POLYHYDROXYALKANOATES/ZINC OXIDE (PHA/ZnO) NANOCOMPOSITES FOR

POLYHYDROXYALKANOATES/ZINC OXIDE (PHA/ZnO) NANOCOMPOSITES FOR

DIELECTRIC APPLICATIONS

BY

FAIZAH FUAD

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

(Materials Engineering)

Kulliyyah of Engineering

International Islamic University Malaysia

MAY 2015

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ABSTRACT

The objective of this research is to develop polymer/metal-oxides nanocomposites based on polyhydroxyalkanoates (PHA) and zinc oxides (ZnO). The nanocomposites with variation of 2, 4, 6, and 8 wt% of ZnO were prepared through melt blending process in an internal mixer followed by compression molded. The mechanical properties of PHA/ZnO nanocomposites were studied through tensile tests and examined their morphology under field emission microscopy (FESEM). The thermal properties were characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). X-ray diffraction (XRD) and fourier transform infra-red (FTIR) analysis also have been carried out in order to evaluate the nanoparticles dispersion, percentage of crystallinity and possible bond formation. The mechanical tests showed an improvement in tensile strength and tensile modulus in increasing the ZnO loadings. The optimum tensile strength was observed at 4 wt% zinc oxide with 14.0 MPa. Degradation of PHA/ZnO nanocomposites was determined slightly shifted to lower temperature at about 10 ^°C.

X-ray diffraction (XRD) and Fourier transform infra-red (FTIR) spectroscopy, higher percentage of crystallinity and formation of new bonds respectively were seen with the addition of zinc oxide indicates on enhancement in thermal and mechanical properties of PHA/ZnO nanocomposites. The electrical conductivity was increased as the ZnO nanofiller increased in terms of electrical resistance shown a decreased value.

These biodegradable nanocomposites show great potential as an alternative to synthetic plastic packaging materials and disposable applications.

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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 fully adequate, in scope and quality, as a thesis for the degree of Master of Science (Materials Engineering).

………..

Noor Azlina Hassan Supervisor

………..

Noorasikin Samat Co-Supervisor

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Ernie Suzana Ali Field Supervisor

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

.……….

Zuraida Ahmad Internal Examiner

………..

Mat Uzir Wahit External Examiner

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

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Mohammad Yeakub Ali

Head, Department of Manufacturing and Materials 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 (Materials Engineering).

……….

Md Noor Bin Salleh

Dean, Kulliyyah of Engineering

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DECLARATION

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

Faizah Fuad

Signature ………. Date ………

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INTERNATIONAL ISLAMIC UNIVERSITY MALAYSIA

DECLARATION OF COPYRIGHT AND AFFIRMATION OF FAIR USE OF UNPUBLISHED RESEARCH

Copyright © 2015 by Faizah binti Fuad. All rights reserved.

POLYHYDROXYALKANOATES/ZINC OXIDE (PHA/ZnO) NANOCOMPOSITES FOR DIELECTRIC APPLICATIONS

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 only be used by others in 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 retrieval system and supply copies of this unpublished research if requested by other universities and research libraries.

Affirmed by Faizah Fuad

……….. ………..

Signature Date

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To my other half

To my beloved parents

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ACKOWLEDGEMENTS

All praises be to Allah, Who gave me the strength, knowledge and returned my soul to me and permitted me to remember Him, granted me with His Merciful to the completion of this thesis.

I would like to express my gratitude to all those who gave me the possibility to complete this research. My thanks to the Kulliyyah of Engineering, IIUM; especially Department of Manufacturing and Materials Engineering, for giving me permission to commence this Master degree provide the necessary facilities.

I am deeply indebted to my supervisor Dr Noor Azlina Hassan for her help, generous ideas, wise advice, and continuous support and encouragement at all-time regarding research and writing the thesis. Also, my thank goes to Dr Noorasikin Samat as co-supervisor for her contributions and support.

