrable matrix, which
could be reinforced with fillers such as carbon or glass fibers, and in general they are petroleumbased.
The second class of polymeric materials under investigation is partially degradable. They
are of similar origin as conventional plastics but designed with the goal of more rapid
degradation. These materials are produced from petroleum or biomass resources. They can also
be reinforced with different fillers. Once the products are disposed, the microbes partly digest the
macromolecules in the polymer matrix. Once the macromolecules are consumed the weakened
material undergoes further degradation until it is totally degraded.
The final type of polymer, which is getting attention from researchers and industries, is
polymers that are biodegradable and/or compostable. These plastics can be also obtained from
petroleum and/or renewable resources. The renewable resources used to derived these types of
polymeric materials are crops such as corn, sugar beets, and stratch; also, they can be obtained
from petroleum resources with polymers with preferred degradable chemical structures such as
poly(butylene-co-adipate-terephthalate) and poly(-caprolactone). These materials can be

6 
 

completely consumed by microorganism, leaving carbon dioxide, humus, and water as byproducts, or they can be composted under specific conditions [2, 6, and 7].
Due to their lower cost and some higher performance factors like good tensile and tear
strength, good barrier to oxygen, carbon dioxide, water and aroma compounds, and heat
sealability, packaging is dominated by petroleum based polymers such as polyethylene (PE),
polypropylene (PP), polyethylene terephthalate (PET), polystyrene (PS), and poly(vinyl chloride)
(PVC), among others [16]. The United States is the largest producer and holds the largest market
for thermoplastic materials. From 1997 to 2001, the growth in sales of thermoplastics for
packaging materials was 4.2% and that of consumer and institutional application was about
2.0%. Overall increase in the growth rate of thermoplastics across all the markets was 3.0% over
the same period [4, 5].
Despite their appreciable advantages over other types of packaging materials, petroleum
based polymers are made from non-renewable resources, which is an increasing concern for
manufacturers and the public in general. Packaging plastic waste has led to a serious ecological
threat, and they are getting accumulating in landfills. Increase of recycling and recovering of
polymers could reduce the amount of plastics sent to landfills. In the last decade, special
attention has been given to compostable plastics. Therefore, new packaging materials produced
from renewable and non-renewable resources that can be recovered through biodegradation
and/or composting are being developed and studied.
The American Society for Testing of Materials (ASTM) and the International Standards
Organization (ISO) define degradable plastic “as those which undergo a significant change in
chemical structure under specific environmental conditions” [8]. Biodegradable polymers
disposed to the environment undergo degradation from the action of naturally occurring

7 
 

microorganisms such as bacteria, fungi and algae. Some of the plastics can also be degraded by
light (photo degradable), oxidation (oxidatively degradable), and hydrolytic activity
(hydrolytically degradable). Biodegradable plastics are generally broken down within a few
months to 2 years under bioactive conditions (i.e., environments in which microorganisms are
active).
The standard specifications and terminologies required to address the compostability of
plastic materials is defined in ASTM D6400, and the procedure used to test the mineralization of
plastic materials is described in ASTM D5338. ASTM D6400-04 defines compostable plastic as
“a plastic that undergoes degradation by biological processes during composting to yield carbon
dioxide, water, inorganic compounds, and biomass at a rate consistent with other known
compostable materials and leaves no visually distinguishable or toxic residues”. ASTM D5338 is
used to determine the mineralization of the biodegradable plastic under simulated or controlled
composting condition. To pass the disintegration, biodegradation and ecotoxicity requirements
the following criteria should be met: 1. After sieving the final compost, the fraction of plastic
material which has size greater than 2 mm should not be more than 10%, 2. The mineralization
must be greater than 60% for homopolymers and random copolymers or 90% for block/graft
copolymers or blends, 3. The concentration of heavy metals in the materials should be less than
50% as described in 40CFR #503.13. 4. The compost obtained from the degradation of the
polymer should be able to support plant growth for at least two species [9-11].
The growing need for materials that can substitute for conventional plastics has led to the
development of biodegradable plastics for packaging applications. Biodegradable plastics have
already found large application in the field of medicine. For example, poly (lactic acid) (PLA)
has been used in biomedical applications since the 1970s. Due to its higher cost, there was not

8 
 

considered for other applications where cheaper options were already available with
conventional plastics [12].
Figure 2.1 shows the classification of biodegradable polymers according to Averous et al.
The four different classifications of polymers are 1) obtained from biomass, 2) obtained by
microbial production, 3) chemically obtained by using biomass based resources, and 4) obtained
from petroleum resources [13].
Many biodegradable plastics are used in packaging applications, but they always lag
behind conventional plastics due to their cost and some performance factors. As higher volumes
of these polymers are being produced, the cost and the challenges of performance are being
solved. Many of these biodegradable polymers, such as PLA, poly(hydroxy butyrate) (PHB),
aliphatic aromatic co polyesters like poly(butylene adipate-co-terephthalate) (PBAT) and poly(tetramethylene adipate-co-terephthalate) (PTAT), poly (ε-caprolactone) (PCL), poly(butylene
succinate) (PBS), and cellulose based polymers are entering the field of packaging. Among
these, one of the most promising biopolymers is PLA, which is widely used in packaging
applications such as films, thermoformed cups and clamshells, and bottles [4, 14].

9 
 

Biodegradable polymers

Biomass Products
From agroresources Agropolymers

Polysaccharides

Protein, Lipids

Starches:
Wheat Potatoes
Maize, ...

Animals:
Casein
Whey
Colagen/Gelatin

Ligno –
cellulosic
products:Wood
Straws, ...

From microorganism
(obtained by
extraction)

PolyHydroxy
Alkatones (PHA)

Poly(hydroxybutyrate
) (PHB)
Poly(hydroxybutyrate
co hydroxyvalerate)
(PHBV), ... 

From
biotechnology
(conventional
synthesis from
bio-derived

From petrochemical
products
(conventional
synthesis from
monomers)

Polylactides

Polycaprolactones
(PCL)

Polylactic acid
(PLA)

Plant:
Zein
Soya
Gluten

Aliphatic copolyesters
Aromatic copolyesters

Others:
Pectins
Chitosan/Chitin
Gums,...
Figure 2.1 Classification of the biodegradable polymers, (adapted from Averous’ et al. [13])
10 
 

Polyesteramides

Poly(lactic acid), PLA
PLA is not a new material since it was developed in 1932 by Carothers and then later by
Dupont and Ethicon. Nowadays, PLA is made from 100% annually renewable resources like
corn and sugar beets and has the potential for commercial large-scale production and
applications in packaging. It exhibits good transparency, and processability with increased
molecular weight. It can be also recycled or composted. It is a stiff and rigid thermoplastic that
can be totally amorphous or semi-crystalline depending on the stereochemistry of the polymer
backbone. D-lactic acid monomers are incorporated to modify the crystallization behavior to
have certain properties and applications. This modified flexible PLA can be used to make a wide
variety of packaging materials [4, 5, 15, and 16].
PLA can be produced with high molecular weight ranges by different techniques. For
example, NatureWorks LLC uses ring opening polymerization technique followed by a novel
distillation method, whereas Mitsui Toatsu uses the solvent based process with azeotropic
distillation to convert the lactic acid into high molecular weight PLA [4]. It has been reported
that commercial PLA can be prepared by two kinds of methods, viz. direct condensation of lactic
acid and ring opening polymerization (ROP) of the cyclic lactide dimer (Figure 2.2) [15].

11 
 

O

O
OH

H2O
OH

O

H

H CH3
L-Lactic Acid

H CH3
L-PLA
O

H2O

H
O

CH3

OH
n

O

CH3

H
O
L-Lactide

 

Figure 2.2 Polymerization routes to polylactic acid, (adapted from Drumright et al.[15])
However, most of the production is based on the latter method, i.e., ROP. Cargill Dow
developed and patented a low-cost continuous process that is based on the melt method rather
than the solution one and is solvent free with substantial economic and environmental benefits.
In this process, a pre-polymer 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 tin catalyst, the PLA prepolymer (around 1,000 Da)
is depolymerized into a mixture of lactide stereoisomers, which is then purified by vacuum
distillation. Finally, the high molecular weight PLA is produced through the ROP 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 (Figure 2.3) [15]. After the polymerization, any remaining monomer is
removed under vacuum and recycled to the beginning of the process (Figure 2.4) [13].

12 
 

CH3

H

O
OH
H

HO
Lactic Acid
H2O
O

H3C
OH Depolymerization
n

H

OH
n

H CH3
High Molecular Weight
Ring
Opening
Polymerization
O

O

O

O

H CH3
Prepolymer Mn-

O

H

H

HO
O

CH3

Figure 2.3 Schematic of PLA via prepolymer and lactide, adapted from Drumright et.al [15].

Lactic
acid

Lactide
Formation

Distillation

Meso
Lactide

Prepolymer

Distillation

Dextrose
Corn

Unconverted
Polymer
PLA
Polymer

Polymerization

Low D
Lactide
Figure 2.4 Nonsolvent process to prepare polylactic acid, adapted from chemical weekly [17].

13 
 

Environmental footprint of PLA
In recent years, demands for sustainability in products, processes and technology have
increased. Process or products that use large quantities of energy, cause pollution to the
environment, or emit more greenhouse gases are considered to be less sustainable. Green
chemistries are processes that use novel chemical techniques to create products that are less
harmful to the environment and also to make those products commercially viable. A common
established method to quantify the environmental footprint of products or processes is life cycle
assessment (LCA). It looks at all factors of the product or process from the raw material to enduse and disposal. The use of energy, pollution of air and water, as well as the hazards of the
chemicals used to develop the product or processes are assessed against alternate products or
solutions.
According to Cargill Dow LLC, their PLA production process (1) prevents pollution at
the source by using lactic acid produced by natural fermentation process, (2) substitutes annually
renewable materials for petroleum based feedstock, (3) avoids the use of solvents or other
hazardous materials, (4) recycles product and by-product streams and (5) uses catalysts to reduce
energy consumption and to improve yield. In addition, PLA can be either recycled or composted
[4]. Cargill Dow stated that PLA produced by them uses from 20 to 50% less fossil fuels than
conventionally available plastic resins (Figure 2.5). This means that up to 2 to 5 times more PLA
can be produced with the same amount of fossil fuel than the petrochemical-based plastic resins.
The ability to produce the polymer on a favorable cost/performance basis is critical to realize
these benefits. This can be achieved through efficient use of raw materials, reduced use of
energy, and elimination of solvents.

14 
 

CO2 is one of the greenhouse gases that contribute to climate change, and CO2
measurements can serve as indicators of the carbon footprint of materials and processes.
According to Gruber [18], PLA has a very low impact on CO2 emission since the CO2 generated
during PLA biodegradation is balanced by the equal amount of CO2 taken from the atmosphere
during the growth of plant feedstocks. Figure 2.6 shows the CO2 emission contribution to the
environment for common plastic products [4, 18]. In 2006, PLA production emitted about 0.27
kg CO2 eq/kg of PLA (Figure 2.7) and the fossil energy used was 27.2 MJ/kg PLA (Figure 2.8).
This represents about 85% and 50% reduction in CO2 emission and fossil energy use,
respectively, when compared to the PLA production in 2003 [19].
14000

Cellophane

12000

MJ/Kg PLA

10000
8000

Nylon 66

6000
4000

PETAM
HIPS

GPPS

2000
0

PP

PLA Year 1

PLA Year 5
PLA Long Term

-2000

Figure 2.5 MJ/Kg of energy required to produce various polymers, adapted from Gruber [18].
The Cargill Dow products are “PLA year 1, PLA year 5, PLA long tem” (“For interpretation of
the references to color in this and all other figures, the reader is referred to the electronic version
of this thesis.”)
15 
 

160

142

CO2 eq. Kg/ton

140
120

92

100

91

87

77

80

76
57

60

34

40
20

5

0

Figure 2.6 CO2 emissions (kg/ton) resulting from production of various polymers, adapted from
Mohanty et al. [4]. The Cargill Dow products are “PLA year 1, PLA year 5, PLA long term”
(“For interpretation of the references to color in this and all other figures, the reader is referred to
the electronic version of this thesis.”)

2.5

Kg Co2 eq./KgPLA

2

PLA 5

1.5
1
0.5

PLA 6

0
-0.5
PLA/NA

-1

Figure 2.7 Cradle-to-polymer-factory-gate greenhouse gas emissions for PLA year 5 (PLA 5),
PLA year 6 (PLA 6) and PLA long term (PLA NA), adapted from Vink et.al [18]. (“For
interpretation of the references to color in this and all other figures, the reader is referred to the
electronic version of this thesis.”)
16 
 

80
70
24.6

60

MJ/Kg PLA

50

0.7

0.5

Renewable feedstock,
biomass (corn)

24.6

Renewable fuels
(wind, hydro,
biomass)
Non-renewable
feedstock (oil, gas)

40
6.7

30
49.7

0.5

5.5
5.5

20
26.7

10

0.3

16.3

0
PLA5

PLA6

PLA/NA

Figure 2.8 Cradle-to-polymer-factory-gate gross energy use for PLA year 5 (PLA 5), PLA year
6 (PLA 6) and PLA long term (PLA NA), adapted from Vink et.al [18]. (“For interpretation of
the references to color in this and all other figures, the reader is referred to the electronic version
of this thesis.”)
PLA properties
Stereochemistry of PLA is very important in the final polymer’s thermal behavior, and its
mechanical properties and thermo-mechanical performance. PLA can be made from three kinds
of stereo isomers: L-lactide, D-lactide and meso-lactide. PLA has a melting point (Tm) of around
180°C with an enthalpy of 40-50 J/g; however, for the semi-crystalline PLA, depending on the
structure, the range is from 130-230°C and the glass transition temperature (Tg) is about 58°C.
An enthalpy of fusion of 93.1 J/g is reported for the 100% crystalline PLLA and PDLA
homopolymers that have “infinite” crystal thickness [5, 15].

