PHOTODEGRADATION OF BIOPOLYMER DOPED WITH TITANIUM

DIOXIDE (TiO2) AS ULTRAVIOLET (UV) STABILIZER

SITI RAHMAH BINTI MOHID

A thesis submitted in

fullfilment of the requirement for the award of the

Degree of Master of Mechanical Engineering

Faculty of Mechanical and Manufacturing Engineering

Universiti Tun Hussein Onn Malaysia

MAY 2015

ABSTRACT

A large amount of waste cooking oil has become an environmental issue around the

world. This oil is renewable and biodegradable than the corresponding products

made from petroleum sources. The major concern in this study focuses on the

resistance of the biopolymer to ultraviolet (UV) light exposure. The virgin oil (VO)

and waste oil (WO) was converted into biomonomer. By adding biomonomer with

an appropriate amount of 4, 4’-methylene diphenyl diisocyanate (MDI) and solvent,

the virgin oil polymer (VOP) and waste oil polymer (WOP) were produced. The

biopolymer (BP) were added with low loading metal oxide filler which is 2.5, 5, 7.5

and 10 % of titanium dioxide (TiO2) to form biopolymer composite (BPC). The

resistance to UV light and mechanical properties of BP and BPC were determined

after exposure the thin films in UV weatherometer for an extended period of time at

250, 500, 750,1000, 2000 and 3000 hours. The results based on the spectroscopic

analysis of UV-Vis and FTIR confirmed the photodegradation processes of BP and

BPC of VOP and WOP. The increasing absorbance in UV-Vis spectra indicated the

formation of quinone after UV-irradiation of BP and BPC of VOP and WOP.

Furthermore, BP thin films shows rapid loss of tensile strength but the increased

loading of TiO2 can improve mechanical performance. Visual inspection based on

the colour changes of the thin films showed quinone (yellow) formation of the

irradiated films of BP and BPC of VOP and WOP. As a conclusion, the effect of

prolonged exposure to UV light, in general promotes photo degradation for BP but

BPC gives slower chemical modification. The innovative biopolymer composite

were successfully designed and developed by adding the TiO2 as UV stabilizer to

reduce the photo-degradation of the biopolymer.

ABSTRAK

Sejumlah besar sisa minyak masak telah menjadi isu alam sekitar di seluruh dunia.

Minyak ini merupakan produk yang boleh diperbaharui dan lebih mudah

terbiodegradasi berbanding produk dari sumber petroleum. Tumpuan utama dalam

kajian ini fokus kepada rintangan biopolimer terhadap pendedahan cahaya ultraungu

(UV). Minyak dara (VO) dan sisa minyak (WO) telah ditukar kepada biomonomer.

Dengan menambah biomonomer dengan jumlah yang sesuai 4, 4’-methylene

diphenyl diisocyanate (MDI) dan pelarut, polimer minyak dara (VOP) dan polimer

sisa minyak (WOP) telah dihasilkan. Biopolimer (BP) telah ditambah dengan pengisi

logam oksida yang rendah iaitu 2.5, 5.0, 7.5 dan 10.0 % daripada titanium dioksida

(TiO2) untuk membentuk biopolimer komposit (BPC). Rintangan kepada cahaya UV

dan sifat mekanik BP dan BPC telah ditentukan selepas pendedahan filem nipis di

dalam alat weatherometer UV untuk tempoh masa yang panjang pada 250, 500, 750,

1000, 2000 dan 3000 jam. Keputusan berdasarkan analisis spektroskopi UV-Vis dan

FTIR menunjukkan proses degradasi foto bagi BP dan BPC dari VOP dan WOP.

Keserapan meningkat di UV-Vis spektrum menunjukkan pembentukan quinone

selepas penyinaran-UV bagi BP dan BPC dari VOP dan WOP. Tambahan pula, BP

filem nipis menunjukkan kehilangan yang cepat bagi kekuatan tegangan tetapi

peningkatan TiO2 boleh meningkatkan prestasi mekanikal. Pemeriksaan visual

berdasarkan perubahan warna daripada filem nipis menunjukkan pembentukan

quinone (kuning) oleh pancaran sinaran filem BP dan BPC dari VOP dan WOP.

Kesimpulannya, kesan pendedahan yang berpanjangan kepada cahaya UV, secara

amnya menggalakkan degradasi foto untuk BP tetapi BPC memberikan

pengubahsuaian kimia secara perlahan. Komposit biopolimer inovatif telah berjaya

direka dan dibangunkan dengan menambah TiO2 sebagai penstabil UV untuk

mengurangkan degradasi foto oleh biopolimer.