My further appreciation to all staffs in Kulliyyah of Engineering, IIUM especially Bro Mohd Hairi, Bro Sanadi, Bro Syamsul and all technicians for guiding and never hesitated to help me whenever I step into the laboratory. Their helpfulness has made my tasks easier.

My sincere gratitude to Nuclear Malaysia (MINT), Dr Moath Tarawneh and Sister Syazana Ahmad Zubir from Universiti Kebangsaan Malaysia and members from Universiti Sains Islam Malaysia, Brother Aslam, and field supervisor, Dr Ernie Suzana Ali for their countless help and guidance. Thanks to my colleagues and friends especially Sister Nurul Faezah, Sister Nur Izzati, Sister Aina Mardhiyah and Sister Norhasnidawani for their encouragement, support, and wisdom.

I am grateful to husband and parents who encourage me to pursue study and for moral support. Last but not least I wish to acknowledge to all persons who give support, advice, and assistance directly or indirectly involved to the success of my degree. Thank you so much, may Allah grant blessings them.

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TABLE OF CONTENTS

Abstract... ii

Arabic Abstract... iii

Approval Page... iv

Declaration... v

Copyright Page... vi

Dedication………. vii

Acknowledgments... viii

List of Figures... xi

List of Tables... xiii

List of Abbreviations... xiv

CHAPTER ONE: INTRODUCTION……… 1

1.1 Overview……….. 1

1.2 Problem Statement………... 4

1.3 Research Objectives………. 6

1.4 Scope of Research……… 6

1.5 Thesis Organization………. 7

CHAPTER TWO: LITERATURE REVIEW……….. 9

2.1 Nanocomposites………... 9

2.2 Metal Oxide Nanocomposites………... 12

2.3 Bio-based polymer / Biopolymer……….. 14

2.3.1 Polyhydroxyalkanoates (PHAs)………... 15

2.3.2 Polyhydroxybutyrate (PHB)……….. 20

2.4 Zinc Oxide (ZnO)………. 21

CHAPTER THREE: METHODOLOGY………. 24

3.1 Materials………... 24

3.1.1 Polyhydroxyalkanoates (PHA)……….. 24

3.1.2 Zinc Oxide………. 24

3.2 Experimental Methods……….. 24

3.2.1 Optimization Parameter Study……….. 24

3.2.2 Preparation of Nanocomposites………. 25

3.3 Mechanical Characterization……… 28

3.3.1 Tensile Test……… 28

3.4 Morphological Characterization………... 28

3.4.1 Field Emission Scanning Electron Microscopy (FESEM)………. 28

3.5 X-Ray Diffraction (XRD)………. 29

3.6 Thermal Characterization………..29

3.6.1 Differential Scanning Calorimetry (DSC)……….. 29

3.6.2 Thermogravimetric Analysis (TGA)……….. 30

3.6.3 Dynamic Mechanical Analysis (DMA)……….. 30

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3.7 Thermal Conductivity………... 31

3.7.1 Thermal Conductivity Analysis (TCA)……….. 31

3.8 Fourier Transform Infra-red (FTIR) Spectroscopy……….. 32

3.9 Electrical Conductivity/Resistivity………... 32

CHAPTER FOUR: RESULTS AND DISCUSSION……… 33

4.1 Introduction……….. 33

4.2 Mechanical Properties………... 34

4.2.1 Tensile Strength……….. 34

4.2.2 Tensile Modulus………. 35

4.3 Field Emission Scanning Electron Microscopy (FESEM)………... 36

4.4 X-ray Diffraction Analysis (XRD)………... 39

4.5 Thermal Properties……… 41

4.5.1 Thermogravimetric Analysis (TGA)……….. 41

4.5.2 Differential Scanning Calorimetry (DSC)………. 43

4.5.3 Dynamic Mechanical Analysis (DMA)………. 45

4.6 Thermal Behaviour………... 48

4.6.1 Thermal Conductivity Analysis………. 48

4.6.2 Thermal Diffusivity……… 49

4.6.3 Heat Capacity………. 50

4.7 Fourier Transform Infra-Red (FTIR) Spectroscopy………. 52

4.8 Electrical Resistivity………. 54

CHAPTER FIVE: CONCLUSION AND RECOMMENDATION……… 56

5.1 Conclusion……… 56

5.2 Recommendation……….. 57

REFERENCES... 58

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LIST OF FIGURES

Figure No. Page No.