17 
 

Pure crystalline PLLA has an estimated density range of 1.37-1.49 g/cc, and solid
amorphous PLA has a density of about 1.25g/cc. The incorporation of other lactic acid
monomers in this mostly naturally produced PLLA will affect its stereochemistry, crystallization,
and other properties, although there will be little effect on Tg. It is also possible to derive purely
amorphous PLA by incorporating about 15% of meso-lactide monomers. It has been reported
that the optimized crystallization temperature (Tc) is in the range of 105-115ºC [5, 15].
Based on the above PLA chemical structures, it is possible to make various kinds of PLA
resins that can be used to produce blown films, cast films, biaxially oriented films, injection
molded or blow molded articles, etc. By controlling certain process parameters at the molecular
level such as branching, molecular weight distribution (MWD), D-isomer content and branching
introduction and by incorporating the L-, D- and meso lactide isomers at various levels in the
PLA back bone, PLA can be tailored for specific applications. PLA has excellent gloss and
transparency and the tensile properties are similar to PET. PLA provides a good barrier for
aromas and flavors, low temperature sealability, and good crease retention and crimp properties.
These make PLA a good choice as a packaging material. Table 2.1 provides some experimental
data for some properties of PLA [1].

18 
 

Table 2.1 Physical properties of PLA, adapted from Siracusa et al. [1]
Experimental Data
Tg(ºC)

PLA
62.1±0.7

Tm(ºC)

150.2±0.5

Percent crystallinity (Xc)
Oxygen transmission rate (OTR)
a
(cc/m2 day)
Oxygen permeability rate (OPC)
b
(kg m m-2s-1Pa-1)
Water vapour transmission rate (WVTR)
a
(g m-2 day-1)
Water vapour permeability rate(WVPC)
c
(kg m m-2s-1Pa-1)

29.0±0.5

a

56.33±0.12
1.21E-18±0.07E-18
15.30±0.04
1.89E-14±0.08E-14

Thickness of 20.0±0.2 mils

b

OPC= OTR x l/ΔP, where l is the thickness in m and ΔP is the difference in
oxygen partial pressure across the film.
c
WVPC= WVTR x l/ΔP, where l is the thickness in m and ΔP is the
difference in water vapour partial pressure across the film.
PLA possesses intermediate water vapor barrier properties and is not as affected by RH
as in the case of nylon. Combined with its relatively intermediate oxygen barrier properties, this
makes it one of the favorable materials for food packaging. It was found that the O2:CO2
permeability ratio of PLA is in the range of 1:7 to 1:12, which makes it suitable for food
packaging where high respiration is needed [14, 16].
The mechanical properties of PLA are comparable to those of conventional polymers
such as PE and PS. PLA has better barrier properties than PS but lower than PET. The physical
properties of PLA are similar to those of PS but not as good as those of PET [16, 21].
Although PLA has properties comparable to those of conventional polymers, its brittle
nature dramatically reduces its application in packaging. Toughening of PLA can be achieved
through plasticization, incorporation of its own isomers during polymerization, or blending PLA
19 
 

with tough polymers. Many studies are underway to improve the toughness of PLA [14]. Many
combinations of blends of PLA with nanocomposites materials have investigated in order to
increase the mechanical, thermo-physical, and barrier properties of the PLA films [22].
Polymeric biocomposites are materials formed by a biodegradable matrix (resin) of
synthetic or natural origin and a reinforcing phase. PLA biocomposites have been used for
medical applications and in the field of structural plastics. In biomaterials, each and every
compound of the composite should be biocompatible. Also, the interface between compounds
should not be affected by the body environment. Normally, biocomposite materials can be
classified into three groups: 1) particulate composites, 2) fibrous composites, and 3) porous
composites [23].
Although PLA has undergone remarkable developments for its application in medicalbased devices, there are still demands to increase the mechanical performance of medical
implants and also their bioactivity. This is normally done by optimizing the amount of fillers
such as zirconia, magnesium oxide, hydroxyapatite, and carbon fibers in selected groups of
biodegradable polymer matrices [23-25]. For example, PLLA composite with 10 % w/w of filler
increases the stiffness of the material but decreases the tensile strength of the material by 30%
[26]. In the case of PLLA-clay composites, the Young’s modulus of the material increases with
increased clay addition levels at filler content below 10 % w/w [27].
Huda et al. [31] compared the properties of PLA composites made with reinforcing glass
fiber to those made with recycled newspaper cellulose fiber by using a twin screw extruder and
an injection molding system. The mechanical and thermo-physical properties of the
PLA/recycled newspaper composite were similar to those of PLA/glass fiber composite. This

20 
 

study suggests that PLA/recycled newspaper composites can be potentially useful technology to
replace PLA/glass composites when very high load bearing requirements are needed.
In addition to macro-scale particles, PLA has been compounded with nano-scale particles
to improve the mechanical, barrier and thermal properties. Some of the nano-particles include
layered silicates, carbon nanotube, hydroxyapatite, layered titanate, and aluminum hydroxide
[29, 30]. According to Thellen et al [31], Montmorillonite (MMT)-PLA composite has a 50%
increase in the oxygen barrier properties and a 20% increase in the storage modulus when
compared to neat PLA.
Porous colloidal particles have attracted renewed interest, from both fundamental and
applied research prespectives. The large internal surface area and adsorbent potential of porous
particles have led to their widespread application in diverse fields, including sensing, catalysis,
and drug delivery. These compounds include zeolite, activated carbon, silica and metal organic
framework (MOF). Porous polymeric membranes are also used in membrane separation process
of gases and liquid due to its adsorption capacity [33].
The accumulation of atoms and molecules on the surface of a material is called
adsorption, which is different from absorption where the substance diffuses to form a solution.
During adsorption, the atoms, which are on the material’s surface, are not fully covered by their
closest neighbors, which helps to attract other atoms or molecules and thus the surface energy
can be decreased [34].
Adsorbates can bond to the surface of the material in a variety of ways. These include: 1)
ontop site, in which the adsorbate forms a single bond with only one atom beneath it; 2) bridging
site, in which the adsorbate forms two bonds between the two surface atoms; and 3) hollow site,
in which the adsorbate bonds with three or more atoms. Depending on the nature of the bonding,

21 
 

the adsorption process can be classified into physical adsorption or physisorption (Van der Waals
bonding) and chemical adsorption or chemisorption (covalent bonding). The materials used to
promote adsorption are called adsorbents [34].
Adsorbents are usually pellets, rods, moldings, or monoliths having 0.5, 10 mm, etc.
hydrodynamic diameter. Due its greater abrasion resistance, thermal stability combined with tiny
pore size the adsorbents exhibit increased surface area, which in turn increases its capacity to
adsorb solvents and gases. The adsorbents should also have a distinct pore size to make them
good candidates for transport of gaseous vapor [35].
The industrial adsorbents are classified into three major categories: 1) compounds based
on oxygen, which are polar and hydrophilic (e.g. silicia gel and zeolites); 2) compounds based on
carbons, which are hydrophobic and non-polar (e.g. activated carbon and graphite); and 3)
compounds which are polymer-based, having polar or a-polar functional groups in the polymer
matrix which are porous [35]. Adsorbents are used in a variety of fields including medical,
petrochemical industry, nuclear industry, agriculture, animal welfare, heating and refrigeration,
detergents, construction, gemstones, aquarium keeping, and space hardware testing. The most
commonly used adsorbents in the science and technology field are zeolites, activated carbon,
alumina, and silica gel [38].
Zeolites are microporous crystalline aluminum silicate minerals of alkali or alkali earth
metals such as sodium, potassium, and calcium. Zeolites are commercially used as adsorbents
and belong to the family of microporous solids known as "molecular sieves”. The primary
building blocks of zeolites are the tetrahedral structural units of silicon and aluminum oxide
(SiO4 and AlO4). The tetrahedral structure of the zeolites can be assembled in different ways,
making it possible to fabricate some 800 crystalline structures. Substituting other elements in
22 
 

place of Al and Si in the framework of zeolites can result in numerous varieties of molecular
sieves. The main interest of the petrochemical industry in zeolite materials is their 12-membered
oxygen rings with a diameter of 8.1Å, which will prohibit large hydrocarbon molecules from
penetrating. Zeolites are used as catalysts in the petrochemical industry and other applications
include molecular separation, water purification, and active packaging [36-40].
Another common adsorbent material is activated carbon, also called activated charcoal or
activated coal. It is a form of carbon that is processed to obtain large micropore and mesopore
volumes and a high surface area. One gram of activated carbon has a surface area of about 500
m2/g as measured by nitrogen adsorption. The pore size of activated carbon varies from
Angstrom to micrometer, which makes activated carbon useful for numerous applications.
Activated carbons with micropores have found application in gas adsorption, and those with
mesopore structures are used for adsorption of larger molecules. Other applications of activated
carbon include gas purification, solvent recovery, and wastewater treatment [38, 41].
Activated alumina is crystalline amphoteric oxide of aluminum, with the chemical
formula Al2O3. It is widely used as a desiccant due to its large capacity to store water. The
geometry of the pores and the surface chemistry can be altered by treating with acid or alkaline
solutions and also by controlled thermal treatment. This makes activated alumina more useful
than silica gel, so it is used as a sorbent material. These materials are also used as oxide ceramics
due to their excellent hardness, corrosion resistance, and ease of processing [38, 42].
Silica gel as a drying agent is extensively used in dehumidification processes because of
its high moisture adsorption capacity and large surface area. It can store water up to 40% of its
weight, and it is easier to regenerate than zeolites. To regenerate, zeolite requires a temperature
of 350°C, but silica gel requires only 150°C. Its surface can be modified by grafting with a
23 
 

monomolecular layer of organic ligand. Silica gels thus modified are being increasingly used for
chromatography applications [38, 43].
Adsorbents are also being used to modify polymer properties in order to increase the
adsorbent capacity for water and other compounds such as gases, vapor, and liquids for use as
functional membranes in industrial applications. In recent years, metal organic frameworks
(MOF) have been widely used in catalysis, gas separation and storage. Compared to zeolites,
carbon, alumina and silica gel the MOF provides more flexibility to control its design and
functionality [44, 45].
Metal Organic Frameworks (MOF)
“Metallic Organic Frameworks (MOFs) are crystalline compounds that contain metal
ions or clusters coordinated to rigid organic molecules to form one-, two-, or three- dimensional
structures that can be porous” [47]. A general comparison of MOFs with other available
adsorbent materials is found in Table 2.2. [46].
Table 2.2 MOF Performance Comparison, adapted from BASOLITE MOF Datasheet [46]
Current Technology
Zeolite

Silica
Alumina
Activated Carbon

MOF performance comparison
MOF have close to an order of magnitude higher surface area
and no dead volume, high uptake capacity, low desorption
energy, and structural variety. Metal atoms are atomically
dispersed for catalytic activity.
MOF have significantly higher surface areas and high uptake
capacity.
Hydrophilic MOF are available with more than one order of
magnitude higher surface area, low desorption energy,
reversibility and stability against water.
An organophilic MOF (Z1200) is available with even higher
surface area, can be reactivated, and is stable at high
temperatures. Custom tailored structures possible in the future.

The surface area of MOFs is close to one order of magnitude higher than that of zeolites
and activated carbon. [46] Besides the increased surface, they also have open internal structures
24 
 

and long-range crystallinity. MOFs with high surface areas and porosity to have promising
properties for high adsorption capacities of various gases. HKUST-1 (copper benzene
tricarboxylate) was first reported by Williams et al., [48] and subsequently studied by numerous
research groups. MOF contain metal sites in their walls where coordination to a gas molecule can
take place [49].
According to Muller et al. [47], the storage of transportation fluids using porous
compounds can be a useful technology for the automobile industry. MOF’s increased surface
area combined with low energy adsorption capacity of gas increases the storage capacity of the
cylinder filled with MOF roughly twice when compared to standard cylinders. MOFs are made
of two important components: a linker (organic molecule) and a metal ion (in some cases a
cluster of metal ions). Mono-, di-, or tri- ligands usually make up the organic units. [45] Based
on the metal and linker the properties and structure of MOFs will be different. For example, the
coordination preference of different metals will determine the geometry of the pores and the
number of ligands that can be bound to the metal and orientation. Table 2.3 lists the common
ligands that have been used in MOFs. [50]

25 
 

Table 2.3 Common ligands (linkers) in MOFs, adapted from David et.al [50]
Common
name

IUPAC name

Oxalic acid

ethanedioic
acid

Malonic acid

Succinic
acid

Chemical formula

Structural formula
O

OH

HO
O

O

HOOC-COOH

propanedioic
acid

HOOC-(CH2)-COOH

butanedioic
acid

HOOC-(CH2)2-COOH

O

HO
O

OH
OH

HO
O

Glutaric acid

Phthalic acid

Isophthalic
acid

Terephthalic
acid

Citric Acid

pentanedioic
acid
benzene-1,2dicarboxylic
acid
o-phthalic
acid
benzene-1,3dicarboxylic
acid
m-phthalic
acid
benzene-1,4dicarboxylic
acid
p-phthalic
acid
2-Hydroxy1,2,3propanetricarb
oxylic acid

O
HO

OH
HO

O

OH

C6H4(COOH)2

O

O
C6H4(COOH)2

C6H4(COOH)2

O

HO

OH

O

OH

HO

O

O

(HOOC)CH2C(OH)(COOH)CH
2(COOH)

 
 

26 
 

O

HOOC-(CH2)3-COOH

O
HO

OH
O
OH

OH

Table 2.3 Cont’d

O
Trimesic
acid

benzene-1,3,5tricarboxylic
acid

OH

C9H6O6

HO

O
O

OH
H
N

1,2,3Triazole

1H-1,2,3triazole

N

C2H3N3

N

H
N
pyrrodiazole

1H-1,2,4triazole

C2H3N3

N
N

HO

O

HO

Squaric acid

3,4Dihydroxy-3cyclobutene1,2-dione

O

C4H2O4

MOF and zeolites are synthesized by growing crystals slowly from metal precursors such
as metal nitrates and organic ligands. This type of synthesis mechanism is called the
hydrothermal or solvothermal technique. The structure directing compounds used to formulate
zeolites are also used for the formulation of MOF. The solvents water and N, Ndiethylformamide have been used to produce MOF for gas storage purposes. This type of
synthesis allows metal sites to expose completely, which allows hydrogen to bind to the sites
[53].