i

CONTENTS

TITTLE

DECLARATION

DEDICATION

ACKNOWLEDGEMENT

ABSTRACT

ABSTRAK

CONTENTS i

LIST OF FIGURE vi

LIST OF TABLE x

LIST OF SYMBOL AND ABBREVIATIONS xii

LIST OF APPENDICES xiv

CHAPTER 1 INTRODUCTION 1

1.1 Introduction 1

1.2 Background of study 3

1.3 Problem statement 4

1.4 Importance/significance of study 5

1.5 Objective of the study 6

ii

1.6 Scope of the study 6

CHAPTER 2 LITERATURE REVIEW 7

2.1 Polymer 7

2.2 Materials for development of biopolymer (BP)

and biopolymer composite (BPC) 12

2.2.1 Monomer based on renewable resources 12

2.2.2 Biopolymer composite (BPC) from

renewable resources 15

2.2.3 Methylene diphenyl diisocyanate (MDI) and

toluene diisocyanate (TDI) as aromatic

isocyanates 17

2.2.4 Titanium dioxide (TiO2) in polymer 19

2.2.5 Titanium dioxide (TiO2) as photocatalyst 22

2.3 Types of polymers degradation 23

2.3.1 Photo-oxidative degradation 24

2.3.2 Thermal degradation 27

2.3.3 Ozone induced degradation 28

2.3.4 Mechanochemical degradation 29

2.3.5 Catalytic degradation 30

2.3.6 Biodegradation 32

2.4 Polymer stabilization 34

2.4.1 Hindered amine lights stabilizer (HALS) 37

2.4.2 UV absorber (UVA) 38

iii

2.4.3 Antioxidant 39

2.4.4 Light screener 41

2.4.5 Radical scavenger 43

2.5 Artificial weathering for polymeric materials 44

2.6 Fourier transform infrared (FTIR) for polymeric

materials 49

2.6.2 FTIR for polymeric materials under UV

irradiation 52

2.7 Mechanical properties of polymer materials 54

2.8 Ultraviolet visible (UV-Vis) spectroscopy 58

2.9 Physical observation of polymeric materials 63

CHAPTER 3 METHODOLOGY 66

3.1 Introduction 66

3.2 Methodology flow chart 67

3.3 Materials and apparatus/instruments 68

3.4 Preparation of biomonomer 69

3.5 Preparation of BP and BPC 70

3.6 Preparation of BP and BPC thin film for UV

irradiation and tensile test 71

3.7 Fourier Transform Infrared Spectroscopy (FTIR) 75

3.8 Ultraviolet visible (UV-Vis) spectrophotometer 77

CHAPTER 4 RESULTS AND DISCUSSION 80

4.1 Introduction 80

iv

4.2 Fourier transforms infrared (FTIR) study for

monomer and biopolymer 80

4.2.1 Biomonomer (VOM and WOM) and

biopolymer (VOP and WOP) 80

4.2.2 Non-UV irradiated and UV irradiated of

BP and BPC of VOP at region

4000-650 cm-1

85

4.3 Mechanical properties of BP and BPC upon

UV irradiation 93

4.4 Carbonyl index (CI) and Hydroxyl index (HI) of

BP and BPC upon UV irradiation 98

4.4.1 Carbonyl index (CI) of BP and BPC upon

UV irradiation 98

4.4.2 Hydroxyl index (HI) of BP and BPC upon

UV irradiation 101

4.5 UV-Vis study for BP and BPC of UV irradiated

thin films 104

4.6 Physical properties of BP and BPC upon

UV irradiation 109

CHAPTER 5 CONCLUSION AND RECOMMENDATION 113

5.1 Conclusion 113

5.2 Recommendation 115

v

REFERENCES 116

APPENDICES 128

VITA 143

vi

LIST OF FIGURES

2.1 Schematic representations of three common classes of

polymer structure 8

2.2 Various type of polymer structures 9

2.3 Stress influences on polymers 11

2.4 Effects of stress influences on polymers 11

2.5 Chemical structure of fats and oils 13

2.6 Hydrolysis reaction produces glycerol and fatty acids 13

2.7 Main fatty acids issued from vegetable and castor oil 14

2.8 Production (million tons and %) of nine major vegetables

oil in 2013/14 15

2.9 Citation trend of (a) publications and (b) patents on

bio-based polymers in recent years 16

2.10 Structures of pure MDI and polymeric MDI 18

2.11 Isomers of toluene diisocyanates 18

2.12 Chemical structure of TiO2 21

2.13 Mechanism of photodegradation 25

2.14 The chemical structures of HALS 37

2.15 The structures of some UV absorbers 38

2.16 Theory of antioxidant 40

2.17 Quinone retard oxidation process 40

2.18 Doping mechanism of nitrogen on titanium dioxide 43

2.19 The UV light spectrum and solar radiation 46

2.20 Correlation table for the infrared bands of polymers 50

2.21 FTIR-ATR spectra of chitin, polyurethane and chitin-

vii

polyurethane biocomposite 51

2.22 Typical FTIR spectra of PU coating before and after

exposures for two different time intervals under the

300 nm cut-on filters in 50 °C/~0% relative humidity

condition 53

2.23 FTIR spectra of chitosan before and after 13 hours of

UV-irradiation 54

2.24 Tensile strength after different periods of weathering 57

2.25 The effect of exposure time on maximum elongation 58

2.26 UV-visible spectra of (a) unstabilized PET (b) with a

detail on the region of 400 nm 59

2.27 Possible reactions leading to the formation of

quinone and diquinone groups 60

2.28 UV-Vis spectrum for thin film (150-200 m) of RS-PU 61

2.29 UV-Vis spectrum for thin film (150-200 m) of SF-PU 61

2.30 Changes in UV-Vis spectra of chitosan/starch blends

(75:25) after UV irradiation (0 - 13 hours) 62

2.31 UV-Vis absorption spectra (diffuse reflectance) of the

original unimplanted pure TiO2 (a) and the Cr ion

implanted TiO2 (b-d), and the solar spectrum which

reaches the earth 63

2.32 Color change after QUV exposure for vinyl ester (VE),

unsaturated polyester (UPE), unsaturated polyester-

urethane hybrid (UPE hybrids) and polyurethane

pultruded profiles (PU) 65

2.33 Colour changes, evident on displayed wood panels for

water based acrylic coatings with stabilizer combinations

and increasing concentrations of nanoparticles of anatase-B

and rutile-A 65

3.1 Flow chart of methodology of BP and BPC 67

3.2 Instruments involve for characterization of

BP and BPC 68

viii

3.3 Waste cooking oil (WO) and virgin oil (VO) 69

3.4 Biomonomer mixed with MDI and TiO2 using

mechanical stirrer 71

3.5 Biopolymer cast into a container 71

3.6 Measurement of dry-film thickness of BP and BPC

using micrometer 72

3.7 The illustration of UV Accelerated Weatherometer 72

3.8 Biopolymer thin film samples on a rack for UV

light exposure 73

3.9 The sample is mounted between two jaws of the tester

and in line with the direction of pull 73

3.10 Schematic illustration of tensile test thin films polymer

according to ASTM D882 75

3.11 Biopolymer as thin film sample for tensile test 75

3.12 FTIR spectrometer-Perkin Elmer 76

3.13 UV-Vis spectrophotometer - UNICO SQ-3802 model 77

3.14 Thin film sample for UV/Vis spectroscopy 78

3.15 Biopolymer thin films were fit into the 4-cell linear

changer before testing 78

4.1 FTIR spectra at region 4000-650 cm-1

of VOM 81

4.2 FTIR spectra at region 4000-650 cm-1

of WOM 82

4.3 FTIR overlay spectra at region 4000-650 cm-1

of

VOM ( ____ ) and WOM ( _ _ _ ) 82

4.4 FTIR spectra at region 4000-650 cm-1

of VOP 83

4.5 FTIR spectra at region 4000-650 cm-1

of WOP 84

4.6 FTIR overlay spectra at region 4000-650 cm-1

of

VOP ( _ _ _ _ ) and WOP ( _____ ) 84

4.7 FTIR overlay spectra of non-UV irradiated and UV

irradiated of BP and BPC of (a) VOP (b) VOP2.5

(c) VOP5 (d) VOP7.5 and (e) VOP10 at 250, 500, 750,

1000, 2000 and 3000 hours 88

4.8 FTIR overlay spectra of non-UV irradiated and UV

irradiated of BP and BPC of (a) WOP (b) WOP2.5

ix

(c) WOP5 (d) WOP7.5 and (e) WOP10 at 250, 500, 750,

1000, 2000 and 3000 hours 91

4.9 Mechanism of photo degradation of BP and BPC after

