A dissertation submitted in fulfilment of the requirement for the degree of Master of Science (Biotechnology

PREPARATION AND CHARACTERIZATION OF POLYLACTIC ACID/EPOXIDIZED PALM OIL/PINEAPPLE LEAF FIBRE COMPOSITES FOR

PACKAGING MATERIAL

BY

NUR LISA FARHANA BINTI MOHAMAD

A dissertation submitted in fulfilment of the requirement for the degree of Master of Science (Biotechnology

Engineering)

Kulliyyah of Engineering

International Islamic University Malaysia

JUNE 2018

iii

ABSTRACT

The environmental impact of the accumulation of nonbiodegradable plastic wastes has prompted researchers to come up with biodegradable alternatives to plastic.

Thermoplastic polylactic acid (PLA) is derived from a renewable source and has the mechanical properties that can rival its synthetic counterparts. However, its brittleness and slow degradation rate are factors that limit its application. The objective of this research is to improve the mechanical and thermal properties of PLA by plasticizing it with epoxidized palm oil (EPO) and reinforcing it with alkaline-treated pineapple leaf fibres (PALFs). In this research, plasticized PLA/pineapple leaf fibre composites (PLA/EPO/PALFs) were developed using the melt blending method. This research is divided into two phases. In the first phase, a fixed loading of PALFs treated with 10 w/v%, 15 w/v%, and 20 w/v% potassium hydroxide (KOH) solution is mixed with PLA and 10 wt% EPO. The effects of alkaline treatment of fibres on PLA/EPO/PALFs on the mechanical and morphological properties were evaluated. It was observed that the composite with 10 w/v% KOH-treated PALFs had the highest elongation-at-break, while the composite with 15 w/v% KOH-treated PALFs had the highest tensile strength.

In the second phase, two treatments of KOH (10 w/v% and 15 w/v%) were selected based on the results of mechanical and morphological properties in the first phase. The second phase of this research involved repeating the steps in the first phase but with the PALF loadings varied (5 wt%, 10 wt%, 15 wt%). The EPO content stayed fixed at 10 wt%. The effect of various PALF loadings on the mechanical and thermal properties of PLA/EPO/PALFs was studied. The addition of EPO as plasticizer and PALFs as reinforcement filler have improved the mechanical and thermal properties of neat PLA composite. It is observed that the concentration of KOH influenced the mechanical properties of the fibre reinforced PLA composites, in which the tensile strengths, moduli, and elongations-at-break increased with increasing KOH concentration, and decreased after an optimum point. The amount of PALF in the composite also influenced the mechanical properties of the reinforced PLA composites, in which it is observed that the stiffness of the composites increased with increasing fibre loadings (increasing glass transition temperature and decreasing elongations-at-break values).

The addition of EPO was observed to improve the flexibility neat PLA through plasticization effects, making it less brittle.

iv

ثحبلا صخلم

كيتسلابلل لئادب راكتبلا نيثحابلا تعفد للحتلل ةلباقلا ريغ ةيكيتسلابلا تافلخملا مكارتل يئيبلا ريثأتلا لا ضماح ديدع ،يرارحلا كيتسلابلا جرختسُي .للحتلل ةلباق كيتكلا

(PLA) ددجتلل لباق ردصم نم

.ةيعانصلا هرئاظن ةسفانم ىلع ةرداقلا ةيكيناكيملا صئاصخلاب عتمتي و و هتشاشه نإف ، كلذ عم و

ريوطت يف ثحبلا اذه نم فدهلا روحمتي .همادختساو هقيبطت نم ناّدحي نلاماع هللحت ءطب كيتكلالا ضماح ديدعل ةيرارحلا و ةيكيناكيملا صئاصخلا تيز ةطساوب هنيدلت قيرط نع PLA

دسكؤملا ليخنلا (EPO)

( ًايولق ةجلاعملا سانانلأا قاروأ فايلأ مادختساب هزيزعت و PALFs

يف .)