27 
 

A typical MOF synthesis flowchart, indicating the different steps of MOF preparation, as
well as recycling of the solvent and further processing of the dried powders, is given in Figure
2.9. A large number of novel MOF structures have been generated over the past decade via to the
steps shown in Figure 9. Some examples of the MOF synthesized are MOF-2, MOF-5, IRMOF8, and Cu-EMOF. These MOFs have already found applications in areas such as magnetism,
catalysis, separations, and gas storage, placing them among the most interesting classes of solidstate materials. [54]
Solution
Formic acid,
Acetic acid,...

Solution
Mg-Source

Solution
Trimesic, ...
acid

Electrolysis

Precipitation, Crystallization

Filtration, Drying

Copper –
metal
Electrode

Sol.
Recycle

Filtration, Drying

Processing, Shaping

Processing, Shaping

Figure 2.9 Simplified flow diagram of industrial metal-organic framework synthesis procedures
via solvothermal (Mg –MOF) and electrochemical (Cu-MOF) routes, adapted from Mueller et al.
[54]
MOF scale up studies have demonstrated that microwaves can be used to nucleate MOF
crystals [55, 56]. Post-synthetic modification is a key to producing advanced MOF materials
suitable for sophisticated and specialized applications. The ability to modify the physical
environment of pores and cavities of MOFs, allows tuning the interaction with guest species.
This modification serves as a route for tailoring the chemical reactivity and stability of the
28 
 

frameworks. The potential advantages offered by post-synthetic modification are: 1) it increases
the possibility to include a variety of functional groups, which would have not been possible due
to MOF synthesis conditions; 2) it is easy to purify and isolate the modified product because the
chemical derivatization is performed directly on the crystalline solid itself; 3) the MOF structures
can be modified using different reagents, thereby generating a wide variety of topologically
identical, but functionally diverse MOFs; and 4) it is possible to fine-tune and optimize the
properties of MOFs by controlling the type of substituent and the degree of modification which
permits multiple functional units to be introduced into a single framework in a combined manner
[57].
MOFs have already found application in hydrogen storage because of their higher
surface areas and chemically tunable structures [58]. Hydrogen molecules are stored in a MOF
by adsorbing to its surface. Since MOFs are free of dead volume there is almost no loss of
storage capacity [45]. Hydrogen binds to surfaces through strong chemical associations
(chemisorption) or by weak dispersive interactions (physisorption) [59]. The latter depends on
the surface area; the greater the surface area the higher the gas uptake. Thus, MOFs with higher
surface area are potential candidates for hydrogen storage applications. In the case of automotive
applications the temperature limits the uptake of hydrogen. But the diverse functionality of
MOFs facilitates enhancing hydrogen storage by tailoring its chemical structure. In this case a
MOF with a complex of platinum and activated carbon increase the storage capacity [58, 60].
Table 2.4 provides a list of MOFs that have been proposed to be most suitable for hydrogen
storage.

29 
 

Table 2.4 MOFs used for hydrogen storage, adapted from references [61-64].
Name of MOF
Zn4O(BTB)2, where BTB =
1,3,5-benzenetribenzoate
(MOF-177)
Zn4O(BDC)3, where BDC=
1,4-benzenedicarboxylate
(MOF-5)

Mn3[(Mn4Cl)3(BTT)8]2,
where BTT = benzene-1,3,5tris(1H-tetrazole)
Cu3(BTC)2(H2O)3, where
BTC = 1,3,5benzenetricarboxylic acid

Properties
MOF-177 with larger pore size compresses the hydrogen in the
holes rather than adsorbing it on the surface. This property
increases the gravimetric uptake but reduces the volumetric
density when compared to MOF-5.
MOF – 5 attracted a great deal of attention from researchers
and scientist due to their unique partial charges on the surface
of the MOF. This provides a means to strengthen the hydrogen
binding through dipole-induced intermolecular attraction. On
the downside MOF-5 has inferior performance at room
temperature.
This MOF has increased hydrogen adsorption due to its open
metal coordination site which in turn increases its performance
at 298 K.  
This MOF received a great deal of attention due to its paddle
2+
wheel complex from Cu and 1,3,5 benzenetricarboxylic acid.
This paddle wheel complex gives excellent control over its
geometry and flexibility.

The general trend in MOFs used for gas storage is that the greater the surface area, the
more gas the MOF can store in its pores, due to increased micropore volume and inherently low
bulk density. In Table 2.5, the surface areas of different industrial MOFs in comparison to
zeolite, activated carbon, alumina, and silica gel are presented.

30 
 

Table 2.5 Surface area of different industrial MOFs and other adsorbents, adapted from Muller
et.al [45] and others [65-67]
Materials
Basolite A100 (Al-MOF)- Al-terephthalate
Basolite C300 (Cu-BTC-MOF) - Cu-benzene-1,3,5tricarboxylate
Basolite F300 (Fe-EMOF) - Fe-benzene-1,3,5tricarboxylate
Basolite Z1200 (Zn-EZIF) - Zn-2-methylimidazole
Basolite M050 (Mg-MOF) - Mg-formate
Zeolite
Alumina
Activated Carbon
Silica gel

2 -1

Langmuir surface area (m g )
1100–1500
1500–2100
1300–1600
1300–1800
400–600
300–800
110-470
250-950
400-600

Other applications of MOF include, gas purification, gas separation, and heterogeneous
catalysis. The open metal site characteristics of MOF give it the ability to attract electron-rich,
odor-generating molecules like alcohol, water, phospines, etc. MOF separates gas molecules
according to their size or kinetic diameter. In recent studies the separation of krypton and xenon
was done using MOF adsorbents. In the case of gas storage, MOFs can store carbon dioxide,
carbon monoxide, methane, etc. Also, the absence of dead volume in MOF increases the
volumetric storage of gas molecules compared to other adsorbents [45].
The adsorption and release of gases in the right amount is important for extending the
shelf life of a product in the case of medical/food packaging. PLA is the most common
biopolymer used for packaging fresh food due to its excellent barrier to flavor and aroma
compounds and selective barrier properties. Because of the large variety and variable properties
of fresh food/medicines, no single biobased packaging material can be said to be ideal for use
with all products. In order to achieve satisfactory performance and also to utilize the extreme
surface area of MOFs, PLA could be melt compounded with MOFs to create highly permeable
porous patches and enhance or create a new functional membrane.
31 
 

REFERENCES

32 
 

REFERENCES
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38 
 

CHAPTER 3. MATERIALS AND METHODS
3.1 Materials
Poly(L-lactic acid), PLA, (94% L-lactide) pellets were supplied by Natureworks LLC
(Blair, NE, USA) under the trade name of Ingeo Biopolymers (PLA 4042D). The density of
3

PLLA was 1240 kg/m , as reported by the company. The pellets were dried at 80°C under
vacuum for at least 4 h prior to processing and then packed in air tight zipper bags.
 

Metallic organic framework, MOF, compounds were manufactured by BASF (Florham
Park, NJ, USA) and procured from Sigma-Aldrich (St Louis, MO, USA) under the trade name of
Basolite

TM

C-300 (copper benzene-1,3,5-tricarboxylate- (C18H6Cu3O12)), with a surface area
2

between 1,500 and 2,000 m /g, particle size distribution 15.96 µm, and bulk density of 0.35 g/cc
3

TM

(350 kg/m ) (CAS No.51937-85-0). The Basolite

C300 was reactivated at 200°C for 24 h

under vacuum (25 mm Hg) before processing, and then it was packed in airtight glass vials.
3.2 Equipment and Preparation:
3.2.1 Twin screw extruder
TM

PLA was extruded in batches of 10 g. Once the PLA resin was dried and the Basolite

C-300 was activated, approximately 1, 3 and 5% wt/wt of MOF was weighed in a Discovery
precision balance (OHAUS, Pine Brook, NJ, USA) and added to 10 g of PLA, mixed thoroughly,
and placed in air tight glass bottles. After preparing the samples, the PLA with and without
MOFs was melt compounded in a DSM Micro 15 cc extruder-compounder (DSM Research,
Geleen, The Netherlands) having a vertical conical co-rotating twin screw extruding unit with
screw length of 150 mm, L/D of 18 and barrel volume of 15 cc. Various kinds of samples such as
39 
 

DMA bars, izod bars, tensile, flexural, and disc specimens were prepared by taking molten PLA
in a preheated transfer cylinder from the extruder and then injecting them into a preheated mold
that was placed in an injection molding unit using an injection pressure of about 120 psi. The
optimized processing conditions for the extruder and injection molder are given in Table 3.1.

Table 3.1 Optimized parameters for extrusion in the DSM micro extruder
Variables

Extruder

Temperature, °C (Top, Middle, Bottom)

190

Screw speed, rpm
Cycle time, min
Melt temperature, °C
Transfer cylinder temperature, °C
Pressure, psi
Mold temperature, °C
Residence time, sec

Injection
Molder

100
5
185
195
150
30
20

3.2.2 Metallic organic framework quantification
The amount of MOF in the 1, 3 and 5% wt/wt of the extruded composite was analyzed by
determining the amount of copper in the MOF powder (control), and in the extruded composite
(1, 3 and 5%). The amount of copper in the extruded composite was correlated with the amount
of copper in the control to find the final percentage of MOF in the extruded composite samples.
The copper content in the MOF was determined by digesting the samples by microwave by using
a Microwave Drying System (Multiwave 3000, Anton Paar, Graz, Austria). A representative
sample of up to 0.5 g was extracted and dissolved in 10 mL concentrated nitric acid, or
alternatively, 9 mL concentrated nitric acid and 3 mL concentrated hydrochloric acid for 10
minutes in the fluorocarbon digestion vessel and heated in a microwave at high temperature and
pressure. After cooling, the vessel contents were filtered, centrifuged, or allowed to settle and
40 
 

then diluted to volume and analyzed by Induction Coupled Plasma – Mass Spectrophotometry
(ICP-MS), ELAN DRC Plus (Perkin Elmer, Waltham, MA, USA). Tests were conducted in
triplicate by the A&L Great Lakes Laboratories Inc. (Fort Wayne, IN, USA). In the ICP-MS, the
samples were converted into fine aerosol droplets by a nebulizer and spray chamber system and
injected into the argon plasma unit, which was then injected into the ICP. The temperature of the
hot plasma was 6000 K, since most elements in the periodic table are more than 90% ionized at
this temperature. The positive ions were then sent to a mass spectrometer where the ion beam is
focused by electrostatic lenses and directed into the quadrupole mass filter. Here the positive
ions are separated based on their mass-to-charge ratio. (The quadrupole mass filter analyzes
singly charged ions from 1 to 300 amu.)

3.2.3 Film preparation
A compression molding machine Model-M, Carver Laboratory Press (Carver Inc.,
Wabash, IN, USA) was used to prepare films from the disc samples obtained from the
microcompounder twin screw extruder. Films were compressed at 165 C, with a residence time
of 5 to 6 min, and a pressure of 5000 lb. The disc samples were placed between Teflon sheets
(Small Parts Inc., FL, USA) while pressing to avoid the molten plastic sticking to the metal
plates or molds.

3.2.4 Surface area of the MOF
The surface area and pore size of the MOF was analyzed using an ASAP 2010
(Micromeritics, Norcross, GA, USA) gas analyzer. An empty sample tube along with the filler
rod fitted with stopper was weighed accurately using a precision balance (OHAUS, Pine Brook,

41 
 

NJ, USA) with the help of a weighing support. About 0.3 to 0.5 g MOF was transferred to the
sample tube along with the filler rod and stopper. The MOF in the sample tube was heated to
about to 200 C for 48 h in the degassing port of the equipment to remove any adsorbed foreign
molecules. The sample tube was then transferred to the analyzing port where a controlled dose of
nitrogen gas was introduced, and the gas was adsorbed or desorbed. The MOF in the sample tube
was placed in a vacuum chamber at a constant temperature of -195.6 °C (liquid nitrogen), and
subjected to a wide range of pressures (7 to 700 mm Hg) to generate adsorption and desorption
isotherms. The amounts of gas molecules adsorbed or desorbed were determined by the pressure
variations of the gas molecules by the MOF (the adsorbent). Knowing the area occupied by one
adsorbate molecule, σ (for example, σ= 16.2 Å for nitrogen), and using an adsorption model, the
total surface area of the material was determined. In this case, the BET (Bruner, Emmer and
Teller) model [1] was used to determine the surface area of the MOF, as expressed by equation
3.1:
P
1
c 1 P


n( Po  P ) cnm cnm Po

3.1

where P, Po, c, n, nm are the adsorption pressure, the saturation vapor pressure, a constant, the
amount adsorbed (moles per gram of adsorbent) at the relative pressure P/Po, and the monolayer
capacity (moles of molecules needed to make a monolayer coverage on the surface of one gram
of adsorbent), respectively. Through the slope and intercept of a plot of P/[n(Po-P)] against
(P/Po), nm can be resolved. Then, the specific surface area, S, can then be derived by the
equation 3.2:

S  NAnm

42 
 

3.2

where, NA is Avogadro’s number. The determination of pore size and pore size distribution of
the MOF can be determined from the adsorption/desorption isotherm using an assessment model,
suitable for the shape and structure of the pores. In this case the pore size was determined using
the isotherm from the BJH (Barret, Joyner and Halenda) equation [3]
3.2.5 Molecular Weight
The molecular weights of the PLA resin and the extruded samples (PLA and PLA with
MOF (1, 3 and 5%)) were analyzed by using a gel permeation chromatograph (GPC) equipped
with a Waters 1515 isocratic pump, a Waters 717 autosampler, a series of Waters Styragel
columns (HR4, HR3, and HR 2), and a Waters 2414 refractive index detector interface with
Water Breeze software (Waters Inc., Milford, MA, USA). Samples of 15 to 20 mg were
dissolved in 10 ml of THF and heated to about 50 C for about 2 h in order to dissolve the
polymer in THF. The mixture was filtered using a 0.45 μm syringe filter, and a 100 μl sample
was used to determine the molecular weight and molecular weight distribution. Polystyrene
3

6

standards with molecular weight in the range of 1.31x10 to 3.64x10 Da were used for
rd

calibrating the GPC. A calibration curve was calculated by using a 3 degree polynomial
equation. The number average molecular weight (Mn), weight average molecular weight (Mw),
and polydispersity index (PI) of PLA were measured. The absolute Mn and Mw were calculated
by using the Mark-Houwink relation, with a= 0.736 and k=0.000174 (µl/s) shown in equation
3.3.

  kM a
where  =instrinic viscosity, M=molecular weight, a and k=constants
43 
 

3.3

3.2.6 Contact Angle
The surface properties of the PLA and MOF were analyzed using a goniometer (RameHart. Inc, Mountain Lakes, NJ, USA) by using the sessile drop method. The sample preparation
methods for the PLA and MOF were as follows.
PLA: The contact angles of the PLA samples were measured in the disc samples produced from
the twin screw extruder. The samples were dried at 80 ºC for 4 h. The contact angle of the PLA
with water and methylene iodide was measured. At least 8 measurements on different samples
were conducted for each liquid.
MOF: To measure the contact angle of the MOF, a colloidal suspension of 2% wt/vol MOF in
de-ionized water was prepared. The colloid was mixed thoroughly with a magnetic stirrer for at
least 5 hr at 23°C and 800 rpm. After the colloid was prepared, it was evenly distributed on a
2

glass microscope plate (1 x 3 in ) using a pipette. Both the pipette and the microscopic glass
plate were previously cleaned with acetone and deionized water to remove impurities. Once the
plates were coated with MOF, they were dried in a laminar flow for 2 d at 23 ºC. After this step,
the microscopic glass plates were dried at 200 ºC for 24 hr under vacuum (25 mmHg). Glass
slides were placed horizontally during the drying process. The contact angle was measured using
the goniometer previously described, with water and methylene iodide. At least 8 measurements
were done for each liquid.