2.1 (a) Nanolayered composite composed of alternating layers of nanoscale dimension; (b) nanofilamentary composites composed of a matrix with embedded nanoscale diameter filaments; (c) nanoparticulates composites composed of a matrix with embedded nanoscale particles

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2.2 General structures of polyhydroxyalkanoates. 16

2.3 PHA biosynthetic pathways. 18

2.4 Zinc oxide powders 22

3.1 Schematic illustration of research flow diagram. 27

3.2 Dumbbell shape of tensile specimen. 28

3.3 Rectangular shape of DMA specimen. 30

3.4 Dimension of TCA specimens. 31

4.1 Tensile strength of PHA/nanocomposites at different weight percent of zinc oxide.

35 4.2 Tensile modulus of PHA/nanocomposites at different

weight percent of zinc oxide.

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4.3 Micrograph of zinc oxide 37

4.4 Picture micrograph of (a) neat PHA, (b) 2 wt% ZnO, (c) 4 wt% ZnO, (d) 6 wt% ZnO, and (d) 8 wt% ZnO.

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4.5 XRD spectrum patterns of neat PHA and PHA/nanocomposites

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4.6 XRD spectrum patterns of zinc oxide 40

4.7 TGA thermogram curves of neat PHA and PHA/nanocomposites

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4.8 DSC thermogram curves of PHA/ZnO nanocomposites. 44 4.9 Storage modulus versus temperature curves for PHA/ZnO

nanocomposites.

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4.10 Tan delta versus temperature behavior of unfilled PHA and PHA/ZnO nanocomposites at various content of nanoparticles by wt%.

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4.11 Thermal conductivity of PHA nanocomposites at different temperatures.

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4.12 Thermal diffusivity of PHA nanocomposites at different temperatures.

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4.13 Specific heat of PHA nanocomposites at different temperatures.

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4.14 FTIR spectrums of pure PHA, zinc oxide, and PHA/ZnO nanocomposites.

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4.15 Resistivity of PHA and its nanocomposites. 55

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LIST OF TABLES

Table No. Page No.

3.1 Composition of nanocomposites 25

4.1 Thermal properties of PHA/ZnO nanocomposites. 42

4.2 DSC of PHA/ZnO nanocomposites. 44

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LIST OF ABBREVIATIONS

DMA Dynamic Mechanical Analysis DSC Differential Scanning Calorimetry et al. (et alia): and others

FESEM Field Emission Scanning Electron Microscopy FTIR Fourier Transform Infra-Red

g gram

kV Kilo-volt

MPa Mega-Pascal

PHA Polyhydroxyalkanoate PLA Polylactic Acid

PP Polypropylene

rpm Revolution per minute TGA Thermogravimetry Analysis T_c Crystallization temperature Tf Final decomposition temperature Tg Glass transition temperature Tβ β-transition temperature

T_i Initial decomposition temperature Tm Melting temperature

wt.% Weight percent XRD X-ray Diffraction

ZnO Zinc Oxide

oC Degree Celsius

%X Percentage of crystallinity

σ Conductivity

ρ Resistivity

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CHAPTER ONE INTRODUCTION

1.1 OVERVIEW

Polymer nanocomposites have existed for decades, as carbon black, pyrogenic silica and diatomite were used as additives in polymers. Nevertheless, their characterizations and the effect of properties induced by the nanometric scale of fillers were not fully understood at those times. The real starting point, corresponding to an understanding of the action of these fillers, is generally considered as corresponding to the first papers on a polyamide-6 filled with nanoclays published by Usuki et al. (1993) and Okada A. (1995), from Toyota R&D. Both these papers called it „hybrid‟ material.

