CONTINUOUS BLENDING APPROACH IN THE MANUFACTURE OF
EPOXIDIZED SOYBEAN-PLASTICIZED POLY(LACTIC ACID) SHEETS AND
FILMS FOR PACKAGING APPLICATIONS
By
Shalini Vijayarajan

A THESIS
Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of
Packaging - Master of Science
2013

ABSTRACT
CONTINUOUS BLENDING APPROACH IN THE MANUFACTURE OF
EPOXIDIZED SOYBEAN-PLASTICIZED POLY(LACTIC ACID) SHEETS AND
FILMS FOR PACKAGING APPLICATIONS
By
Shalini Vijayarajan
A single-step processing system in which an extruder and a peristaltic injector
pump attached in tandem was developed for a continuous and accurate incorporation of
epoxidized soybean oil (ESO) into poly (lactic acid) (PLA) matrix in order to
manufacture sheet/film with improved flexibility and toughness. The impact strength of
plasticized sheets increased significantly with increasing ESO content, indicative of the
toughening capacity of ESO as a plasticizer. The ductility of plasticized PLA sheets
followed similar trends and the brittle-to-ductile transition occurred in the range of 5-10
wt % ESO content, in agreement with the impact strength results. In contrast, both the
tensile strength and the modulus of the sheets decreased with increasing ESO content due
to the plasticization effect, which induced a decrease in the glass transition temperature.
Burst pressure and seal strength of PLA films were not affected by the addition of
plasticizer or by the sealing temperature range studied. The tensile properties of blown
film plasticized with 15 wt % ESO, tested at periodic intervals of storage time, indicated
no significant change in the ductility and the tensile strength at yield as the storage time
increased, implying the good permanence of ESO in the plasticized PLA films. In
contrast, the tensile modulus showed a slight but a statistically significant increase in
stiffness after only 7 storage days, indicating a possible loss of plasticizer from the film
as the storage time increased. This contradictory trend will be investigated further.

Dedicated to my parents
Vijayarajan and Bhuvaneswari

iii

ACKNOWLEDGEMENTS

I am forever indebted to my advisor Dr. Laurent Matuana for his constant support
and guidance. He has been a great source of inspiration and a teacher. He helped me
develop my scientific writing, research and communication skills. He has also taught me
some invaluable life lessons which I am sure will be of great asset in my career. I am also
thankful to my committee members Dr. Susan Selke (School of Packaging) and Dr.
Andre Y. Lee (Department of Chemical Engineering & Materials Science) for their time
and support.
My special thanks go to my colleagues Dr. Kojo Afrifah and Dr. Carlos Diaz for
their interest and valuable input in my research. They were always available for advice
and encouragement. I would also like to thank Sarah Jedla, Brett Farnsworth and Megan
Pignone, all undergraduates in the School of Packaging, who helped me in my research.
I am grateful to my parents without whom this thesis would not have been
possible. They have always been my source of strength and it gives me immense pleasure
in dedicating this thesis to them. I would also like to thank my brother and sister-in-law
for their constant care and support. Also, I am grateful to my friends who have been a
moral support through my years in the US, Priyadarshini, Kavitha, Radha, and Sumit. A
special thanks to all my other MSU friends who have been my family away from home.

iv

TABLE OF CONTENTS

LIST OF TABLES ......................................................................................................... vii
LIST OF FIGURES ..........................................................................................................x
Chapter 1
INTRODUCTION ............................................................................................................1
1.1 Introduction .................................................................................................................1
1.2 Objectives ...................................................................................................................7
1.3 Structure of thesis .......................................................................................................7
1.4 References .................................................................................................................10

Chapter 2
BACKGROUND AND LITERATURE REVIEW ........................................................12
2.1 Introduction ...............................................................................................................12
2.2 Poly (lactic acid) .......................................................................................................12
2.2.1 Synthesis of PLA .......................................................................................12
2.2.2 Properties of PLA ......................................................................................14
2.2.3 Property modification of PLA ...................................................................17
2.2.3.1 Copolymerization ........................................................................17
2.2.3.2 Melt blending with other polymers .............................................18
2.2.3.3 Plasticization ...............................................................................19
2.3 Soybean oils ..............................................................................................................20
2.3.1 Synthesis of ESO .......................................................................................21
2.3.2 Use of ESO as a plasticizer ........................................................................23
2.4 Processing technologies of PLA ...............................................................................24
2.4.1 Drying and extrusion..................................................................................24
2.4.2 Injection molding .......................................................................................25
2.4.3 Stretch blow molding .................................................................................25
2.4.4 Thermoforming ..........................................................................................26
2.4.5 Cast film and sheet .....................................................................................26
2.4.6 Extrusion blown film .................................................................................27
2.5 References ................................................................................................................29

Chapter 3
EXPERIMENTAL ..........................................................................................................33
3.1 Materials ...................................................................................................................33
3.2 Sample manufacturing ..............................................................................................34
3.2.1 Manufacture of plasticized sheets ..............................................................34
3.2.2 Manufacture of plasticized films ...............................................................38
3.3 Property evaluation ...................................................................................................39

v

3.3.1 Mechanical properties ................................................................................39
3.3.2 Thermal property .......................................................................................41
3.3.3 Phase morphology evaluation ....................................................................42
3.3.4. Statistical analysis .....................................................................................42
3.4 References ............................................................................................................. …44

Chapter 4
RESULTS AND DISCUSSION .....................................................................................45
4.1 Effect of ESO content on the notched Izod impact strength of PLA sheets .............45
4.2 Effect of ESO content on the tensile properties of PLA sheets ................................48
4.2.1. Ductility ....................................................................................................48
4.2.2. Tensile Strength and Modulus ..................................................................53
4.3 Effect of ESO on package related properties ............................................................55
4.3.1 Burst pressure of PLA films ......................................................................55
4.3.2 Seal strength of PLA films .........................................................................56
4.3.3 Tensile properties of plasticized films as a function of storage time .........57
4.4 References .................................................................................................................60

Chapter 5
CONCLUSIONS.............................................................................................................61
5.1 Conclusions ...............................................................................................................61
5.2 Future work ...............................................................................................................63
5.3 References .................................................................................................................65

APPENDICES
APPENDIX I - IMPACT STRENGTH DATA OF PLA SHEETS ................................67
APPENDIX II - TENSILE PROPERTIES DATA OF PLA SHEETS ..........................70
APPENDIX II-1 - The Effect of ESO Content on the Tensile Modulus of PLA Sheets 71
APPENDIX II-2 - The Effect of ESO Content on the Tensile Strength at Yield of
PLA Sheets......................................................................................................................74
APPENDIX II-3 - The Effect of ESO Content on the Ductility of PLA Sheets ............77
APPENDIX III - TENSILE PROPERTIES DATA OF PLA FILMS ............................81
APPENDIX III-1 - The Effect of Storage Time on the Tensile Strength at Yield of
PLA Films Plasticized with 15 wt % ESO......................................................................82
APPENDIX III-2 - The Effect of Storage Time on the Tensile Modulus of PLA Films
Plasticized with 15 wt % ESO ........................................................................................85
APPENDIX III-3 - The Effect of Storage Time on the Energy to Break of PLA Films
Plasticized with 15 wt % ESO ........................................................................................88
APPENDIX III-4 - The Effect of Storage Time on the Ductility of PLA Films
Plasticized with 15 wt % ESO .......................................................................................91
APPENDIX IV - BURST PRESSURE AND SEAL STRENGTH DATA OF PLA
FILMS .............................................................................................................................95

vi

APPENDIX IV-1 - Effect of Sealing Temperature on the Burst Pressure of PLA
Films ...............................................................................................................................96
APPENDIX IV-2 - Effect of Sealing Temperature on the Seal Strength of PLA Films 99

vii

LIST OF TABLES
Table 2.1

Comparison of PLA properties with other petroleum based polymers .......16

Table 3.1

Characteristics of PLA (2002D) resin used in this study ............................33

Table 4.1 Effect of ESO content on the glass transition (Tg) of PLA (2002D)
measured by DSC and DMA ..............................................................................54
Table 4.2 Effect of sealing temperature on the burst pressure and sealing strength of
unplasticized (neat) PLA and plasticized PLA films ..........................................56
Table 4.3 Variations in tensile properties of plasticized PLA films as a function of
storage time .........................................................................................................58
Table A.1 Effect of ESO content on the impact strength of PLA sheets .....................68
Table A.2 Analysis of variance for the effect of ESO content on the impact strength
of PLA .................................................................................................................69
Table A.3 Pairwise comparison of impact strength of PLA/ESO blends ....................69
Table A.4 Effect of ESO content on the tensile modulus of PLA sheets .....................72
Table A.5 Analysis of variance for the effect of ESO content on the tensile modulus
of PLA .................................................................................................................73
Table A.6 Pairwise comparison of tensile modulus of PLA/ESO blends ....................73
Table A.7 Effect of ESO content on the tensile strength at yield of PLA sheets .........75
Table A.8 Analysis of variance for the effect of ESO content on the tensile strength
at yield of PLA ....................................................................................................76
Table A.9 Pairwise comparison of tensile strength at yield of PLA ............................76
Table A.10 Effect of ESO content on the tensile strain at break and at yield of PLA
sheets ...................................................................................................................78
Table A.11 Effect of ESO content on the ductility of PLA sheets .................................79
Table A.12 Analysis of variance for the effect of ESO content on the ductility of PLA80
Table A.13 Pairwise comparison of ductility of PLA/ESO blends ................................80

viii

Table A.14 Effect of storage time on the tensile strength at yield of plasticized PLA
films ....................................................................................................................83
Table A.15 Analysis of variance for the effect of storage time on the tensile strength
at yield of plasticized PLA films ........................................................................84
Table A.16 Pairwise comparison of tensile strength at yield of plasticized PLA films .84
Table A.17 Effect of storage time on the tensile modulus of plasticized PLA films .....86
Table A.18 Analysis of variance for the effect of storage time on the tensile modulus
of plasticized PLA films .....................................................................................87
Table A.19 Pairwise comparison of tensile modulus of plasticized PLA film ..............87
Table A.20 Effect of storage time on the energy at break of plasticized films ..............89
Table A.21 Analysis of variance for the effect of storage time on the energy at break
of plasticized PLA film .......................................................................................90
Table A.22 Pairwise comparison of energy at break of plasticized PLA film ...............90
Table A.23 Effect of storage time on the tensile strain at break and at yield of
plasticized films ..................................................................................................92
Table A.24 Effect of storage time on the ductility of plasticized films .........................93
Table A.25 Analysis of variance for the effect of storage time on the ductility of
plasticized PLA films ..........................................................................................94
Table A.26 Pairwise comparison of ductility of plasticized PLA films .........................94
Table A.27 Effect of sealing temperature on the burst pressure of unplasticized and
plasticized films ..................................................................................................97
Table A.28 Analysis of Variance for the effect of sealing temperature and
plasticization on the burst pressure PLA films ...................................................98
Table A.29 Pairwise comparison of burst pressure of PLA films ..................................98
Table A.30 Effect of sealing temperature on the seal strength of unplasticized films .100
Table A.31 Effect of sealing temperature on the seal strength of plasticized films .....101
Table A.32 Analysis of variance for the effect of sealing temperature and
plasticization on the seal strength PLA films ...................................................102

ix

Table A.33 Pairwise comparison of seal strength of PLA films ..................................102

x

LIST OF FIGURES
Figure 2.1 Chemical structures of L-lactic acid and D-lactic acid ............................13
Figure 2.2 Chemical structures of LL-lactide, meso or LD-lactide and DD-lactide .14
Figure 2.3 Schematic representation of triglyceride structure in vegetable oils ........21
Figure 2.4 Structure of epoxidised soy oil (ESO) ......................................................22
Figure 3.1 The schematic representation of the tandem extrusion-injection pump
system used in this study............................................................................35
Figure 3.2 Calibration curve for determining the amount of extruded PLA in the
blends .........................................................................................................36
Figure 3.3 Calibration curve for determining the amount of ESO injected in the
blends .........................................................................................................37
Figure 4.1 Effect of ESO content on the impact strength of PLA...............................45
Figure 4.2 SEM micrographs of PLA plasticized with various amounts of ESO: (a) 0
wt %, (b) 10 wt %, and (c) 20 wt % ...........................................................47
Figure 4.3 Stress-strain curves of (a) Unplasticized PLA and PLA plasticized with
various amounts of ESO showing well defined yield points and (b)
Plasticized PLA showing stable necking beyond yield point ....................49
Figure 4.4 Tensile deformation showing the stress whitening in unplasticized PLA
(left) and PLA plasticized with 10 wt % ESO (right) ................................50
Figure 4.5 Effect of ESO content on the ductility of the PLA sheet ...........................52
Figure 4.6 Effect of ESO content on the tensile stress at yield and tensile modulus of
PLA sheets .................................................................................................54

xi

Chapter 1
INTRODUCTION
1.1 Introduction
Petroleum-based polymers have served mankind in numerous ways and are
widely used in many applications in the United States. However, the continued increase
in oil prices, U.S. dependency on foreign oil and environmental concerns has led to a
growing interest in bio-based plastics [1]. Replacing petroleum-based polymers with
natural bio-based polymers obtained from renewable resources, which can be
biodegraded, could be an attractive alternative for a sustainable environment [2, 3].
The most common biodegradable polymers are the aliphatic polyesters such as
polylactic acid (PLA), polyglycolic acids (PGA), polycaprolactone (PCL) and
polyhydroxybutyrate (PHB). Among these polymers, PLA obtained from corn and sugar
beets is commercially gaining a lot of interest recently. PLA has attracted the interest of
many researchers as it has relatively high modulus, reasonable strength, thermal
plasticity, excellent flavor and aroma barrier capability, good heat sealability and easy
processing, thereby making it one of the most promising bio-based polymers [4, 5]. It
possesses properties that are equivalent or better than many petroleum-based plastics; for
instance it has the stiffness and tensile strength of polyethylene terephthalate and
processing characteristics of polystyrene [6].
Despite these attractive properties, PLA has few commercial applications
concentrating mainly in textile and specialty biomedical niches such as sutures and drug
delivery devices due to its bio-degradability and bio-compatibility [6, 7]. Additionally, it
is being used as a commodity polymer for packaging food and consumer goods where the