44 
 

3.2.7 Hansen’s Solubility Parameters
To determine the affinity of PLA with MOF, the Hansen’s solubility parameters
methodology was used [4]. Specifically, the three Hansen’s parameters were determined:


 d , the energy from dispersion bonds



 p , the energy from polar bonds



 h , the energy from hydrogen bonds
These three parameters can be treated as coordinates for a point in three dimensions known

as the Hansen space. The nearer two molecules are in this three-dimensional space, the more
likely they are to dissolve into each other. To determine if the parameters of two molecules
(usually a solvent and a polymer) are within range of solubility a value called the interaction
radius (R0) is given to the substance being dissolved. This value determines the radius of the
sphere in the Hansen space, with its center is determined by the three Hansen parameters. To
calculate the distance (Ra) between the Hansen parameters in Hansen space, equation 3.4 was
used:
3.4

Ra 2  4( d 2   d1)2  ( p 2   p1)2  ( h2   h1)2

where the subscripts 1 and 2 indicate the dispersive, polar and hydrogen bond energy of the two
materials under test.
Combining Equation 3.5 with the interaction radius gives the relative energy difference (RED) of
the system, which can be calculated by:
RED  Ra / Ro
A general guideline is:
RED < 1 the molecules are alike and will dissolve

45 
 

3.5

RED = 1 the system will partially dissolve
RED > 1 the system will not dissolve 
To determine the Hansen’s Solubility Parameters for PLA and MOF, they were dissolved in
a number of solvents and the mixture was subjected to 1 and 15 min sonification. After 1 and 15
min the samples were visually observed and a number on the scale of 1 to 6 was given based on
the dispersion of the compound in the solvent as shown in Table 3.2
The solvents used for dissolving the PLA and MOF samples are listed in Table 3.3, with their
dispersion, polar, and hydrogen bonding forces.
Table 3.2 Scoring scale for determining the Hansen’s solubility parameters
Score
1
2
3
4
5
6

Comments
Easily dispersed, very stable dispersion
Takes a bit of effort to disperse, reasonably stable
Disperses but fairly soon starts to settle
Pretty reluctant to disperse
Some hint of dispersal
Just sits and laughs at the solvent

46 
 

Table 3.3 Solvents used for determining the Hansen’s solubility parameters

Solvent
Dichloro methane
Toluene
Tetra chloro ethane
Methyl Ethyl Ketone
Cyclohexane
Diethylene Glycol
Chloroform
Acetone
THF
Acetonitrile
Dimethyl Sulfoxide
Ethyl Acetate
Methanol
Phenol
DMF
Hexane
Ethanol
Gamma Butyro Lactone

IUPAC Name & CAS. No.
Dichloromethane (75-09-2)
Methylbenzene (108-88-3)
1,1,2,2-Tetrachlorethane
(79-34-5)
Butan-2-one (78-93-3)
Cyclohexane (110-82-7)
(2-hydroxyethoxy)ethan-2ol
(111-46-6)
Chloroform (67-66-3)
Propanone (67-64-1)
Oxacyclopentane (105-999)
Acetonitrile (75-05-8)
Dimethyl Sulfoxide (67-685)
Ethyl Acetate (141-78-6)
Methanol (67-56-1)
Hydroxybenzene (108-95-2)
N,N-dimethylmethanamide
(68-12-2)
Hexane (110-54-3)
Ethanol (64-17-5)
Dihydrofuran-2(3H)-one
(96-48-0)

D
P
H
2
2
2
(mJ/m ) (mJ/m ) (mJ/m )
18.2
6.3
6.1
18
1.4
2
18

5

0

16
16.8

9
0

5.1
0.2

16.6

12

20.7

17.8
15.5

3.1
10.4

5.7
7

16.8

5.7

8

15.3

18

6.1

18.4

16.4

10.2

15.8
15.1
17.4

5.3
12.3
4.1

7.2
22.3
13.5

17.4

13.7

11.3

15.8

8.8

19.4

19

16.6

7.4

3.2.8 Scanning Electron Microscopy (SEM)
The morphology of the MOF powders and impact fracture surfaces of PLA and
PLA/MOF composites were observed using a JOEL JSM-6400 (Joel Ltd., Tokyo, Japan)
scanning electron microscope equipped with a LaB6 gun. Before collecting the micrographs, the
powders and fractured surfaces of the composites were coated with a thin layer of gold using an

47 
 

Emscope SC500 sputter coater (Emscope Laboratories Ltd, Ashford, UK). Micrographs were
collected from the secondary electron images obtained with a beam energy of 15 kV.

3.2.9 FTIR Spectrophotometer
The IR spectroscopic analysis of pure PLA and of PLA with 1, 3, and 5 wt% of MOF was
done using an IR Prestige-21 spectrometer (Shimadzu Corporation, Tokyo, Japan). A
-1

background scan was done between wavenumbers of 4000 and 550 cm

by keeping the

resolution at 4 and the number of scans at 40. After the background scan, film samples were
placed in the sample holder and scanned at the same rate as the background scan. Three
measurements were taken of each sample.

3.2.10 Ultraviolet/Visible Spectroscopy
The ultraviolet/visible spectroscopic analysis of the PLA and PLA/MOF film samples
was obtained using a Perkin-Elmer Lambda 25 UV/Visible spectrometer (Waltham, MA, USA).
A PLA blank was first placed in the UV/VIS spectrometer and scanned in the range of 190 to
800 nm. After scanning of the PLA blank, the film samples were scanned in the same range.
Three measurements were obtained for each sample.
 

3.2.11 Colorimetry
The color of the film samples was analyzed using a Labscan XE colorimeter (Hunter
Laboratories, Reston, VA, USA). The CIE L*a*b* system was used to characterize the color of
the samples. The CIELAB system can be visualized as a cylindrical coordinate system in which
the axis of the cylinder is the lightness variable L*, ranging from 0 to 100%, and the radii are the
48 
 

chromaticity variables a* and b*. Variable a* changes from green (negative) to red (positive)
and variable b* changes from blue (negative) to yellow (positive). Three measurements were
taken of each sample. ΔE (distance between two colors) was calculated using equation 3.6:

E  L2  a 2  b2      

3.6

where, ΔL = L Sample - L Standard, Δa = a Sample - a Standard and Δb = b Sample - b
Standard.

3.2.12 Dynamic mechanical analyzer (DMA)
A dynamic mechanical analyzer DMA Q800 (TA instruments, New Castle, DE, USA)
was used to measure the thermo-mechanical properties of PLA and PLA/MOF composites. The
heat deflection temperature (HDT) of the samples was measured according to ASTM D5023.
The DSM molded rectangular specimens were used for the experiments. Three point bending
mode was used at a controlled force of 0.25-0.28 N to measure the HDT, which was measured at
0.2% percent of strain while heating from room temperature to 100ºC under a constant load. The
preload force was calculated by using equation 3.7:
Preload Force 

2 2
t w  
3l

3.7

where, l is the span length of the specimen (50 mm), σ is the stress (66 psi), t is the thickness,
and w is the width of the specimen. At least three replicates were tested for each treatment.
The loss modulus, storage modulus and tan delta were measured according to the ASTM
D4065 standard using the dual cantilever mode at an amplitude of 15μm and frequency of 1 Hz.
The specimens were heated from 0 to 100 °C at the rate of 5 °C/min under the DMA-multi-

49 
 

frequency strain. The glass transition temperature was determined from the storage modulus, loss
modulus and tan delta. At least three replicates were tested for each treatment.

3.2.13 Izod Impact Tester
A monitor Izod impact tester TMI 43-02-01 (Testing Machines Inc., Ronkonkoma, NY,
USA) was used with a l-1b pendulum to measure the notched izod impact strength of samples at
ambient conditions according to the ASTM D256 standard. A TMI notching cutter (model – 2205) was used to notch the samples as per the standard. At least five specimens were tested for
each treatment.

3.2.14 Tensile test
A universal testing machine UTS SFM – 20 (United Calibration Corporation, Huntington
Beach, CA, USA) was used to measure the tensile properties of the PLA and PLA/MOF samples
(i.e., % elongation at break, % elongation at strain, tensile strength, and the modulus of
elasticity.) The tensile testing was done as per ASTM D638 standard except the sample size and
the gauge length, since the DSM micro-extruder produces samples that are smaller in size than
the standard ASTM samples. Therefore, a gauge length of 1 in was followed instead of the
standard 2 in gauge length. At least five specimens were tested for each sample and a load cell of
1000 lb was used for the experiments.

3.2.15 Differential scanning calorimetry (DSC)
The thermal properties of PLA and PLA/MOF composites extruded samples and films
were studied by using a differential scanning calorimeter, DSC Q200 (TA Instruments, New

50 
 

Castle, DE). A heat-cool-heat cycle was used to measure the glass transition temperature (Tg),
onset of cold crystallization temperature (Tcc onset), Tcc, onset of melting temperature (Tm
onset) and Tm of the samples. Samples of 7 to 10 mg were non-hermetically sealed in an
aluminum pan. After placing the sample and the reference in the DSC cell, the cell was heated
from room temperature to 200°C at 10°C/min. After the completion of the first heating cycle,
the cell was cooled from 200 to 0°C at 10°C/min, and for the second heating cycle the same
ramping conditions were used as that of the first heating cycle. Tcc onset and Tcc are reported
from the first heating run, and Tg, Tm onset and Tm were obtained from the second heating run.
The percent crystallinity of the extruded samples from DSM was calculated using equation 3.8:

X c ( wt.%)  100*

H m  | H c |
H f (1  x)

3.8

H m = enthalpy of melting, H c = enthalpy of cold crystallization, H f = enthalpy of fusion of
-1

100% crystalline PLA, which is 93.7 J-g , and x is the weight fraction of MOF in the composite.
At least three specimens were tested for each composite combination.

3.2.16 Barrier properties
The Barrier properties of the films were measured using the film samples produced in the
compression molding machine. The water vapor transmission rate (WVTR) was determined
using a Permatran W3/31 (MOCON Inc, Minneapolis, MN, USA). The conditions used for the
2

experiment were as follows: area of the film 3.14 cm ; RH: 100%; carrier gas N2; temperature
23°C. The WVTR values were used to calculate the water vapor permeability from equation 3.9:
51 
 

Water vapor permeability 

Water vapor transmission rate(q )* thickness(l )

3.9

partial pressure(p) * time( s ) * area(m2 )

The oxygen transmission rate (O2TR) was determined with an Oxtran 100 –Twin
(MOCON Inc., Minneapolis, MN, USA). The conditions used for the experiment were as
2

follows: area of the film 3.14 cm ; permeant = 0.21 atm of O2; carrier gas, N2 containing 2% H2;
temperature 23°C; and 0% relative humidity. The OTR values were used to calculate the oxygen
permeability by using equation 3.10:
Oxygen permeability 

Oxygen transmission rate(q)* thickness (l )
partial pressure(p ) * time( s ) * area(m 2 )

3.10

3.2.17 Isotherm
The moisture sorption and desorption of the MOF, PLA and PLA/MOF composite of the
compression-molded film was examined by gravimetric analysis using a SGA-100 from VTI
Corporation (Florida, USA). The films (5-10 mg) were exposed to relative humidity of 10, 30,
40, 50, 60, 70, and 90% at 23ºC and the sorption and desoprtion isotherms of the films were
plotted.
3.2.18 Statistical analysis
At least two runs (i.e. extrusion using twin screw extruder) for each treatment (i.e. 1, 3, 5
% wt/wt) were conducted for each property. If needed, a third run was conducted for further
analysis. Repeated measure analysis of variance (ANOVA) and Tukey tests were used to test the
significant differences between the treatment and control means.

52 
 

REFERENCES

53 
 

REFERENCES
1. S. Brunauer, P.H. Emmett, E. Teller, “Adsorption of gases in multimolecular layers”.
Journal of the American Chemical Society. 1938, 60, pp. 309–319.
2. J.C.Groen, L.A.A. Peffer, J.P.Ramirez, “Pore size determination in modified micro- and
mesoporous materials. Pitfalls and limitations in gas adsorption data analysis”,
Microporous and Mesoporous Materials, 60, 2003, pp. 1-17.
3. E.P. Barrett, L.G. Joyner and P.P. Halenda, “The Determination of Pore Volume and
Area Distributions in Porous Substances. I. Computations from Nitrogen Isotherms”,
Journal of American Chemical Society, 73, 1951, pp. 373-380.
4. R. Auras, B. Harte, S. Selke, “Sorption of ethyl acetate and d-limonene in poly(lactide)
polymers”, Journal of the science of food and agriculture, 86, 2006, pp. 648-656.
 