ريوطت مت ,ثحبلا اذه جزملا ةقيرط مادختساب سانانلأا قاروأ فايلأ تابكرم و نّدلملا PLA

ت ،ىلولأا ةلحرملا يف .نيتلحرم ىلإ ثحبلا اذه مّسقي .رهصلاب نم ةتباث ةيمك طلخ م

PALFs

ب ةجلاعم 10

، مجح/نزو % 15

و مجح/نزو % 20

ديسكورديه لولحم نم مجح/نزو %

( مويساتوبلاا عم ) KOH

و PLA 10 نم ًانزو % ةيولقلا ةجلاعملا راثآ مييقت مت مث نم . EPO

نم ٍّّلك ىلع فايللأل PLA/EPO/PALFs

.ةّيلكشلا و ةيكيناكيملا اهصئاصخ و

ىلع يوتحي يذلا بكرملا نأ ظحولو 10

ـلا نم % PALFs

ناك مويساتوبلا ديسكورديهب جلاعملا

ـب هتجلاعم تمت يذلا بكرملا نأ نيح يف ، رسكلا دنع ةلاطتسا ىلعأ هل 15

ديسكورديه نم %

كورديهب ةجلاعملا نم نيعون رايتخا مت ،ةيناثلا ةلحرملا يف .دشلل ةمواقم ىلعأ هل ناك مويساتوبلا ديس

( مويساتوبلا َو مجح/نزو 10%

ةيكيناكيملا صاوخلا جئاتن ىلع ًءانب )مجح/نزو % 15

ةلحرملا يف تاوطخلا راركت ثحبلا اذه نم ةيناثلا ةلحرملا تنمضت .ىلولأا ةلحرملا يف ةّيلكشلاو ةيمك توافت عم ىلولأا PALF

( فاضملا 5%

،ًانزو 10 ،ًانزو % 15

ىوتحم يقب .)ًانزو %

دنع اًتباث EPO 10

نم ةفلتخم تايمك ةفاضإ ريثأت ةسارد تمت .ًانزو % صاوخلا ىلع PALF

ـل ةيرارحلاو ةيكيناكيملا PLA / EPO / PALFs

ةفاضإ . و ندلمك EPO

PALFs دق ُمّعدمك

بكرمل ةيرارحلاو ةيكيناكيملا صئاصخلا تنّسح ديسكورديه زيكرت نأ ظحول .يقنلا PLA

ا ىلع رّثأ دق مويساتوبلا تابكرمل ةيكيناكيملا صاوخل

ةوق تدادزا ثيح ،فايللأاب ةمّعدملا PLA

تضفخناو ، مويساتوبلا ديسكورديه زيكرت ةدايز عم رسكلا دنع ةلاطتسلااو ةنويللاو دشلا ةمواقم ةيمك ترثأ امك .ىلثملا ةطقنلا دعب تابكرمل ةيكيناكيملا صاوخلا ىلع بكرملا يف PALF

PLA

أ ظحول ثيح ، ةمّعدملا لاقتنا ةرارح ةجرد ةدايز( فايللأا ةدايز عم تداز تابكرملا ةبلاص ن

ةفاضإ ّنأ ظحول دقو .)رسكلا دنع ةلاطتسلاا ةميق ضافخناو جاجزلا ةنورم نم تنّسح EPO

.ةشاشه لقأ هلعج امم ، نيدلتلا للاخ نم يقنلا PLA

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APPROVAL PAGE

I certify that I have supervised and read this study and that in my opinion, it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Master of Science (Biotechnology Engineering)

………..

Fathilah binti Ali Supervisor

………..

Azlin Suhaida bt Azmi Co-Supervisor

I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Master of Science (Biotechnology Engineering)

………..

Hazleen bt Anuar Internal Examiner

………..

Wan Mohd Fazli Wan Nawawi Internal Examiner

This dissertation was submitted to the Department of Biotechnology and is accepted as a fulfilment of the requirement for the degree of Master of Science (Biotechnology Engineering)

………..

Faridah Yusof Head, Department of Biotechnology Engineering This dissertation was submitted to the Kulliyyah of Engineering and is accepted as a fulfilment of the requirement for the degree of Master of Science (Biotechnology Engineering)

………..

Erry Yulian Triblas Adesta Dean, Kulliyyah of Engineering

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DECLARATION

I hereby declare that this dissertation is the result of my own investigations, except where otherwise stated. I also declare that it has not been previously or concurrently submitted as a whole for any other degrees at IIUM or other institutions.

(Nur Lisa Farhana binti Mohamad)

Signature ... Date ...

vii

INTERNATIONAL ISLAMIC UNIVERSITY MALAYSIA

DECLARATION OF COPYRIGHT AND AFFIRMATION OF FAIR USE OF UNPUBLISHED RESEARCH

PREPARATION AND CHARACTERIZATION OF

POLYLACTIC ACID/EPOXIDIZED PALM OIL/PINEAPPLE LEAF FIBRE COMPOSITES FOR PACKAGING MATERIAL

I declare that the copyright holders of this dissertation are jointly owned by the student and IIUM.