UV irradiation 92

4.10 Average thickness for BP and BPC of (a) VOP and

(b) WOP 93

4.11 Graph of tensile strength (MPa) against UV

irradiation time for BP and BPC of VOP 94

4.12 Graph of tensile strength (MPa) against UV

irradiation time of BP and BPC for WOP 96

4.13 Graph of elongation at break (%) against UV

irradiation time (Hours) for BP and BPC of VOP 96

4.14 Graph of elongation at break (%) against UV

irradiation time (Hours) for BP and BPC of WOP 97

4.15 Carbonyl index (CI) for non-UV irradiated and UV

irradiated BP and BPC of VOP at 250, 500, 750,

1000, 2000, and 3000 hours 99

4.16 Carbonyl index (CI) non-UV irradiated and UV

irradiated BP and BPC of WOP at 250, 500, 750,

1000, 2000, and 3000 hours 100

4.17 Hydroxyl index (HI) for non-UV irradiated and UV

irradiated BP and BPC of VOP at 250, 500, 750,

1000, 2000, and 3000 hours 102

4.18 Hydroxyl index (HI) for non-UV irradiated and UV

irradiated BP and BPC of WOP at 250, 500, 750,

1000, 2000, and 3000 hours to UV light 103

4.19 UV-Vis overlay spectra of absorbance for BP and

BPC of (a) VOP (b) VOP2.5 (c) VOP5 (d) VOP7.5

and (e) VOP10 106

4.20 UV-Vis overlay spectra of absorbance for BP and

BPC of (a) WOP (b) WOP2.5 (c) WOP5 (d) WOP7.5

and (e) WOP10 108

x

4.21 Yellowing changes of colour with extended UV

irradiation time for BP and BPC of VOP; (a) non-UV

irradiated and UV irradiated (b) 250, (c) 500, (d) 750,

(e) 1000, (f) 2000, and (g) 3000 hours 110

4.22 Yellowing changes of colour with extended UV

irradiation time for BP and BPC of WOP; (a) non-UV

irradiated and UV irradiated (b) 250, (c) 500, (d) 750,

(e) 1000, (f) 2000, and (g) 3000 hours 111

xi

LIST OF TABLE

2.1 Properties of titanium dioxide, TiO2 20

2.2 Properties of anatase and rutile 21

2.3 Various research on the TiO2 photocatalyst 23

2.4 Various research on the polymer stabilization 36

2.5 Three ranges of solar UV radiation spectrum 46

2.6 Study on the sample preparation and UV irradiation

for polymeric materials 48

2.7 Typical tensile strength for polymer 56

2.8 Correlation between wavelength, colour, and

complementary colour 58

3.1 BP and BPC of VOP and WOP doped with different

percentage of TiO2 70

xii

LIST OF SYMBOL AND ABBREVIATIONS

A/Abs - Absorbance

ASTM - American Society for Testing Materials

ATR - Attenuated total reflection

CO2 - Carbon dioxide

FTIR - Fourier Transform Infrared

H - Hours

MDI - Methylene diisocyanate

MPa - Mega Pascal

TiO2 - Titanium dioxide

% - Percent

eV - 1.6 x 10-19

Joule

λ - Wavelength

nm - Nanometer

µm - Micrometer

°C - Degree Celsius

BP - Biopolymer

BPC - Biopolymer composite

CI - Carbonyl index

HI - Hydroxyl index

UV - Ultraviolet

UV-Vis- Ultraviolet visible

VO - Virgin oil

VOM - Virgin oil monomer

xiii

VOP - Virgin oil polymer

WO - Waste oil

WOM - Waste oil monomer

WOP - Waste oil polymer

xiv

LIST OF APPENDICES

APPENDIX TITLE PAGE

A Presented paper 129

B Chemical and apparatus 136

C Experimental data 138

CHAPTER 1

INTRODUCTION

1.1 Introduction

In recent years, increasing interest in the development of more environment friendly

polymer products such as plastics is observed. This trend has been spurred not only

by the realization that the supply of fossil resources is inherently finite, but also by a

growing concern for environmental issues, such as volatile organic solvent emissions

and recycling or waste disposal problems at the end of a resin’s economic lifetime.

Furthermore, developments in organic chemistry and fundamental knowledge on the

physics and chemistry of paints and coatings enabled some problems encountered in

vegetable oil based products to be solved. This resulted in the development of

coatings formulations with much improved performances that are based on

renewable resources (Derksen et al., 1996).

Palm oil is one of the most widely used plant oils in the world, which is

grown in mass plantation in tropical countries. The competitive environment of the

industry provides the drive needed to develop plastic materials that utilize less

expensive material. Palm oil differs from its major competitors (soybean, sunflower

seed, and rapeseed oil) in that it is obtained from a perennial tree crop and drought

impacts are less severe in comparison to oilseed crops. Palm oil which contains

significant amount of saturated bonds that presumably contribute to the non-drying

2

property of the resin synthesized. The non-drying alkyds have made tremendous

improvement in quality of nitrocellulose lacquers. Preparation of the alkyd resin from

non-drying palm oil may expand the application of the oil in various areas as

environment-friendly materials, because of its abundance and renewability. There is

no study reported on the synthesis of alkyd resin based on palm oil so far. However,

the use of petroleum based monomers in the manufacture of polymers is expected to

decline in the coming years because of spiraling prices and the high rate of depletion

of the stocks. This has inspired the technologists all over the world to investigate

renewable natural materials as an alternate source of monomers for the polymer

industry as substitute for the petroleum-based monomers to manufacture polymers

(Issam and Cheun, 2009).

The evaluation of the resistance to weathering of materials can be done by

direct weathering outdoors, but for most purposes it is more practical in economical

and time consumption terms to assess material performance by exposed to artificial

light sources that accelerate the degradation. Degradation of polymeric materials by

exposure to solar radiation or light is referred to as photo-oxidation. It is a free

radical process, progressing even at low temperatures by the combine action of light

and oxygen. Thermal oxidation is always superimposed on photo-oxidation

(Robinson et al., 2011).

Under the action of sunlight, polymer materials undergo a series of oxidative

reactions that lead to chemical degradation, with consequences like brittleness, loss

of brightness, colour change, opacity and formation of surface cracks. Besides the

reduction in molecular weight, a number of changes take place in the molecules

during photodegradation with the formation of chemical groups like carbonyl,

carboxylic acids and hydroperoxides (Rabek, 1995).

Products like fibres and films tend to deteriorate under UV exposure to UV

light, resulting mainly in fragility and loss of transparency. The degradation and

stabilization of some types of polymer, like polyethylene were extensively

investigated throughout the years and hence the degradation mechanisms and their

controlling factors are reasonably well established (Fechine et al., 2002). The

common polymers normally photo degrade are fairly well known, but various aspects

of the mechanisms involve remain uncleared. It is important to take into account very

significant influence of compounding additives in modifying the chemical pathways,

3

which are pigments, extenders, photo stabilizers and thermal stabilizers (Al-

Shammary, 2011).

