She inspired me greatly to work in this project

(1)

THE EFFECT OF NANOSILICA FILLER ON CURING CHARACTERISTICS, MECHANICAL AND MORPHOLOGICAL PROPERTIES OF STANDARD

CAMBODIAN NATURAL RUBBER NANOCOMPOSITES

by

LAY MAKARA

Thesis submitted in fulfillment of the requirements for the degree of Master of Science

September 2013

(2)

THE EFFECT OF NANOSILICA FILLER ON CURING CHARACTERISTICS, MECHANICAL AND MORPHOLOGICAL PROPERTIES OF STANDARD

CAMBODIAN NATURAL RUBBER NANOCOMPOSITES

LAY MAKARA

UNIVERSITI SAINS MALAYSIA 2013

(3)

ACKNOWLEDGEMENTS

Firstly, I would like to acknowledge to my scholarship sponsor AUN/SEED.Net for its financial support (Grant no – 6050218) during my master program. I would like to convey my special thanks to Dean, Deputy Dean, lecturers and all staffs of School of Materials and Mineral Resources Engineering (SMMRE) for their kind assistants and supports. Many thanks to Universiti Sains Malaysia (USM) and SMMRE for research facilites.

I would like to express my sincere appreciation to my supervisors, Assoc.

Prof. Dr. Azura binti A. Rashid for the valuable guidance and advice. She inspired me greatly to work in this project. Her willingness to motivate me contributed tremendously in this project. I also would like to extend my gratitude to my co- supervisor, Dr. Nadras Othman, who has given me a very helpful advice and valuable comments on writing of this thesis.

Special thanks to Mr. Shahril Amir, Mr. Suharuddin who help me directly and indirectly to operate the equipments in rubber lab and all the technicians in SMMRE who help me for testing my samples.

Finally, an honourable mention goes to my beloved parents and my family for their care, understanding and encouragement to me in completing this project.

Special thanks to all my friends in SMMRE for their support.

(4)

TABLE OF CONTENTS

ACKNOWLEDGEMENTS... ii

TABLE OF CONTENTS... iii

LIST OF TABLES... viii

LIST OF FIGURES ...x

LIST OF ABBREVIATIONS...xv

LIST OF SYMBOLS ... xvii

ABSTRAK...xix

ABSTRACT ...xx

CHAPTER 1: INTRODUCTION 1.1 Research Background...1

1.2 Problem Statements...2

1.3 Objectives of the study...5

1.4 Scope of the study...6

1.5 Organization thesis...6

CHAPTER 2: LITERATURE REVIEW 2.1 Natural Rubber...8

2.1.1 Properties of Natural Rubber ...11

2.2 Cambodian Rubber ...12

2.2.1 History of Cambodian rubber plantation...12

2.2.2 Current development of the Cambodian rubber...14

2.3 Fillers...18

2.3.1 Type of particulate fillers ...19

2.3.1 (a) Nanosilica...20

2.3.1 (b) Maerogel ...22

(5)

2.3.1 (c) Calcium carbonate (CaCO3)...26

2.3.1 (d) China Clay...27

2.3.1 (e) Mica ...28

2.3.2 Effect of fillers ...29

2.3.2 (a) Particle size, shape and structure ...30

2.3.2 (b) Rubber-filler and filler-filler interaction...31

2.3.3 Effect of hybrid fillers on NR composites...34

2.4 Rubber Compounding Ingredients...37

2.4.1 Sulphur ...37

2.4.2 Activators...38

2.4.3 Accelerators ...39

2.4.4 Antioxidants...42

2.3.5 Silane coupling agents...44

2.4 Sulphur vulcanization systems: CV, Semi-EV and EV ...49

CHAPTER 3: METHODOLOGY 3.1 Introduction ...53

3.2 Materials...54

3.3 Equipments...56

3.4 Compound formulation ...56

3.4.1 Effect of different types of fillers (maerogel and nanosilica)...57

3.4.2 Effect of Silane coupling agent on NR...57

3.4.3 Effect of different curing systems on NR with silane coupling agents (CV and Semi-EV systems) ...59

3.5 Compounding process...61

3.6 Cure Characteristics ...64

(6)