 
 
 
 
 
 
 
 

54 
 

CHAPTER 4. RESULTS AND DISCUSSION
4.1 DSM samples
Disc, rectangular and dumb-bell shaped samples were produced using the micro-extruder.
Disc samples were used for measuring optical, physical and barrier properties. Rectangular
samples were used for measuring thermo-mechanical properties and Izod impact strength. The
tensile strength of the samples was analyzed by using the dumb-bell shaped samples. The
samples produced from the micro-extruder are shown in Figure 4.1.

55 
 

A

PLA

PLA + 1% MOF

PLA + 3% MOF

PLA + 5% MOF
 

B

PLA

PLA + 3% MOF

PLA + 1% MOF

PLA + 5% MOF
 

C

PLA

PLA
+
1% MOF

PLA
+
3% MOF

PLA
+
5% MOF

 

Figure 4.1 DSM specimens (A) disc; (B) rectangular; and (C) dumb-bell samples. (“For
interpretation of the references to color in this and all other figures, the reader is referred to the
electronic version of this thesis.”)
56 
 

4.2 Compression molding
Compression molded films were used for analyzing thermal, optical and barrier
properties. The PLA and PLA/MOF composite films (1, 3 and 5% wt/wt) produced by
compression molding are shown in Figure 4.2.

Figure 4.2 Compression molded film samples: (1) PLA, (2) PLA + 1%MOF, (3) PLA + 3%
MOF, and (4) PLA + 5%MOF (“For interpretation of the references to color in this and all other
figures, the reader is referred to the electronic version of this thesis.”)
 

57 
 

4.3 Quantification of MOF
The actual amount of MOF in the 1, 3 and 5% wt/wt of the extruded composite samples
was determined by ICP-MS, and the values are shown in Table 4.1. The MOF % was calculated
by dividing the copper content in the extruded composite with the value of the copper content
from the pure MOF (control). MOF content in the extruded composite was lower than the actual
MOF % that was added to the PLA while preparing the samples. This loss could occur due to
MOF loss during transferring from the weighing pan to the bottle filled with PLA and also
during loading of the samples into the DSM Micro Extruder. The MOF powders are highly
electrostatic, so they tend to get stuck in the weight pan, bottle and feeder of the extruder. The
same observation was reported by Hilal during the quantification of zeolite in polypropylene
composite films. In the case of 4% wt/wt loading of zeolite in polypropylene films the amount
quantified by TGA was about 2%.[1] In case of PLA/MOF, much lower losses were found in the
extruded samples.
Table 4.1 Quantification of MOF content in the extruded samples
Material
MOF
1%MOF

3%MOF

5%MOF

Introduced
wt. (%)
Control
0.99
0.99
0.99
2.91
2.91
2.91
4.76
4.76
4.76

Copper Content
(mg/kg)
260075
1659.9
1329.6
1639.7
5594.7
5343.4
5252.7
11589
11091.6
11697.2

58 
 

MOF wt.
(%)
Control
0.64
0.51
0.63
2.15
2.05
2.02
4.46
4.26
4.50

Average wt.
(%)
Control
0.59±0.07

2.08±0.07

4.41±0.12

Although the actual final concentration of the MOF in samples was lower than the
introduced, the samples will still be indentified in this thesis as PLA, PLA plus 1, 3, and 5%
MOF for simplicity. The reader should note that the actual values of MOF in the samples are the
indicated in Table 4.1.
4.4 Contact Angle
Contact angle measurement indicates the angle at which the liquid/vapor interface meets
the solid surface. It is based on the thermodynamic equilibrium between three phases (i) liquid
(ii) solid and (iii) vapor phase. Young’s relationship forms the basis to determine the equilibrium
contact angle. Young’s equation assumes a perfectly flat surface, and it does not addresses
surface roughness and impurities, which might cause a deviation in the contact angle. Based on
Young’s equation many theories and equations have been developed, including Fowkes,
geometric mean, Wu harmonic mean, acid-base, and the equation of state. Table 4.2 shows these
equation and their terminology.

59 
 

Table 4.2 Main theories and equation of contact angle (Young, Geometric mean, Wu-harmonic
mean, Acid-base, Equation of state)
Theory
Young
Fowkes

Mathematical representation

 L cos    S   SL

d d
 L (1  cos  )  2  S  L

Geometric mean

p p
d d
 L (1  cos  )  2  S  L  2  S  L

Wu-harmonic mean

 L (1  cos  )  4
Acid-base

 

d d
SL

d
S

d
L

4

 

p p
S L

p
p
S L

 

LW LW
 
 
 L (1  cos  )  2  S  L  2  S  L  2  S  L

Equation of state

 

 L (1  cos  )  2  S  L 1  1 ( S   L )2   




 L = Surface tension of liquid,  S = Surface tension of solid,  SL = Surface tension of
liquid-solid,
of liquid,

d
d
 S = Dispersive surface tension of solid,  L = Dispersive surface tension

p
p
 S = Polar surface tension of solid,  L = Polar surface tension of liquid,

LW
LW
 S = Lifshitz- van der Waals (LW) component of surface tension of solid,  L =

Lifshitz- van der Waals (LW) component of surface tension of liquid,
acceptor parameter of solid,
donor parameter of solid,

 = Contact angle.


 S = Electron



 L = Electron donor parameter of liquid,  S = Electron


 L = Electron acceptor parameter of liquid, 1 = constant, and

Initially, the contact angle of the PLA and MOF was measured using water (polar) and
diiodomethane (non-polar). The Wu harmonic and geometric mean theory was used to calculate
the surface energy of PLA and MOF for assessing their blending capability. The contact angle
determined by using water and diiodomethane combination could not be used to calculate the
60 
 

surface energy of the PLA and MOF due to its large variation between the PLA and MOF. In
order to overcome this limitation, several polar (ethylene glycol, formamide) and non-polar
(hexane, octane) liquids were used to estimate the surface energy. The surface tensions,
dispersive and polar components of various solvents are given in Table 4.3. The sessile drop
images of the PLA and MOF with various solvents are shown in Figures 4.3 and 4.4. Ethylene
glycol and diiodomethane (methylene oxide) combination were used to estimate the surface
energy of PLA and MOF. The contact angle, surface energy, polarity and work adhesion
parameters of the PLA and MOF determined by using the Wu-harmonic mean and Geometric
mean method are shown in Table 4.4. The interfacial tension and spreading coefficient are shown
in Table 4.5.
Table 4.3 Surface tension, dispersive and polar component of test liquids

Liquid

Surface Tension
-2
(mJ.m )

Dispersive Component
-2
(mJ.m )

Hexane
Water
Formamide
Diiodomethane
Ethylene Glycol

18.4
72.8
58.0
50.8
47.7

0
25.5
2.28
0
26.4

61 
 

Polar
Component
-2
(mJ.m )
0
25.5
3.96
0
21.3

Table 4.4 Contact angle and surface energy parameters of PLA and MOF
Harmonic Mean Method
Ethylene Glycol

-2

Methylene Iodide

Surface energy mJm

Mat.
θ

Dispersive

Total

37.6±3.3 0.8±0.0 3.1±1.2

39.2±2.9

42.2±2.0

57.1±3.3

0.5±0.1

θ

Cos θ

Polar

MOF 53.3±2.5 0.6 ±0.0 45.4±4.3 0.7±0.1 6.0±1.3

31.8±2.9

37.8±1.9

-2

0.1±0.0
0.2±0.0

PLA

Cos θ

Polarity

Work
Adhesion
mJm

62.1±3.2
Geometric Mean Method
Ethylene Glycol

-2

Methylene Iodide

Surface energy mJm

Mat.
θ
PLA
MOF

Cosθ

57.1±3.3

0.5±0.1

θ

Cosθ

Polar

Total

37.6±3.3 0.8±0.0 0.7±0.5

45.2±2.3

45.9±1.9 0.02±0.0

53.3±2.5 0.6 ±0.0 45.4±4.3 0.7±0.1 1.7±0.9

39.5±3.3

41.2±2.5 0.04±0.0

62 
 

Dispersive

Polarity

Work
Adhesion
-2

mJm

82.2±4.3

Table 4.5 Interfacial tension and spreading coefficient of PLA and MOF
Surface energy
mJ.m

Method

-2

Work
adhesion
mJ.m

-2

Interfacial
Tension
mJ.m

-2

Spreding
Coefficient
mJ.m

-2

PLA
Geometric
Mean
Harmonic
Mean

MOF

45.9±1.9

41.2±2.5

82.2±4.3

16.3±4.3

13.2±4.3

42.2±2.0

37.8±1.9

62.1±3.2

36.4±6.3

33.3±6.3

The contact angle of PLA with diiodomethane coincides well with the work done
by Schwach et.al. [7] The MOF contact angles were not found reported in the literature.
The MOF particles can be tailored with either hydrophobic or hydrophilic properties, and
have good ion exchange properties higher than zeolites. [8, 9] The contact of angle of
silica has been reported. [9, 10] The contact angle of porous materials increases as their
polarity of the organic group decreases. It was reported that the contact angle of
carboxyl-, hydroxyl-, vinyl- and methyl- terminated alkylsilane on silica were 32, 48, 97
and 108°. For MOF, the measured contact angle with water was found to be 145° which
is higher than that of 114° reported for Organo TricholoroSilane (OTS) -silylated silica
surface [12] and lower when compared to that of 163° reported for C18- zeolite with
OTS. However, contact angle of particles with higher surface areas such as zeolites,
silica, and MOF need to be interpreted with caution, due to surface roughness,
deformation of particles and particle porosity. [13, 14]
The interfacial tension and the work adhesion parameter value derived through
the Wu harmonic and geometric mean can be used to assess the compatibility of two
materials. The greater the theoretical work adhesion and lower the interfacial tension, the
more compatible the materials are. According to Table 4.3, the greater theoretical work
63 
 

adhesion parameter of PLA and MOF may indicate that the PLA and MOF composite
will have good compatibility. Also, the positive spreading coefficient indicates that MOF
may disperse in PLA. In the case of mixed matrix membranes (MMMs), the affinity
between the two phases is an important factor. The compatibility between inorganic filler
and amorphous rubbery polymer was good due to the greater mobility of polymer chains
when compared to amorphous glassy polymers. [15 – 17] But, amorphous glassy
polymers are widely used in gas separation due to their greater transport characteristics.
The dispersion of inorganic fillers into the matrix of glassy polymers cause defects at the
interface due to the rigidity of the polymer chains. The addition of zeolite to the polymer
matrix increased the permselectivity and decreased the permeability due to blockage of
pores by the polymers. [18] The affinity of the MOF with polymer matrices is not yet
reported in the research literature, but the contact angle studies revealed that MOF may
disperse into the PLA matrix.

64 
 

Diiodomethane

Water

Ethylene Glycol

Formamide

Figure 4.3 Sessile drop images of MOF on diiodomethane, water, ethylene glycol and
formamide
Diiodomethane

Ethylene Glycol

Formamide

Water

Figure 4.4 Sessile drop images of PLA on diiodomethane, ethylene glycol, formamide,
and water.

65 
 

4.5 Solubility parameters
Solubility parameters were determined according to the Hansen’s solubility
parameter methodology. The solubility scoring numbers according to the methodology
explained in the section 3.2 for the PLA and MOF when dissolved in serious of solvents
are given in Table 4.6.
Table 4.6 Scoring of PLA and MOF in various solvents, according to the scoring scale
defined in Table 3.3
IUPAC Name & CAS. No.

Solvent

Dichloromethane (75-09-2)
Dichloro Methane
Methylbenzene (108-88-3)
Toluene
1,1,2,2-Tetrachlorethane (79-34-5) Tetra Chloro Ethane
Butan-2-one (78-93-3)
Methyl Ethyl Ketone
Cyclohexane (110-82-7)
Cyclo Hexane
(2-hydroxyethoxy)ethan-2-ol
Diethylene Glycol
(111-46-6)
Chloroform (67-66-3)
Chloroform
Propanone (67-64-1)
Acetone
Oxacyclopentane (105-99-9)
THF
Acetonitrile (75-05-8)
Acetonitrile
Dimethyl Sulfoxide (67-68-5)
Dimethyl Sulfoxide
Ethyl Acetate (141-78-6)
Ethyl Acetate
Methanol (67-56-1)
Methanol
Hydroxybenzene (108-95-2)
Benzanol
N,N-dimethylmethanamide (68-12-2) DMF
Hexane (110-54-3)
Hexane
Ethanol (64-17-5)
Ethanol
Dihydrofuran-2(3H)-one (96-48-0) Gamma Butryo Lactone

Assigned
Numbers
MOF
PLA
3
2
3
6
3
2
6
6
6
6
5
5
3
3
3
3
3
3
3
3
4
6

6
2
6
2
6
6
5
6
6
6
6
6

3

6

PLA dissolved completely in THF, tetrachloroethane, dichloromethane and
chloroform. Figure 4.5 shows PLA in these solvents, as completely dissolved in these
66 
 

solvents. In the other solvents, PLA did not dissolve settled to the bottom without any
visual flurries, swelling or reaction with the solvent.
THF 

Tetrachloroethane 

Dichloromethane

Chloroform 

Figure 4.5 Dissolution of PLA in THF, tetrachloroethane, dichloromethane, and
chloroform (“For interpretation of the references to color in this and all other figures, the
reader is referred to the electronic version of this thesis.”)
MOF powder did not completely dissolve in any of the solvents used for
measuring the solubility parameters. Instead it was dispersed when the solvent was added
to it, and after sonication started to settle down. The settling time varied according to the
density of the solvent, the higher the density the more time the MOF took to settle down.
Figure 4.6 indicates how the MOF was dispersed in various solvents after 15 min of
sonication. In some solvents the MOF settled down completely, and in others it started to
settle down after 15 min sonication.

67 
 

1 

2 

3 

4 

5

7

6

8

9

10

11  12  13 

Figure 4.6 Dispersion of MOF particles in various solvents (1- Dichloro Methane, 2Tetra chloro ethane, 3- Toluene, 4- Cyclo Hexane, 5- Diethylene Glycol , 6- Methyl Ethyl
ketone, 7- Methanol, 8- THF, 9-Chloroform, 10- Dimethyl Sulfoxide, 11- Ethyl Acetate,
12- Acetone, 13- Acetonitrile) (“For interpretation of the references to color in this and
all other figures, the reader is referred to the electronic version of this thesis.”)
 