Copyright © 2018 Nur Lisa Farhana Mohamad and International Islamic University Malaysia. All rights reserved.

No part of this unpublished research may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise without prior written permission of the copyright holder except as provided below

1. Any material contained in or derived from this unpublished research may be used by others in their writing with due acknowledgement.

2. IIUM or its library will have the right to make and transmit copies (print or electronic) for institutional and academic purposes.

3. The IIUM library will have the right to make, store in a retrieved system and supply copies of this unpublished research if requested by other universities and research libraries.

By signing this form, I acknowledged that I have read and understand the IIUM Intellectual Property Right and Commercialization policy.

Affirmed by Nur Lisa Farhana Mohamad

……..……….. ………..

Signature Date

viii

ACKNOWLEDGEMENTS

In the name of Allah, the Most Gracious and Most Merciful.

Foremost, praises be to the sole Creator for granting me good health, strength, knowledge, patience and determination in my endeavor to complete my thesis.

I would like to express my greatest gratitude and appreciation to my supervisor, Asst Prof Dr. Fathilah Ali, for her generous guidance and support throughout my study and research period, as well as her endless patience and encouragement in motivating me to give my best in my work. I would also like to thank my co-supervisor, Asst Prof Dr Azlin Suhaida Azmi, for her advice and support towards my finishing this thesis.

Special thanks to all the staff of Biotechnology Engineering Department for their valuable assistance during my research period. I would also like to express my gratitude to my colleagues for their constant support and motivation throughout my entire study period. I am blessed to have great people who inspired me to work hard.

Lastly, I would like to thank my beloved parents and family, for without their continuous advice, support, love, and encouragement, I would have never been able to complete this thesis.