Normally polymers such as plastics are susceptible to auto-oxidation initiated

by heat or UV-light during processing or long term use. In order to prevent the

degradation of polymers, much kind of stabilizers have been developed and are now

use widely in many applications. Normally for coloured materials, combination of

UV absorbers and light stabilizer are used to achieve a measure of protection and

prevent photo-oxidation (Gugumus, 1993). The aim of this study was to investigate

the effect of UV stabilizers on the photodegradation of biopolymer composite. Film

samples were exposed in the UV weatherometer and tested for mechanical properties

and physical changes.

1.2 Background of study

Great interest towards biobased polymer in various applications is due to limited

resources of petroleum based polymers and increased environmental concern. The

development of novel feedstocks for polyurethanes derived from renewable materials

has become important because the use of polyurethane polymers is increasing at a

rate of 1 million tonnes a year. The reaction of organic isocyanate with compounds

containing OH (hydroxyl) groups is capable of wide application in polymer

formation. Thus the urethane linkage, –(NHCOO)- can be produced by reacting

compounds containing active hydrogen atoms with isocyanate, where polymer

formation can take place if the reagents are di- or polyfunctional.

In this study, virgin and waste monomer was converted into a biopolymer

composite with low loading of filler. This filler is widely used as a white pigment

because of its brightness, very high refractive index (n = 2.4), cheap and abundance.

It is also an effective opacifier in powder form or as a pigment to provide whiteness

and opacity to products such as paints, coating, plastics, paper, inks, foods and most

toothpaste. Titanium dioxide (TiO2) is a semiconductor, with a band gap of 3.1 eV

for rutile and tends to lose oxygen and become sub-stoichiometric. TiO2 shows

relatively high reactivity and chemical stability under ultraviolet light (λ<387 nm).

TiO2 of photostabilizer is non-toxic and chemically stable (Zaleska, 2008; Anika

4

Zafiah, 2008). The applications of metal oxide filler as polymer additives included

superhydrophobic photocatalysis as self-clean coating and photovoltaic solar cell

(Anika Zafiah, 2013).

The primary end-use markets are construction, furniture, packaging and

automotive industrial. Automotive interior and under hood parts, electrical

connectors and microwaveable containers are examples of applications requiring

high temperature resistance.

1.3 Problem statement

Environmental polution and destruction on a global scale have drawn attention to the

vital need for totally new, safe and clean chemical technologies and processes, the

most important challenge facing chemical scientists for the 21st century. A large

amount of waste cooking oil has become an environmental issue around the world.

The Energy Information Administration in the United States estimated that some 100

million gallons of waste cooking oil is produced per day in USA, where the average

per capita waste cooking oil was reported to be 9 pounds (Radich, 2006). In the

European countries, the total waste cooking oil production was approximately

700,000-1,000,000 tons/year (Kulkarni and Dalai, 2006).

Synthetic polymers are produced from petrochemicals that cost very

expensive. It also can burden to the environmental because it non-degrade and

harming wildlife when they are dispersed in nature. Management of such oils and

fats pose a significant challenge because of their disposal problems and possible

contamination of the water and land resources As large amounts of waste cooking

oils are illegally dumped into rivers and landfills, causing environmental pollution,

so the use of waste cooking oil to produce biomonomer as biopolymer substitute

offers significant advantages because of the reduction in environmental pollution.

The potential of biodegradable polymers has been recognized for a long time

since they could be an interesting way to overcome the limitation of the

petrochemical resources in the future. The fossil fuel and gas could be partially

replaced by green agricultural resources, which would also participate in the

reduction of CO2 emissions (Avareus and Pollet, 2012). Due to concerns over

5

sustainability, environmental issues and raw material costs, the use of renewable

resources such as waste cooking oil is very attractive to industries. It is because it

most valuable to develop as raw materials for biopolymer composite and offers great

choice with biodegradability, clean, safer and it relatively low cost with acceptable

mechanical properties and wide range of application such as in coating field.

Such varnishes, lacquers or paints are usually made of highly crosslinked

polymers which must exhibit a great resistance to solar radiation, moisture, pollutants

and chemicals in order to ensure a long lasting protection. By lowering the mobility

of the polymer chains, the network structure reduces the extent of both the

production of initiating species (cage effect) and the propagation step, thus making

crosslinked polymers more resistant to photo-oxidation. The durability of organic

coatings can be further enhanced by the addition of light stabilizers (Decker et al.,

1995).

Polymers, such as plastics and coatings, are susceptible to photodegradation

initiated by heat or UV-light during processing or long-term use. In order to prevent

the photodegradation of polymers, different types of stabilizers have been developed

and are now used widely in many applications. With the increasing use of polymers

in exterior applications, there seems to be a growing need for excellent UV

stabilizers such as TiO2 to protect polymers from photodegradation (Kikkawa, 1995).

1.4 Importance/significance of the study

Biodegradable polymer composites have been developed from natural oils like

epoxidized palm oil that has been used as monomer for production of resins. These

vegetable oils have their own particular advantages like they are renewable products

derived from natural oils and fats and are more readily biodegradable than the

corresponding products made from petroleum sources.

Polymeric materials are commonly used of long-lasting products such as

engineering applications, packaging, catering, surgery and hygiene. These polymers

bring a significant contribution to a sustainable development in view of the wider

range of disposal options with minor environmental impact.

6

The used of metal oxide as stabilizer with bio polymer in a coating

application such as paint is a major concern in this study as the use of TiO2 give no

harm to environment. The stability of the biopolymer composites were tested under

UV light using accelerated weathering tester which equivalent to the real outdoor

weather condition.

1.5 Objective of the study

The main objectives of this project are:

(i) To prepare biopolymer (BP) and biopolymer composites (BPC) for

mechanical properties determination; tensile of unirradiated and UV

irradiated for degradation study.

(ii) To study the influence of UV irradiation on physical properties of BP and

BPC.

1.6 Scope of the study

In this study, biopolymer (BP) and biopolymer composite (BPC) produced based on

monomer of virgin and waste cooking oil. Waste cooking oil was obtained from

Small and Medium Industries (SMIs). These BP components were named based on

the starting vegetables oil such as virgin oil polymer (VOP) and waste oil polymer

(WOP). BPC samples were doped with 2.5, 5, 7.5 and 10 wt. % of Titanium Dioxide

(TiO2). These samples were exposed using UV weatherometer at 250, 500, 750,

1000, 2000, and 3000 hours. The effects of UV light on the properties of BP and

BPC were determined by tensile test and visual inspection based on the colour

changes of the thin films. Meanwhile, Fourier transforms infrared (FTIR)

spectroscopy and UV-Vis spectroscopy were used to provide valuable information of

functional groups which can be used to determine the photo degradation of the BP

and the influence of TiO2 on the biopolymer composite. In addition, UV-Vis

spectrophotometer was used to obtain the absorption spectra of BP and BPC.