1

physical properties of PLA make it suitable for manufacture of rigid containers and
bottles. However, the widespread applicability of PLA in flexible sheets and films is
limited because of its brittleness, lower impact resistance at room temperature and narrow
processing windows [5-8]. These factors severely hinder its applicability, particularly in
packaging applications where production lines for flexible films cannot tolerate film
cracking or tearing when folded or subjected to force during manufacturing [1].
Processing of PLA in thermoforming and film blowing production lines is still difficult
due to its low melt strength [9-12]. Therefore, it is of paramount importance to find a
tougher and ductile variant of the polymer in order to overcome these difficulties and
broaden the range of its commercial applications [6].
In order to improve the properties of PLA, it is often blended or copolymerized
with other materials [9-12]. The compatibility of the two components in the blend affects
the properties such as glass transition temperature (Tg), melting temperature (Tm),
crystallinity, and morphology. Consequently, these properties determine the properties of
the macroscopic material such as processibility, rigidity, impact and tensile strength,
barrier properties and degradation. Blending is more cost-effective than copolymerization
and hence more frequently used method [11]. PLA is most commonly blended with a
second polymer or with plasticizers [9-12].
Blending of PLA with a biodegradable second polymer such as poly(vinyl
alcohol),

poly(caprolactone),

poly(ethylene

glycol),

polyhydroxyalkanoate,

and

poly(butylenes succinate) has predominantly been used in biomedical applications to
maintain the bio-compatibility and biodegradability while also improving the mechanical
properties [8]. For example, significant improvement in flexibility (up to 180%

2

elongation at break compared to 4% for neat PLA) and impact resistance (over 200%
increase) were obtained with the use of up to 10 wt % low molecular weight
poly(ethy1ene-glycol) (PEG) [9]. However, these additives are relatively exorbitant
rendering their PLA blends expensive. Alternatively, the use of inexpensive nonbiodegradable

polymers

such

as

poly(ethylene

oxide),

poly(vinyl

acetate),

polyisopropene, acrylonitrile/butadiene/styrene copolymer, and polyethylene has
successfully reduced cost. The PLA blends with these polymers require an additional
component such as a compatibilizer to improve the miscibility of the blend [8].
Eliminating the use of compatibilizer, a study by other investigators focused on the use of
petroleum-based ethylene/acrylate copolymer (EAC), which is compatible and miscible
with PLA, to improve the impact and tensile properties of PLA [8].
Alternatively, the use of plasticizers such as low molecular weight esters,
oligomeric lactic acid, etc., has been investigated to obtain PLA with improved
mechanical properties without the addition of a compatibilizer [9, 10]. In the case of
semicrystalline polymers like PLA, an efficient plasticizer reduces the glass transition
temperature (Tg) thereby increasing the flexibility to overcome the difficulties of
cracking or tearing, especially in packaging film production lines [10].
PLA film has been gaining a lot of attention in flexible packaging applications
and many studies have been conducted to characterize and understand the physical,
mechanical and barrier properties of the film [11,13]. Investigations of PLA blended with
monomeric and oligomeric plasticizers such as citrates and PEG resulted in films with
enhanced flexibility and thereby reduced brittleness [11]. Coating PLA films with SiOx,
an anti UV layer and varnish has been shown to improve the physical, mechanical and

3

barrier properties of the films for food packaging applications [13]. Transparent films
with enhanced mechanical properties have also been produced using PLA plasticized
with adipates [7].
Although blending PLA with the aforementioned plasticizers improves its
properties and may broaden its applications, the majority of these plasticizers are
derivatives of crude oil and non-biodegradable [14]. Hence, it is essential to blend PLA
with renewable and biodegradable plasticizers that could withstand the practical
application while their biodegradation properties are maintained [12].
Recently, modified vegetable oils have gained a lot of interest as a renewable
source of plasticizer for polymers [14]. Soybean oil (SO) is one such renewable material
that has been investigated as a plasticizer for PLA, poly(vinyl chloride) (PVC),
polybutylene succinate (PBS), etc. [15]. Soy oil is a mixture of triglycerides with various
saturated and unsaturated fatty acids [16]. Epoxidation of the unsaturated bonds that
occur along with the fatty acid chains produces more reactive oxirane groups. This threemember ring provides a more energetically favorable site for reaction and represents a
chemical intermediate [17]. Epoxidized soy oil (ESO) is prepared on an industrial scale
and is being used for polymers, coatings, adhesives, laminate materials, etc. [17].
Currently, research studies are directed towards the use of ESO as a plasticizer for both
non-biodegradable and biodegradable polymers [16].
In relation to non-biodegradable polymers, such as PVC compounds, phenolic
resins, and chlorinated rubbers, ESO has been used as a non-toxic plasticizer to improve
the polymer stability and flexibility [16]. Studies on the effect of ESO on polyvinyl
chloride/epoxidized natural rubber thermoplastic elastomer (PVC/ENR) indicate that

4

ESO-plasticized blends exhibit good tear strength, good tensile strength and lower Tg
[18]. Investigation on phenolic resins plasticized with ESO prepared for laminate
materials has shown not only increased flexibility of the phenolic resins but also
improved electrical properties, solvent resistance, and heat resistance of the laminates
[19].
Biodegradable polymers such as poly(3-hydroxybutyrate-co-3 hydroxyvalerate)
(PHBV) and PLA have been plasticized with ESO [20-22]. PHBV plasticized with ESO
resulted in reduced Tg as well as increased elongation at break and impact strength [20,
21]. Other investigations have shown that the addition of ESO into PLA lowers the Tg,
storage modulus, and viscosity of the blend while improving the elongation at break [17,
22]. Higher melt strength was obtained by adding higher ESO content into PLA, resulting
in higher elongation of the blend [17].
Although ESO has been reported as an effective plasticizer for bio-degradable
polymers due to its excellent permanency and efficiency of plasticization [16], the
research conducted so far on PLA plasticized with ESO has mostly focused on the effect
of plasticizer types and/or addition levels on the mechanical properties without due
consideration of the production methods for these blends.
Several multi-step approaches to formulating PLA/ESO blends have been
investigated [10, 14]. In most studies ESO is pre-mixed with PLA prior to shaping the
blend in an extruder or using other processing techniques [17]. Melt blending of PLA
with ESO in an internal mixer prior to compression molding of the blend in a hot press
has also been reported [22]. Another reported approach for using EPO as a PLA

5

plasticizer consists of first dissolving each material in a chloroform solution and
subsequently mixing the two solutions to obtain a blended mixture, which was then dried
to form sample pellets for further processing [23].
The above described processes involve multiple steps, including pre-blending
PLA and ESO in a batch mixer prior to film production in another processing system [10,
14]. In these multi-step approaches, the resultant PLA polymer is subjected to repetitive
cycles of high processing temperature, which could affect the miscibility of PLA and
ESO and also the phase separation between the two at different composition levels. This
multi-step approach could be efficient at the research laboratory level for small scale
production of the blends. However, the multiple steps involved in the production of
flexible films make such a process both time consuming and very energy intensive, thus
preventing its scalability. A more efficient and effective technique is required that avoids
the additional step of pre-mixing before extrusion.
The main goal of this study is to take the next step to manufacture flexible PLA
films using a novel one step-process. It is believed that the elimination of the preblending steps will reduce the processing energy, and therefore will lead to a costeffective process for the production of fully biodegradable flexible PLA films to be used
in sustainable packaging applications. This study will explore the feasibility of a
continuous method of blending ESO and PLA needed for the manufacture of flexible
PLA sheet and film.

6

1.2 Objectives
The goal of this study is to develop a single-step process that efficiently
incorporates ESO into a PLA matrix in order to manufacture PLA sheet/film with
improved ductility, flexibility and impact resistance. To achieve this aim, the following
specific objectives must be accomplished:
1. Explore the feasibility of a novel single-step method that continuously introduces
a metered amount of ESO into the PLA matrix, thereby eliminating the
intermediate step of mixing the polymer and plasticizer prior to extrusion.
2. Evaluate the effect of different concentrations of ESO on the impact strength,
ductility and other tensile properties of plasticized PLA with the ultimate goal of
identifying the brittle to ductile transition in the PLA/ESO blend.
3. Examine the miscibility and phase morphology of the PLA/ESO blends to gain an
in-depth understanding of the interactions between PLA and ESO.
4. Manufacture PLA/ESO films by varying the amounts of ESO in the films and
characterize their physico-mechanical properties.
5. Characterize the properties of the plasticized films as a function of time in order
to determine the permanence or leachability of the plasticizer in the films.

1.3 Structure of thesis
This thesis is structured as follows: the first chapter introduces the rationale of
this research. Background on polylactic acid, ESO and their blending techniques is
reviewed in Chapter 2. The experimental details, including the material specifications,
property testing methods and equipment are discussed in Chapter 3. The results of the

7

effect of ESO addition levels and storage time on the different properties of plasticized
PLA are discussed in Chapter 4. Conclusions drawn from experimental data and
recommendations for future work are given in Chapter 5.

8

REFERENCES

9

1.4 References
1. Matuana, L.M., Solid state microcellular foamed poly(lactic acid): Morphology and
property characterization, Bioresource Technology, 99: 3643- 3650 (2008).
2. Haq, M., Burgueno, R., Mohanty, A.K., and Misra, M., Hybrid bio-based composites
from blends of unsaturated polyester and soybean oil reinforced with nanoclay and
natural fibers, Composites Science and Technology, 68: 3344-3351 (2008).
3. Wool, R.P and Sun, X.S., Bio-Based Polymers and Composites, Elsevier Inc., edition
1, pp 56-111 (2005).
4. Lee, S.Y., Kang, I.A., Doh, G.H., Yoon, H.G., Park, B.D. and Wu, Q., Thermal and
mechanical properties of wood flour/talc-filled polylactic acid composites: effect of
filler content and coupling treatment, Journal of Thermoplastic Composite Materials,
21 (3): 209-223 (2008).
5. Pilla, S., Gong, S., O’Neill, E., Rowell, R.M., and Krzysik, A.M., Polylactide-pine
wood flour composites, Polymer Engineering and Science, 48: 578-587 (2008).
6. Schreck, K.M. and Hillmyer, M.A., Block copolymers and melt blends of polylactide
with Nodax™ microbial polyesters: preparation and mechanical properties, Journal of
Biotechnology, 132: 287-295 (2007).
7. Martino, V.P., Jimenez, A., and Ruseckaite, R.A., Processing and characterization of
poly(lactic acid) films plasticized with commercial adipates, Journal of Applied
Polymer Science, 112: 2010-2018 (2009).
8. Afrifah, K.A., Matuana, L.M., Impact modification of polylactide with a
biodegradable ethylene/acrylate copolymer, Macromolecular Materials and
Engineering, 295: 802-811 (2010).
9. Jacobsen, S. and Fritz, H.G., Plasticizing polylactide - the effect of different
plasticizers on the mechanical properties. Polymer Engineering and Science, 39,
1303-1310 (1999).
10. Baiardo, M., Frisoni, G., Scandola, M., Rimelen, M., Lips, D., Ruffieux, K. and
Wintermantel, E., Thermal and mechanical properties of plasticized poly(L-lactic
acid), Journal of Applied Polymer Science. 90: 1731-1738 (2003).
11. Ljungberg, N. and Wesslen, B., Preparation and properties of plasticized poly(lactic
acid) films, Biomacromolecules, 6: 1789-1796 (2005).
12. Semba, T., Kitagawa, K., Ishiaku, U.S., and Hamada, H., The effect of crosslinking
on the mechanical properties of polylactic acid/polycaprolactone blends, Journal of
Applied Polymer Science, 101, 1816-1825 (2006).

10

13. Siracusa, V., Blanco, I., Romani, S., Tylewicz, U., Rocculi, P., and Rosa, M.D.,
Poly(lactic acid)-modified films for food packaging application: physical,
mechanical, and barrier behavior, Journal of Applied Polymer Science, 125: E390E401(2012).
14. Robertson, M.L., Chang, K., Gramlich, W.M., and Hillmyer, M.A., Toughening of
polylactide with polymerized soybean oil, Macromolecules, 43: 1807-1814 (2010).
15. Gramlich, W.M., Robertson, M.L., and Hillmyer, M.A., Reactive compatibilization of
poly(L-lactide) and conjugated soybean oil, Macromolecules, 43: 2313-2321 (2010).
16. Zhao, Y., Qu, J., Feng, Y., Wu, Z., Chen, F., and Tang, H., Mechanical and thermal
properties of epoxidized soybean oil plasticized polybutylene succinate blends,
Polymers for Advanced Technologies, 23: 632-638 (2012).
17. Xu, Y.Q., Qu, J.P., Mechanical and rheological properties of epoxidized soybean oil
plasticized poly(lactic acid), Journal of Applied Polymer Science, 112: 3185-3191
(2009).
18. Ishiaku, U.S., Shaharum, A., Ismail, H., and Mohd Ishak, Z.A., The effect of an
epoxidized plasticizer on the thermo-oxidative ageing of poly(vinyl
chloride)/epoxidized natural rubber thermoplastic elastomers, Polymer International,
45: 83-91 (1998).
19. Konii, S., Yoshimura, Y., Nanaumi, K., Yasuzawa, K., Yoshida, T., and Shinko, T.,
Process for producing internally plasticized phenolic resins, US patent P4209429
(1980).
20. Choi, J.S. and Park, W.H., Effect of biodegradable plasticizers on thermal and
mechanical properties of poly(3-hydroxybutyrate), Polymer Testing, 23: 455-460
(2004).
21. Choi, J.S. and Park, W.H., Thermal and mechanical properties of poly(3hydroxybutyrate-co-3-hydroxyvalerate) plasticized by biodegradable soybean oils,
Macromolecular Symposia, 197: 65-76 (2003).
22. Ali, F., Chang, Y.W., Kang, S.C., and Yoon, J.Y., Thermal, mechanical and
rheological properties of poly(lactic acid)/epoxidized soybean oil blends, Polymer
Bulletin 62: 91-98 (2009).
23. Al-Mulla, E.J., Yunus, W.M., Ibrahim, N.A., and Rahman, M.Z., Properties of
epoxidized palm oil plasticized polylactic acid, Journal of Materials Science,
45:1942-1946 (2010).

