PREPARATION AND CHARACTERIZATION OF 
ENVIRONMENTALLY FRIENDLY POLYMERIC BLENDS USING 
SYNTHETIC AND NATURAL POLYMERS 
by 
G. M. Gayani Dhamrnika Dias 
This Thesis was submitted to Department of Chemical and Process Engineering of the 
University of Moratuwa in partial fulfillment of the requirement for the Degree of 
Master of Science in Polymer Technology 
Univers i ty o f M o r a t u i v a 
79628 
Department of Chemical and Process Engineering 
y ; ^ Tresis Coll-
University of Moratuwa 
Sri Lanka 1 ^ G s 2 < 3 
February 02, 2004 
79628 
DECLARATION 
I hereby declare that this submission is a result of a work carried Out by me and to the 
best of my knowledge, it contain no material previously written or published by 
another person nor material which has been accepted for the award of any degree or 
acceptable qualification of a university, or other Institute of higher learning, except 
where the due reference to the material is made. 
(G.M.Gayani Dhammika Dias) 
February 02, 2004 
To the best of my knowledge, the above particulars are correct. 
(Dr. B A J K Premachandra) 
1 
ABSTRACT 
This thesis is consisted of four chapters. Chapter one contains \an introductory part 
including scope and the objectives of the research. Since the present research is 
divided in to three major parts, chapter two, three and four is arranged accordingly. 
Each chapter includes an introduction discussing the relevant literature, the 
experimental work, results and discussions and finally, the conclusions drawn. The 
contents of this thesis can be best summarized as follows. 
Mechanical properties and biodegradability of composites of LDPE with tapioca 
starch 
A series of LDPE/starch composites containing different amounts of starch (as wt %) 
were prepared using tapioca starch in its native granular form. Mixing was done by 
dissolving LDPE in cyclohexane pre-heated to its boiling point and subsequently 
dispersing starch granules by using Silverson emulsifier. The composites were studied 
by using Fourier Transform Infra-red spectroscopy (FTIR). The failure modes, 
mechanical properties, water absorption, biodegradation and the biodegradation after 
thermal incubation were investigated as a function of the composition of the 
composite. It was found that the incorporation of starch into LDPE matrix has reduced 
the ductility of the composite. The mechanical properties of the composites, 
especially the tensile strength and elongation at break were significantly low 
compared to those of neat LDPE. A significant improvement in modulus was shown 
by the composites. It was found that the mechanical properties were depended on the 
composition of the composite. 
The extent of the biodegradability, after exposure to a-amylase enzyme solution, was 
assessed by weight loss measurements and loss of mechanical properties such as 
tensile strength and percentage elongation. It was found that these composites are 
biodegradable and the rate of biodegradation increases with increasing starch content. 
The extent of biodegradation after thermal incubation was assessed by the loss of 
tensile strength measurements of the composites after incubation of the samples in an 
ii 
air circulation oven at 70 C and subsequently exposing to cc-amylase enzyme 
solution. It was found that the degradability of the samples was not significantly 
affected by the thermal incubation. 
Preparation and characterization of long chain fatty acid esters of tapioca starch 
A series of starch esters witii different degree of substitution (DS) were prepared and 
studied. The esters were prepared by acylation of tapioca starch with appropriate acid 
chlorides such as stearoyl and oleoyl chlorides. Fourier transform infrared (FTIR) 
spectroscopy confirmed the formation of the starch esters and their DS. As a 
measurement of the DS of an ester the peak height ratio responsible for O-H bond 
stretching to C = 0 bond stretching of the esters were considered. The DS of starch 
stearates were 5.3, 4.5, 2.6, 2.0 and 1.60. The DS of starch oleates were 3.55, 2.0, 1.90 
and 1.21. With increasing DS the color intensities of the esters were improved. 
Melting temperatures of the esters were determined by using Differential thermal 
analyzer. The thermo-oxidation degradation of tapioca starch and starch esters, were 
assessed by using Fourier Transform Infra-red (FTIR) spectroscopy, after the 
incubation of the samples in an air circulation oven at 70 °C. The presence of thermo-
oxidative degradation was shown in both types of the starch esters. Starch has not 
shown thermo-oxidative degradation. 