CHAPTER 2

LITERATURE REVIEW

2.1 Polymer

Polymer is materials that the molecular structure consists of one or more structural

units (monomers) repeated any number of times (Fried, 2008). Homopolymer has

only one kind of structural unit which is repeated, while a copolymer has two or

more different structural units which are repeated (Oil and Colour Chemists

Association Southern Africa, 2011).

A polymer, from the Greek poly, meaning “many”, and meros meaning “part”

is a long molecule consisting of many small units (monomers) joined end to end. A

polymer is analogous to a necklace made from many small beads (monomers). There

are many types of polymers including synthetic and natural polymers. Certain

polymer, such as proteins, cellulose, and silk, are found in nature which are produced

by living organism, known as biopolymers, while many others, including

polystyrene, polyethylene, and nylon are produced only by synthetic route (Mc Crum

et al., 2003; Wicks et al., 2007).

Another common name for many synthetic polymers is plastic which comes

from the Greek word "plastikos", suitable for moulding or shaping. Many objects in

daily use from packing, wrapping, and building materials include half of all polymers

are synthesized. Other uses include textiles, TV's, CD's, automobiles, and many other

8

all are made from polymers. There are many types of polymers including synthetic

and natural polymers. Most commonly, the continuously linked backbone of a

polymer used for the preparation of plastics consists mainly of carbon atoms. A

simple example is polyethylene, whose repeating unit is based on ethylene monomer

(Peacock and Calhoun, 2006).

Polymers can be made in a variety of structures; three important classes are

shown in Figure 2.1. When the mers are linked in chains, the polymers are linear

polyrners, a term that is potentially misleading because the large molecules seldom

form a straight line-they twist and coil. If there are forks in the chains, as in Figure

2.1(b), the polymer are called branched polymers. A class of importance in plastic

results from the bonding of chains with each other at several sites to form cross-

linked, or network, polymers, as in Figure 2.1(c). These polymers are branched

polymers where the branches covalently are bound to other molecules, so the mass of

polymer consists mainly of a single, interconnected molecule. Reactions that join

polymer or oligomer molecules are called crosslinking reactions. Polymers and

oligomers that can undergo such reactions are frequently called thermosetting

polymers. Some confusion can result because the term thermosetting is applied not

only to polymers that cross-link when heated, but also to those that can cross-link at

ambient temperature. A polymer that does not undergo cross-linking reactions is

called a thermoplastic polymer, because it becomes plastic (softens) when heated

(Wicks et al., 2007).

(a) Linear (b) Branched (c) Cross-linked

Figure 2.1: Schematic representations of three common classes of polymer

structure (Wicks et al., 2007).

9

Polymer also can display a range of different structures (Figure 2.2). In the

simplest case, they process a simple linear structure. However, polymers can be

branched, depending on the method of polymerization. They may also display a

cross-linked structure. Some more unusual polymer structures include star polymer,

which contain three or more polymer chains connected to a central unit ladder

polymers, which consist of repeating ring structures, and dendrimers, which show a

star-like structure with branching. These different sorts of microstructures have an

effect on the properties of the polymers (Stuart, 2004).

Figure 2.2: Various type of polymer structures (Stuart, 2004).

Ideally oils would have great competitive advantage if they could be directly

polymerized into products. Since oils have multi-functional starting materials, the

product is a cross-linked material. Direct polymerization of oils has been used to

make ink resins, which however have to be post-cured after application by oxidative

coupling as in coatings. Some oils, like tung and linseed, are used in paints directly

or slightly modified. For other applications, oils have to be functionalized, and that is

done through double bond reactions such as epoxidation, hydrofomylation,

Linear

Dendrimer

Ladder

Star Cross-linked

Branched

10

metathesis, or through ester bond reactions (transesterification, transamidation).

There are different approaches to make polymers from vegetables oils. One might

consider functionalized fatty acids as starting material or the alternative might be to

use triglycerides. The argument for the first approach is that ester bonds are

hydrolysable and thus the products would be sensitive to water attack. This is

however true only if ester bonds are exposed to extremely humid conditions for a

prolonged time or to strong bases (Petrovic, 2008).

Polymer materials do find increasingly access in products with a lifetime of a

few years up to several decades. Newer material and compound developments

achieve technical material properties (e.g. tensile strength) like those of metals and

ceramics, and provide a number of advantages compared to the materials approved

over centuries (e.g. moulding, weight saving, impact-strength, and etc.). Though

many polymers are subject to some changes of physical (e.g. changing of the

morphology) and chemical provenience (e.g. oxidation) during processing and

service, nowadays it is possible to adjust specific requirements in regard to life

expectancy by suitable modification (e.g. co-polymerisation, additives) (Affolter,

1999).

The requirements on long-term products are versatile and have to be defined

before developing. Figure 2.3 summarizes the relevant stresses. Normally some of

the mentioned stresses occur at the same time or by terms which complicate an exact

definition of the requirements as well as the stress simulation tests of the chosen

material. The most relevant stresses or stress combinations for long-term use of

polymer material are autooxidation, resistance to chemical attacks and possibly to

additional simultaneous mechanical stress (σ) (environmental stress cracking

behaviour, (ESC)), and also biodegradation.

Durable static or dynamic stress leads to a technical break down of a material.

Figure 2.4 summarizes relevant effects. It has to be mentioned, that mainly chemical

modifications influence the visible and physical changes.

11

Figure 2.3: Stress influences on polymers (Affolter, 1999).

Figure 2.4: Effects of stress influences on polymers (Affolter, 1999).

12

2.2 Materials for development of biopolymer (BP) and biopolymer

composite (BPC)

2.2.1 Monomer based on renewable resources

In the recent years, bio-based and biodegradable products have raised great interest

since sustainable development policies tend to expand with the decreasing reserve of

fossil fuel and the growing concern for the environment. These polymers bring a

significant contribution to the sustainable development in view of the wider range of

disposal options with minor environmental impact.

A monomer from Greek mono meaning “one” and meros meaning “part” is a

molecule that may bind chemically to other molecules to form a polymer (Young,

1987). The most common natural monomer is glucose, which is linked by glycosidic

bonds into polymers such as cellulose and starch, and is over 77 % of the mass of all

plant matter.

Natural oils are considered to be the most important class of renewable

sources. They can be obtained from naturally occurring plants, such as sunflower,

cotton, rapeseed, and linseed. They consist predominantly of triglycerides. Among

the triglyceride oils, linseed, sunflower, castor, soybean, oiticica, palm, tall and

rapseed oils are commonly used for synthesis of oil-modified polymers. Although

fatty acid pattern varies between crops, growth conditions, seasons, and purification

methods, each of triglyceride oils has special fatty acid distribution (Guner et al.,

2006).