11

Chapter 2
BACKGROUND AND LITERATURE REVIEW
2.1 Introduction
Consistent with the scope of this study, a background and literature review on the
current studies of epoxidized soybean oil (ESO) plasticized poly(lactic acid) (PLA)
blends are presented in this chapter. The review focuses on the effects of ESO on the
mechanical and thermal properties of PLA as well as on the manufacturing methods of
the ESO plasticized PLA films.

2.2 Poly (lactic acid)
Polylactic acid belongs to the family of aliphatic polyesters and is biodegradable,
compostable, and biocompatible. It is a thermoplastic derived from 100% renewable
resources such as corn and sugar beets for use primarily in industrial packaging or bioabsorbable medical devices [1]. In addition to being an environmental friendly polyester,
it has excellent properties including relatively high modulus, high strength, excellent
flavor and aroma barrier, good heat sealability, and easy fabrication using existing
processing technology and techniques [2-4].

2.2.1 Synthesis of PLA
The basic building block of PLA is lactic acid, which can be manufactured by
carbohydrate fermentation or chemical synthesis [5]. Lactic acid (2-hydroxy propionic
acid) is the simplest hydroxyl acid with an asymmetric carbon atom and exists in two
optically active configurations, the L(+) and D(-) isomers (Figure 2.1). The L(+) isomer

12

is produced in humans and other mammals, while both the D(-)- and L(+)- isomers are
produced in bacterial systems. The majority of lactic acid commercially produced today
is by bacterial fermentation of carbohydrates using modified strains of the genus
Lactobacilli, which are exclusively form lactic acid [6].

Figure 2.1: Chemical structure of L-lactic acid and D-lactic acid

[7]

High molecular weight PLA can be produced using 3 different methods: (a) direct
condensation polymerization, (b) azeotropic dehydration condensation, and (c)
polymerization through lactide formation. Among these three methods, polymerization
through lactide formation also called the ring opening polymerization of lactide, patented
by Cargill Inc., is currently the most commonly used method for the production of PLA.
In this method, lactide is formed by the condensation of two lactic acid molecules as
follows: L- lactide (two L-lactic acid molecules), D- lactide (two D-lactic acid molecules)
and meso-lactide (an L-lactic acid and a D-lactic acid molecule) (Figure 2.2) [5].

13

CH3
CH3

CH3

CH3
CH3

CH3

Meso or LDDD-Lactide
Lactide
[8]
Figure 2.2: Chemical structures of LL-lactide, meso or LD-lactide and DD-lactide
LL-Lactide

Many important properties of PLA are controlled by the type of lactide used and
their sequence of arrangement in the polymers. For instance, the isotactic homopolymers
(where the monomers in the chain are of the same optical composition): poly(L-lactide)
(PLLA) and poly(D-lactide) (PDLA) are semicrystalline. However, random copolymers
of L-, D-, and mesolactide result in amorphous PLAs [5]. Commercial PLAs are mostly
blends of PLLA and PDLA or copolymer PDLLA obtained by the polymerization of
LLA and DLLA [9]. PLA with 90% or more PLLA content tends to be crystalline while
that with lower optical purity is amorphous [9].

2.2.2 Properties of PLA
Thermal properties such as glass transition temperature (Tg), melting temperature
(Tm), and degree of crystallinity depend on various factors including the molecular
weight, relative amounts of L- and D-lactic acid stereoisomers, thermal history, etc. Poly
(L-lactic acid) (PLLA) and poly (D-lactic acid) (PDLA) made from L-lactide and Dlactide respectively, are semi crystalline polymers due to their stereoregularity. The

14

extent of crystallinity can be controlled by tuning the relative amounts of L- and D-lactic
stereoisomers in the polymer. For instance, PLA containing more than 90% L-lactic acid
is semicrystalline while lesser amounts of L-lactic acid, between 50% and 90%, will
result in amorphous PLA. Most commercial grades of PLA are made of L-lactide with
fewer amounts of Meso- and D-lactide [5].
Glass transition temperature and melting temperature can vary among different
PLA types. In general, PLA has a glass transition temperature range between 40 and
70°C and a melting temperature between 130 and 180°C [10]. Thermal properties are
also affected by the L-lactic acid content; higher L-lactic acid content increases the Tm
and Tg [11].
PLA possesses good mechanical properties such as high tensile strength and high
modulus when compared to other traditional plastics (Table 2.1). It also has lower impact
resistance and lower strain at break than other petroleum based plastics. The impact
strength increases with increasing molecular weight and crystallinity [5].

15

Table 2.1: Comparison of PLA properties with other petroleum based polymers
HIPS

[12, 13]

Properties

PLA

PET

PS

PP

Tg (ºC)

55

75

105

-10

Density (g/cc)

1.24

1.33

1.05

0.9

Heat Capacity (BTU/lb. ºF)

0.39

0.44

0.54

0.3

Notched Izod (ft.lb/in)

0.24

2.6

0.5

2.3

2

Gardner Impact (in.lb)

0.5

2.8

4.5

100

7

Tensile Strength @ Break (psi)

7700

7900

6500

3300

4500

Tensile Modulus (Kpsi)

500

400

420

300

130

% Elongation

6

130

7

45

120

80-360

110

670

1.80

0.74

0.74

Water vapor permeability
-3

2

225

(×10 ) (kg m/m s Pa)
Cost $US/lb

16

0.77

0.68

The barrier property of a polymer, which is the ability of a molecule to permeate
through its membrane or be obstructed by it, is very critical in designing any package
system. Barrier properties are generally characterized by parameters such as permeability,
diffusivity, and solubility coefficients [14]. PLA is a good barrier to carbon dioxide but is
a poor barrier to oxygen and water vapor. PLA has a CO2 permeation coefficient of 1.76
× 10

-17

2

kgm/m sPa and oxygen permeation coefficient of 3.3 × 10

-17

2

kgm/m sPa

[15].

2.2.3 Property modification of PLA
Properties of PLA can be modified in different ways such as by copolymerization,
blending with other resins, plasticization, etc. Modification is performed to obtain
improved material properties compared to the neat PLA so that the material becomes
suitable for a specific application.

2.2.3.1 Copolymerization
Copolymerization is a method by which two or more monomers are combined
into one polymeric chain to achieve specific properties. The mechanical properties of
copolymerized PLA have been extensively investigated for various packaging
applications.
Copolymerization of PLA can be conducted through polycondensation of lactic
acid with other monomers. However, ring opening copolymerization of lactide with other
cyclic monomers is widely preferred because of the precise control of the chemistry and
the higher molecular weight of the copolymers produced. Depending on the different

17

molecular architecture of the copolymers they can be classified as random, block, graft or
cross-linked copolymers [16].
Monomers that have been copolymerized with lactic acid include glycolide
derivatives, lactones, cyclic amide esters, cyclic ether esters, and cyclic carbonates. For
example, poly(lactic-glycolic acid), a copolymer of lactic acid and glycolic acid, is
approved by the Food and Drug Administration (FDA) for clinical uses [17]. Although
these copolymerized PLAs have a wide range of mechanical properties; they are not
economically viable or cannot be produced in a large scale for packaging applications
[18].

2.2.3.2 Melt blending with other polymers
Melt blending of existing polymers is considered a more economical and
convenient method to achieve specific properties than synthesizing new polymers. PLA
has been blended with various polymers for different purposes [16]. Blending of PLA
with rubbery polymers has been predominantly emphasized in biomedical applications,
resulting in the use of biodegradable and biocompatible polymers such as poly(vinyl
alcohol), poly(ε-caprolactone), poly(ethylene glycol), polyhydroxyalkanoate, and
poly(butylene succinate) as the second polymer phase [19].
The impact strength of PLA can considerably be improved by direct mechanical
blending with inexpensive non-degradable polymers such as poly(ethylene oxide),
poly(vinyl

acetate), polyisoprene, acrylonitrile-butadiene-styrene

copolymer

and

polyethylene. However, the majority of these modifiers are also thermodynamically
immiscible with PLA and lack favorable interactions due to differences in their chemical

18

structures which results in weak interfacial adhesion (indicated by poor dispersion, very
broad size distribution and distinct particle interfaces) and poor mechanical properties.
Compatibilizers are therefore required to improve the interaction between PLA and the
other polymers in order to improve the properties of the blend [20]. For instance,
significant improvement in the impact strength and impact fracture toughness was
reported for PLA/polycaprolactone (PCL) blends compatibilized with dicumyl peroxide
and lysine triisocyanate [16]. However, a recently reported study eliminated the need for
compatibilizer by using ethylene/acrylate copolymer (EAC), a petroleum-based impact
modifier which is compatible with PLA. It was found that melt blending PLA with EAC
improved the mechanical properties of the PLA while also maintaining its
biodegradability at low concentrations [20].

2.2.3.3 Plasticization
The brittleness and lower impact resistance of PLA greatly limit its applicability
in the packaging industry. In packaging applications, films are required to be flexible
because industrial production lines cannot tolerate film cracking or tearing when folded
or subjected to force during manufacturing [21]. Softening of PLA with plasticizers
increases the flexibility and toughness of the produced films. In general, the plasticizers
used with PLA should have the following characteristics: non-toxic, miscible, not prone
to migration, not volatile and biodegradable [22]. Usually the introduction of a plasticizer
into a plastic decreases its glass transition temperature (Tg) while increasing the
flexibility of the polymer chains, which in turn lowers the tensile strength and modulus of
the plastic.

19

Ljungber and Wesslèn studied triacetine, tributyl citrate, acetyl tributyl citrate,
triethyl citrate, and acetyl triethyl citrate and their plasticizing effect on PLA through
dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) and
observed significant reduction in the Tg [22]. Investigations of PLA blended with
monomeric and oligomeric plasticizers such as citrates and PEG resulted in films with
enhanced flexibility and thereby reduced brittleness [23]. Transparent films with
enhanced mechanical properties have been produced from PLA plasticized with adipates
[24].
Although plasticizing PLA with the aforementioned plasticizers improves its
properties and may broaden its applications, the majority of these plasticizers are
derivatives of crude oil and are non-biodegradable [25]. Hence, it is essential to blend
PLA with renewable and biodegradable plasticizers that could withstand the practical
application while their bio-degradation properties are maintained. Epoxidized soybean oil
(ESO) is one such renewable material that has been investigated as a plasticizer for PLA
[26, 27].

2.3 Soybean oils
Vegetable oils have become more attractive recently since they are obtained from
renewable resources and also have other environmental benefits. They are triglyceride
molecules to which three fatty acid groups or esters are attached (Figure 2.3). The long
fatty acid chains of vegetable oils impart desirable flexibility and toughness to some
brittle resin systems such as epoxy, urethane and polyester resins [28]. The different
types of triglyceride vegetable oil include soybean, sunflower, castor, linseed, peanut, etc.

20

Soybean oil is one of the major vegetable oils that is being cultivated and used in
hundreds of products. Having a wide range of uses from food to inks and paints to
plastics, soybeans are an important ingredient in many industrial productions [29]. Out of
the 8.3 million tons of soybean oil consumed in USA, only 3% is used for industrial
applications. Functionalized soybean oil is available for various applications in coatings
and plasticizer additives [30].

O
CH2

O

C

(CH3)4

CH2

CH2

(CH3)4

CH3

O
CH2

O

C

(CH3)7

CH

CH

CH2

O

C

(CH3)5

CH2

CH2

(CH3)7
(CH3)5

CH3
CH3

O

Figure 2.3: Schematic representation of triglyceride structure in vegetable oils

[31]

2.3.1 Synthesis of ESO
The conventional method of preparing epoxidized vegetable oils involves a
reaction where the carbon double bonds of unsaturated fatty acids are epoxidized via
catalysis, producing epoxy functional groups (Figure 2.4). Vegetable oils with a high
content of unsaturated fatty acid produce materials with high epoxy functionality [32].
Most fatty acids in soybean oil are unsaturated, constituted of about 94.4% of
triglycerols, thereby enabling it to have high epoxy functionality materials. The major

21

fatty acid in soybean oil is linoleic acid, followed by oleic, palmitic, linolenic, and steric
acids [28, 29].

O
CH2

O C

O
(CH3)7

CH

CH

O
O

CH

C

(CH3)7 CH

O
CH

CH2

O
CH2

O

C

(CH3)7

(CH3)4

CH2

O
CH

CH

CH2

CH3

(CH3)4

CH3

(CH3)4 CH3

Figure 2.4: Structure of Epoxidised Soy Oil (ESO)

[33]

There are four known technologies to produce epoxides from olefinic molecules:
(a) epoxidation with percarboxylic acids, the most widely used in the industry, which can
be catalyzed by acids or by enzymes; (b) epoxidation with organic and inorganic
peroxides which includes alkaline and nitrile hydrogen peroxide epoxidation as well as
transition metal catalyzed epoxidation; (c) epoxidation with halohydrins, using
hypohalous acids (HOX) and their salts as the reagents for the epoxidation of olefins with
electron deficient double bonds; and (d) epoxidation with molecular oxygen [28].