Mechanical properties and biodegradability of composites of LDPE with fatty 
acid esters of tapioca starch 
A series of Low Density Polyethylene (LDPE) composites containing different 
amounts of fatty esters of starch were prepared. Mixing was done by dissolving 
LDPE, in cyclohexane pre-heated to its boiling temperature, and subsequently, mixing 
starch esters using Siverson Emulsifier. Two different types of starch esters, starch 
stearate and oleate with different (DS) were utilized in the preparation of these LDPE 
composites. Polarized light micrographs were used to assess the miscibility of LDPE 
with starch esters. 
iii 
The miscibility of the eomponents was found to be improved with increasing DS of 
the ester. Water absorption, mechanical properties, biodegradation and biodegradation 
after thermal incubation were investigated as a function of the composition of the 
composite. Comparing with the LDPE/starch composites a significant reduction in the 
water absorption was resulted in the LDPE/starch ester composites. It was found that 
as the amount of esters increases in the composite, the tensile strength and especially 
the elongation at break decrease non-linearly. The LDPE/starch ester composites 
containing starch esters of high DS have shown improved tensile properties than those 
of LDPE/starch composites. As expected, the fatty ester chains in the starch ester 
molecules have not shown the plasticizing effect in the composite. The percentage 
elongation properties were significantly reduced with the introduction of the esters 
into LDPE. 
The extent of the biodegradability of the composites after exposure to a-amylase and 
lipase enzyme solutions was assessed by weight loss and mechanical properties 
measurements. The rate of biodegradation of LDPE/starch ester composites was 
relatively low compared to that of LDPE/starch composites. The rate of 
biodegradation of these LDPE/starch ester composites further decreases with 
increasing DS of the ester in the composite. The extent of the biodegradation of the 
composites after incubation of the samples at air circulation oven at 70 °C and 
subsequently immersing in the enzymatic solutions was assessed by the tensile 
strength measurements. It was found that the degradability of the ester composites 
was significantly high and the degradation rate increases with the increasing DS of the 
ester. Highest rate of degradation was observed in the LDPE/starch ester composite 
containing starch oleate of the highest DS. 
iv 
To my parents, 
the first teachers in my life, 
To my husband, 
for his motivation towards the success in my life, 
To my son, 
whose smile gave me a new hope to my life, 
I dedicated this thesis, 
with joy and happiness, 
to owe my gratitude to them. 
Without them, their love and blessing, I may not finish this thesis today. 
ACKNOWLEDGEMENTS 
I wish to express my deepest gratitude to my supervisor, to whom I am deeply 
indebted, Dr Jagath K Premachandra, Department of Chemical and Process 
Engineering, University of Moratuwa. His interest in this study, advice and criticism 
have motivated me immensely and guided me on the pathway to the successful 
completion of this work. I would like to express my deep gratitude to Dr. Shantha 
Walpalage, Head of the Polymer Division, Department of Chemical and Process 
Engineering, University of Moratuwa for the helpful ideas, special advices and 
motivation provided which always strengthened me to successfully complete this 
work. 
I would like to acknowledge Dr. Gamini Senevirathna, Deputy Director General, 
Rubber research Institute, Mrs. Dilhara Edirisinghe, for granting permission to 
carryout practical in their institute premises. I render my heartiest gratitude and 
special thank to Mr. Chandralal Perera and Mrs. Indra Denawake, for their immense 
corporation and assistance towards my research and further, acknowledge all staff 
members and technical officers of Rubber Research Institute, Ratmalana, for their 
kind corporation. 
My deep gratitude goes to Dr. N Munasinghe, Head of the Materials Engineering 
Department, University of Moratuwa, for his kind assistance in granting me to use 
laboratory equipments in his department. I further, extend my gratitude and special 
thank to the academic staff member Mr. V S C Weragoda and the senior staff 
technical officer, Mr. Sarath Chandrapala for their immense corporation and 
assistance towards my research work. 
I further, acknowledge Dr. Sudantha Liyanage, Head of the Polymer Division, 
Department of Chemistry, University of Sri Jayawardenapura and Prof. 
Bamunuarachchi, Head of the Department of Food Technology, University of Sri 
Jayawardenapura for granting me permission to use laboratory facilities in their 
vi 
departments. I acknowledge with special thanks to the Technical officer Mr. Sagara 
Dias, for his immense assistance given to me. 