The term „nanocomposites‟ was found first use in 1994 (Lan & Pinnavaia, 1994; Lan et al., 1995; Giannelis, 1996). The meaningful contribution from these pioneers has been a jump-start for a lot of researchers studied on various fillers. The demand for continual improvement in the performances of thermoplastic and thermoset polymer materials has led to the emergence of new technologies.

Several nanocomposites have been developed by incorporating various types of fillers such as clay, raw fibers, cellulose, or carbon nanotube (CNT). Besides reinforcing fillers, where the main role is to improve mechanical and barrier properties of the packaging materials (Hubbe et al., 2008), there are also several reinforcement that provide „smart‟ properties to the packaging system such as antimicrobial activity and biosensor.

Polymer-inorganic composites were first prepared by Blumstein in 1960s by polymerizing methyl methacrylate in presence of clay and found unusual properties in

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the composites he prepared. In early 1990s, polymerization of caprolactam in presence of montmorillonite clay by Toyota researchers improved several properties. This report encouraged the research in the field of polymer nanocomposites as reported by Zhang et al. (2008). Lei and Su (2007), report about many studies on conducting polymer nanocomposites in view to find their applications in advanced techniques.

As we know, advances in petroleum-based fuels and polymers have benefited mankind in numerous ways. Petroleum-based plastics can be disposable and highly durable depending on their composition and specific application. However, petroleum resources are finite, and in the future, the prices are likely to continue to rise. In addition, the disposal items made of petroleum-based plastics such as fast-food utensils, packaging containers and trash bags also creates an environmental problem.

Due to these problems, it has spurred efforts to develop biodegradable or biobased plastics. This new generation of biodegradable polymer is based on renewable biobased plant and agricultural stock. It can form sustainable, eco-efficient products that can compete in markets currently dominated by products based on petroleum feedstock in applications such as packaging, automotives, building products, furniture and consumer goods.

One of the most promising biodegradable polymers is Polyhydroxyalkanoates (PHA). PHA, an organic polymer is derived from renewable biomass sources, such as vegetable oil, corn starch, pea starch, or microbe. This biopolymer was designed to biodegrade. Thus, PHA had gain interest among researchers as an alternative for petroleum derived plastic. Currently PHA is widely used as materials in fine chemical, coatings, food products, packaging pharmaceutical and medical industries. PHA has rich properties depending on the structures. Homopolymers, random copolymers, and block copolymers of PHA can be produced depending on the bacterial species and

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growth conditions. With over 150 different PHA monomers being reported, PHA with flexible thermal and mechanical properties has been developed.

The incorporation of inorganic nanoparticles into polymer nanocomposites has great attention to a lot of researcher because inorganic-polymer nanocomposites improve the physical properties of conventional polymers such as mechanical, thermal, electrical, and optical (Gaur et al., 2010). Wacharawichanant et al. (2008), reported that aluminium oxide, titanium oxide and zinc oxide are among filler that been used in research of nanocomposites. Between these nanofiller, zinc oxide has much attention due to its properties for example wide band gap (3.4 eV), large excitation binding energy (60 meV), good chemical stability, and low dielectric constant (Mu et al., 2011). These interesting properties make zinc oxide unique as it helps in applications such as antireflection coating, flat panel displays, transparent electrodes, ultraviolet light-emitting diodes and piezoelectric devices. We believe that incorporation of ZnO nanoparticles in PHA may result in new material with useful properties.

4 1.2 PROBLEM STATEMENT

The increased use of plastics all over the world has caused a raised in plastic waste.

For this reason, the development of biodegradable polymers has been a subject of great interest in materials science for both ecological and biomedical perspectives.