Biodegradable composites have also been developed from natural oils like

epoxidized soya oil that has been used as monomer for production of resins. These

vegetable oils have their own particular advantages; such as they are renewable

products derived from natural oils and fats and are more readily biodegradable than

the corresponding products made from petroleum sources. Hence their impact on the

environment is less. The long fatty acid chains of vegetable oils impart desirable

flexibility and toughness to otherwise brittle resin systems such as epoxy, urethane

and polyester resins. This oil can be successfully polymerised photochemically in the

presence of initiators under defined conditions (Pandey et al., 2005).

13

According to Shakhashiri (2008), fats and oils belong to a group of biological

substances called lipids where lipids are biological chemicals that do not dissolve in

water. They serve a variety of functions in organisms, such as regulatory messengers

(hormones), structural components of membranes, and as energy storehouses. Fats

and oils generally function in the latter capacity. Fats differ from oils only in that

they are solid at room temperature, while oils are liquid. Fats and oils share a

common molecular structure, which is represented in Figure 2.5.

Figure 2.5: Chemical structure of fats and oils (Shakhashiri, 2008).

This structural formula in Figure 2.6 shows that fats and oils contain three

ester functional groups which is tri-alcohol, glycerol (or glycerine). In the fatty acids,

Ra, Rb, and Rc, represent groups of carbon and hydrogen atoms in which the carbon

atoms are attached to each other in an unbranched chain (Shakhashiri, 2008).

According to Liu (2000), vegetable oils are triglycerides (tri-esters of glycerol

with long chain fatty acids) with varying composition of fatty acids depending on the

plant, season, crop and growing conditions. The word „oil‟ is refers to the

triglycerides that are in liquid form at room temperature.

Figure 2.6: Hydrolysis reaction produces glycerol and fatty acids (Shakhashiri, 2008).

triglyceride glycerol fatty acids

14

Meanwhile, Shakhashiri (2008) reported triglyceride molecules contain

mostly carbon and hydrogen atoms, with only six oxygen atoms per molecule. This

means that fats and oils are highly reduced (that is, un-oxidized). Fats and oils are

esters of the tri-alcohol, glycerol (or glycerine). Therefore, fats and oils are

commonly called triglycerides, although a more accurate name is triacylglycerols.

One of the reactions of triglycerides is hydrolysis of the ester groups. This hydrolysis

reaction produces glycerol and fatty acids, which are carboxylic acids derived from

fats and oils.

According to Tschan (2012) triglycerides contained in vegetable oils are

triesters of glycerol and fatty acids. Only five major fatty acids are contained in

vegetable oils as the triglyceride shows Figure 2.7 where two saturated acids; stearic

acid and palmitic acid and three unsaturated acid; oleic acid, linoleic acid and

linolenic acid which containing one, two and three carbon–carbon double bonds

respectively. Ricinoleic acid, namely cis-12-hydroxyoctadeca-9-enoic acid produced

from hydrolysis of castor oil is of interest, as it is a bifunctional fatty acid containing

a hydroxyl group on the fatty chain (Tschan, 2012).

Figure 2.7: Main fatty acids issued from vegetable and castor oil (Tschan, 2012).

Stearic acid

Palmitic acid

Oleic acid

Linoleic acid

Linolenic acid

Ricinoleic acid (RA)

15

In polymer industry, vegetable oils such as palm oil which represent a major

potential source of chemicals have been utilized as an alternative feedstock for

monomers (Suresh et al., 2007; Anika Zafiah, 2009). Studied by Liu (2000), the

degradation pattern of biodegradable polymers leading to the production of fully

nontoxic substances or the starting monomers, is the most adequate to satisfy

environmental requirements.

United State Department of Agriculture (USDA) has reported that there are

nine major vegetables oil for worldwide productions which are coconut, cotton seed,

olive, palm, palm kernel, peanut, rapeseed, soybean, and sunflower seed. In year

2013-2014, the highest production of vegetable oil was palm oil which conquers 35

% from overall vegetable oils production as shown in Figure 2.8.

Figure 2.8: Production (million tons and %) of nine major vegetables oil in 2013-

2014 (USDA, 2014).

2.2.2 Biopolymer composite (BPC) from renewable resources

According to Babu et al. (2013), the worldwide interest in bio-based polymers has

accelerated in recent years due to the desire and need to find non-fossil fuel-based

polymers. As indicated by (a) ISI Web of Sciences and (b) Thomas Innovations,

2% 3% 2%

35%

4% 3%

15%

27%

9%

Coconut

Cottonseed

Olive

Palm

Palm Kernel

Peanut

Rapeseed

Soybean

Sunflowerseed

16

there is a tremendous increase in the number of publication citations on bio-based

polymers and applications in recent years, as shown in Figure 2.9.

(a) (b)

Figure 2.9: Citation trend of (a) publications and (b) patents on bio-based polymers

in recent years (Babu et al., 2013).

According to Liu (2000), the design of novel polyester-based biodegradable

materials represent one of the most promising families of biodegradable polymers,

whose potential applications as packaging for industrial products, mulching for

agriculture, or bioresorbable biomaterials for hard tissue replacement and controlled

drug delivery systems.

Besides, Che (2012) mentioned composite materials can be naturally

occurring or synthesized. They are composed of two, very different materials which

exhibit synergistic properties when combined. The major component of a composite

is the matrix: the binder for the filler component, which is usually fibers, but can also

be particles. Fiber fillers have a high aspect ratio and are used to reinforce polymer

properties. Composites have inherently high strength-to weight ratios. Under stress,

most of the load is transferred to the fibers in tension and only a very small portion of

the load is sustained by the matrix. Since fibers are lighter and less matrix material is

required to obtain the required properties, the overall weight is reduced (Che, 2012).

Anika Zafiah (2009) studied the effect of TiO2 on material properties for

renewable rapeseed and sunflower polyurethane where the different percentages of

TiO2 (such as 2.5, 5.0, 7.5, and 10.0 % equivalent weight of polyol) were added into

the biopolymer.

17

Future study on biopolymer doped with superhydrophilic metal oxide filler

applied for surface coating, known as TOP to improve the quality and stability of the

surface finishing for outdoor and building application. The study focused on the

biopolymer composite prepared by reacting methylene diisocyanate (MDI) with

biomonomer where the biopolymer preparation is consist of biomonomer, toluene as

solvent, aromatic isocyanate and additives such as TiO2 (Mohid, 2013).

2.2.3 Methylene diphenyl diisocyanate (MDI) and toluene diisocyanate (TDI)

as aromatic isocyanates

Diisocyanates (also commonly known as isocyanates) are highly reactive and

versatile chemicals with widespread commercial and consumer use. Allport et al.,

(2003) reported over 90% of the diisocyanates market is dominated by two

diisocyanates and their related polyisocyanates: Methylene diphenyl diisocyanate

(MDI) and Toluene diisocyanate (TDI).