After two days of storage, the MOF in all the liquids settled down completely as shown
in Figure 4.7

1 

2 

3 

9 

4 

5 

10

11

6 

7 

8 

12

Figure 4.7 MOF particles in various solvents after 2 days of storage (1- Dimethyl
Sulfoxide, 2- Ethyl Acetate, 3- Tetrachloro ethane, 4- Methanol, 5- Diethylene Glycol , 6Toluene, 7- Methyl Ethyl ketone, 8- Acetonitrile, 9- Dichloro Methane, 10- Cyclo
Hexane, 11- Chloroform, 12- THF) (“For interpretation of the references to color in this
and all other figures, the reader is referred to the electronic version of this thesis.”)

68 
 

HSPiP® software (Horsholm, Denmark) was used to calculate the Hansen
solubity parameters using the data from Table 4.6 obtained by dispersing the PLA and
MOF in the mentioned solvents. Each solvent has unique polar, dispersion and hydrogen
forces as reported in Table 3.2. The dispersion, polar, hydrogen forces and interaction
radius as calculated from the HSPiP® software are shown in Table 4.7.

Table 4.7 Dispersion, polar, and hydrogen parameters for PLA and MOF

Material

Dispersion
1/2
D (MPa )

Polar P
1/2
P(MPa )

Hydrogen Force
1/2
H (MPa )

Interaction
Radius
R

PLA
MOF

17.63
17.92

5.86
9.9

6.36
10.68

2.9
3.9

The modified difference between the HSP for the MOF and PLA (Ra) was
calculated using equation 4.1

( Ra ) 2  4( D 2   D1 ) 2  ( P 2   P1 ) 2  ( H 2   H 1 ) 2

4.1

Based on the δD, δP, δH, obtained from the HSPiP® software, the Ra was found to
be 5.94 for the PLA and MOF. The Relative Energy Difference (RED = Ra/Ro) can be
used to assess the affinity of the two materials in terms of its solubility. A RED number
of 0 is found for no energy difference. RED number less than 1 indicates high affinity,
RED equal to or close to 1 is the boundary condition, and progressively higher RED
numbers indicates lower affinity between two materials. The calculated RED of the PLA
and MOF is 1.5. This indicates poor affinity between PLA and MOF. This is different
from the results predicted from the contact angle measurements, which assessed the PLA
and MOF to be compatible. [19]
69 
 

4.6 Molecular weight
Weight average molecular weight (Mw), number average molecular weight (Mn),
and molecular weight distribution (PDI) of PLA resin and PLA with and without MOF
were determined by GPC and are shown in Table 4.8. PLA degrades when exposed to
high temperature and humidity. The reduction of Mn of the extruded samples when
compared to the pure PLA resin can be attributed to the thermal degradation of the PLA
during extrusion due to the presence of residual moisture in the resin after drying. These
factors cause chain scission and consequently decrease the molecular weight and the
chain length. It was reported that amorphous PLA reduced its Mw when exposed to 60ºC
and 80% RH for less than a month [20]. The addition of MOF during melt compounding
of PLA did not significantly change the Mw, Mn, and PDI of the PLA, significantly. This
confirms that the addition of MOF does not have a detrimental effect on the chain length
of the PLA. Sinha Ray et.al. and Yuzay et.al. reported that the incorporation of
montmorillonite and zeolite to PLA resulted in a reduction of Mn and Mw of the PLA
matrix of up to 12 and 14%, respectively. [3]

70 
 

Table 4.8 Number average molecular weight (Mn), weight average molecular weight
(Mw), and molecular weight distribution (PDI) of PLA resin and PLA/MOF composites
Samples

Mn(kDa)

Mw(kDa)

PLA Resin

87.1±1.04

PLA

82.09±0.65

PLA+1%MOF

83.91±1.92

PLA+3%MOF

81.89±1.01

PLA+5%MOF

81.71±1.15

a

123.81±0.86
b

120.79±0.23

b

123.76±3.68

b

119.97±1.01

b

119.39±0.51

PDI
a
a
a
a
a

1.42±0.01
1.47±0.01
1.45±0.03
1.47±0.02
1.46±0.02

a
a
a
a
a

Note: Values are represented as averages ± standard deviation. Values with different
superscript letters in the same column are significantly different at α = 0.05 (Tukey –
HSD)
4.7 Surface Area
The surface area, pore volume, and the pore diameter as reported by the ASAP
2010 is tabulated in Table 4-9. The surface area coincided with the specification from
2

Sigma Aldrich (1400 – 2100 m /g). The change in surface area between the two runs
could be due to the MOF being from different batches as well as experimental
uncertainty. The pore diameter was not reported by the supplier, and it was found to be in
the range of 1.86 to 3.54 nm as determined by the BET and the BJH methods,
respectively. The nitrogen adsorption and desorption isotherm are shown in Figure 4-8
and 4-9. The adsorption and desorption isotherms were used to calculate the surface area
and pore size distribution of the porous materials. The amount of gas adsorbed is
expressed as a function of the equilibrium relative pressure, P/Po. The data from the

71 
 

nitrogen adsorption isotherm can be plugged into equations 3.1, 3.2 and 3.3 to calculate
the surface area and pore size distribution of the MOF particles. [21]

Table 4.9 BET surface area, micropore volume, and pore diameter of MOF

RUN
1
2

BET surface
area
2
(m /g)
1683.94 ± 37.76
1449.79 ± 33.46

Micropore
Volume
3
(cm /g)
0.634
0.549

Pore Diameter by
BET
(nm)
1.86
1.89

Pore Diameter by
BJH
(nm)
3.54
3.66

Figure 4.8 Nitrogen adsorption isotherm (“For interpretation of the references to color in
this and all other figures, the reader is referred to the electronic version of this thesis.”)

72 
 

Volume Desorbed cm3/g STP

900
800
700
600
500
400
300
200
100
0
0

0.2

0.4

0.6

0.8

1

1.2

Relative Pressure (P/Po)

Figure 4.9 Nitrogen desorption isotherm (“For interpretation of the references to color in
this and all other figures, the reader is referred to the electronic version of this thesis.”)

73 
 

4.8 Scanning Electron Microscopy (SEM)
Figure 4.10 shows a microscopic image of the geometry of MOF powders, which
are irregular polyhedra in shape and range from 5-20 μm in size.
(a) 

(b

Figure 4.10 SEM images of MOF powders. a) Magnification: 1000X, scale bar: 20 μm,
b) Magnification: 3000X, scale bar: 10 μm (Images were obtained and provided by
Yuzay, I.)
Figure 4.11 displays the SEM images of PLA and PLA/MOF composites. Figure
4.11 (a) exhibited a typical brittle fracture of the PLA specimen and the fracture surface
appeared to be very smooth. After inclusion of MOF, a ductile fracture surface became
characteristic in all the micrographs (Figure 4.11 (c-i)).
The composite samples produced using 2 min mixing time in the mini-extruder
exhibited a non-uniform distribution of MOF. The MOF powders tend to agglomerate in
the PLA matrix (Figure 4.11 (c-d)). A better dispersion of MOF powders within the PLA
samples was observed when a mixing time of 5 min was used (Figure 4.11 (e-i)). The
images taken at high magnification levels revealed void formation at the interface of the
PLA matrix and the MOF (Figure 4.11 (h-i)). The formation of voids shows poor
interfacial adhesion between the PLA matrix and the MOF powders, which was opposite
to the contact angle predictions.
74 
 

(a) 

(b)

(c) 

(d)

 
 

(g)

(f) 

(e

 
 
 
(h) 

(i)

Figure 4.11 SEM images of PLA and PLA composites with 5 wt% MOF fabricated using
2 and 5 min mixing time in the micro-compounder (Images were obtained and provided
by Yuzay, I.)
a) PLA magnification: 100X, scale bar: 200 μm, b) PLA magnification: 1000X, scale
bar: 20 μm c) PLA/MOF 5wt%, 2 min mixing time, magnification: 100X, scale bar: 200
μm d) PLA/MOF 5wt%, 2 min mixing time, magnification: 1000X, scale bar: 20 μm e)
PLA/MOF 5wt%, 5 min mixing time, magnification: 100X, scale bar: 200 μm f)
PLA/MOF 5wt%, 5 min mixing time, magnification: 1000X, scale bar: 20 μm g)
PLA/MOF 5wt%, 5 min mixing time, magnification: 1600X, scale bar: 20 μm h)
PLA/MOF wt%, 5 min mixing time, magnification: 1600X, scale bar: 20 μm i)
PLA/MOF 5wt%, 5 min mixing time, magnification: 2500X, scale bar: 10 μm
75 
 

4.9 FTIR Spectrophotometer
An FTIR transmission graph of the PLA and MOF blends at wt% of 1, 3 and 5 is
shown in Figure 4-12. The MOF used for the experiment was BasoliteTM C300
(containing copper benzene-1,3,5-tricarboxylate). According to Robinson et.al,[4] the
-1

benzene rings shows a characteristic peak between 1500 to 2000cm which corresponds
to the C=C stretching. The PLA/MOF blend at 1 and 3% loading did not show any
distinct peak in the fingerprint region for the benzene ring. However, the PLA/MOF
-1

composite at 5% loading shows an absorption at 1537cm , corresponding to the C=C
stretching. The peak assignments of Figure 4.12 are shown in Table 4.10.

76 
 

PLA
1%MOF

%T

3%MOF
5%MOF
3215

3651

3502

1537
2879
1645

954
893

1355

2993 2945

4000

3600

3200

2800

1755

2400

2000

1800

1600

1381

1263
1244

1134

1182 1056

705
867
756

1450

1400

1200

1000

800

1/cm

Figure 4.12 IR Spectra of PLA, PLA + 1% MOF, PLA + 3% MOF, and PLA +5% MOF (“For interpretation of the references to color
in this and all other figures, the reader is referred to the electronic version of this thesis.”)

77 
 

Table 4.10 FTIR absorption bands of PLA/MOF composite films
Wavenumber
-1
cm

Assignment

Wavenumber
-1
cm

Assignment

3502
-OH Stretch(free)
2993(asym),2945(sym),2879 -CH Stretch

1263
1182,1134

-C=O bend
-C-O- Stretch

1755

1056

-OH bend

954

-CH3 rocking

867,756,705

-C-C- stretch

1537
1450
1382,1355

-C=O Carbonyl
stretch
-C=C aromatic ring
stretch
-CH3 bend
-CH- Sym,, Asym.
bend

4.10 Ultraviolet/Visible Spectroscopy
The UV/Visible spectrum of the film samples shown in Figure 4.13 give a distinct
absorbance and transmittance peak in the 190 to 800 nm range (UV A, B, C and visible
range). The MOF (BasoliteTM C300) is Cyan (Blue + Green) in color due to the presence
of copper (Cu) ions in the matrix. The cyan color showed an increased absorbance in the
red region (620 – 750 nm). On the other hand, the transmittance is greater in the blue and
green region (450-570 nm). It is also evident from the spectra that as the percentage of
MOF increases, the transmittance decreases.

78 
 

90
PLA

80

PLA+1%MOF

70

PLA+3%MOF
Transmittance(%)

60
50

PLA+5%MOF

40
30
20
10
0
190 240 290 340 390 440 490 540 590 640 690 740 790
Wavelength (nm)

Figure 4.13 UV spectra of PLA, PLA + 1% MOF, PLA + 3% MOF, and PLA + 5%
MOF (“For interpretation of the references to color in this and all other figures, the reader
is referred to the electronic version of this thesis.”)
4.11 Colorimeter
The L* a* b* and ∆E values of the PLA and MOF blends at wt% of 1, 3 and 5
are shown in Table 4.11. The higher the L value, the lighter the samples are. As the
percentage of MOF increases (i.e. 1, 3, and 5%), the L* values of the film samples
decrease indicating that the clarity of the film samples diminishes as the percentage of
MOF increases. The decreasing a* values in the case of 1, 3, and 5% loading indicate
that the addition of MOF gives a green tone to the film. The positive b* values indicate
the presence of yellow color in the samples. The increasing b* values in the case of 1, 3,
79 
 

and 5% loading indicates the addition of MOF gives a yellow tone to the film. The ∆E
value is an indicative of magnitude of the difference in color with respect to PLA. The
∆E value increases significantly as the percent of MOF increases. The above L* a* b*
and ∆E indicates that the addition of MOF (Cyan in color due to the presence of copper)
changes the color of the sample to cyan (blue + yellow).
Table 4.11 CIE L*a*b* Values of for PLA and MOF samples
ΔE

Material

L*

PLA

92.5±0.1

-1.1±0.01

0.9±0.03

N/A

PLA+1%MOF

87.8±1.2

-3.7±0.5

2.3±0.4

5.5

PLA+3%MOF

81.7±1.7

-7.2±0.7

2.4±0.1

12.5

PLA+5%MOF

76.8±1.3

-9.1±0.6

2.2±0.2

17.7

a

b
c

d

a*

a

b
c

d

b*

a

b
b
b

a
b
c

Note: Values are represented as averages ± standard deviation. Values with different
superscript letters in the same column is significantly different at α = 0.05 (Tukey –
HSD)
4.12 Dynamic mechanical analyzer (DMA)
The heat deflection temperature (HDT) and Tg obtained from Tan Δ are shown in
Table 4.12 for run 1 and 2 of the PLA and PLA/MOF composite. The HDT and Tg by
Tan Δ do not show any significant difference between PLA and PLA/MOF composites
within the runs. In run 1, even at 5% loading of MOF, HDT and Tg by Tan∆ were found
to be 54.7 and 64.7 ºC in comparison to the HDT and Tg by Tan∆ of 53.4 and 65.4 ºC for
the control (PLA). Significant differences were found between samples in runs 1 and 2
samples. These differences can be attributed to the differences in the processing
conditions of the extruder, and also due to the inherent variability of the testing machines.
80 
 

The storage modulus and loss modulus of PLA/MOF composites did not change when
compared to the neat PLA even at 5% wt/wt loading of MOF. The storage modulus and
loss modulus of PLA and PLA/MOF composite were found to be around 3150 and 700
MPa. The study of PLA/Zeolite composites done by Yuzay et.al [3] reported that addition
of 5% wt/wt of zeolite increased the storage modulus of PLA from 3100 to 3854 MPa.
The loss modulus values also increased with zeolite loading. The loss modulus of PLA
with 5% wt/wt zeolite reached 901 MPa when compared to pure PLA, which was about
668 MPa. The current results show that the addition of MOF does not change the
dissipation capacity of PLA for vibrational energy. Figure 4.14 and 4.15 show the storage
and loss modulus curves of the PLA and PLA/MOF composites.
Table 4.12 HDT and Tg by Tan delta results of PLA, PLA + 1% MOF, PLA + 3% MOF,
and PLA + 5% MOF samples
Run

HDT(⁰C)

Treatment

a,A

PLA

52.43±0.23

PLA + 3%MOF

52.47±0.18
53.12±0.19

PLA
2

PLA + 1%MOF
PLA + 5%MOF

1

52.45±0.25

53.44±0.66

PLA + 1%MOF

54.10±0.34

PLA + 3%MOF

54.63±0.38

a,A
a,A
a,A
a,B
a,B
a,B

Tg by
Tan∆(⁰C)
67.16±0.37
67.07±0.15
66.90±0.2
67.50±0.0

a,A
a,A

a,A
a,A

65.40±0.2
65.20±0.3
65.00±0.3

a,B
a,B
a,B

a,B
a,B
PLA + 5%MOF
54.72±0.18
64.70±0.1
Note: Values are represented as averages ± standard deviation. Values within runs with
different lower-case superscript letters are significantly different at α = 0.05 (Tukey –
HSD). Values between runs with different upper-case superscript letters are significantly
different at α = 0.05 (Tukey – HSD).