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TABLE OF CONTENTS

Abstract ... iii

Abstract (Arabic)... iiiv

Approval Page ... iv

Declaration ... vii

Copyright Page ... vii

Acknowledgements ... viiii

Table of Contents ... xiix

List of Tables ... xii

List of Figures ... xiii

List of Abbreviations ... xiiii

CHAPTER ONE: INTRODUCTION ... 1

1.1 Background ... 1

1.2 Problem Statement ... 2

1.3 Research Objectives... 3

1.4 Research Scope ... 3

CHAPTER TWO: LITERATURE REVIEW ... 4

2.1 Introduction... 4

2.2 Bioplastics and Biopolymers ... 5

2.3 Polylactic Acid (PLA) ... 6

2.3.1 Advantages of PLA ... 8

2.3.2 Disadvantages of PLA ... 9

2.4 Modifications of PLA ... 10

2.4.1 Addition of Plasticizers ... 10

2.4.2 Addition of Natural Fibres as Reinforcement ... 11

2.4.2.1 Advantages of Natural Fibre ... 12

2.4.2.2 Disadvantages of Natural Fibre ... 12

2.4.2.3 Surface Modification of Natural Fibre ... 13

2.4.2.3.1 Alkali treatment ... 14

2.4.2.4 Pineapple Leaf Fibre (PALF) ... 15

2.5 Natural Fibre Reinforced Polymer Composites ... 16

2.5.1 Applications of Natural Fibre Reinforced Composites ... 16

2.5.1.1 Natural Fibre Reinforced Composites as Packaging ... 17

2.5.2 Biodegradability of Natural Fibre Reinforced Composites ... 17

2.5.2.1 Soil Degradation Test ... 18

2.6 Chapter Summary ... 18

CHAPTER THREE: RESEARCH METHODOLOGY ... 19

3.1 Overview... 19

3.2 Experimental Flowchart... 20

3.3 Materials ... 21

3.4 Experimental Methods ... 21

3.4.1 Screening Process ... 21

3.4.1.1 Preparation of PALFs ... 21

x

3.4.1.2 Alkaline Treatment of PALFs ... 21

3.4.1.3 Preparation of PLA/EPO/PALFs ... 22

3.4.2 Optimization Process ... 22

3.5 Characterization Tests ... 24

3.5.1 Tensile Test ... 24

3.5.2 Differential Scanning Calorimetry (DSC) ... 24

3.5.3 Scanning Electron Microscopy (SEM) ... 24

3.5.4 Biodegradation Test ... 25

3.6 Chapter Summary ... 25

CHAPTER FOUR: RESULTS AND DISCUSSION ... 26

4.1 Introduction... 26

4.2 The Effects Of Alkaline Treatment Of PALF On PLA/EPO/PALFs ... 26

4.2.1 Tensile Test ... 26

4.2.2 Scanning Electron Microscopy (SEM) ... 30

4.3 The Effects Of Varied PALF Loadings on PLA/EPO/PALFs ... 32

4.3.1 Tensile Test ... 32

4.3.2 Differential Scanning Calorimetry (DSC) ... 35

4.4 Biodegradation Test ... 39

4.5 Chapter summary ... 40

CHAPTER FIVE: CONCLUSION AND RECOMMENDATIONS ... 41

5.1 Conclusion ... 41

5.2 Recommendation ... 43

REFERENCES ... 44

APPENDIX A: THE EFFECT OF KOH TREATED PALF AND PALF LOADINGS ON MECHANICAL PROPERTIES OF PLA, PLAEPO AND PLA/EPO/PALFs ... 51

APPENDIX B: TENSILE TEST SAMPLES ... 53

LIST OF PUBLICATIONS ... 54

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LIST OF TABLES

Table 3.1 Material composition for PLA, PLAEPO, and PLA/EPO/PALFs

22

Table 3.2 Material composition for PLAEPOf10 composites 23 Table 3.3 Material composition for PLAEPOf15 composites 23 Table 4.1 Mechanical properties of PLA, PLAEPO, and

PLA/EPO/PALFs

27

Table 4.2 Mechanical properties of PLA, PLAEPO, and PLA/EPO/PALFs

32

Table 4.3 Mechanical properties of PLA, PLAEPO, and PLA/EPO/PALFs

33

Table 4.4 Thermal properties of PLA, PLAEPO, and PLAEPOf10 composites

37

Table 4.5 Thermal properties of PLA, PLAEPO, and PLAEPOf10 composites

37

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LIST OF FIGURES

Figure 2.1 The structure of PLA 6

Figure 2.2 (a) L-lactic acid and (b) D-lactic acid 7

Figure 3.1 Experimental flowchart 20

Figure 4.1 Tensile measurements of PLA, PLAEPO, and PLA/EPO/PALFs

28

Figure 4.2 (a) PLA and (b) PLAEPO 30

Figure 4.3 (a) PLAEPOfUT, (b) PLAEPOf10, (c) PLAEPOf15, (d) PLAEPOf20

31

Figure 4.4 Tensile measurements of PLAEPOf10 composites 33 Figure 4.5 Tensile measurements of PLAEPOf15 composites 34 Figure 4.6 DSC thermograms of PLA, PLAEPO, and PLAEPOf10

composites

36

Figure 4.7 DSC thermograms of PLA, PLAEPO, and PLAEPOf15 composites

36

Figure 4.8 Weight losses of PLA, PLAEPO, and PLA/EPO/PALFs 39

xiii

LIST OF ABBREVIATIONS

PLA Polylactic acid

PALF Pineapple leaf fibre

SEM Scanning Electron Microscope

DMA Dynamic Mechanical Analysis

DSC Differential Scanning Calorimetry

EPO Epoxidized palm oil plasticizer

PLAEPO PLA mixed with EPO composite

PLA/EPO/PALF PLA mixed with EPO and PALF composite

PLAEPOfUT PLA mixed with EPO and untreated fibre composite PLAEPOf10 PLA mixed with EPO and 10%-KOH treated fibre

composite

PLAEPOf10-5 PLA mixed with EPO and 10%-KOH treated fibre composite (fibre weight is 5%)

PLAEPOf10-10 PLA mixed with EPO and 10%-KOH treated fibre composite (fibre weight is 10%)

PLAEPOf10-15 PLA mixed with EPO and 10%-KOH treated fibre composite (fibre weight is 15%)

PLAEPOf15 PLA mixed with EPO and 15%-KOH treated fibre composite

PLAEPOf15-5 PLA mixed with EPO and 15%-KOH treated fibre composite (fibre weight is 5%)

PLAEPOf15-10 PLA mixed with EPO and 15%-KOH treated fibre composite (fibre weight is 10%)

PLAEPOf15-15 PLA mixed with EPO and 15%-KOH treated fibre composite (fibre weight is 15%)

PLAEPOf20 PLA mixed with EPO and 20%-KOH treated fibre composite

1

CHAPTER ONE

INTRODUCTION

1.1 BACKGROUND

Around one-third of the municipal solid waste (MSW) generated annually in the EU is comprised by packaging waste, which is estimated to be 67 million tons, and plastics contribute up to 19% of the packaging waste generated (Song, Murphy, Narayan, & Davies, 2009). Managing MSW is a challenging task for every country, especially developing ones such as Malaysia (Zainu & Songip, 2017), whose population is projected to reach around 36 to 37 million by year 2030 (Chien Bong et al., 2017;

Tan et al., 2014). The production rate of MSW in Malaysia is expected to exceed 9 million tons/day in 2020 (Chien Bong et al., 2017).