22

2.3.2 Use of ESO as a plasticizer
ESO is used as a non-toxic plasticizer for non-degradable polymers such as PVC
compounds, phenolic resins, and chlorinated rubbers to improve stability and flexibility
[34]. The work by Ishiaku and coworkers indicated that ESO is an ideal plasticizer for the
PVC/ENR (epoxidized natural rubber) system, with the blend exhibiting good tear
strength, good tensile strength, and a lower glass transition temperature [35]. Other
investigators observed that ESO increases the flexibility of phenolic resins and improves
the electrical properties, solvent resistance, and heat resistance of laminates [36].
Recently, ESO has been reported to be an effective plasticizer for biodegradable
polymers because of its excellent plasticizer performance and great efficiency of
plasticization [37].
ESO has been used as a plasticizer for PLA to improve its properties. Studies
have been conducted on the rheological and tensile properties of PLA/ESO blends [26,
27]. Investigations have shown that the addition of ESO into PLA lowers the Tg, storage
modulus and viscosity of the blend while improving the elongation at break [26]. Other
studies reported increased elongation at break and melt strength in PLA/ESO blends
compared to neat PLA [27]. Additionally, the melt strength was correlated with the ESO
content and higher melt strength was obtained by adding higher ESO content in the
blend, which resulted in higher elongation at break for the blend [27].
Although ESO has been reported to be an effective plasticizer for bio-degradable
polymers due to its excellent permanency and efficiency of plasticization [37], research
conducted so far on PLA plasticized with ESO has mostly focused on the effects of
plasticizer types and/or addition levels on the mechanical properties without due

23

consideration of the processing methods for these blends. Several multi-step approaches
of formulating PLA/ESO blends have been investigated [23, 25]. In most studies ESO is
pre-mixed with PLA prior to shaping the blends in an extruder or using other processing
techniques [27]. This study will explore the feasibility of a novel one-step continuous
process of blending of ESO and PLA needed for the manufacture of flexible PLA sheet
and film.

2.4 Processing technologies for PLA
The main conversion methods for PLA involve melt processing, where PLA is
melted and then formed into desired shapes and dimensions before cooling to stabilize
the parts. These methods include conventional processing technologies such as extrusion,
injection molding, injection stretch blow molding, casting, blown film, thermoforming,
etc. Since all of these methods are based on melt processing, it is essential to understand
the thermal, crystallization, and melt rheological properties of PLA to optimize the
processes [38].

2.4.1 Drying and extrusion
Prior to melt processing, PLA is required to be dried sufficiently to prevent
excessive hydrolysis which affects the physical properties of the polymer [38]. Typically,
the polymer is dried to less than 100 ppm moisture content before extrusion. Extrusion is
the most important technique for continuous melt processing of PLA. An extruder is
usually a part of forming machine systems for injection molding, blow molding, film
blowing and melt spinning [38].

24

2.4.2 Injection molding
Injection molding is the most widely used converting process for thermoplastic
articles requiring complex shape with high dimensional precision. Most injection
molding machines for PLA are based on the reciprocating screw extruder, although twostage systems, which integrate a shooting pot and extruder in a single machine, are also
being used for injection molding of preforms for PLA bottles. The two-stage system
consists of an in-line extruder integrated to a shooting pot. In the two-stage systems, the
extruder plasticizes and feeds the melt into the shooting pot under relatively low injection
pressure, from which the melt is injected into the hot runner under high pressure by a
plunger in the shooting pot. While the reciprocating machine must stop the screw during
the injection and packing phases, the screw for the two-stage machine can rotate during
the majority of the cycle. The two-stage system presents some advantages over its
reciprocating counterpart, including shorter cycle time, small screw motor drive, more
consistent melt quality, and more consistent shot size [39]. In general, injection molded
PLA articles are relatively brittle due to rapid physical aging. Process parameters such as
mold temperature, packing pressure, cooling rate, and post-mold cooling treatment are
expected to influence the PLA aging behavior [38].

2.4.3 Stretch blow molding
The food industry has shown sustained interest in the use of PLA bottles for
beverages that are not sensitive to oxygen such as water or pasteurized milk. These PLA
bottles are generally produced by the injection stretch blow molding technique which
involves biaxial orientation of PLA to improve physical and barrier properties. The

25

molecular orientation induced in this process also reduces effects of aging by stabilizing
the polymer free volume [40]. This technique involves the formation of a parison, which
is then transferred to a blow molding machine where it is stretched in the axial direction
and blown in the hoop direction to achieve biaxial orientation [38].

2.4.4 Thermoforming
Thermoforming is commonly used in making packaging containers that do not
require complicated features. PLA has been thermoformed into disposable cups, food
trays, and blister packaging. The technique involves heating the PLA sheet to soften the
polymer and forcing it either pneumatically or mechanically against the mold, following
by cooling and removing from the mold. In the thermoformed PLA containers, the
regions that are highly drawn are less brittle indicating that orientation increases
toughness in PLA. Typically aluminum molds are used when thermoforming PLA
containers [38].

2.4.5 Cast film and sheet
Typically films ( 0.076 mm or 0.003 in thick) and sheets are ( 0.254 mm or
0.01 in thick) are produced in a similar method by the cast film extrusion technique.
Sheet and film forming is achieved on a three-roll horizontal stack where the molten PLA
is extruded through a die and quenched on polished chrome rollers that are cooled with
circulating water. The rate of extrusion, draw rate, temperature and ratio determine the
thickness of the sheet or film produced. PLA can be co-extruded with other polymers to
form multi-layer structures using this technique, to enhance its properties [38].

26

2.4.6 Extrusion blown film
In extrusion blown film technique, PLA is extruded through an annular die to
form a tube that is inflated into a bubble by blowing air through the die head. The bubble
is then cooled and flattened at the nip rollers and collected by the winder. Films of
different thickness and different degree of orientation can be obtained by varying the
blow-up-ratio (ratio of bubble diameter to the die diameter), screw speed, air pressure,
and winder speed. The weak melt strength of PLA makes it difficult to form a stable
bubble and hence requires the use of additives such as viscosity enhancers to increase its
melt strength. Also, since PLA is brittle, stiff and has low elongation, flattening of the
bubble at the nip rollers tends to produce wrinkles that are permanent, due to the high
dead-fold properties of PLA. This can be overcome by the use of fillers which can reduce
the adhesion between films [38].
Thellen and coworkers produced plasticized blown film with an average thickness
of 0.076 mm and studied the effects of process parameters such as screw speed and feed
rate on the properties of montmorillonite layered silicate (MLS)/ PLA films. The biaxial
orientation of the blown film produced improved the dispersion of the MLS platelets in
the PLA polymer matrix [41]. Other investigators produced blown films (45 µm thick)
from a mono extrusion blown molding machine to test the biodegradation of PLA under
natural conditions [42]. However, we found no reports of PLA/ESO blown films. This
study will explore the feasibility of a novel one-step continuous method of blending of
ESO and PLA needed for the extrusion of flexible PLA blown films.

27

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28

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poly(l-lactide) blown films, Polymer, 46: 11716-11727 (2005).
42. Sedlarik, V., Saha, N., Sedlarikova, J., and Saha, P., Biodegradation of blown films
based on poly(lactic acid) under natural conditions, Macromolecular Symposia, 272:
100-103 (2008).

32

Chapter 3
EXPERIMENTAL
3.1 Materials
Semi-crystalline PLA (2002D grade) from NatureWorks (USA) was used as the
resin in this study. Its properties are listed in Table 3.1. Galata Chemicals supplied the
epoxidized soybean oil, commercially known as Drapex 6.8, which was used as a
3

plasticizer. It had a density of 0.992 g/cm , flash point of 290oC, oxirane content of 7%,
iodine value of 1.6, and was insoluble in water.

[1]

Table 3.1. Characteristics of PLA (2002D) resin used in this study
a

Melt properties
Density of

MFR

m

solid (g/cm )

(g/10 min)

1.256

3.4

.

Thermal properties
χc

Tm

(g/cm )

(%)

(oC)

1.142

15

b

149

3

32

a

MFR and m are the melt flow rate and melt density of PLA, respectively.

b

Tm and c are the melting temperature and percent crystallinity of PLA,
respectively.

33

3.2 Sample manufacturing
Both sheets and films were evaluated. The methods employed to manufacture
these samples were as follows:

3.2.1 Manufacture of plasticized sheets
Several multi-step approaches to formulating PLA/ESO blends have been
investigated [2, 6]. The goal of this study was to develop a one step approach of blending
PLA with ESO during sheet manufacturing. To achieve this goal, it was crucial to
develop a continuous and accurate system for incorporating ESO into the matrix during
processing. This was attained by attaching an extruder and an injection pump in a tandem
way so that accurate amounts of plasticizer could be injected into the molten PLA in the
barrel of the extruder.
A co-rotating segmented twin screw extruder (TSE DSE 25) (C.W. Brabender
Instruments Inc.) with a screw diameter of 25 mm and a length-to-diameter ratio of 32:1
was used to melt and shape the blends into sheets. Its segmented screws were composed
of conveying, shearing, and mixing elements. The extruder was fitted with a rectangular
profile die with dimensions of 50.8 mm (width) by 3 mm (thickness) and was powered by
a 5.6 kilowatt (7.5 hp) Intelli-Torque Plasti-Corder Torque Rheometer® (C.W. Brabender
Instruments Inc.). Additionally, a single screw dosing unit (Color-Exact Type 1000
Plastic Recycling Machinery Aps) was connected to the extruder. A digital variable speed
peristaltic injector pump (Omega Inc.), which is an externally controllable pump, was
used to accurately meter various amounts of plasticizer into the PLA blends. The

34

schematic of the tandem extrusion-injection pump system used in this study is shown in
Figure 3.1.

Figure 3.1: The schematic representation of the tandem extrusion-injection pump system
used in this study.

Prior to blending PLA with plasticizer, it was important to individually calibrate
the dosing unit attached to the extruder and the injector pump as well as in order to derive
regression equations needed in the calculations of the desirable nominal amounts of PLA
and plasticizer in the blends.
Since the flow rate (extruded output) of melted plastic is independent of the
rotational screw speed in a segmented twin screw extruder, the calibration of the amount
of PLA needed in the blends was carried out by changing the screw speed of the dosing
unit instead, which resulted in various melt flow rates for PLA. From the hopper of the
dosing unit, a feed screw conveyed PLA pellets at different speeds to a dome through

35

which they fell freely into the feeding barrel of the extruder with screws running at a
constant rotational speed of 100 rpm throughout the experiments. Starting from the
hopper to the die, the melt blending temperature profile was set at 180-175-175-170165oC. The dosed quantities of melted PLA were then collected over a period of time,
and weighed for flow rate measurements from which a calibration curve was plotted and
the regression equation derived (Figure 3.2).

PLA output (g/min)

60
45
30
15

y = 10.491x + 2.9474
R2 = 0.9966

0
0

2

4

6

Speed (rpm)

Figure 3.2: Calibration curve for determining the nominal amount of extruded PLA in the
blends.

The calibration of the nominal amount of plasticizer (ESO) injected into the
molten PLA during processing was performed similarly. Various amounts of ESO were
injected in an empty beaker by changing the percent injection speed of the pump. Dosed
quantities of ESO were collected over a period of time and weighed to determine the
output, from which the calibration curve was plotted and the regression equation derived
(Figure 3.3).
36

ESO output (g/min)

16
12

8
y = 0.1422x + 0.406
R2 = 0.9978

4
0
0

25

50

75

100

125

Speed (%)

Figure 3.3: Calibration curve for determining the nominal amount of ESO injected in the
blends.

The regression equations and/or calibration curves shown in Figures 3.2 and 3.3
were utilized to determine the amounts of injected ESO and dosed PLA so that the blends
contained accurate concentrations of each component. For example, to extrude 50 g of
PLA/ESO blend made of 80% PLA (40 g of PLA) and 20% ESO (10 g of ESO), one
should set the dosing unit’s screw speed and the pump injection percent speed at
approximately 3.53 rpm and 67.5%, respectively. This approach was followed throughout
the experiments to produce sheets containing various ESO contents (0 to 20 wt %). It
o

should be mentioned that PLA was dried in an oven at 55 C for at least 24 hours prior to
processing to remove residual moisture.

37

3.2.2 Manufacture of plasticized films
Films were produced for only unplasticized PLA (neat PLA) and PLA plasticized
with 15 wt % ESO. The blend of PLA plasticized with 15 wt % ESO was melt mixed
using the system and processing conditions described above. The melt blended materials
were cooled for about an hour at room temperature and granulated in a Conair Wortex
granulator (Model JC-5). Granulated samples were then dried in an oven at 55oC for
about 24 hours and blown into films using a 19 mm single-screw extruder (C.W.
Brabender Instruments Inc.) with a length-to-diameter ratio of 15:1. This extruder was


powered by a 3.73 kilowatt (5 hp) Prep Center D52 (C.W. Brabender Instruments Inc.)
and fitted with a blown film die 25.4 mm in diameter with 0.889 mm (0.035") extrudate
wall thickness. Starting from the hopper to the die, the temperature profile of the extruder
o

was set at 180-175-170-165 C.
Processing parameters such as the blow up ratio (BUR), the extruder’s rotational
screw speed, the speed of the pull up nip rollers or draw ratio (DR), and the air pressure
inside the inflated plastic have strong effects on the thickness of the films. All these
variables were kept constant throughout the experiments. Specifically, the speeds of the
extruder’s rotational screw and the pull up rolls for film take off were set at 30 rpm and
25 rpm, respectively, while the air pressure used to inflate the film varied slightly
between 0.310 and 0.379 MPa (45 and 55 psi) during the extrusion process. The blow up
ratio and draw ratio of blown films (~0.076 mm thick) were calculated using the
following equations and were found to be approximately 3 and 11.7, respectively.

38

BUR 

Rf
Ro

T
DR  o
Tf

(3.1)

(3.2)

where Rf and Ro are the radius of the annular die and the radius of the final tubular film,
respectively, and To and Tf are the thicknesses of the undrawn (0.889 mm) and extrusion
blown films, respectively.