81 
 

3500

PLA + 5% MOF

PLA

PLA + 3% MOF

3000

Storage Modulus (MPa)

PLA + 1% MOF
2500
2000
1500
1000
500
0
0

10

20

30

40

50

60

70

80

90

Temperature (°C)

Figure 4.14 DMA Curve for Storage Modulus of PLA, PLA+1%MOF, PLA+ 3%MOF
and PLA+5%MOF (“For interpretation of the references to color in this and all other
figures, the reader is referred to the electronic version of this thesis.”)

82 
 

100

800
700

Loss Modulus (MPA)

600
500
PLA

400

PLA+1% MOF
PLA+3%MOF

300

PLA+5%MOF
200
100
0
0

20

40
60
Temperature (°C)

80

100

Figure 4.15 DMA Curve for Loss Modulus of PLA, PLA+1%MOF, PLA+ 3%MOF and
PLA+5%MOF (“For interpretation of the references to color in this and all other figures,
the reader is referred to the electronic version of this thesis.”)
4.13 Differential Scanning Calorimetry
The films made by compression molding and the samples extruded from the twin
screw extruder were analyzed for their thermal properties using DSC. The Tg, Tc, Tm,
Hc, ΔHm, and crystallinity of the films and extruded samples are tabulated in Tables 4.12
& 4.13. For the compression molded films the addition of MOF did not affect the glass
transition temperature (Tg) and the percent crystallinity (Xc). However, there was a
change in the melting temperature (Tm) and cold crystallization. The compression
molded PLA and PLA/MOF composites had a Tg around 60°C.
83 
 

On heating from the Tg, the PLA and PLA/MOF composites reached the cold
crystallization temperature where the polymer chains oriented themselves to form
crystallites. A lower cold crystallization temperature is associated with fast
crystallization. The Tc of PLA was found to be 129.2±0.3°C. As the percentage of MOF
increased, the cold crystallization shifted to lower temperatures (Tc = 115.0±0.8°C for
PLA with 5% MOF). This reduction can be attributed to a nucleating effect caused by the
addition of MOF particles in the PLA matrix. The same effect has been reported by
Yuzay et al [3] upon combining PLA with zeolites to form PLA/zeolite composites.
The compression molded films, which were subjected to two thermal cycles,
exhibited bimodal melting peaks for the PLA/MOF composites. The PLA/MOF
composites showed melting peak Tm1 at 149.6±0.0 °C and another peak Tm2 at
154.9±0.2°C. Figure 4.16 shows the DSC graphs of the PLA and PLA plus 1, 3 and 5%
wt/wt MOF composite films. These double melting peaks can be attributed to the
presence of different crystallite structures. The Tm1 can be attributed to  crystallites of
PLA, and Tm2 can be attributed to the  -crystallites. PLA crystallizes in three forms , 
and . The -form, which is more stable than the  and  forms, is commonly found and
distinguished by 2 values of 15, 17 and 19, and is described by two antiparallel chains
in a left-handed 103 helix conformation packed in a pseudoorthorhombic unit cell (a=10.6
Å, b=6.10 Å, and c=2.8 Å). [22] From Table 4.13, the addition of increasing amounts of
MOF did not affect the Tm1 & Tm2 temperatures of the bimodal melting peaks, but the

84 
 

peaks became more prominent upon increasing the amount of MOF. The low % Xc of the
samples indicated a mostly amorphous sample.
In case of the thermal properties of extruded PLA and PLA plus 1, 3 and 5%
wt/wt MOF composite samples (disc samples), we did not observe the decreasing cold
crystallization temperature or the bimodal peaks in case of PLA/MOF composites. As
seen in the Table 4.14, there was no significant difference between the Tg, Tcc, Tm and
the Xc of the PLA and PLA/MOF composites.

85 
 

Table 4.13 Thermal Properties of PLA/MOF Composites (films)
Treatment
PLA

Tg (° C)

Tc (° C)

60.1±0.1

129.2±0.2

a

a

Tm1 (° C)

Tm2 (° C)

Hc (J/g)

Hm (J/g)

Xc (%)

12.5±0.4

13.9±0.2

1.5±0.2

a

151.3±0.3

a

a

PLA+1%
a
b
a
a
b
b
a
59.8±0.2 123.2±0.7 149.6±0.0 154.9±0.2 23.9±2.2 25.6±2.3 1.8±0.9
MOF
PLA + 3%
a
c
a
a
c
c
a
59.2±0.1 117.1±0.1 148.1±0.1 155.2±0.1 32.9±0.6 34.7±0.7 1.9±0.5
MOF
PLA+ 5%
a
d
a
a
c
c
a
59.2±0.2 115.0±0.8 147.3±0.2 154.9±0.1 33.5±0.7 34.9±1.2 1.7±1.1
MOF
Note: Values are represented as averages ± standard deviation. Values with different superscript letters in the same column is
significantly different at α = 0.05 (Tukey – HSD)
Table 4.14 Thermal Properties of PLA/MOF Composites (extruded disc samples)
Treatment
PLA

Tg (° C)

Tc (° C)

61.0±0.2

130.7±0.3

a

a

Tm (° C)

Hc (J/g)

Hm (J/g)

Xc (%)

152.1±0.1

7.1±0.3

7.9±0.4

0.8±0.1

a

a

a

a

PLA+1%
a
a
a
b
b
a
61.1±0.2
131.0±0.2
152.3±0.4
5.2±0.5
5.9±0.4
0.8±0.2
MOF
PLA + 3%
a
a
a
c
b
a
61.5±0.1
131.4±0.2
152.3±0.4
4.2±0.2
5.2±0.2
1.2±0.2
MOF
PLA+ 5%
a
a
a
c
b
a
61.3±0.2
131.6±0.1
152.4±0.4
3.8±0.2
4.6±0.2
0.9±0.1
MOF
Note: Values are represented as averages ± standard deviation. Values with different superscript letters in the same column is
significantly different at α = 0.05 (Tukey – HSD)

86 
 

PLA
1% MOF

E 
X 
O 

3% MOF

E 
N 
D 
O 

5% MOF

Figure 4.16 Thermograph of PLA and PLA films plus 1, 3, and 5% wt/wt MOF
composites (“For interpretation of the references to color in this and all other figures, the
reader is referred to the electronic version of this thesis.”)

87 
 

4.14 Thermal Gravimteric Analysis
 
120

Weight Change (%)

100

PLA
PLA with 1% MOF

80

PLA with 3% MOF
PLA with 5% MOF

60
40
20
0
0

100

200

300

400

500

600

Temperature (°C)

-20

 

Figure 4.17 TGA curves of PLA and PLA/MOF composites (“For interpretation of the
references to color in this and all other figures, the reader is referred to the electronic
version of this thesis.”)

Table 4.15 TGA analysis of PLA and PLA/MOF Composites
MOF content
(% wt)
0
1
3
5

T5%
Weight
loss
352
355
353
355

T50%
Weight loss

T95% Weight
loss

Tdmax

386
390
387
385

403
409
408
411

419
420
420
420

Weight
Loss
(%)
98.84
97.94
95.16
94.08

 

The TGA analyses of the PLA and PLA/MOF composites are shown in Figure
4.17. The onset and termination of the degradation temperature did not change between
the PLA and PLA/MOF composite as shown in Table 4.15. On average, the degradation
88 
 

started at around 310°C, and terminated at about 420°C. The weight losses of the PLA
and PLA/MOF composite films were found to be 98.84, 97.94, 95.16 and 94.08 for the
control and addition of 1, 3, and 5% MOF, respectively. Although the PLA/MOF
composite sample should contain 1, 3 and 5% of MOF, the TGA results did not agree
with this, indicating that the MOF also degrades at the same temperature as PLA. A
thermogram of the degradation of MOF is presented in figure 4.18.
120

Weight Change (%)

100
80
60
40
20
0
0

100

200

300
400
Temperature (°C)

500

600

700

Figure 4.18 TGA curve of MOF activated at 200°C in vacuum

As shown in figure 4-18, the first weight loss from 30 to 100°C can be attributed
to the evaporation of water bound in the pores of the MOF, and then the MOF started to
degrade at 310 to around 400˚C, the same temperature as PLA. But in the case of
PLA/Zeolite composites, the zeolite does not decompose at these higher temperatures, so
the amount of zeolite in the extruded PLA samples could be determnined by TGA. The

89 
 

addition of MOF does not affect the degradation temperature of PLA. Yuzay et al. [3]
reported a slight reduction in decomposition temperature when zeolite is added to the
PLA matrix. A similar reduction in degradation temperature is reported for PLA when
titanium oxide and clay nanoparticles were added to the PLA. [23 - 26] So, the actual
amount of MOF in PLA was determined by ICP-MS as described in section 3.2.2. The
weight loss of the MOF is about 80% and the 5%, 50% reduction temperature and Tdmax
are about 58˚C, 377˚C and 597˚C respectively.

4.14 Izod impact Testing Machine
Stiffness and toughness are critical properties in the performance of composites
and its applications. Notched impact strength is related to the toughness of a polymer.
The notched impact strength of the PLA and the PLA/MOF composites are shown in
Table 4.16. Two runs (i.e. extrusion using twin screw extruder) for each treatment (i.e. 1,
3, 5 % wt/wt) were conducted to analyze the difference in impact strength between the
PLA and PLA/MOF composite. According to run 1, there was no significant difference
between PLA and 1% wt/wt MOF loading, but it found that there was a significant
difference for 3 and 5% wt/wt MOF loading when compared to the PLA and 1% MOF
loading. In run 2 there was a significant difference between PLA and PLA/MOF
composite (i.e. 1, 3 and 5%). The results from runs 1 and 2 were different. We can
conclude from run 1 and run 2 that there is a difference in impact strength between the
control (PLA) and PLA + 3 and 5% MOF. However, further testing is needed to
determine the differences between PLA + 1% MOF. Huda et al. [5] reported the impact
strength properties of PLA/wood fiber composites. The addition of wood decreased the
90 
 

impact strength of PLA from 25.7 to 21.9 J/m. In this study, the addition of MOF
significantly increased the impact strength and toughness of the PLA+MOF samples. The
increased impact strength is due to the homogenous distribution of MOF in the PLA
matrix. The surface area of the MOF is able to absorb much of the impact energy, and the
void between the MOF and PLA matrix acts as a cushion , which absorb the impact force.
Table 4.16 Impact strength of PLA and PLA/MOF composites

26.76±1.27

PLA + 1%MOF

27.30±0.76

PLA + 3%MOF

31.18±1.17
31.11±3.06

PLA
2

Impact Strength
(J/m)

PLA + 5%MOF

1

Specimen
PLA

RUN

26.80±0.45

PLA + 1%MOF

28.31±0.47

PLA + 3%MOF

28.42±0.72

a.A
a,A
b,A
b,A
a,A
b,A
b,B

b,A
PLA + 5%MOF
29.47±0.92
Note: Values are represented as averages ± standard deviation. Values within runs with
different lower-case superscript letters are significantly different at α = 0.05 (Tukey –
HSD). Values between runs with different upper-case superscript letters are significantly
different at α = 0.05 (Tukey – HSD).

4.15 Tensile test
Table 4.17 shows the tensile strength, modulus of elasticity, strain at yield, and
strain at break of the PLA and PLA/MOF composites. Mechanical properties were
assessed for samples made from three runs in order to account for the variability
associated with the extrusion of the samples. Tensile strength of the samples decreased
as the percentage of the MOF in the sample increased. For example, run 2 samples had
tensile strength of the PLA of about 9.52±0.26 kPsi while PLA with 5% MOF had tensile
91 
 

strength about 6.95±0.19 kPsi, which was found to be significantly different. The
decrease in tensile strength can be attributed to the poor interfacial adhesion between the
MOF and PLA, as predicted by the solubility parameter measurements. Yuzay et. al., [6]
reported that adding zeolite to a PLA matrix did not change the tensile strength of the
composite sample significantly. This was attributed to the good interfacial adhesion
between PLA and zeolite. It was found that the modulus of elasticity was not
significantly difference between PLA and PLA/MOF composites for run 1. The samples
tested from run 2 exhibited a significant difference between PLA and PLA/MOF
composites. The difference between the runs could be due to the variability in the mixing
during the extrusion.
Table 4.17 Mechanical Properties of PLA/MOF Composite

Treatment
PLA

1

Tensile
Strength

Modulus of
Elasticity

Strain at
yield

Strain at
Break

(Kpsi)

Run

(Kpsi)

(%)

(%)

9.32±0.26

a,A

PLA+1%MOF 8.69±0.19b,A
PLA+3%MOF 8.47±0.36c,A

PLA+5%MOF 6.95±0.20d,A
PLA
2

9.52±1.49

a,A

PLA+1%MOF 8.92±1.22b,A
PLA+3%MOF 8.3±1.30c,A

a,A

479.53±11.14

2.45±0.21

488.16±30.73

2.46±0.21

468.32±41.60

2.68±0.15

490.39±32.26

2.28±0.16

a,A
a,A
a,A
a,A

451.71±22.72

2.42±0.32

400.52±20.23

2.54±0.10

400.70±22.36

2.54±0.12

b,B
b,B

a,A
a,A
a,A
a,A
a,A
a,A
a,A

1.17±0.30
>170
>170
>170

b,A
b,A
b,A

3.58±0.33
>170
>170

a,A

a,A

b,A
b.A

b,A
PLA+5%MOF 7.66±0.72d,A 436.01±18.36b,A 2.37±0.04a,A
>170
Note: Values are represented as averages ± standard deviation. Values within runs with
different lower-case superscript letters are significantly different at α = 0.05 (Tukey –
HSD). Values between runs with different upper-case superscript letters are significantly
different at α = 0.05 (Tukey – HSD).