Common plastics (also often called “commercial” or “conventional”) are usually made from synthetic polymers such as polyethylene terephthalate (PET), polystyrene (PS), polypropylene (PP), which are petrochemical based (Kuruppalil, 2011). Synthetic polymers are considered invaluable due to their ability to be used in diverse applications of plastics such as in medical, packaging, and agriculture industries due to their attractive properties (high durability, high strength, corrosion-resistant, high thermal and electrical insulation properties) (Thompson, Moore, vom Saal, & Swan, 2009).

Generally, plastics can be divided into two groups: thermoplastics and thermosets (Zheng, Yanful, & Bassi, 2005) . Thermoplastics are re-formable; they can be repeatedly heated and formed over and again, enabling this type of plastics to be recycled. Thermosets, on the other hand, cannot be re-melted; once formed, reheating

2

will ultimately cause degradation and not reformation. Common plastics are mostly thermoplastics, and they are stable and do not degrade easily in an ambient environment, which is why these plastics posed a significant problem to the environment (Zheng et al., 2005).

The accumulation of nonbiodegradable plastic wastes contribute to land and water pollution, as well as being aesthetically unpleasing to the eye and a hazard to maritime lives like fish (Geyer, Jambeck, & Law, 2017; Thompson et al., 2009; Zheng et al., 2005). Awareness on detrimental effects of plastic wastes to the environment led to an increase in research to find an alternative solution, specifically in the potential of bio-based polymers as a substitute to nonbiodegradable plastics (Babu, O’Connor, &

Seeram, 2013).

1.2 PROBLEM STATEMENT

Plastic recycling alone is still not enough to make a monumental difference despite the increasing practice in the recent years (Song et al., 2009). As a result, researchers have focused on developing a biodegradable plastic that 1) is derived from renewable resources instead of petroleum, 2) could compete with common plastics in terms of functionality and processability, and 3) could rapidly degrade in nature through composting or anaerobic digestion (Song et al., 2009).

Polylactic acid (PLA) is a type of biodegradable polymer which is also a material of interest in bioplastic manufacturing. PLA has attracted significant attention for its versatility, biocompatibility, and biodegradable characteristics, and yet its brittleness is a major hindrance (Senawi, Alauddin, Saleh, & Shueb, 2013). Therefore, certain modifications are needed to improve the properties of PLA. One common method is to blend PLA to form a composite with a reinforcement filler material

3

(Nuthong, Uawongsuwan, Pivsa-Art, & Hamada, 2013), which can be either synthetic or natural fibre. For this study, pineapple leaf fibre (PALF) is selected as the filler reinforcement for PLA due to the abundance of this biomass in Malaysia.

Even so, there is a lack of interfacial adhesion between the PLA matrix and the reinforcement fibre due to different polarities (Senawi et al., 2013). A way to overcome this problem is to carry out further modification on the reinforcement fibre by the way of chemical treatment and/or adding a third component to the composite (plasticizer).

1.3 RESEARCH OBJECTIVES

1. To prepare alkaline treated pineapple leaf fibres (PALFs) using potassium hydroxide (KOH) treatment

2. To investigate the effects of alkaline treatment on the mechanical and morphological properties of PLA/EPO/PALF composites

3. To characterize the effects of varied PALF loadings on the mechanical and thermal properties of PLA/EPO/PALF composites

4. To study the biodegradation of PLA/EPO/PALF composites

1.4 RESEARCH SCOPE

This study is divided into two parts. The first part included preparing 3 different concentrations of KOH for treatment of PALFs (10%, 15%, 20%), and then investigating the effects of different alkaline treatment concentrations on mechanical, thermal, and morphological properties of the PLA/EPO/PALFs. The second part included preparing three (3) different compositions of PALFs (5%, 10%, 15%) into PLAEPO, and investigating the effects of varied PALF loadings on mechanical, thermal, and degradability of PLA/EPO/PALFs.

4 CHAPTER 2

LITERATURE REVIEW 2.1 INTRODUCTION

The growing economy and global urbanization over the years has led to the increase in consumption of plastic and, in turn, plastic waste. The usage of plastics to replace packaging materials made from metals, ceramics, and papers is widely accepted, and in fact has increased extensively. For instance, in the food packaging industry, synthetic polymers (e.g. polyethylene, polypropylene, polystyrene, polyethylene terephthalate (PET)) is appealing to be utilized for reasons that they are lightweight, easy to process, low in cost, and they provide mechanical, chemical, and microbial protection from the environment (Arora & Padua, 2010).