3.3 Property evaluation

3.3.1 Mechanical properties
The mechanical properties of both sheets and films were characterized, including
the tensile strength, tensile modulus, elongation at yield, elongation at break, notched
Izod impact strength, burst pressure, and sealing strength. These tests were carried out in
a walk-in conditioning room at 23oC ± 2oC and 50% ± 4% relative humidity.
Tensile properties of the sheets (~ 2.75 mm thick) were measured with an Instron
5585H testing machine using the Instron Bluehill 2, version 2.14 software, in accordance
with the procedures outlined in ASTM standard D 638. Each formulation included ten
tested replicates to obtain a reliable mean and standard deviation, using a crosshead speed
of 5 mm/min. From the tensile results, the ductility, or the material’s ability to undergo
plastic deformation without fracture, was determined using the following relation:

39

Ductility 

Failure strain
Yielding strain

(3.3)

Notched Izod impact tests of sheets were performed at room temperature in
conformance to ASTM standard D 256 on a Tinius Olsen Izod impact tester (Model 892).
o

The ten specimens tested for each composition were V-notched at a 45 angle using a
Tinius Olsen specimen notcher (Model 899).
Tensile and Izod impact properties were used to assess the effect of plasticizer
concentration on the mechanical properties of the extruded sheets. The results of this part
of the study led to the identification of the amount of ESO that caused the brittle to
ductile transition in PLA samples as well as the optimum amount of ESO that produced
maximum ductility.
As a result, tensile properties of blown films were characterized for unplasticized
PLA (control) but only one plasticized PLA formulation containing 15 wt % ESO
(optimized amount from previous tests as will be discussed later). Unlike for the sheet
samples, tensile properties of plasticized films were measured as a function of time over a
span of 125 days to understand the aging of films stored over a long period of time under
normal environmental conditions. Tensile properties of the film (~ 0.076 mm thick) were
measured with an Instron 5565H testing machine using the Instron Bluehill 2, version
2.21 software and in accordance with the procedures outlined in ASTM standard D882.
Ten replicates were tested to obtain a reliable mean and standard deviation using a
crosshead speed of 12.5 mm/min. From tensile results, the ductility was determined using
equation 3.3.

40

The sealing strengths of neat PLA film and its counterpart plasticized with 15 wt
% ESO were also measured as a function of sealing temperatures. An Impulse sealer
Vertrod (Model 14EP-WC) with sealing voltage in the range of 115-120 AC was used to
seal the samples using three different sets of high point and low point temperatures of
o

o

o

100-120 C, 100-135 C, and 100-150 C. The strength of the seals was tested in
accordance with the procedures outlined in ASTM standard F88. Ten replicates of each
of the sealing conditions were tested to obtain a reliable mean and standard deviation.
Similarly, the burst pressures of pouches made with neat PLA film and its
counterpart plasticized with 15 wt % ESO were measured as a function of sealing
temperature using the Test-A-Pack 2000. The samples were cut into a 10 cm ×10 cm
pouches and sealed (3 side-sealed) using the impulse sealer at the three different sealing
temperatures mentioned above. The equipment was set to an air supply of 0.621 MPa (90
psi) and prefilled before burst testing. Three replicates of samples sealed at each of the
different sealing temperatures were tested.

3.3.2 Thermal properties
The glass transition temperatures (Tg) of PLA plasticized with various amounts of
ESO were determined using a Q200 Differential Scanning Calorimeter (TA instruments).
Samples weighing less than 10 mg were tested in the temperature range of 40ºC to 200ºC
o

at a heating rate of 10 C/min. A dynamic mechanical analyzer (TA instruments) was also
used as a complimentary technique to determine the Tg of the different PLA/ESO blends.

41

Samples were subjected to a dual cantilever at a frequency of 1 Hz and were heated over
o

o

o

a temperature range of 25 C to 140 C at the rate of 5 C/min.

3.3.3 Phase morphology evaluation
The miscibility and the phase morphology of the blends were examined by
scanning electron microscopy (SEM) analysis. A Carl Zeiss EVO LS 2 with an
acceleration voltage of 15kV was used to obtain the micrographic images of the different
blends of PLA/ESO. Micrographic images of neat PLA and blends with 10 wt % ESO
were taken at 20 µm scale, while blends with 20 wt % ESO was taken at a 30 µm scale to
better understand the phase morphology at such high concentration of ESO. SEM
micrographs were taken after coating the surfaces with a thin layer of gold.

3.3.4. Statistical analysis
Unless otherwise mentioned, a one-way analysis of variance (ANOVA) was
performed on all mechanical properties of the sheets and the data were analyzed to
distinguish statistical differences (p < 0.05) between unplasticized (control) and PLA
sheets plasticized with various amounts of ESO. Similarly, a one-way ANOVA was used
for the statistical analysis of the effect of storage time on the ductility of plasticized films.
However, for the burst pressure and seal strength, a two-sample t-test and Duncan's
multiple range tests were employed to determine the statistical differences among the
variables investigated, at a 95% significance level. Comparisons were done between neat
and plasticized samples under different sealing temperatures. All statistical analyses were
performed using Design Expert software (v. 7) from Stat-Ease (Minneapolis, MN).

42

REFERENCES

43

3.4 References
1. Matuana, L.M., Faruk, O., and Diaz, C.A., Cell morphology of extrusion foamed
poly(lactic acid) using endothermic chemical foaming agent, Bioresources
Technology, 100 (23): 5947-5954 (2009).
2. Baiardo, M., Frisoni, G., Scandola, M., Rimelen, M., Lips, D., Ruffieux, K. and
Wintermantel, E., Thermal and mechanical properties of plasticized poly(L-lactic
acid), Journal of Applied Polymer Science. 90: 1731-1738 (2003).
3. Ljungberg, N. and Wesslen, B., Preparation and properties of plasticized poly(lactic
acid) films, Biomacromolecules, 6: 1789-1796 (2005).
4. Semba, T., Kitagawa, K., Ishiaku, U.S., and Hamada, H., The effect of crosslinking
on the mechanical properties of polylactic acid/polycaprolactone blends, Journal of
Applied Polymer Science, 101, 1816-1825 (2006).
5. Siracusa, V., Blanco, I., Romani, S., Tylewicz, U., Rocculi, P., and Rosa, M.D.,
Poly(lactic acid)-modified films for food packaging application: physical,
mechanical, and barrier behavior, Journal of Applied Polymer Science, 125: E390E401(2012).
6. Robertson, M.L., Chang, K., Gramlich, W.M., and Hillmyer, M.A., Toughening of
polylactide with polymerized soybean oil, Macromolecules, 43: 1807-1814 (2010).

44

Chapter 4
RESULTS AND DISCUSSION
4.1 Effect of ESO content on the notched Izod impact strength of PLA sheets
The variation of impact strength with different amounts of ESO in the blends is
illustrated in Figure 4.1. The impact strength of the blends remained nearly unchanged up
to 5 wt % ESO content and then increased significantly with increasing ESO content.
Figure 4.1 clearly shows the brittle-to-ductile transition of the impact strength of PLA
with an increase in ESO concentration. The threshold ESO content at which the transition
from brittle-to-ductile behavior in PLA blends occurred in the range between 5 and 10 wt
% ESO content.

Impact strength (J/m)

60
50

40
30
20
10
0
-5

0

5

10

15

20

25

ESO content (wt. %)

Figure 4.1: Effect of ESO content on the impact strength of PLA.

45

It was essential to understand the morphology of the ESO and its miscibility with
PLA in order to explain the brittle-to-ductile transition of the PLA/ESO blend.
Miscibility plays an important role in toughening of the blend and can be inferred from
the solubility parameters of the two components that are blended. The solubility
parameters of PLA and ESO are 20.2 (MPa)

1/2

1/2

and 16.8 (MPa)

, respectively [1].

These values show that ESO is partially miscible with PLA since the solubility
parameters of PLA and ESO are not the same but are close to each other [1, 2].
Consequently, when ESO is blended with PLA, it may form a second dispersed phase but
will not form a complete miscible phase with PLA [2].
The second dispersed phase of ESO has an effect on the crack propagation in the
blended polymer. Neat PLA is highly brittle and failure occurs by crazing or microcracking where the cracks spread easily and freely. But with the addition of ESO, cracks
do not spread freely due to the dispersed second ESO phase. The dispersed second ESO
phase can be seen in the SEM images of PLA plasticized with 10 wt % ESO [Figure 4.2
(b)] and 20 wt % ESO [Figure 4.2 (c)] where the plasticizer is seen as droplets dispersed
evenly in the PLA matrix. This dispersed ESO phase dissipates a large part of the fracture
energy during the crack bifurcation and alters the crack path. This causes increased
fracture toughness resulting in increased impact strength [3, 4].

46

(b)

(a)

(c)

Figure 4.2: SEM micrographs of PLA plasticized with various amounts of ESO: (a) 0 wt
%, (b) 10 wt %, and (c) 20 wt %.

The impact strength increased significantly from 5 wt % to 10 wt % ESO and
reached a maximum at 10 wt % ESO and started leveling off with any further addition of
ESO. Addition of 15 wt % and 20 wt % ESO did not have any statistical significance in
the impact strength over 10 wt % ESO. In the blends with 10 wt % ESO or more, PLA
and the ESO were assumed to exist in a continuous phase since ESO is partially miscible
with PLA. PLA would form the continuous phase owing to its higher concentration in the
blend and ESO would form the second dispersed phase that dissipates the fracture energy
resulting in improved impact strength.

47

4.2 Effect of ESO content on the tensile properties of PLA sheets

4.2.1. Ductility
Stress-strain curves showing the effect of ESO content on the tensile properties of
plasticized PLA sheets are shown in Figure 4.3. A well-defined yield point before
fracture was observed in all stress-strain curves. However, at up to 5 wt % ESO, the
stress-strain curves of plasticized sheet overlapped with that of neat PLA [Figure 4.3.
(a)], implying an insignificant plasticizing effect when up to 5 wt % ESO was added into
PLA matrix. Additionally, the specimens stretched on a relatively narrow range of strain
(less than 4%) and no localized neck was formed beyond the yield point, indicative of the
brittle nature of the material [5]. These results are in agreement with the impact strength
data shown in Figure 4.1, where the incorporation of up to 5 wt % ESO into PLA did not
toughen the matrix. By contrast, with 10 wt % or more ESO in PLA, the specimens
yielded with stable necking [Figure 4.3. (b)] showing cold-drawing behavior. These
blends underwent tensile deformation as indicated by their stress whitening (Figure 4.4),
caused by void formation due to crazing of the ductile PLA/ESO blends [6]. This is a
morphological indication of the increased toughness in the PLA/ESO blends when
compared to that of neat PLA. Additionally, these specimens stretched on a wide range of
strain, which is typically observed with toughened plastics.

48

60

0%

(a)
Stress (MPa)

5%

10%
40

15%
20%

20

0
0

1

2

3

4

5

6

Strain (%)

60
(b)

20% ESO

Stress (MPa)

15% ESO
40

10% ESO

20

0
0

40

80

120

Strain (%)

Figure 4.3: Stress-strain curves of (a) unplasticized PLA and PLA plasticized with
various amounts of ESO showing well defined yield points and (b) Plasticized PLA
showing .stable necking beyond yield point.

49

Figure 4.4: Tensile deformation showing the stress whitening in unplasticized PLA (left)
and PLA plasticized with 10 wt % ESO (right).

50

Unplasticized PLA was very brittle, as indicated by its low ductility value (Figure
4.5). The addition of up to 5 wt % ESO into PLA did not affect the ductility of the
specimens. Above this concentration, however, a significant increase in ductility occurred
by increasing ESO content, confirming the toughening and plasticizing effects of ESO.
Notice that the brittle-to-ductile transition also happened in the range between 5 and 10
wt % (Figure 4.5), in agreement with the impact strength results shown in Figure 4.1.
This increased flexibility could also be attributed to the partial miscibility between ESO
and the PLA matrix where the ESO forms a continuous phase with the PLA, as
previously discussed. This morphology results in ductile drawing at the fracture
interfaces due to plastic deformation [3].
Like in the case of impact strength, with further increase in the amount of
plasticizer, we would expect the ductility values to level off at 10 wt % ESO. However,
there was a significant increase in ductility by increasing the ESO content from 10 to 15
wt %. This was followed by a decreased ductility from 49% to 30%, when ESO content
was further increased from 15 to 20 wt %. This discrepancy in trend between ductility
and impact strength could be due to the systematic errors during experimentation and
testing as clearly indicated by the wide error bars (standard errors) of the ductility results
shown in Figure 4.5. Nevertheless, the trend showing the brittle-to-ductile transition was
still a good indication of the toughening capacity of ESO as a plasticizer for PLA.

51

100

Ductility

75
50
25
0
-25
-5

0

5

10

15

20

25

ESO content (wt. %)

Figure 4.5: Effect of ESO content on the ductility of the PLA sheet.

52

4.2.2. Tensile strength and Modulus
In the case of semi crystalline polymers like PLA, an efficient plasticizer
generally reduces the glass transition temperature (Tg) of the matrix, thereby increasing
its flexibility but at the expense of the tensile strength and modulus, which decrease.
Therefore, the Tg of PLA decreased with the increasing ESO content in the blends as
expected (Table 4.1), suggesting increased segmental mobility of the PLA chains due to
plasticization. The decreased Tg was significant when more than 5 wt % ESO was added
into PLA matrix.
As expected, this plasticization affected the tensile strength at yield and tensile
modulus of the blends (Figure 4.6). Up to 5 wt %, the addition of ESO did not influence
the strength or the stiffness of PLA, in agreement with the Tg results. However,
increasing the ESO content above 5 wt % led to a significant decrease in both yield
strength and modulus, due to the increased plasticization level of the matrix. As the
plasticizer content increased, PLA became softer, more flexible as indicated by the
reduced Tg, more extensible and tougher, resulting in reduced strength and modulus.
Similar results were reported for PVC plasticized with dioctyl phthalate [5].

53

Table 4.1: Effect of ESO content on the glass transition (Tg) of PLA (2002D) measured
by DSC and DMA.
Tg (oC)
ESO content (wt %)

DSC

DMA

0

59.5

71.3

5

58.7

71.9

10

55.4

69.7

15

55.0

69.4

20

53.2

66.0

2800

100

80
2400
60
2000

40
1600

Strength (MPa)

Modulus (MPa)

modulus
strength

20
-5

0

5

10

15

20

25

ESO content (wt. %)

Figure 4.6: Effect of ESO content on the tensile stress at yield and tensile modulus of
PLA sheet.