The highlight on sustainability, eco-efficiency and green chemistry also has led to intensive search for renewable and environmentally friendly resources. Bio-based plastics are sustainable, largely biodegradable and biocompatible. They reduce our dependency on depleting fossil fuels and carbon dioxide (CO₂). Examples of biodegradable polymeric materials are polycaprolactone (PCL), polyesteramide (PEA), polylactic acid (PLA), and polyhydroxyalkanoates (PHA). They were used as an alternative to the conventional polymers.

Among these biopolymers, PHAs attract more attention regarding its physical and chemical properties. The polymers have similarities in physical properties with synthetic polymers such as polypropylene, polystyrene, and polyethylene. The major advantage of PHAs is that both the physical properties and the rate of degradation of PHAs can be altered by changing the bacterial source of the polymer and the corresponding fermentation conditions used (Gao et al., 2011). They are able to fully degrade into water and carbon dioxide. However, in order to achieve in applying bio- based polymer materials, Azeredo (2009) reported that, there are few limitations to look for associated to properties (such as brittleness, poor gas barrier), processing (such as low processing temperature), and cost.

In order to enhance some of the mentioned properties, new approaches are sought like blending with other polymers or filling with nanofillers such as nanoclay carbon nanotubes and inorganic particles. Example of inorganic particles used in polymer nanocomposites were PVC/Al composites (Bishay et al., 2010), PP/SiO₂

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(Erdam et al., 2009), epoxy/TiO2 (Chau et al., 2009), PC/SiO₂ (Rathore et al., 2012), and PP/ZnO (Majid et al., 2011). Among inorganic materials, zinc oxide possesses more interesting properties that has been found used in solar cell, light emitting diodes and laser diodes have binding energy excitations a little bit higher (60 meV) over in GaN (25 meV) (Rodnyi & Khodyuk, 2011). Zinc oxide has become focus in recent research due to its availability, biocompatibility and low cost. It also shows higher antibacterial effect on Staphylococcus aureus than other metal oxides like MgO, TiO2, Al₂O₃, or CuO (Zhang et al., 2007), thus considered to be non-toxic and do not cause any damage to the DNA of human cells (Yamada et al., 2007). In particular, ZnO nanoparticles have been shown to be very effective for enhancing the mechanical properties, barrier and antibacterial properties of polymers for examples poly(ether ether ketone) (Diez-Pascual et al., 2014), polylactic acid (Murariu et al., 2011), and polycaprolactone (Elen et al., 2012).

6 RESEARCH OBJECTIVES

The objectives of this research are as follow:

1. To determine the optimum properties of PHA.

2. To evaluate the effect of zinc oxide loadings (2, 4, 6, and 8 wt.%) on the mechanical, thermal, and electrical properties of PHA nanocomposites and their compatibility through morphological examination.

1.4 RESEARCH SCOPE

The optimization processing of PHA was studied before proceed to the development of nanocomposites, in terms of temperature and rotor speed. The mixing time was fixed at 12 minutes. The temperature for processing was varied between 140 and 160 °C while rotor speed varied at 70-110 revolution per minutes (rpm).

Then the PHA/ZnO nanocomposites were prepared at optimum parameters. The ZnO loadings were varied at different percentage by weight between 2-8 wt.%. The influences of ZnO on PHA nanocomposites were studied on its mechanical and thermal properties. The morphological were examined under field emission spectroscopy to evaluate the distribution and uniformity of filler in the matrix. X-ray diffraction and Fourier Transform Infrared spectroscopy also been used to evaluate the structure and substances presence in the nanocomposites. In order to achieve the dielectric application purposes, other testing for instance resistivity and thermal conductivity analysis were conducted to evaluate the tendency of filler content upon heat and electricity supplied. The obtained results were recorded and discussed.

7 1.5 THESIS ORGANIZATION

The thesis is separated into five bodies and classified as Chapter 1, Chapter 2, Chapter 3, Chapter 4, and Chapter 5. Chapter 1 is the introductory will briefly review the background of studies including the environmental issues arise due to non-degradable plastics materials and how the usage of biodegradable materials could be applied in packaging field.