Malaysian households annually produce 19,000 metric tons of waste, in which plastic waste comprises 24% of all solid waste (Afroz et al., 2016; Zainu & Songip, 2017). The production of plastics rising from 1.5 million tonnes (1950) annually to 300 million tonnes (as of 2013) (Chidambarampadmavathy, Karthikeyan, & Heimann, 2017), and is unfortunately way ahead of the current waste disposal infrastructures.

Thus, there is an urgent need for solutions to alleviate the problem of inadequate waste disposal systems (Zheng et al., 2005).

The usage of petroleum-based plastics in disposable applications created an issue concerning their long-term impact on the environment because fossil fuels take a long time to be replenished, and these plastics are non-compostable and non- biodegradable (Kuruppalil, 2011; Souza et al., 2012). Besides that, it is an arduous, expensive process to separate plastics from other solid wastes and clean them. This is why only a small fraction of plastics can be recycled while the rest is left in the landfill.

5

Moreover, the cost of recycling common plastics such as polyethylene terephthalate (PET) is higher than producing new plastics (Kuruppalil, 2011).

For the past 30 to 40 years, the development of biologically-derived biodegradable plastics has increasingly become popular and well-accepted, as this type of plastics promises to solve landfilling problems of non-biodegradable plastics and fossil fuel consumption, as well as greenhouse gas emissions (Chidambarampadmavathy et al., 2017; Mostafa, Farag, Abo-dief, & Tayeb, 2014).

2.2 BIOPLASTICS AND BIOPOLYMERS

Bioplastics can be either bio-based (derived from renewable feedstock) or biodegradable (possess the ability to degrade in nature), or both (Iwata, 2015;

Mekonnen, Mussone, Khalil, & Bressler, 2013). Bioplastics can also be made of completely renewable polymers, or a combination of renewable and non-renewable (fossil-based) polymers, therefore using the terms bio-based plastic and biodegradable plastic interchangeably is incorrect (Mekonnen et al., 2013; Reddy et al., 2013). Among the common bio-based plastics are polylactic acid (PLA) and polyhydroxyalkanoates (PHAs) (Chidambarampadmavathy, Karthikeyan, & Heimann, 2017; Mekonnen et al., 2013)

There are four categories of biopolymers, which include polymers (a) directly extracted from natural raw materials such as polysaccharides (e.g. starch or cellulose) or proteins (e.g. gelatin or casein), (b) produced via chemical synthesis from bio-derived monomers (e.g PLA), (c) produced directly from microbial systems (e.g.

polyhydroxylalkanoates, PHA), and (d) produced from crude oil (e.g. aliphatic and aromatic polyesters) (Jamshidian, Tehrany, Imran, Jacquot, & Desobry, 2010).

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Biopolymers can be used in a diverse range of applications such as medical, cosmetics, food packaging, and biosensors (Onar Çamlıbel, 2004).

Biodegradable biopolymers are those that are able to break down in an industrial composter (Thompson et al., 2009). Currently, polylactic acid (PLA) is the most widely sought after synthetic biodegradable polymer (Luckachan & Pillai, 2011). However, PLA possesses a few limitations to its use such low degradation rate, low thermal and physical properties, and high production costs, therefore certain improvements must be made.

2.3 POLYLACTIC ACID (PLA)

PLA belongs to the family of aliphatic polyesters commonly made from alpha- hydroxy acids. Aside from being biodegradable and compostable, PLA is a polymer that can be made from annually renewable resources like corn. The structure of PLA is as illustrated in Figure 2.1.

Figure 2.1 The structure of PLA (Petinakis, Yu, Simon, & De, 2013)

PLA is known for its easy processability, which means that it is easily processed on standard plastics equipment to yield moulded parts, film, or fibres (Garlotta, 2001).

It is one of the few polymers in which the stereochemical structure can easily be modified by polymerizing a controlled mixture of the L- or D-isomers (as illustrated in Figure 2.2) to yield high molecular-weight amorphous or crystalline polymers that can

7

be used for food contact and are generally recognized as safe (GRAS) (Garlotta, 2001;

Vroman & Tighzert, 2009).