3.7 Moulding process...65

3.8 Mechanical test ...65

3.8.1 Tensile test ...65

3.8.2 Tear test ...66

3.8.3 Compression set test...67

3.8.4 Hardness test ...69

3.9 Crosslink Density measurement ...69

3.10 Scanning Electron Microscopy analysis ...70

3.11 Thermogravimetric analysis ...71

3.12 Fourier transform infrared analysis...71

CHAPTER 4: RESULTS AND DISCUSSION Preliminary work of different types of fillers...73

4.1.1 Curing Characteristics ...74

4.1.2 Mechanical properties ...75

4.1.2 (a) Tensile properties...75

4.1.2 (b) Tear properties...79

4.1.2 (c) Compression set...80

4.1.2 (d) Hardness test...81

4.1.3 Morphology analysis ...82

4.1.3 (a) SEM ...82

4.1.4 Chemical analysis...84

4.1.4 (a) FTIR ...84

4.1.5 Thermal analysis ...86

4.1.5 (a) TGA ...86

4.2 Effect of different silane coupling agents with NS filled in NR ...89

(7)

4.2.1 Curing characteristics ...89

4.2.2 (c) Compression set test...93

4.2.3 Morphology analysis ...95

4.2.3 (a) SEM ...95

4.2.4 (a) FTIR ...98

4.3 Effect of different curing systems on NR with silane coupling agents (CV and Semi-EV)...100

4.3.2 (c) Compression set test...103

4.3.3 Crosslink Density measurement...105

4.4 Effect of NS hybrid with CaCO3, China clay and Mica ...106

4.4.2 (b) Compression set test ...111

4.4.2 (c) Hardness test...112

4.4.3 Morphology Analysis ...113

(8)

4.4.3 (a) SEM ...113

4.4.4 (a) FTIR ...117

4.4.5 Thermal analysis ...119

4.4.5 (a) TGA ...119

CHAPTER 5:CONCLUSION AND SUGGESION FOR FUTURE WORK 5.1 Conclusion...122

5.2 Suggestions for future work ...124

REFERENCES ...125

APPENDICES...132

(9)

LIST OF TABLES

Table 2.1 Some important Natural rubber and synthetic rubber, its properties and

common uses (Chaiear, 2001). ...9

Table 2.2 Some Common Rubber-Bearing Plant Species (MacGregor, 2005) .12 Table 2.3 Natural rubber plantation situaion, 2007-2008 (Hang, 2009) ...15

Table 2.4 Cambodia’s cultivation, production and exports of natural rubber (MAFF, 2011)...17

Table 2.5 Grades classification of SMR L and SMR 10 (Fulton and Thorpe, 1996)...18

Table 2.6 Maerogel Innovation properties (Tan, 2006)...25

Table 2.7 Effect of Zinc oxide and Zinc stearate on NR compounds (Hewitt, 2007) ...39

Table 2.8 Technical effects of organic accelerators in natural rubber vulcanizates (Blow, 1971, Blow and Hepburn, 1982, Datta, 2002) ...41

Table 2.9 Some Antioxidants can be used in NR compounds (ASTM D3853-97) ...43

Table 2.10 CV, Semi-EV, and EV Vulcanization system (Datta, 2002)...50

Table 2.11 Vulcanisate structure and their final product properties (Datta, 2002) ...52

Table 3.1 The summary of the materials used in this project. ...55

Table 3.2 The equipments used in this research...56

Table 3.3 Formulations for Gum compound and filled SCRL composites. ...57

Table 3.4 Formulation for the effect of different silane coupling agents with NS on SCRL composites...58

Table 3.5 The weight of APTES/Si-69, ethanol and water used in surface treatment for different weight of NS...59

(10)