54

4.3. Effect of ESO on package related properties
Flexible packaging films are used in several applications and can have multiple
purposes such as to protect packages during shipment, extend product shelf life, enhance
product presentation, etc., which require that a package be designed. This study examined
the effect of plasticizer on the heat sealability of PLA film during pouch manufacture by
measuring both the burst pressure and seal strength of the pouches.

4.3.1 Burst pressure of PLA films
Burst pressure is an indication of the pressure resulting in package failure and is
commonly used to evaluate the integrity of retortable pouches. The internal burst test is
considered a good overall measure of the ability of the pouch to withstand transport and
handling [7].
The burst pressures of pouches made with neat PLA film and its counterpart
plasticized with 15 wt % ESO were measured as a function of sealing temperatures
(Table 4.2). Adhesive failure did not occur at the interface of the seal, i.e., non peelable
seal. Instead, material failure occurred in all pouches, irrespective of the sealing
temperature used and the addition of plasticizer in the films. Nevertheless, pouches made
of plasticized PLA films failed at a lower burst pressure than their counterparts with
unplasticized film (Table 4.2), mainly attributable to the plasticizing, which lowered the
strength of plasticized specimens compared to neat PLA films (Figure 4.6). As
mentioned, the sealing temperatures investigated did not influence the burst pressure
because the package did not experience adhesive failure, i.e., the seals remained intact
during burst tests.

55

4.3.2 Seal strength of PLA films
The integrity of a seal is also a critical step in evaluating the quality of a pouch in
packaging. The seal strengths of neat PLA film and its counterpart plasticized with 15 wt
% ESO were also measured as a function of sealing temperature using the peel test that
measures the maximum force per unit width required to pull apart the seal [7]. The seal
strength of PLA was not affected by the addition of plasticizer nor by the sealing
temperature studied (Table 4.2).

Table 4.2. Effect of sealing temperature on the burst pressure and sealing strength of
unplasticized (neat) PLA and plasticized PLA films.
Burst pressure (kPa)
Sealing
temperature
(oC)

1

Sealing strength (kN/mm)

Plasticized

Neat

2

Plasticized

Neat

A

40.1  1.7

B

10.1  0.2

A

39.1  3.0

B

135-100

69.2  1.7

9.9  0.1

68.2  1.7

A

41.2  3.6

B

150-100

10.1  0.4

120-100

66.3  5.3

1

1

2

A

9.9  0.2

A

A

10.1  0.9

A

A

10.3  1.0

A

The different superscript letters denote that the difference between two treatments
isstatistically significant (p<0.05).
2

Plasticized PLA films contained 15 wt % ESO.

56

4.3.3 Tensile properties of plasticized films as a function of storage time
The tensile properties of blown films were characterized for blown PLA films
plasticized with 15 wt % ESO (optimized amount). The properties of plasticized films
were measured as a function of time over a span of 125 days to understand the aging of
the films stored under normal environmental conditions (Table 4.3).
The ductility remained the same with increasing storage time, indicating that the
flexibility of plasticized film did not change over the period of time tested. This is an
indication of the permanence characteristics of ESO in the PLA/ESO blends. Similar
trend was observed for tensile strength; the plasticized PLA films exhibiting the same
yield strength values (no statistical significance) after 4 months storage period.
In contrast, the tensile modulus showed a slight but a statistically significant
increase in stiffness after only 7 storage days but did not significantly change for the
remaining of the testing period (Table 4.3). The modulus of elasticity increased
significantly with increasing ESO content to a value closer to that of unplasticized PLA,
indicating that the film behaved like unplasticized samples as the storage time increased.
The modulus of elasticity of plasticized film increased from 2.29 GPa to 2.55 GPa when
tested immediately and 125 days after its manufacture, respectively. These results could
indicate a possible loss of plasticizer from the film as the storage time increased.
Additional work must be performed to verify this trend, which cannot be explained at the
moment.

57

Table 4.3. Variations in tensile properties of plasticized PLA films as a function of
storage time.
1,2

Tensile properties
Storage times
Yield Strength

Modulus

(MPa)

(days)

(GPa)

Ductility

A

33.6  2.1

A

2.29  0.13

A

A

34.8  1.8

A

2.44  0.13

B

40.4  8.7

A

33.3  1.8

A

2.51  0.16

B

A

34.1  2.0

A

2.65  0.16

B

92

30.3 15.7
29.7 17.1

A

32.7  3.0

A

2.55  0.23

B

125

0

39.7  14.3

7

42.5  11.4

45

1

The yield strength and tensile modulus of neat PLA films (unplasticized) were 57.1 MPa
and 2.59 GPa, respectively.
2

The different superscript letters denote that the difference between two treatments is
statistically significant (p<0.05).

58

REFERENCES

59

4.4 References
1. Karst, D. and Yang, Y., Using the solubility parameter to explain disperse dye
sorption on polylactide, Journal of Applied Polymer Science, 96(2): 416-422 (2005).
2. Zhao, Y., Qu, J., Feng,Y., Wu, Z., Chen, F., and Tang, H., Mechanical and thermal
properties of epoxidized soybean oil plasticized polybutylene succinate blends,
Polymers Advanced Technology, 23(3): 632-638 (2012).
3. Zheng, S., Wand, J., and Guo, Q., Miscibility, morphology and fracture of epoxy
resin/poly(styrene-co-acrylonitrole) blends, Polymer, 37(21): 4667-4673 (1996).
4. Afrifah, K.A. and Matuana, L.M., Impact modification of polylactide with a
biodegradable ethylene/acrylate copolymer, Macromolecular Materials and
Engineering, 295: 802-811 (2010).
5. Matuana, L.M., Park, C.B., and Balatinecz, J.J., The effect of low levels of plasticizer
on the rheological mechanical properties of polyvinyl chloride/newsprint-fiber
composite, Journal of Vinyl and Additive Technology, 3(4): 265-273 (1997).
6. Ali, F., Chang, Y.W., Kang, S.C., and Yoon, J.Y., Thermal, mechanical and
rheological properties of poly(lactic acid)/epoxidized soybean oil blends, Polymer
Bulletin 62: 91-98 (2009).
7. Yam, K.L., Rossen, J., and Wu, X.F., Relationship between seal strength and burst
pressure for pouches, Packaging Technology and Science, 6: 239-244 (1993).

60

Chapter 5
CONCLUSIONS
5.1 Conclusions
This study was aimed at developing a single-step process that efficiently
incorporates ESO into a PLA matrix in order to manufacture PLA sheet/film with
improved flexibility without affecting other package characteristics. Earlier, several
multi-step approaches to formulating PLA/ESO blends have been investigated [1, 5]. To
achieve this goal, a processing system in which an extruder and a peristaltic injector
pump attached in tandem was developed for a continuous and accurate incorporation of
the plasticizer into the molten matrix.
The effect of ESO addition levels on impact and tensile properties of plasticized
PLA sheets was examined. The flexibility of plasticized specimens and the phase
morphology between the plasticizer and the matrix were characterized through glass
transition measurement and scanning electron microscopy, respectively. Additionally,
this study examined the effect of plasticizer on the heat sealability of PLA film during
pouch manufacture by measuring both the burst pressure and seal strength of the flexible
pouches sealed at different sealing conditions. Finally, the tensile properties of plasticized
PLA blown films as a function of storage time over a span of 125 days was examined.
The following conclusions were drawn from the experimental data.
1. The tandem extrusion-injection pump system developed in this study was
found to be an effective and efficient approach for a continuous and accurate
incorporation of the plasticizer into the molten matrix.

61

2. The impact strength of the blends remained nearly unchanged up to 5 wt %
ESO content and then increased significantly with increasing ESO content.
The threshold ESO content at which the transition from brittle-to-ductile
behavior in PLA blends occurred was in the range between 5 and 10 wt %
ESO content. The impact strength increased significantly from 5 wt % to 10
wt % ESO and reached a maximum at 10 wt % ESO and leveled off with any
further addition of ESO.
3. The ductility of plasticized PLA sheets followed similar trends as the impact
strength results. Notice that the brittle-to-ductile transition also occurred in the
range between 5 and 10 wt % ESO, in agreement with the impact strength
results.
4. Both the tensile strength and the modulus of the sheets decreased with
increasing content of ESO in the blend. This was expected due to the
plasticization effect, which induced a decrease in the glass transition
temperature resulting in mobility of the PLA polymer chains.
5. Flexible pouches made of plasticized PLA films failed at a lower burst
pressure than their counterparts with unplasticized films, mainly attributable
to the plasticizing effect, which lowered the strength of plasticized specimens
compared to neat PLA films. The range of sealing temperatures investigated
did not influence the burst pressure because the package failed due to material
failure while the seals remained intact during burst tests (non peelable seals).
The seal strength of pouches made with PLA films was not affected by the
addition of plasticizer or by the sealing temperatures studied.

62

6. Both the ductility and yield strength of films plasticized with 15 wt % ESO
tested over a 4 months storage period remained the same with increasing
storage time. The results implied that the flexibility of plasticized film did not
change over the period of time tested, which indicate the permanence
characteristics of ESO in the PLA/ESO blends. In contrast, the tensile
modulus showed a slight but a statistically significant increase in stiffness
after only 7 storage days, indicating a possible loss of plasticizer from the film
as the storage time increased. This contradictory trend will be investigated
further.

5.2 Future work
While this study mainly focused on the mechanical properties of the plasticized
PLA films and sheets, the effect of ESO content on the barrier properties of plasticized
PLA must also be studied for other packaging applications. This study showed possible
loss of plasticizer from the film as the storage time increased. It would be appropriate to
perform a thorough migration study to gain an in-depth understanding of the
permanence/leachability of ESO from plasticized PLA films. Distribution properties such
as vibration, impact properties and shock absorption could also be studied for packages
designed with ESO-plasticized PLA films.

63

REFERENCES

64

5.3 References
1. Baiardo, M., Frisoni, G., Scandola, M., Rimelen, M., Lips, D., Ruffieux, K. and
Wintermantel, E., Thermal and mechanical properties of plasticized poly(L-lactic
acid), Journal of Applied Polymer Science. 90: 1731-1738 (2003).
2. Ljungberg, N. and Wesslen, B., Preparation and properties of plasticized poly(lactic
acid) films, Biomacromolecules, 6: 1789-1796 (2005).
3. Semba, T., Kitagawa, K., Ishiaku, U.S., and Hamada, H., The effect of crosslinking
on the mechanical properties of polylactic acid/polycaprolactone blends, Journal of
Applied Polymer Science, 101, 1816-1825 (2006).
4. Siracusa, V., Blanco, I., Romani, S., Tylewicz, U., Rocculi, P., and Rosa, M.D.,
Poly(lactic acid)-modified films for food packaging application: physical,
mechanical, and barrier behavior, Journal of Applied Polymer Science, 125: E390E401(2012).
5. Robertson, M.L., Chang, K., Gramlich, W.M., and Hillmyer, M.A., Toughening of
polylactide with polymerized soybean oil, Macromolecules, 43: 1807-1814 (2010).

65

APPENDICES

66

APPENDIX I
IMPACT STRENGTH DATA OF PLA SHEETS

67

Table A.1 Effect of ESO content on the impact strength of PLA sheets
Impact Strength (J/m)
ESO content

0%

5%

7.5%

10%

15%

20%

19.28

24.07

38.65

38.45

52.73

41.17

18.50

14.72

35.07

39.02

39.78

39.40

24.08

17.06

33.08

53.47

41.81

41.01

5.85

17.43

33.80

36.87

45.68

42.10

13.57

12.90

34.96

39.24

42.34

41.47

15.17

14.81

39.78

45.81

63.49

41.18

16.23

20.73

35.98

42.67

41.68

42.99

13.31

16.20

34.96

41.08

57.97

41.59

15.75

17.24

37.09

58.70

49.92

47.13

15.75

17.24

37.22

44.94

35.62

45.80

Avg

15.75

17.24

36.06

44.03

47.10

42.38

Std

4.70

3.18

2.12

7.07

8.78

2.35

Dev

68

Table A.2. Analysis of variance for the effect of ESO content on the impact strength of
PLA
Source

Sum of
Squares

DF

Mean
Square

F Value

Prob > F

Model

10,566.64

5

2,113.33

78.90

< 0.0001

ESO
content

10,566.64

5

2,113.33

78.90

< 0.0001

Pure Error

1,692.98

60

28.22

Cor Total

12,259.62

65

Significant

Table A.3. Pairwise comparison of impact strength of PLA/ESO blends
ESO
Content

Mean
Difference

DF

Standard
Error

t for Ho
Coeff = 0

Prob > |t|

1 vs 2

-1.25

1

2.27

-0.55

0.5818

1 vs 3

-19.56

1

2.27

-8.64

< 0.0001

1 vs 4

-27.52

1

2.27

-12.15

< 0.0001

1 vs 5

-31.36

1

2.27

-13.85

< 0.0001

1 vs 6

-27.21

1

2.27

-12.01

< 0.0001

2 vs 3

-18.31

1

2.27

-8.08

< 0.0001

2 vs 4

-26.26

1

2.27

-11.60

< 0.0001

2 vs 5

-30.11

1

2.27

-13.29

< 0.0001

2 vs 6

-25.96

1

2.27

-11.46

< 0.0001

3 vs 4

-7.96

1

2.27

-3.51

0.0008

3 vs 5

-11.80

1

2.27

-5.21

< 0.0001

3 vs 6

-7.65

1

2.27

-3.38

0.0013

4 vs 5

-3.84

1

2.27

-1.70

0.0950

4 vs 6

0.31

1

2.27

0.14

0.8922

5 vs 6

4.15

1

2.27

1.83

0.0719

ESO Contents: 1 – 0 %, 2 – 5 %, 3 – 7.5 %, 4 – 10 %, 5 – 15 %, and 6 – 20 %

69

APPENDIX II
TENSILE PROPERTIES DATA OF PLA SHEETS

70

APPENDIX II-1
The Effect of ESO Content on the Tensile Modulus of PLA Sheets

71

Table A.4 Effect of ESO content on the tensile modulus of PLA sheets
Tensile Modulus (MPa)
ESO content