I further extend my deep gratitude to Dr. (Mrs.) Padma Amarasinghe, Head of the 
Department of Chemical and Process Engineering, University of Moratuwa, all 
academic staff and the laboratory staff of the department for their support in 
numerous ways, for which I will always be thankful. I will indebted to Asian 
Development Bank for granting financial assistance for the course of study. 
Finally, I owe many thanks and heartiest gratitude to my parents, especially, to my 
patient mother, and to my husband who capably typed and retyped many parts of this 
text and for their immense corporation in numerous ways, which motivated me to 
successfully complete this work. 
vn 
TABLE OF CONTENTS 
Page No. 
Declaration i 
Abstract ii 
Acknowledgements v 
Table of contents viii 
List of Tables xii 
List of Figures xiii 
List of Abbreviations xvi 
CHAPTER ONE - INTRODUCTION 
1.1. Background motivation 2 
1.2. Objectives 5 
CHAPTER TWO - STRUCTURE, MECHANICAL PROPERTIES AND 
BIODEGRADABILITY OF COMPOSITES OF LDPE WITH 
TAPIOCA STARCH 6 
2.1.INTRODUCTION 7 
2.1.1. The process of biodegradation 7 
2.1.2. Biodegradation of polymers 8 
2.1.3. Biodegradable thermoplastic materials 10 
2.1.4. Starch 11 
2.1.5. Polymeric materials containing starch as a component 14 
2.2. Theories on the effect of fillers on the failure modes and mechanical properties 
of a composite 18 
2.2.1. The effect of fillers on the failure modes of a polymeric composite 18 
2.2.2. Effect of fillers on extension 18 
2.2.3. Effect of fillers in tensile strength of a polymeric composite 19 
2.2.4. Effect of fillers in modulus of a composite 20 
viii 
2.3. EXPERIMENTAL 22 
2.3.1. Materials 22 
2.3.2. Preparation of LDPE/starch composites 22 
2.3.3. FTIR analysis of LDPE/starch composites ' 2 2 
2.3.4. Analysis of the morphology of LDPE/starch composites 23 
2.3.5. Determination of the mechanical properties of the LDPE/starch 
composites 23 
2.3.6. Determination of the water absorptivity of LDPE/starch composites 23 
2.3.7. Determination of the biodegradability of LDPE/starch composites 23 
2.3.8. Determination of the biodegradability of LDPE/starch composites 
after thermal incubation 24 
2.4 RESULTS AND DISCUSSION 
2.4.1. FTIR spectrometric analysis of LDPE/starch composites 25 
2.4.2. Analysis of the morphology of LDPE/starch composites 27 
2.4.3. Analysis of the failure modes of LDPE/starch composites 27 
2.4.4. Mechanical properties of LDPE/starch composites 31 
2.4.5. Water absorptivity of LDPE/starch composites 36 
2.4.6. Weight loss of LDPE/starch composites after enzymatic degradation 36 
2.4.7. Variation in mechanical properties after enzymatic degradation of 
LDPE/starch composites 40 
2.5. CONCLUSIONS 44 
CHAPTER THREE - PREPARATION CHARACTERIZATION 
OF LONG CHAIN FATTY ACID ESTERS OF TAPIOCA STARCH 45 
3.1. INTRODUCTION 46 
3.2. EXPERIMENTAL 49 
3.2.1. Materials 49 
3.2.2. Preparation and purification of starch esters 49 
3.2.3. FTIR spectrometric analysis of starch esters 50 
3.2.4. Determination of the melting temperatures of starch esters 50 
ix 
4 
3.2.5. Determination of thermo-oxidative degradation of starch esters 50 
3.3. RESULTS AND DISCUSSION 51 
3.3.1. FTIR spectrometric analysis of starch esters \ 51 
3.3.2. Thermal analysis of starch esters 58 
3.3.3. Analysis of thermo-oxidative degradation of starch esters 60 
3.4 CONCLUSIONS 65 
CHAPTER FOUR - STRUCTURE, MECHANICAL PROPERTIES AND 
BIODEGRADABILITY OF COMPOSITES OF LDPE AND FATTY 
ACID ESTERS OF TAPIOCA STARCH 66 
4.1 INTRODUCTION 67 
4.2 EXPERIMENTAL 73 
4.2.1. Materials 73 
4.2.2. Preparation of LDPE/starch ester composites 73 
4.2.3. Characterization of LDPE/starch ester composites 73 
4.3. RESULTS AND DIASCUSSION 75 
4.3.1. FTIR spectral analysis of LDPE/starch ester composites 75 
4.3.2. Analysis of the morphology of LDPE/starch ester composites 75 
4.3.3. Analysis of the failure modes of LDPE/starch ester composites 78 
4.3.4. Determination of the mechanical properties of LDPE/starch 
ester composites 86 
4.3.5. Analysis of water absorptivity of LDPE/starch ester composites 95 
4.3.6. Analysis of the biodegradation of LDPE/starch ester composites 98 
4.3.7. Determination of the Biodegradability and thermo-oxidative 
degradability of LDPE/starch ester composites 104 
4.4 CONCLUSIONS 108 
x 
CHAPTER FIVE 
5.1. FUTURE WORK 
5.2. LIST OF REFERENCES 
LIST OF TABLES 
Page No. 