Methylene diphenyl diisocyanate (MDI) is the most used isocyanate in

polyurethane factories, and is widely used in the production of industrial materials

such as rubber and elastomeric composite; molding materials for ships and

automobiles; and polyurethane resins for painting, and thermal insulation materials

(Allport et al., 2003; EPA, 2011).

MDI is standing for methylene diphenyl diisocyanate, the aromatic

diisocyanate that widely used in coating. MDI is available in several grades which

are bis (4-isocyanatophenyl) methane, a mixture of 55 % of the 2,4‟ isomer and 45 %

of the 4,4‟ isomer, and several oligomeric (frequently called polymeric) MDI with

longer chains of methylene phenyl groups. The cost is lower than toluene

diisocyanate (TDI) and the volatility (particularly of the oligomeric grades) is low

enough to reduce toxic hazard (Wicks et al., 1999).

In 2008, the U.S. demand for pure MDI was 192.1 million pounds and for

polymeric MDI was 1,418 million pounds. U.S. Environmental Protection Agency

(2011) reported that there are two types of polyurethane products in the marketplace:

(a) with foams, representing the largest sector of the polyurethane industry and (b)

18

non-foam polyurethane, use sectors of pure MDI and polymeric MDI (Figure 2.10)

include coatings, adhesives, binders, and sealants (EPA, 2009).

Figure 2.10: Structures of pure MDI and polymeric MDI (EPA, 2009).

The diisocyanates having the greatest commercial importance originate from

the aromatic content (benzene and toluene). Diisocyanates are obtained by

phosgenation of diamines which are produced, via a number of intermediate steps,

from aromatic hydrocarbons. The diisocyanates with the greatest technical

importance are tolylene diisocyanate (TDI) and diphenylmethane diisocyanate (MDI)

(Bousted, 2005).

Some examples of diisocyanates are 2, 4-toluene diisocyanate, 2, 6-toluene

diisocyanate as shown in Figure 2.11, 1,6-hexamethylene diisocyanate, and 1,5-

naphthalene diisocyanate, among others. The reactivity of isocyanates depends on

their chemical structures. Aromatic isocyanates are usually more reactive than their

aliphatic counterparts (Narine and Kong, 2006). Polymeric isocyanates (such as

polymeric MDI) are extremely thermally stable and produce thermally stable

polymer.

Figure 2.11: Isomers of toluene diisocyanates (Allport, 2003; Bousted, 2005).

4,4‟

2,4‟

2,2‟

Pure MDI‟s

Polymeric MDI‟s

2,4-TDI 2,6-TDI

19

Toluene as solvents are substances that are capable of dissolving or

dispersing one or more other substances, widely used as an industrial feedstock to

dissolve paints, paint thinners or silicone sealants. Toluene is a common aromatic

hydrocarbon solvents used in paints and coatings other than benzene, ethylbenzene,

mixed xylenes (BTEX) and high flash aromatic naphthas. The present work using

toluene as solvent for biopolymer coating and it is formerly known as toluol, is a

clear, water insoluble liquid with the typical smell of paint thinners.

Besides, toluene should not be inhaled due to its health effects. However,

toluene is much less toxic than benzene and has largely replaced it as an aromatic

solvent in chemical preparation. For example, benzene is a known carcinogen,

whereas toluene has very little carcinogenic potential.

MDI and TDI have unique properties and functional versatility, and contain

free isocyanate functional groups (-N=C=O). When isocyanates are combined with

other compounds that contain free hydroxyl functional groups (i.e. –OH) they react

and begin to form polyurethane polymers. This chemical reaction is completed when

all of the initially free – N=C=O groups are bound within the polymer network. This

process is commonly referred to as “curing.” Products that contain free –N=C=O

groups are intended to react and undergo “curing” in the process of use (EPA, 2011).

2.2.4 Titanium dioxide (TiO2) in polymer

Titanium dioxide (TiO2) is a powdered insoluble solid which provides optical

properties such as colour, reflectance, and opacity. The term is also used in the

coatings/ink industry for powders which, when dispersed in a liquid or solid binder,

may also provide properties such as UV protection, corrosion inhibition or for

modifying mechanical and flow properties.

TiO2 is the most important and most widely used inorganic pigments or

additives applied in many branches of industry such as in pharmaceutical, cosmetic

and food industries. It commonly used as pharmaceutical excipients because they are

non-toxic, not metabolised and neutral to human body and its organs. The most

desirable features of TiO2 from the point of view of thin film as coating applications

include the ability of whitening, covering power, brightness, and resistance to

20

environmental factors, chemical neutrality and non-toxicity (Chattopadhyay and

Raju, 2007).

An important attribute of polymers is the ability to modify their inherent

physical properties by the addition of fillers while retaining their characteristic

processing ease (Anika Zafiah, 2009). Polymers can be coloured, made stronger,

stiffer, electronically conductive, magnetically permeable, flame retardant, harder,

and more wear resistant by the incorporation of various additives. Most of these

modifications are made by the addition of inorganic fillers to the polymer. These

fillers, present in varying degrees, also affect the basic mechanical properties of the

polymer (Siwinska et al., 2009).

There is various review study on the TiO2 such as structure and properties of

TiO2 surfaces (Diebold, 2002), doped-TiO2 (Zaleska, 2008), the anatase to rutile

phase transformationa (Hanaor and Sorrel, 2011), and polymer TiO2 nanocomposites

(Chaudhari, 2013). Properties of titanium dioxide, TiO2 can be classified as shown in

Table 2.1. Table 2.2 outlines the basic properties of rutile and anatase, and chemical

structure of TiO2 as shown in Figure 2.12.

Table 2.1: Properties of titanium dioxide, TiO2 (Anpo, 2000)

Properties

IUPC name Titanium dioxide

Molecular formula TiO2

Molar mass 79.866 g/mol

Appearance White solid

Density 4.23 g/cm3

Melting point 1843 °C

Boiling point 2972 °C

21

Table 2.2: Properties of anatase and rutile (Hanaor and Sorrell, 2011)

Property Anatase Rutile

Crystal structure Tetragonal Tetragonal

Atoms per unit cell (Z) 4 2

Lattice parameters (nm) a = 0.3785

c = 0.9514

a = 0.4594

c = 0.29589

Unit cell volume (nm3)a 0.1363 0.0624

Density (kg m-3) 3894 4250

Calculated indirect band gap (eV)

(nm)

3.23–3.59

345.4–383.9

3.02–3.24

382.7–410.1

Experimental band gap

(eV)

(nm)

~3.2

~387

~3.0

~413

Refractive index 2.54, 2.49 2.79, 2.903

Solubility in HF Soluble Insoluble

Solubility in H2O Insoluble Insoluble

Hardness (Mohs) 5.5–6 6–6.5

Bulk modulus (GPa) 183 206

Figure 2.12: Chemical structure of TiO2 (Anpo, 2000).