0%

5%

10%

15%

20%

2,860.73

2,722.15

2,353.02

2,409.86

2,530.32

2,564.51

2,758.41

2,389.90

2,087.68

2,112.13

2,686.62

2,613.61

2,082.57

2,077.50

2,274.66

2,665.25

2,811.13

2,446.84

2,328.59

2,394.28

2,581.39

2,304.45

2,505.97

2,296.96

1,876.32

2,335.16

2,394.75

2,355.87

2,331.35

2,269.45

2,490.15

2,361.11

2,497.43

2,215.09

2,016.55

2,553.62

2,404.51

2,475.10

2,273.89

2,299.79

2,594.91

2,591.85

2,259.28

2,397.66

2,034.15

2,616.25

2,551.33

2,340.23

2,351.98

2,200.85

Average

2,594.86

2,551.33

2,370.62

2,277.06

2,200.85

Std Dev

135.70

189.83

128.37

117.06

206.42

72

Table A.5. Analysis of variance for the effect of ESO content on the tensile modulus of
PLA
Source

Sum of
Squares

Mean
Square

F Value

Model

1,165,043

4

291,260.7

12.2892 < 0.0001

ESO content

1,165,043

4

291,260.7

12.2892 < 0.0001

Pure Error

1,066,520

45

23,700.44

Cor Total

2,231,563

49

DF

Prob > F
Significant

Table A.6. Pairwise comparison of tensile modulus of PLA/ESO blends
ESO
Content

Mean
Difference

DF

Standard
Error

t for Ho
Coeff = 0

Prob > |t|

1 vs 2

43.53

1.00

68.85

0.63

0.5304

1 vs 3

224.24

1.00

68.85

3.26

0.0021

1 vs 4

317.80

1.00

68.85

4.62

< 0.0001

1 vs 5

394.01

1.00

68.85

5.72

< 0.0001

2 vs 3

180.71

1.00

68.85

2.62

0.0118

2 vs 4

274.27

1.00

68.85

3.98

0.0002

2 vs 5

350.48

1.00

68.85

5.09

< 0.0001

3 vs 4

93.57

1.00

68.85

1.36

0.1809

3 vs 5

169.77

1.00

68.85

2.47

0.0175

4 vs 5

76.21

1.00

68.85

1.11

0.2742

ESO Contents: 1 – 0 %, 2 – 5 %, 3 – 10 %, 4 – 15 %, and 5 – 20 %

73

APPENDIX II-2

The Effect of ESO Content on the Tensile Strength at Yield of PLA Sheets

74

Table A.7 Effect of ESO content on the tensile strength at yield of PLA sheets
Tensile Strength at Yield (MPa)
ESO content

0%

5%

10%

15%

20%

57.74

61.28

36.15

30.78

26.10

56.70

51.94

36.19

27.97

24.48

56.12

58.98

34.56

30.61

26.07

56.69

62.75

39.22

28.55

29.87

58.99

59.01

37.65

28.53

23.91

58.04

61.96

36.53

29.90

27.33

56.09

61.56

36.38

31.91

28.56

55.98

58.22

37.40

28.33

27.43

57.37

55.71

39.01

30.77

28.82

57.19

59.05

36.95

30.06

27.19

Average

57.09

59.05

37.00

29.74

27.19

Std Dev

0.97

3.46

1.39

1.32

1.69

75

Table A.8. Analysis of variance for the effect of ESO content on the tensile strength at
yield of PLA
Sum of
Squares

Source
Model

DF

Prob >
F

Mean Square F Value

9,192.416

4

2,298.104

610.024

< 0.0001

ESO content

9,192.416

4

2,298.104

610.024

< 0.0001

Pure Error

169.5254

45

3.767232

Cor Total

9,361.941

Significa
nt

49

Table A.9. Pairwise comparison of tensile strength at yield of PLA
ESO
Content

Mean
Difference

DF

Standard
Error

t for Ho
Coeff = 0

Prob > |t|

1 vs 2

-1.96

1.00

0.87

-2.25

0.0291

1 vs 3

20.09

1.00

0.87

23.14

< 0.0001

1 vs 4

27.35

1.00

0.87

31.51

< 0.0001

1 vs 5

30.11

1.00

0.87

34.69

< 0.0001

2 vs 3

22.04

1.00

0.87

25.39

< 0.0001

2 vs 4

29.31

1.00

0.87

33.76

< 0.0001

2 vs 5

32.07

1.00

0.87

36.95

< 0.0001

3 vs 4

7.26

1.00

0.87

8.37

< 0.0001

3 vs 5

10.03

1.00

0.87

11.55

< 0.0001

4 vs 5

2.77

1.00

0.87

3.19

0.0026

ESO Contents: 1 – 0 %, 2 – 5 %, 3 – 10 %, 4 – 15 %, and 5 – 20 %.

76

APPENDIX II-3

The Effect of ESO Content on the Ductility of PLA Sheets

77

Table A.10 Effect of ESO content on the tensile strain at break and at yield of PLA sheets
Tensile Strain (%)
0% ESO

5% ESO

10% ESO

15% ESO

20% ESO

Break

Yield

Break

Yield

Break

Yield

Break

Yield

Break

Yield

6.25

2.64

3.43

3.30

82.92

2.25

100.93

1.57

42.83

1.33

4.94

3.10

2.51

2.48

58.32

2.30

38.88

1.85

54.3

1.43

3.4

2.91

3.33

3.13

106.14

2.34

95.72

1.82

37.37

1.44

3.33

3.03

3.23

3.05

84.82

2.16

80.99

1.52

77.56

1.57

5.95

3.281

4.43

4.12

80.84

2.09

57.09

1.57

45.16

1.95

6.77

3.66

4.07

3.99

95.73

2.23

66.81

1.57

21.97

1.67

5.07

3.46

3.89

3.87

25.18

1.92

79.77

1.74

36.88

1.90

4.59

3.20

4.3

3.54

91.06

2.19

89.87

1.59

50.31

1.67

4.54

3.13

3.67

3.03

102.96

2.59

115.48

1.65

72.2

1.54

3.69

3.19

3.65

3.39

88.21

2.23

80.62

1.66

48.73

1.61

Avg

4.85

3.16

3.65

3.39

81.62

2.23

80.62

1.66

48.73

1.61

Std.
Dev.

1.19

0.28

0.57

0.50

23.87

0.17

22.18

0.11

16.49

0.20

78

Table A.11 Effect of ESO content on the ductility of PLA sheets
Ductility
ESO content

0%

5%

10%

15%

20%

2.37

1.04

36.89

64.09

32.23

1.59

1.01

25.39

20.97

38.04

1.16

1.06

45.24

52.57

25.89

1.10

1.06

39.17

53.09

49.25

1.81

1.08

38.50

36.25

23.13

1.85

1.02

42.91

42.42

13.13

1.46

1.00

13.12

45.87

19.38

1.43

1.21

41.43

56.47

30.06

1.45

1.21

39.72

69.70

46.82

1.15

1.08

39.54

49.05

30.88

Average

1.54

1.08

36.19

49.05

30.88

Std Dev

0.39

0.07

9.67

13.91

11.44

79

Table A.12. Analysis of variance for the effect of ESO content on the ductility of PLA
Source

Sum of
Squares

DF

Mean Square

F Value

Prob > F

Model

18,530.59

4

4,632.648

55.3916

< 0.0001

ESO content

18,530.59

4

4,632.648

55.3916

< 0.0001

Pure Error

3,763.548

45

83.63441

Cor Total

22,294.14

49

Significant

Table A.13. Pairwise comparison of ductility of PLA/ESO blends
ESO
Content

Mean
Difference

DF

Standard
Error

t for Ho
Coeff = 0

Prob > |t|

1 vs 2

0.46

1.00

4.09

0.11

0.9108

1 vs 3

-34.65

1.00

4.09

-8.47

< 0.0001

1 vs 4

-47.51

1.00

4.09

-11.62

< 0.0001

1 vs 5

-29.34

1.00

4.09

-7.17

< 0.0001

2 vs 3

-35.11

1.00

4.09

-8.59

< 0.0001

2 vs 4

-47.97

1.00

4.09

-11.73

< 0.0001

2 vs 5

-29.80

1.00

4.09

-7.29

< 0.0001

3 vs 4

-12.86

1.00

4.09

-3.14

0.0030

3 vs 5

5.31

1.00

4.09

1.30

0.2008

4 vs 5

18.17

1.00

4.09

4.44

< 0.0001

ESO Contents: 1 – 0 %, 2 – 5 %, 3 – 10 %, 4 – 15 %, and 5 – 20 %.

80

APPENDIX III

TENSILE PROPERTIES DATA OF PLA FILMS

81

APPENDIX III-1
The Effect of Storage Time on the Tensile Strength at Yield of PLA Films
Plasticized with 15 wt % ESO

82

Table A.14. Effect of storage time on the tensile strength at yield of plasticized PLA
films
Tensile Strength at Yield (MPa)
Storage Time

0 days

7 days

45 days

92 days

125 days

35.56

34.50

32.07

34.51

28.45

31.09

32.91

33.79

34.39

31.66

34.29

38.25

32.16

34.95

32.81

34.90

39.52

37.55

33.35

31.77

30.16

34.21

33.13

32.84

36.46

32.87

35.70

33.67

37.25

31.58

32.52

39.40

31.90

33.19

38.57

36.74

34.97

34.43

36.48

31.17

33.91

28.13

32.58

30.04

34.64

33.78

30.78

32.51

33.60

30.00

Average

33.58

34.84

33.38

34.06

32.71

Std Dev

1.99

3.66

1.69

2.01

3.04

83

Table A.15. Analysis of variance for the effect of storage time on the tensile strength at
yield of plasticized PLA films
Source

Sum of
Squares

DF

Mean
Square

F Value

Prob > F

Model

25.13

4

6.28

0.94

0.4514

Storage time

25.13

4

6.28

0.94

0.4514

Pure Error

301.83

45

6.70

Cor Total

326.96

49

Not
significant

Table A.16. Pairwise comparison of tensile strength at yield of plasticized PLA films
ESO
Content

Mean
Difference

Standard
Error

t for Ho
Coeff = 0

Prob > |t|

1 vs 2

-1.25

1.00

1.16

-1.08

0.2849

1 vs 3

0.20

1.00

1.16

0.17

0.8620

1 vs 4

-0.48

1.00

1.16

-0.41

0.6814

1 vs 5

0.87

1.00

1.16

0.75

0.4559

2 vs 3

1.46

1.00

1.16

1.26

0.2152

2 vs 4

0.77

1.00

1.16

0.67

0.5070

2 vs 5

2.12

1.00

1.16

1.83

0.0732

3 vs 4

-0.68

1.00

1.16

-0.59

0.5594

3 vs 5

0.67

1.00

1.16

0.58

0.5666

4 vs 5

1.35

1.00

1.16

1.17

0.2500

DF

Storage days: 1 – 0 day, 2 – 7 days, 3 – 45 days, 4 – 92 days, and 5 – 125 days

84

APPENDIX III-2

The Effect of Storage Time on the Tensile Modulus of PLA Films Plasticized with 15
wt % ESO

85

Table A.17. Effect of storage time on the tensile modulus of plasticized PLA films
Tensile Modulus (MPa)
Storage Time

0 days

7 days

45 days

92 days

125 days

2,433.52

2,518.34

2,555.18

2,702.09

2,332.75

2,281.20

2,295.16

2,246.60

2,699.53

2,411.47

2,411.76

2,492.07

2,480.21

2,707.00

2,399.35

2,308.12

2,514.13

2,801.84

2,668.89

2,360.62

2,107.45

2,377.00

2,471.46

2,631.10

2,902.41

2,342.31

2,513.23

2,507.46

2,819.72

2,497.61

2,091.88

2,654.83

2,394.79

2,387.74

2,972.66

2,395.58

2,412.59

2,657.79

2,887.82

2,572.77

2,210.09

2,175.37

2,423.34

2,369.19

2,665.57

2,289.39

2,442.25

2,544.21

2,616.96

2,364.55

Average

2,287.13

2,439.50

2,508.29

2,649.00

2,547.98

Std Dev

119.5318

133.9929

150.0888

164.386

230.6409

86

Table A.18. Analysis of variance for the effect of storage time on the tensile modulus of
plasticized PLA films
Source

Sum of
Squares

DF

Mean
Square

F Value

Prob > F

Model

726,191.7

4

181,547.9

6.72466

0.0002

Storage time

726,191.7

4

181,547.9

6.72466

0.0002

Pure Error

1,214,879

45

26,997.31

Cor Total

1,941,071

49

Significant

Table A.19. Pairwise comparison of tensile modulus of plasticized PLA film
ESO
Content

Mean
Difference

DF

Standard
Error

t for Ho
Coeff = 0

Prob > |t|

1 vs 2

-152.37

1.00

73.48

-2.07

0.0439

1 vs 3

-221.16

1.00

73.48

-3.01

0.0043

1 vs 4

-361.87

1.00

73.48

-4.92

< 0.0001

1 vs 5

-260.85

1.00

73.48

-3.55

0.0009

2 vs 3

-68.79

1.00

73.48

-0.94

0.3542

2 vs 4

-209.51

1.00

73.48

-2.85

0.0066

2 vs 5

-108.48

1.00

73.48

-1.48

0.1468

3 vs 4

-140.72

1.00

73.48

-1.92

0.0619

3 vs 5

-39.69

1.00

73.48

-0.54

0.5918

4 vs 5

101.03

1.00

73.48

1.37

0.1760

Storage days: 1 – 0 day, 2 – 7 days, 3 – 45 days, 4 – 92 days, and 5 – 125 days

87

APPENDIX III-3

The Effect of Storage Time on the Energy to Break of PLA Films Plasticized with 15
wt % ESO