Table 2.1. Infrared Vibrations and Assignments for PE and PES composites 25 
Table 2.2. Mechanical properties of PES composites 31 
Table 3.1. Infrared Vibrations and Assignments of starch, starch esters, 
fatty acids and acid anhydrides 51 
Table 3.2. Degree of substitution and the appearance of the starch esters 55 
Table 4.1. Mechanical properties of LDPE/starch ester composites 87 
Table 4.2. Mechanical properties of LDPE/starch ester composites after 
enzymatic degradation 101 
Table 4.3. Tensile strength properties of LDPE/starch ester composites after 
thermo-oxidative and subsequent enzymatic degradation 106 
LIST OF FIGURES 
Page No. 
Figure 1.0. Schematic representation of amylose , \ 12 
Figure 2.0. Schematic representation of amylopectin 13 
Figure 2.1. FTIR spectra of (a) PE and composites of (b) PES-5 26 
(c) PES-15 and (d) PES-25 
Figure 2.2. Polarized light micrographs of LDPE and LDPE/starch 28 
composites containing different amounts of starch 
Figure 2.3 Stress strain curves for (•) PE, (•) PES-5, ( A ) PES.15 and 30 
(—) PES-25 composites 
Figure 2.4 (a). Variation in the tensile strengths as a function of the 
starch content 32 
Figure 2.4 (b). Variation in % Elongation at break as a function of the 
starch content 34 
Figure 2.4 (c). Young's Modulus as a function of the starch content 35 
Figure 2.5. Percentage weight change of (•) PES-5, (•) PES-15 and 37 
( A ) PES-25 composites during immersion in water 
Figure 2.6. Weight loss of PES samples after enzymatic degradation 39 
Figure 2.7 (a). Variation in tensile strength of PE and PES samples 41 
(•) before the degradation, (•) after enzymatic degradation ( A ) enzymatic 
degradation after thermal incubation 
Figure 2.7 (b). Variation in % elongation of PE and PES samples 42 
(•) before the degradation, (•) after enzymatic degradation and 
( A ) enzymatic degradation after thermal incubation 
Figure 3.1. FTIR spectra of (a) tapioca starch and (b) starch stearate 53 
Figure 3.2. FTIR spectra of (a) starch stearate and (b) starch oleate 54 
Figure 3.3. FTIR spectra of starch stearates with different DS 56 
Figure 3.4. FTIR spectra of starch oleates with different DS 57 
Figure 3.5. Thermogram of a starch oleate 59 
i 
Figure 3.6. FTIR spectra of starch oleate (a) before and (b) after thermal 61 
incubation 
Figure 3.7. FTIR spectra of starch stearate (a) before and (b) after thermal 62 
incubation 
Figure 3.8. FTIR spectra of starch (a) before and (b) after thermal incubation 64 
Figure 4.0. The biodegradation mechanism of polyethylene 71 
Figure 4.1. FTIR spectra (a) LDPE, LDPE/starch and LDPE/starch 76 
/ stearate composite 
Figure 4.2 (a). Polarized light micrographs of PESS composites 77 
Figure 4.2 (b). Polarized light micrographs of PESO composites 79 
Figure 4.3 (a). Stress-strain curves for PESS 5.3 composites containing 80 
starch tearate of (•) 5, (•) 15 and ( A ) 25 wt % 
Figure 4.3 (b). Stress-strain curves for PESS 2.6 composites containing 81 