This study should be added TiO2 as modification of mechanical property,

surface property, or as an optical agent. TiO2 has an important role as a (white)

colourant in synthetic polymers such as poly (vinyl chloride) which is used as a

building material (windows, doors, fascia boards) (Diebold, 2002) and polyethylene

film (the familiar supermarket shopping bag material) (Anika Zafiah, 2009).

22

2.2.5 Titanium dioxide (TiO2) as photocatalyst

In the past two decades, TiO2 heterogeneous photocatalyst has been extensively

investigated (Fujishima, 2000; Anpo, 2000). As well as its low cost,

biocompatibility, and non-toxicity the relatively high photo-efficiency of TiO2 in

decomposing and some inorganic pollutants, have made this material one of the best

candidates for environmental treatments, and purification purposes. TiO2 is used in

heterogeneous catalysis (Diebold, 2002) and it identified to make this catalyst more

efficient and more applicable such as thin and thick film coatings, powders, and

membranes (Arana, 2002).

Anpo (2000) found that TiO2 thin films have found to exhibit a unique and

useful function (i.e. a super-hydrophilic property). Usually, metal oxide surfaces such

as TiO2 become cloudy when water is dropped on them because the contact angle of

the water droplet and the surface is 50–80 degrees. However, under UV light

irradiation this contact angle becomes smaller, its extent depending on the irradiation

time. Thus, under UV light irradiation, titanium oxide surfaces never become cloudy,

even in the rain. Similar study by Anika Zafiah et al. (2013), biopolymer doped with

TiO2 superhydrophobic photocatalysis can be as self-cleaning coating for lightweight

composite.

Kobayashi and Kalriess (1997) were studied on the photocatalytic activity of

TiO2 and ZnO and they conclude that TiO2 especially the ultrafine grades supplied

with inorganic coatings, such as Al2O3 and/or ZrO2, to lower the photoreactivity,

while ZnO do not require inorganic coatings to ensure good light stability. Other

study by Mukherjee (2011) found that the characterization of TiO2/polymeric film as

photocatalysts and presents the photocatalytic degradation of methyl orange under

UV light.

A review of the anatase to rutile phase transformation of TiO2 by Hanaor and

Sorrel (2011) mentioned that at all temperatures and pressures, rutile is the stable

phase of TiO2 while anatase is metastable but it can be considered to be kinetically

stabilised at lower temperatures where TiO2 is an important photocatalytic material

that exists as two main polymorphs, anatase and rutile. However, Gesenhues (2000)

studied on a nanocrystalline rutile powder, an anatase white pigment and a

photoactive as well as a photostable rutile pigment to examine for their influence of

23

TiO2 on the photodegradation of poly(vinyl chloride). There are many researches on

the TiO2 photocatalyst that have been summarizing as in Table 2.3.

Table 2.3: Various research on the TiO2 photocatalyst

Research study Photocatalyst Author

The effect of nano-particle

TiO2 fillers on structure and

transport in polymer

electrolytes

TiO2 (Degussa P25, 21 nm,

dried at 250 °C for 24 h) Forsyth et al. (2002)

Photocatalytic activity and

biodegradation of

polyhydroxybutyrate (PHB)

films containing TiO2

Nanosized TiO2 photocatalysts (P-25, ca. 80 % anatase, 20 %

rutile; BET area, ca. 50 m2

g_1) provided by JJ Degussa

Co., Malaysia

Saw et al. (2006)

Biopolymer Doped with TiO2

Superhydrophobic Photocatalysis as Self-Clean

Coating for Lightweight

Composite (LC)

Doped with different

percentages of

superhydrophilic

photocatalysis fillers of TiO2 named as TOP which were 1.0

%, 1.5 %, 2.0 %, and 2.5 %

equivalent to weight of

monomer

Anika Zafiah et al. (2013)

Influence of N2 and H2O of UV

Irradiated Biopolymer

Composite

10 % TiO2 Kronos Anika Zafiah et al.

(2014)

2.3 Types of polymers degradation

Degradation of polymers includes all the changes in the chemical structure and

physical properties of the polymers due to external chemical or physical stresses

caused by chemical reactions, involving bond scissions in the backbone of the

macromolecules that lead to materials with characteristics different from (usually

worse than) those of the starting material.

Polymer degradation in broader terms includes biodegradation, pyrolysis,

oxidation, and mechanical, photo- and catalytic degradation. According to their

chemical structure, polymers are vulnerable to harmful effects from the environment.

This includes attack by chemical deteriogens-oxygen, its active forms, humidity,

harmful anthropogenic emissions and atmospheric pollutants such as nitrogen oxides,

24

sulfur dioxide and ozone – and physical stresses such as heat, mechanical forces and

radiation (Pielichowski and Njuguna, 2005). Nik Yusof (2011) have focused on the

resistance to thermal, photo and bio-degradation of polymer thin films from

renewable resources based on virgin and waste vegetable cooking oil.

According to ASTM D4674-89 (1989), the method for photodegradation is

by using artificial weathering method/laboratory test. Pure laboratory testing involves

using environmental chambers and artificial light sources to approximately replicate

outdoor conditions but with a greatly reduced test time under highly controlled

conditions. Laboratory testing can quickly assess the relative stability of plastics but

has the major disadvantage that the quicker the tests lower is the correlation to real

behavior in the field. Fechine et al. (2004) have studied accelerated weathering of

unstabilized PET film and PET with UV absorber.

Therefore, depending upon the nature of the causing agents, polymer

degradations have been classified as (a) photo-oxidative degradation, (b) thermal

degradation, (c) ozone-induced degradation, (d) mechanochemical degradation, (e)

catalytic degradation and (f) biodegradation (Grassie and Scott, 1985).

2.3.1 Photo-oxidative degradation

Photo-oxidative degradation is the process of decomposition of the material by the

action of light, which is considered as one of the primary sources of damage exerted

upon polymeric substrates at ambient conditions. Most of the synthetic polymers are

susceptible to degradation initiated by UV and visible light. Solar radiation reaching

the surface of the earth is characterized by wave lengths from approximately 295 up

to 2500 nm. The solar radiation classified as UV-B (280–315 nm) has an energy of

426 – 380 KJ mol-1

. Fortunately, the higher energetic part of UV-B; 280–295 nm, is

filtered by the stratosphere and does not reach the earth‟s surface, UV-A (315–400

nm), has energy between 389 and 300 KJ mol-1

and is less harmful for organic

materials than UV-B Visible (400 – 760 nm) and infrared (760 – 2500nm) (Pospisil

and Nespurek, 2000). Normally the near-UV radiations (290-400 nm) in the sunlight

determine the lifetime of polymeric materials in outdoor applications (Sheldrick and

Vogl, 2004).

116

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