A literature review on previous research work in various areas which is relevant to this research is presented in Chapter 2. The literature started with a comprehensive literature survey on the raw materials being used in the research. A review of the nanocomposite materials and their application in this study is also included in this chapter. This chapter also reviewed previous findings related to the alternative to petroleum-based polymer and conductive composite metal-based fillers.

Chapter 3 presents the study on fabrication and methodology of polymer nanocomposites embedded with various loadings of zinc oxide fillers. The techniques of characterization to determine the thermal, mechanical, morphological and dielectrical properties of nanocomposite also been discussed. The mechanical part investigated the tensile modulus and strength of neat PHA and PHA/ZnO nanocomposite and with the aid of morphological study by using FESEM. The thermal properties of nanocomposites were investigated by using TGA, DSC, and DMA. Dielectric part involved the study of resistivity, thermal conductivity, thermal diffusivity and specific heat by using Nanoflash.

Chapter 4 is the results and discussion on the mechanical properties under several tensile tests. Thermal properties of the nanocomposites and dynamic mechanical analysis are also discussed in the chapter with the proof of the morphology studies.

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Finally, the thesis concluded with an overview of this research and recommendations for future works as presented in Chapter 5.

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CHAPTER TWO LITERATURE REVIEW

2.1 NANOCOMPOSITES

Nanocomposites are relatively new class of composites in the polymer area; typically consist of particle-filled polymers where at least one dimension of dispersed particles is in the nanometer range.

The most important preparation of improved performance is the fine and homogeneous dispersion of the nanoparticles and a strong interface adhesion between matrix and nanofillers. Various approaches have been taken for the preparation of nanocomposites by melt mixing, solution mixing, in situ polymerization, electrospinning and many more. Preparation methods for polymer nanocomposites can be the same as for traditional polymer composites by blending the components together or by in situ polymerization in the presence of nanoparticles. The blending can be carried out either in a polymer melt (Kim & White, 2003; Ton-That et al., 2004), or in a polymer solution (Pourabas et al., 2005). In situ polymerization in the presence of the nanoparticle is possible in all different polymerizations (Yu et al., 2005). Regardless of the preparation method of the polymer nanocomposites, a good compatibility between the components is important. Compatibility can be improved by selecting suitable external blending conditions, such as by adjusting the temperature and the mixing intensity or by chemical modifications of the filler or the polymer. The novelty of melt mixing of the polymeric matrix with the filler is the most convenient and economical way in obtaining composite.

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Fillers play an important part in reinforced biopolymer. Nanofillers can significantly improve or adjust the different properties of the materials into which they are incorporated, such as mechanical, thermal, electrical, optical and fire-retardant properties. Incorporation of filler in biopolymer might show improvement or worsen the mechanical properties. As reported by Weng and Cao (2005), the incorporation of 5 wt% of bamboo fibers into Polyhydroxybutyrate (PHB) matrix has resulted in decrease of the biocomposite tensile strength form 10.99 MPa to 9.73 MPa. The reduction in the tensile strength was correlated to the insufficient reinforcement in the matrix, and the fiber only act as flaw in the biocomposite and became the stress concentration point. The same effect will be observed in very high filler loading due to the possibilities of agglomeration and lack of proper adhesion between filler and matrix.

However, to maintain its integrity, nanocomposite supposed to withstand the normal stress encountered during its application and further handling and transportation of the product especially in plastic packaging application. Angles et al.

(2001) proved that incorporation of microcrystalline cellulose palm fiber (MCPF) has positively affected the tensile strength of rice starch form 5.16 MPa to 44.23 MPA with 40% fiber loading. The increment in tensile strength was believed due to high compatibility. Elongation at break result showed increment until at 20% fiber loading and decrease above 25% fiber loading. High content of fibers tend to form heterogeneous film structure and discontinuities might result in this reduction in elongation at break.

Instead of increasing or decreasing the tensile strength, there a few cases occurred where the incorporation of filler did not change or only showed low reinforcing effect. Weng and Cao (2006) had reported that the cellulose whiskers