Figure 2.2 (A) L-Lactic acid and (B) D-Lactic acid (Xiao, Wang, Yang, & Gauthier, 2006)

PLA is degraded by simple hydrolysis of the ester bond and does not require the presence of enzymes to catalyse this hydrolysis (Garlotta, 2001). Lactic acid, the basic building block of PLA, is made by a fermentation process. PLA can be prepared via two methods: direct condensation of lactic acid, or ring-opening polymerization of cyclic lactide dimer (Henton, Gruber, Lunt, & Randall, 2005).

Being a versatile thermoplastic polymer, PLA is currently used in a wide range of areas of applications, including food packaging, fibre and textile, film, and interior automotive parts (Senawi et al., 2013). Besides that, PLA is also used in the biomedical field, in which it is utilized in manufacturing tissue engineering scaffolds, delivery system materials. PLA is also employed in dermatology and cosmetics (Xiao et al., 2006). Other than that, PLA is also exploited in the production of surgical thread, implant materials, and minimally invasive surgery (Park, et al., 2015).

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PLA is produced in large scales (140 000 tons per year) by NatureWorks, a company that is active in the USA and Thailand (Senawi et al., 2013), and its production is expected to increase to 800 000 tons per year by 2020 (Stahl, 2012).

2.3.1 Advantages of PLA

PLA is deemed an attractive option compared to other biomaterials due to a few reasons. Firstly, PLA is biodegradable and renewable. The fact that it is derived from renewable agricultural means signifies that the usage of PLA can reduce dependency on fossil fuels. Simultaneously, the usage of PLA provides a solution to environmental disposal problems that are caused by non-biodegradable polymers, specifically petroleum-based plastics (Garlotta, 2001; Jamshidian et al., 2010).

Secondly, PLA makes an appealing option due to its biocompatibility. PLA possesses an easy to modify stereochemical structure, and by polymerizing a controlled mixture of the L- or D-isomers of PLA, high-molecular-weight amorphous or crystalline polymers can be produced which are safe for food contact (Garlotta, 2001).

The degradation of PLA only involves a simple hydrolysis of the ester bond and without requiring any catalyst enzymes (Garlotta, 2001). Unlike petroleum-based plastics, when properly disposed of, PLA hydrolyses into natural products, CO2 and H2O. These products are neither toxic nor carcinogenic, therefore are harmless to human beings and the environment. For this too, PLA is perfect to be utilized in biomedical applications such as sutures, clips, and drug delivery systems (DDS) (Xiao, et al., 2012).

Besides that, PLA also possesses a shorter degradation time (a range of six months to two years) compared to standard plastics like polystyrene (PS) and polyethylene (PE). Both PS and PE require up to 1000 years to fully be degraded (Garlotta, 2001).

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Third, PLA is coveted for its easy processability. There are several ways of processing PLA, namely film casting, extrusion, blow moulding, and fibre spinning.

These methods are conceivable for PLA has a superior thermal processability to other biomaterials like poly(ethylene glycol) (PEG), poly(hydroxyalkanoates) (PHAs), and poly(ɛ-caprolactone) (PCL), henceforth the application of PLA in industries such as textiles and food packaging are made feasible (Xiao et al., 2006).

Moreover, the production of PLA requires low energy. PLA production uses up 25-55% less fossil energy in comparison to petroleum-based polymers (Xiao et al., 2006). As a result, lower consumption of fossil energy is expected, consequently leading to reducing emissions of air and water pollutants.

Besides that, the production of PLA requires the least amount of energy and releases the least amount of carbon dioxide compared to other petroleum-based plastics such as polypropylene and polyethylene terephthalate (PET) (Darie-Niţə, Vasile, Irimia, Lipşa, & Râpə, 2016).

Additionally, PLA offers superior tensile strength and modulus compared to other polymers such as polystyrene (PS), polypropylene (PP), and high-density polyethylene (HDPE) (Jamshidian et al., 2010).

2.3.2 Disadvantages of PLA

Nevertheless, PLA also has its limits and disadvantages. A lot of research pointed out the brittleness of this material hindering its application (Nuthong, et al., 2013; Senawi, et al., 2013; Rajesh & Prasad, 2014). PLA lacks mechanical properties (Park, Abdal-hay, Abdel-Jaber, & Lim, 2013), and it also shows poor ductility, slow

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degradation rate, and poor hydrophilicity (Xiao et al., 2006). The unanimous solution to these shortcomings is to perform modifications to PLA.