starch stearate of (•) 5, (•) 15 and ( A ) 25 wt % 
Figure 4.3 (c). Stress-strain curves for PESS 1.6 composites containing 82 
starch stearate of (•) 5, (•) 15 and ( A ) 25 wt % 
r
 Figure 4.4 (a). Stress-strain curves for PESO 3.55 composites containing 83 
starch oleate of (•) 5, (•) 15 and ( A ) 25 wt % 
Figure 4.4 (b). Stress-strain curves for PESO 2.0 composites containing starch 84 
oleate of (•) 5, (•) 15 and ( A ) 25 wt % 
Figure 4.4 (c). Stress-strain curves for PESO 1.21 composites containing 85 
starch oleate of (•) 5, (•) 15 and ( A ) 25 wt % 
Figure 4.5 (a). Variation in tensile strength of (•) PESS- 5.3, ( A ) PESS- 2.6, 88 
(A) PESS-1.6 and (•) PES samples 
Figure 4.5 (b). Variation in tensile strength of (•) PESO-3.55, ( A ) PESO- 2.0, 89 
f (A) PESO- 1.21 and (•) PES samples 
Figure 4.5 (c). Percentage reduction of tensile strengths vs composition 91 
of the composites of(«) PES, (•) PESS 5.3, ( A ) PESS 2.6, (A) PESS 1.6, 
(•) PESO 3.55,(*) PESO 2.0 and (o) PESO 1.21. 
Figure 4.6 (a). Variation in % Elongation at break with the starch/starch 93 
ester content of ( £ ) PES, (%) PESS-5.3, ( • ) PESS 2.6, and 
(m) PES 1.6 samples 
Figure 4.6 (b). Variation in % Elongation at break with the starch/starch ester , 94 
xiv 
content of ( £ ) PES, (#!)PESO-3.55, ( • ) PESO-2.0, and 
( = ) PESO-1.21 samples 
Figure 4.7 (a). Percentage weight change of (•) PESS 2.6-5, (•) PESS 2.6-15 96 
and ( A ) PESS 2.6-25 composites during immersion in water 
Figure 4.7 (b) Percentage weight change of (•) PES-15, (•) PESS 2.6-15, 97 
(x) PESO 3.55-15 and ( A ) PESS 5.3-15 composites during immersion in water 
Figure 4.8. % Weight loss during enzymatic degradation of (^ )PES, 99 
(%) PESS-2.6, ( • ) PESO 3.55, and ( • ) PESS 5.3 samples 
Figure 4.9 (a). % Reduction in tensile strength after enzymatic degradation of 102 
(•) PES, ( A ) PESS 2.6, (A) PESS 2.6 and (•) PESS 5.3 samples 
Figure 4.9 (b). % Reduction in elongation at break after enzymatic degradation 103 
of (•) PES, ( A ) PESS 2.6, (A) PESS 2.6 and (•) PESS 5.3 samples 
Figure 4.10. % Reduction in tensile strength after thermo-oxidative and 107 
enzymatic degradation of ( A ) PESO 3,55, (•) PESS 3.55 and 
(•) PESS 2.6 samples 
y 
XV 
LIST OF ABBREVIATIONS 
C a C 0 3 - Calcium Carbonate 
DS - Degree of Substitution 
EAA - Ethylene Acrylic Acid 
EVOH - Ethylene Vinyl Alcohol 
FTIR - Fourier Transform Infra- Red 
h - Hours 
HC1 - Hydro Chloric Acid 
HDPE - High Density Polyethylene 
LDPE/PE - Low Density Polyethylene 
MPa - Mega Pascal 
PCL - Poly Caprolactone 
PET - Polyethylene Terephthalate 
PES - Low Density Polyethylene/ Starch Composite 
PESO - LDPE/ Starch Oleate Composite 
PESS - LDPE/ Starch Stearate Composite 
PG - Poly Glycolide 
PHB - Poly Beta hydroxy Butyrate 
PHV - Poly Hydroxy Valarate 
PL - Poly Lactic 
rpm - Rounds per minutes 
T i 0 2 - Titanium dioxide 
T m - Melting temperature 
- Glass transition temperature 
w t % - Weight percentage