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As the MOF is introduced into the PLA matrix, the strain at break of the samples
increased by 2 orders of magnitude. For example, pure PLA extension at break was about
3.6±0.3 % but the addition of 1% wt/wt MOF increased the strain at break to greater than
170 % (run 2). A laser beam was used as a strain detector in the UTS machine. Due to
necking of the samples (which is common in small dumb-bell shaped samples), the laser
could not exactly quantify the ultimate extension of samples after extension of about 170
%. In order to unify the data, the MOF sample extension at break is reported as >170%.
The addition of starch to PHB increased the impact strength of the polymer to 130% at 25
wt% loading, but the impact strength decreased significantly as the amount of starch
added to the PHB increased. The same effects were observed when flax fiber was added
to HDPE to form a composite material. The addition of starch and flax fiber to the
polymer matrix increases the tensile strength and decrease the elongation of break of the
polymer samples. [27, 28] But, the addition of MOF to the PLA matrix increased the
elongation of break and decreased the tensile strength. This is due to poor interfacial
addition of MOF with the PLA matrix, which resulted in void formation in the extruded
samples. These voids resulted in the reduced tensile strength, which in turn increased the
flexibility of the PLA/MOF composite samples and the elongation at break. In the case of
PLA/zeolite composites, the addition of zeolite decreased the elongation at break from
10.96 to 6.68 % and slightly increased the tensile strength due to high interfacial adhesion
between PLA and zeolite matrix. [6]

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4.16 Barrier Properties:
The permeability to water and oxygen plays a major role in determining polymer
performance and application and the design of a functional membrane. The water vapor
-2 -1

-1

permeability (WVP) and oxygen permeability (OP) in kg.m.m s Pa of PLA and
PLA/MOF composite samples are shown in Table 4.17. In case of the WVP, there was no
significant difference between the PLA and PLA/MOF composites between runs 1 and 2,
and also between the treatments within the runs. This indicates that the addition of MOF
did not increase or decrease the permeability of PLA to water. The same trend was
followed in case of OP, where the addition of MOF did not change the PLA permeability
to oxygen. Significant differences were not found between the OP values for runs 1 and
2.
Table 4.17 Barrier properties of PLA/MOF Composites
WVP
Run

(kg-m/m2skpa)
x10-13

Material - ID

OP
(kg-m/m2skpa)
x10-13

a,A

a,A

PLA
PLA+1%MOF

2.5±0.5

4.3±0.2

PLA+3%MOF

2.5±0.01

4.0±0.3

2.5±0.5

4.8±0.7

PLA
2

4.9±0.5

PLA+5%MOF

1

3.1±0.5

2.4±0.2

5.0±0.4

PLA+1%MOF

2.5±0.6

4.7±0.3

PLA+3%MOF

2.1±0.2

4.6±0.4

a,A
a,A

a,A
a,A
a,A
a,A

a,A
a,A
a,A
a,A
a,A
a,A

a,A
a,A
PLA+5%MOF
4.6±0.9
2.5±0.3
Note: Values are represented as averages ± standard deviation. Values within runs with
different lower-case superscript letters are significantly different at α = 0.05 (Tukey –
HSD). Values between runs with different upper-case superscript letters are significantly
different at α = 0.05 (Tukey – HSD).

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4.17 Sorption
The sorption isotherm represents the relationship between the amount of water
vapor amount in the environment and the water activity of a material at a constant
temperature. Measurement of the sorption isotherm in polymer membranes is important
for many industrial applications such as fuel cells, gas separation, packaging, and drug
delivery systems. Compounding PLA with highly porous MOF particles should have
greatly affected the polymer sorption capacity for water. To study the sorption isotherm
of the PLA and PLA/MOF composites, PLA and PLA +5%wt MOF samples were
subjected to various relative humidity levels and the sorption isotherms of the films were
obtained. Table 4.18 depicts the weight change (%) (i.e., grams of water/gram of dry
polymer x 100) of the PLA and PLA with 5% MOF composite films at various relative
humidity.) Figure 4.17 shows the sorption isotherm of PLA and PLA with 5% MOF
composite film. The addition of MOF increased the adsorption capacity of the polymer to
water. The sorption capacity of the MOF composite films to water started increasing from
10% RH at 0.1 ± 0.0 % through 90% RH at 1.6 ± 0.4 %, respectively. Roughly the
sorption capacity of the films modified with MOF doubled compared to the pure PLA.
This indicates the MOF has greater affinity to water molecules due to its porous nature.
The water molecules started accommodating into the pores of the MOF. The kinetic
diameter of a water molecule is 0.27 nm and thus gets easily accommodated in the 1.86
nm pores of MOF. The water absorption of neat PLA coincides well with the results
reported by Wang et.al. [29] Also the higher variability of PLA/MOF composite film at
90% RH could be due to the uneven distribution of MOF in the PLA matrix of the

95 
 

pressed film, and the saturation of the film with water producing varied results between
replicates.
Table 4.18 Weight change of PLA and PLA/MOF composite between 0 and 90% RH
Weight Change (%)
RH(%)
PLA with 5%
PLA
MOF
a,A
a,A
0
0.00±0.00
0.00±0.00
a,A
b,B
10
0.03±0.01
0.09±0.00
b,A

30

0.16±0.02

40

0.21±0.02

50

0.26±0.02

60

0.33±0.01

70

0.43±0.03

80

0.58±0.02

0.31±0.01

c,A

0.40±0.02

d,A

d,B

0.46±0.04

e,A

c,B
e,B

0.59±0.04

f,A

0.78±0.12

g,A

1.12±0.33

f,B

g,B
h,B

h,A
i,B
90
0.76±0.03
1.59±0.40
Note: Values are represented as averages ± standard deviation. Values within runs with
different lower-case superscript letters are significantly different at α = 0.05 (Tukey –
HSD). Values between runs with different upper-case superscript letters are significantly
different at α = 0.05 (Tukey – HSD).
2.500

Weight Change (%)

2.000
1.500
PLA

1.000

PLA with 5% MOF

0.500
0.000
0

20

40
60
RH (%)

80

100

Figure 4.19 Water sorption of PLA and PLA+5%MOF composite at 23°C and 40%RH
(“For interpretation of the references to color in this and all other figures, the reader is
referred to the electronic version of this thesis.”)
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4.18 Desorption
The desorption isotherm is the curve used to determine the behavior of the
material while drying. Since films modified with MOF adsorbed an increased amount of
water, a desorption isotherm was measured to analyze its drying behavior. The desorption
isotherm of PLA with 5% MOF composite films is shown in Figure 4.18. As expected the
sorption and desorption curves do not follow the same trend due to the hysteresis effect
typical of many desorption isotherms for foods and polymers for the experimental time
period. Since the MOF does not have any dead volume (the amount of solvent adsorbed
will be desorbed without any loss), the hysteresis effect is mainly produced by PLA. The
same effect is also reported by Hsu et.al., [30] for all of the poly(methyl methacrylate)
PMMA blends. Because of the limited amount of data, it was not possible to conclude
whether the hysteresis in the PLA/MOF blends is time dependent or not. Schult and Paul
[31] also found a hysteresis effect for blends of poly(vinyl pyrrolidone) and polysulfone.

97 
 

2.5

Wt.Change(%)

2
1.5

De-Sorption

1
Sorption

0.5
0
0

20

40

60

80

100

RH(%)

Figure 4.20 Water desoprtion isotherm of PLA + 5% MOF (“For interpretation of the
references to color in this and all other figures, the reader is referred to the electronic
version of this thesis.”)

98 
 

REFERENCES

99 
 

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12. D.L. Angst, G.W. Simmons, “Moisture absorption characteristics of
organosiloxane self-assembled monolayers”, Langmuir, 7(10), 1991, pp.22362242.
13. G. Buckton, J.M. Newton, “Assessment of the wettability of powders by use of
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14. M. Jia, K.V. Peinemann, R.D. Behling, “Molecular sieving effect of the zeolitefilled silicone rubber membranes in gas permeation”, Journal of Membrane
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15. J.M. Duval, “Adsorbent filled polymeric membranes”, Ph.D thesis. The
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18. G. Clarizia, C. Algieri, A. Regina, E. Drioli, “Zeolite based composites PEEKWC membranes: Gas transport and surface properties”, Microporous and
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21. K.S.W. Sing, “Physisorption of Nitrogen by Porous Materials”, Journal of Porous
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22. D. Brizzolara, H.J. Cantow, K. Diderichs, E. Keller, A.J. Domb, “Mechanism of
the Stereocomplex Formation between Enantiomeric Poly(lactide)s”,
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23. N. Nakayama, T. Hayashi, “Preparation and characterization of poly(L-lactic
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24. D.F. Wu, L. Wu, L.F. Wu and M. Zhang, “Rheology and thermal stability of
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25. J. Chang, Y.U. An, G.S. Sur, “Poly(lactic acid) nanocomposites with various
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30. W.P. Hsu, R.J. Li, A.S. Myerson, T.K. Kwei, “Sorption and diffusion of water
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31. K. A. Schult and D. R. Paul, “Water sorption and transport in blends of poly(vinyl
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CHAPTER 5. CONCLUSION
Poly(lactic acid) (PLA), resin and metallic organic framework (MOF) were
successfully compounded in a twin screw extruder in batches of 10 g, and rectangular,
disc and dumb-bell shaped samples were prepared in the amounts of 1, 3 and 5% wt/wt.
With these samples the structural, physical, optical, thermal, thermo-mechanical,
mechanical and sorption properties of the PLA/MOF composites were analyzed.
Based on the contact angle measurements, the theoretical work of adhesion and
positive spreading coefficient indicated that MOF might disperse well in PLA. But, the
higher Relative Energy Difference (RED) of the solubility parameter study indicates
otherwise suggesting that MOF may not disperse well with the PLA. In order to resolve
these opposite findings, the interfacial adhesion of PLA and MOF was inspected using
SEM. The SEM results revealed voids at the interface of PLA and MOF. From these
visual pictures, it was clear that there was existed a poor interfacial adhesion between
PLA and MOF.
The FTIR, UV and colorimetric studies showed selected absorption at particular
wavelengths indicated the presence of MOF in the PLA/MOF composites. The DMA
results revealed that the heat deflection temperature (HDT), storage modulus, loss
modulus and Tan ∆ of the PLA/MOF composites did not change when compared to the
neat PLA samples. The DSC results of the PLA/MOF composite films showed two
significant melting peaks, which can be attributed to the presence of different crystallite
structures. The Tm1 can be attributed to β-crystallites of PLA, and the Tm2 can be
attributed to the α-crystallites. These different crystallite structures (varied lamella

103 
 

structures and spherulite size) were formed during cooling in the compression molding of
PLA/MOF composite films.
The mechanical properties of the PLA/MOF composites samples changed
significantly. The Izod impact strength of the PLA/MOF composite samples increased up
to 15% when compared to the control (PLA sample). The tensile strength of the
PLA/MOF composites decreased as the amount of MOF in the PLA samples increased.
The brittleness of the PLA/MOF composite sample decreased as the amount of MOF in
the PLA increased. The elongation at break (break strain) of the PLA/MOF composite
samples was up to 170%, compared to about 2 % for the PLA samples.
The mass transfer properties of the PLA/MOF composite were evaluated. The
permeability of PLA/MOF composite films to oxygen and water did not change when
compared to the neat PLA film. However, the sorption capacity of the PLA/MOF
composite films increased up to two fold at each relative humidity to which they were
exposed. This shows that the addition of MOF significantly increased the sorption
capacity of the PLA films. The sorption and desorption curves of the PLA/MOF
composite films showed the typical hysteresis present in polymers.
Future Work
PLA and MOF composites were successful produced, which resulted in an invention
disclosure form and a pending patent application. However, many details and new
research questions arose during this work. Some of future topics to further investigate
are:
1. The compatibility of the Cu-MOF with PLA is not proven to be good from the
compatibility results between the PLA matrix and MOF. There are four types of

104 
 

MOF currently available in the market 1. Cu-based, 2. Ag- based, 3. Zn-based,
and 4. Fe-based. Silver based zeolites were proven to have a good compatibility
with PLA in previous studies. So, in order to increase the interfacial between PLA
and MOF the silver based MOF can be used with PLA. In addition, the
compatibility of the PLA with the other types of MOFs (Zn, Ag, Fe based) should
be studied and their properties evaluated.
2.

The sorption and desorption properties to water were evaluated in this research.
In order to use these membranes for packaging, the sorption properties of the
PLA/MOF composite film to different solvents such as d-limonene, ethyl acetate,
and acetaldehyde should be studied.

3. MOF structures can be tailored; therefore, the interfacial adhesion of PLA with
MOF after modifying the MOF structure may be increased.
4. Since the thickness profile of the compression-molded film was not completely
uniform, there might be little variation in the permeability results of the
PLA/MOF composite film to water and oxygen. In order to reduce this variation
the PLA/MOF composite film can be cast instead of compression molding.
 
 

105