There are two types of modifications that can be done, which are 1) bulk modification, and 2) surface chemistry modification. Bulk modification includes physical modification (blending different polymers with PLA, addition of plasticizers, and addition of filler materials), and chemical modification (copolymerization, cross- linking of PLA). Surface chemistry modification, on the other hand, includes using physical methods (surface coating, entrapment, plasma treatment) and chemical modification (Xiao et al., 2006)

2.4 MODIFICATIONS OF POLYLACTIC ACID 2.4.1 Addition of Plasticizers

Plasticizers are small, relatively non-volatile, organic molecules that are proven effective in improving the flexibility of synthetic plastics such as polyvinyl chloride (PVC) and epoxy resins (Mekonnen et al., 2013). Plasticizers are normally employed in a range of 1% to 10%; plasticizers might not be able to work effectively below 1%, and might leach out of the material above 10% (Chieng, Ibrahim, Then, & Loo, 2014;

Silverajah, Ibrahim, Yunus, Hassan, & Woei, 2012)

When added to polymers, plasticizers help in reducing brittleness, improving flexibility and toughness, increase ductility, decreasing crystallinity, and reducing the glass transition and melting temperatures. A research carried out by Tanrattanakul &

Bunkaew (2014) discovered that plasticizers have a profound effect on the mechanical and physical properties of thermoplastic elastomers (TPE), which is increasing tensile strength of the material. They also found that plasticizers are responsible in decreasing the hardness, the resilience and the transition temperature of TPE as the flexibility of

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PLA increased (Tanrattanakul & Bunkaew, 2014). Likewise, Mekonnen et al. (2013) asserts that plasticizers improve flexibility and durability by decreasing polymer- polymer contacts, hence decreasing the rigidity of their three-dimensional structure, subsequently permitting deformation without rupture.

Among the known plasticizers of PLA include tributyl citrate (TBC), tributyl acetyl citrate (TBAC), triacetin or glycerol triacetate (GTA), and triethyl acetyl citrate (TEAC) (Tanrattanakul & Bunkaew, 2014). The other common plasticizer is vegetable oil-based plasticizer, which is feasible for it is biodegradable, renewable, environmental friendly, and easily obtained and produced in mass bulk at a competitive cost (Chieng et al., 2014).

An example of a vegetable oil-based plasticizer is palm oil, derived from palm trees, that is low in both cost and toxicity as well as readily available (Al-Mulla, Yunus, Ibrahim, & Rahman, 2010; Chieng et al., 2014). By adding epoxidized palm oil (EPO), tensile strength and modulus of the PLA/polycaprolactone (PCL) blend prepared via solution casting process is reduced while it increased elongation at the break of the blend (Chieng et al., 2014).

In this study, 10 wt% of EPO is used to plasticize PLA as the amount is found to be the optimum value that improved the thermal properties of PLA (Ali, Awale, Fakhruldin, & Anuar, 2016).

2.4.2 Addition of Natural Fibre as Reinforcement

At present, reinforced composites have been rapidly gaining interest due to their promising properties; all individual components in a composite material maintain their individual physical and chemical properties, but nonetheless combine to produce a new

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set of qualities that are otherwise unattainable alone (Taj, Munawar, & Khan, 2007). In the case of PLA, reinforcement materials such as natural or synthetic fibres can be added to the structural matrix to improve the mechanical and thermal properties of the polymer. The interest in natural fibres as reinforcement materials compared to their synthetic counterparts has been increasing due to natural fibres having lesser costs, higher biodegradability, higher strength and corrosion resistance (Bhoopathi, Ramesh,

& Deepa, 2014; Mukherjee & Kao, 2011; Taj et al., 2007)

Natural fibres are an important agricultural biomass contributing to Malaysian economy (M Asim et al., 2015). Some of the types of materials include rice husks, coconut trunk fibres, kenaf, and oil palm biomass. These materials have the potential to serve as alternative resources to conventional synthetic materials and to be commercially manufactured into a variety of bio-composite products. Some natural fibres such as flax, hemp, jute, straw, wood fibre, and rice husks have been investigated for use in plastics (Taj et al., 2007). Natural fibres are utilized progressively in automotive and packaging materials (Nuthong et al., 2013).

2.4.2.1 Advantages of Natural Fibre

There are many advantages to natural fibres compared to synthetic fibres.

Natural fibres are widely available, easily recyclable, biodegradable, renewable, and have relatively high strength and stiffness (Taj et al., 2007). Compared to glass fibres, natural fibres also have relatively lower costs, requires lesser energies during production, causes no abrasion to machines, and have no health risk when inhaled (Mohamed, Sapuan, Shahjahan, & Khalina, 2009).

Natural fibres contain cellulose fibres that can provide reinforcing effect to the PLA matrix. According to Nuthong et al. (2013), the quality of the fibre-matrix interface