88

Table A.20. Effect of storage time on the energy at break of plasticized films
Energy at Break (J)
Storage Time

0 days

7 days

45 days

92 days

125 days

5.79

6.80

4.64

1.23

2.40

11.94

4.82

7.57

1.01

2.34

3.27

9.06

5.29

4.08

4.02

3.44

7.75

3.63

0.50

0.91

9.24

4.02

5.60

3.10

4.14

5.81

3.37

5.80

3.54

2.60

4.32

6.06

6.20

1.97

3.33

9.04

7.36

4.65

3.35

4.62

4.37

6.45

7.90

2.41

3.69

6.35

4.18

7.47

2.69

3.64

Average

6.36

5.99

5.87

2.39

3.17

Std Dev

2.86

1.85

1.42

1.19

1.11

89

Table A.21. Analysis of variance for the effect of storage time on the energy at break of
plasticized PLA films
Source

Sum of
Squares

DF

Mean
Square

F Value

Prob > F

Model

8.263008

4

2.065752

12.2568

< 0.0001

Storage time

8.263008

4

2.065752

12.2568

< 0.0001

Pure Error

7.584243

45

0.168539

Cor Total

15.84725

49

Significant

Table A.22. Pairwise comparison of energy at break of plasticized PLA film
ESO
Content

Mean
Difference

DF

Standard
Error

t for Ho
Coeff = 0

Prob > |t|

1 vs 2

0.047403

1

0.183597

0.258192

0.7974

1 vs 3

0.059688

1

0.183597

0.325102

0.7466

1 vs 4

0.976866

1

0.183597

5.320717

< 0.0001

1 vs 5

0.718153

1

0.183597

3.911581

0.0003

2 vs 3

0.012285

1

0.183597

0.06691

0.9469

2 vs 4

0.929463

1

0.183597

5.062525

< 0.0001

2 vs 5

0.67075

1

0.183597

3.653389

0.0007

3 vs 4

0.917178

1

0.183597

4.995615

< 0.0001

3 vs 5

0.658466

1

0.183597

3.586479

0.0008

4 vs 5

-0.25871

1

0.183597

-1.40914

0.1657

Storage days: 1 – 0 day, 2 – 7 days, 3 – 45 days, 4 – 92 days, and 5 – 125 days

90

APPENDIX III-4

The Effect of Storage Time on the Ductility of PLA Films Plasticized with 15 wt %
ESO

91

Table A.23. Effect of storage time on the tensile strain at break and at yield of plasticized films
Tensile Strain (%)
0 Days

7 Days

45 Days

92 Days

125 Days

Break

Yield

Break

Yield

Break

Yield

Break

Yield

Break

Yield

76.79

1.82

91.06

1.72

54.48

1.90

22.70

1.46

37.31

1.54

109.15

1.94

55.17

1.76

90.93

1.80

22.35

1.48

29.49

0.60

43.13

1.80

113.76

1.95

76.59

1.96

65.60

1.49

70.73

2.45

58.65

1.92

87.55

1.84

57.81

1.98

9.75

1.29

16.46

3.09

117.96

1.80

63.79

1.80

82.06

1.95

72.81

1.36

77.52

1.78

63.06

1.92

52.67

1.90

79.04

1.93

61.99

2.08

42.18

2.76

74.33

2.21

96.73

1.85

67.59

1.97

44.23

1.97

67.46

2.32

104.64

1.97

96.44

1.84

81.07

1.96

70.73

1.38

83.94

2.05

46.11

2.08

73.92

1.94

99.64

1.99

51.87

1.50

64.55

1.38

77.15

1.95

53.03

1.84

97.15

1.80

47.77

1.47

86.05

1.39

Avg

77.10

1.94

78.41

1.84

78.63

1.93

46.98

1.55

57.57

1.94

Std.
Dev.

26.07

0.13

21.69

0.07

15.26

0.07

22.15

0.26

24.38

0.75

92

Table A.24. Effect of storage time on the ductility of plasticized films
Ductility
Storage Time

0 days

7 days

45 days

92 days

125 days

42.17

52.86

28.61

15.55

24.20

56.39

31.43

50.39

15.14

49.38

23.90

58.28

39.17

43.94

28.82

30.56

47.65

29.19

7.56

5.32

65.37

35.35

42.06

53.43

43.48

32.85

27.68

40.85

29.74

15.28

33.56

52.19

34.31

22.44

29.13

53.15

52.49

41.46

51.30

40.95

22.13

38.19

49.99

34.62

46.65

39.64

28.86

53.84

32.42

61.79

Average

39.97

42.50

40.99

30.61

29.72

Std Dev

14.34

11.42

8.67

15.67

17.07

93

Table A.25. Analysis of variance for the effect of storage time on the ductility of
plasticized PLA films
Sum of
Squares

Source
Model

DF

Mean
Square

F Value

Prob > F

795.489

4

198.8722

1.63055

0.1884

795.489

4

198.8722

1.63055

0.1884

Pure Error

4,268.818

35

121.9662

Cor Total

5,064.307

Not
significant

39

Storage time

Table A.26. Pairwise comparison of ductility of plasticized PLA films
ESO
Content

Mean
Difference

DF

Standard
Error

t for Ho
Coeff = 0

Prob > |t|

1 vs 2

-4.03

1.00

5.52

-0.73

0.4706

1 vs 3

-1.90

1.00

5.52

-0.34

0.7328

1 vs 4

8.38

1.00

5.52

1.52

0.1379

1 vs 5

4.29

1.00

5.52

0.78

0.4422

2 vs 3

2.13

1.00

5.52

0.39

0.7024

2 vs 4

12.41

1.00

5.52

2.25

0.0310

2 vs 5

8.32

1.00

5.52

1.51

0.1409

3 vs 4

10.28

1.00

5.52

1.86

0.0710

3 vs 5

6.19

1.00

5.52

1.12

0.2698

4 vs 5

-4.09

1.00

5.52

-0.74

0.4636

Storage days: 1 – 0 day, 2 – 7 days, 3 – 45 days, 4 – 92 days, and 5 – 125 days

94

APPENDIX IV

BURST PRESSURE AND SEAL STRENGTH DATA OF PLA FILMS

95

APPENDIX IV-1
Effect of Sealing Temperature on the Burst Pressure of PLA Films

96

Table A.27. Effect of sealing temperature on the burst pressure of unplasticized and
plasticized films
Unplasticized PLA

Plasticized PLA

100-120
(°C)

100-135
(°C)

100-150
(°C)

100-120
(°C)

100-135
(°C)

100-150
(°C)

61,539

70,920

66,217

38,596

35,784

37,202

65,396

67,461

69,129

39,666

41,731

44,269

71,990

69,054

69,228

41,905

39,715

42,254

Avg

66,308

69,145

68,191

40,056

39,077

41,242

Std
Dev

5,286

1,731

1,711

1,689

3,025

3,641

97

Table A.28. Analysis of Variance for the effect of sealing temperature and plasticization
on the burst pressure PLA films
Sum of
Squares

DF

Model

3.49E+09

5

6.97E+08

70.78

< 0.0001

Sealing
temperature

3.49E+09

5

6.97E+08

70.78

< 0.0001

Pure Error

1.18E+08

12

9,851,038

Cor Total

3.6E+09

17

Source

Mean Square F Value

Prob > F
Significant

Table A.29. Pairwise comparison of burst pressure of PLA films
ESO
Content

Mean
Difference

DF

Standard
Error

t for Ho
Coeff = 0

Prob > |t|

1 vs 2

-2,836.67

1.00

2,562.69

-1.11

0.2900

1 vs 3

-1,883.00

1.00

2,562.69

-0.73

0.4766

1 vs 4

26,252.67

1.00

2,562.69

10.24

< 0.0001

1 vs 5

27,231.67

1.00

2,562.69

10.63

< 0.0001

1 vs 6

25,066.67

1.00

2,562.69

9.78

< 0.0001

2 vs 3

953.67

1.00

2,562.69

0.37

0.7163

2 vs 4

29,089.33

1.00

2,562.69

11.35

< 0.0001

2 vs 5

30,068.33

1.00

2,562.69

11.73

< 0.0001

2 vs 6

27,903.33

1.00

2,562.69

10.89

< 0.0001

3 vs 4

28,135.67

1.00

2,562.69

10.98

< 0.0001

3 vs 5

29,114.67

1.00

2,562.69

11.36

< 0.0001

3 vs 6

26,949.67

1.00

2,562.69

10.52

< 0.0001

4 vs 5

979.00

1.00

2,562.69

0.38

0.7091

4 vs 6

-1186.00

1.00

2,562.69

-0.46

0.6518

5 vs 6

-2165.00

1.00

2,562.69

-0.84

0.4147

Storage days: 1 – 100-120 Neat PLA film, 2 – 100-135 Neat PLA film, 3 – 100-150 Neat
PLA film, 4 – 100-120 Plasticized PLA film, 5 – 100-135 Plasticized PLA film, and 6 –
100-150 Plasticized PLA film

98

APPENDIX IV-2
Effect of Sealing Temperature on the Seal Strength of PLA Films

99

Table A.30. Effect of sealing temperature on the seal strength of unplasticized films
Sealing Temperature (°C)
100-120

100-135

100-150

Max
Load
(lbf)

Tensile
Extension
(in)

Seal
Strength
(lbf/in)

Max
Load
(lbf)

Tensile
Extension
(in)

Seal
Strength
(lbf/in)

Max
Load
(lbf)

Tensile
Extension
(in)

Seal
Strength
(lbf/in)

8.00

0.14

57.15

8.00

0.14

57.15

9.00

0.16

56.25

7.00

0.12

58.34

9.00

0.16

56.25

6.00

0.10

60.01

6.00

0.10

59.99

8.00

0.14

57.15

4.00

0.06

66.66

7.00

0.12

58.34

8.00

0.14

57.15

5.00

0.08

62.49

8.00

0.14

57.15

9.00

0.16

56.25

6.00

0.10

60.73

8.00

0.14

57.15

9.00

0.16

56.25

4.00

0.06

66.67

8.00

0.14

57.15

9.00

0.16

56.25

5.00

0.07

68.67

8.00

0.14

57.15

9.00

0.16

56.25

9.00

0.16

56.25

8.00

0.14

57.15

7.00

0.12

58.34

8.00

0.14

57.15

8.00

0.14

57.15

9.00

0.16

56.25

8.00

0.14

57.14

Avg

7.60

0.13

57.67

8.50

0.15

56.73

6.40

0.11

61.20

Std
Dev

0.70

0.01

0.96

0.71

0.01

0.71

1.96

0.04

4.72

100

Table A.31. Effect of sealing temperature on the seal strength of plasticized films
Sealing Temperature (°C)
100-120

100-135

100-150

Max
Load
(lbf)

Tensile
Extension
(in)

Seal
Strength
(lbf/in)

Max
Load
(lbf)

Tensile
Extension
(in)

Seal
Strength
(lbf/in)

Max
Load
(lbf)

Tensile
Extension
(in)

Seal
Strength
(lbf/in)

10.00

0.18

55.56

8.00

0.14

57.15

10.00

0.18

55.56

10.00

0.18

55.56

10.00

0.18

55.56

7.00

0.12

58.34

8.00

0.14

57.15

10.00

0.14

71.43

7.00

0.12

58.34

10.00

0.18

55.56

11.00

0.20

55.00

8.00

0.14

57.15

7.00

0.12

58.34

10.00

0.18

55.56

6.00

0.08

74.99

8.00

0.14

57.15

10.00

0.18

55.56

9.00

0.16

56.25

10.00

0.18

55.56

9.00

0.16

56.25

10.00

0.18

55.56

10.00

0.18

55.56

10.00

0.18

55.56

10.00

0.18

55.56

8.00

0.14

57.15

7.00

0.12

58.34

6.00

0.10

60.00

11.00

0.20

55.00

10.00

0.18

55.56

9.00

0.16

56.25

Avg

9.20

0.16

56.26

9.50

0.17

57.60

8.20

0.14

58.80

Std
Dev

1.32

0.03

1.09

1.18

0.03

4.96

1.62

0.04

5.88

101

Table A.32. Analysis of variance for the effect of sealing temperature and plasticization
on the seal strength PLA films
Source
Model

Sum of
Squares

Mean
Square

DF

F Value

Prob > F

1.177442

5

0.235488

0.68634

0.6358

Sealing
temperature

1.177442

5

0.235488

0.68634

0.6358

Pure Error

18.5277

54

0.343106

Cor Total

19.70514

Not
significant

59

Table A.33. Pairwise comparison of seal strength of PLA films
ESO
Content

Mean
Difference

DF

Standard
Error

t for Ho
Coeff = 0

Prob > |t|

1 vs 2

0.16

1.00

0.26

0.63

0.5317

1 vs 3

0.03

1.00

0.26

0.10

0.9201

1 vs 4

0.25

1.00

0.26

0.94

0.3492

1 vs 5

0.01

1.00

0.26

0.05

0.9614

1 vs 6

-0.20

1.00

0.26

-0.76

0.4531

2 vs 3

-0.14

1.00

0.26

-0.53

0.5992

2 vs 4

0.08

1.00

0.26

0.31

0.7540

2 vs 5

-0.15

1.00

0.26

-0.58

0.5638

2 vs 6

-0.36

1.00

0.26

-1.39

0.1717

3 vs 4

0.22

1.00

0.26

0.84

0.4026

3 vs 5

-0.01

1.00

0.26

-0.05

0.9586

3 vs 6

-0.22

1.00

0.26

-0.86

0.3955

4 vs 5

-0.23

1.00

0.26

-0.90

0.3743

4 vs 6

-0.45

1.00

0.26

-1.70

0.0948

5 vs 6

-0.21

1.00

0.26

-0.80

0.4247

Storage days: 1 – 100-120 Neat PLA film, 2 – 100-135 Neat PLA film, 3 – 100-150 Neat
PLA film, 4 – 100-120 Plasticized PLA film, 5 – 100-135 Plasticized PLA film, and 6 –
100-150 Plasticized PLA film
102