Table 3.6 Formulation for the effect of different vulcanization systems; CV and Semi-EV with NS and APTES on properties of NR composites. ...60 Table 3.7 Formulation for the effect of hybrid fillers (NS/CaCO3, NS/china clay and NS/mica) loadings with APTES coupling agent on the properties of NR composites...61 Table 3.8 Compounding sequence for standard gum compound. ...62 Table 3.9 Compounding sequence for filled NR composites. ...63 Table 4.1 Tensile properties of the effect of silica, maerogel and nanosilica on SCRL composites...73 Table 4.2 Curing characteristics of NR composites. ...75 Table 4.3 Initial decomposition temperature, maximum weight loss and maximum decomposition temperatures of gum rubber, NR/Maerogel, NR/NS composites...88 Table 4.4 Effect of Si-69 and APTES on curing characteristics of NR composites ...89 Table 4.5 Curing characteristics of different curing systems; CV and Semi-EV on NR/NS/APTES composites. ...101 Table 4.6 Effect of hybrid filler;NS/ CaCO3, NS/china clay and NS/mica with ratios of 0/20, 1/19, 2/18, 3/17 and 3/17 with 1.5 phr of APTES on curing characteristic of NR composites. ...107 Table 4.7 Initial decomposition temperature, maximum weight loss, and maximum decomposition temperatures of gum rubber, NR/Maerogel, NR/NS composites...121

(11)

LIST OF FIGURES

Figure 2.1 World Rubber production (Board, 2012) ...10 Figure 2.2 World Rubber comsumption 2000-2012 (Board, 2012) ...10 Figure 2.3 Repeat unit for NR (polyisoprene) (Simpson, 2002) ...11 Figure 2.4 Natural rubber production in Cambodia 1921-2011 (MAFF, 2011) ..14 Figure 2.5 Rubber production areas (Gergely, 2007) ...16 Figure 2.6 SEM image of silica nanoparticles measurements (Rahim et al., 2011) ...21 Figure 2.7 TEM image of silica nanoparticles (a): without surface treatment with high agglomeration and (b): with surface treatment with reduced agglomeration where the nanosilica particles are relatively in nanodispersed (Rahim et al., 2011)...22 Figure 2.8 Micropgraphs of this aerogel and of a SiO2 aerogel; (Michel et al., 2011) ...24 Figure 2.9 The process of maerogel product (Halimaton, 2005) ...25 Figure 2.10 SEM microphotograph of various NR/Mica compositions (Daniel et al., 2003)...29 Figure 2.11 Classification of fillers according to average particles size (Leblanc, 2002)...31 Figure 2.12 Aggregates and agglomerates formation of carbon black primary particle (Fröhlich et al., 2005). ...32 Figure 2.13 Purposed of simple model for carbon black wetting and dispersion, and bound rubber formation (Leblanc, 2002)...33 Figure 2.14 Bound rubber formation during mixing (Cotten, 1984, Cotten, 1987) ...33 Figure 2.15 Physical interpretation of the Mullins effect (Chazeau et al., 2010) ..34

(12)

Figure 2.16 SEM photomicrographs of fracture surface specimens filled with silica/CB of NR composites at different ratios: (a) 0/50, (b) 10/40, (c)

20/30, (d) 30/20, (e) 40/10 and (f) 50/0 (Rattanasom et al., 2007)...35

Figure 2.17 The effect of carbon black/maerogel loadings and Si-69 coupling agent on tensile strength of hybrid filler NR composites before and after ageing at 100 °C (Siti Rohana, 2011) ...36

Figure 2.18 The effect of carbon black/maerogel loadings and Si-69 coupling agent on tear strength of hybrid filler NR composites before and after ageing at 100 °C (Siti Rohana, 2011) ...37

Figure2.19 Structure of N-cyclohexylbenzothiazole-2-sulfenamide (CBS) (Datta,2002)...41

Figure 2.20 General structure of PPDs, R1and R2are subtituents (Dick, 2003) ...43

Figure 2.21 TGA curve of NR composites with and without IPPD (Siti Rohana, 2011) ...44

Figure 2.23 Chemical structure of Si-69 (Sae-oui et al., 2006)...47

Figure 2.24 Chemical structure of APTES (Sardon et al., 2010)...47

Figure 2.25 The primary reaction of silica with a silane (White et al., 2009) ...48

Figure 2.26 The secondary reaction of silica with a silane (White et al., 2009)....48

Figure 2.27 Schematic representation of accelerated sulphur vulcanization process of NR (Aprem et al., 2003)...51

Figure 2.28 Type of sulfidic linkages (Habeeb Rahiman et al., 2005)...51

Figure 3.1 The overall flow chart of the research...54

Figure 3.2 Shape and dimension of specimens for tensile test...66

Figure 3.3 Shape and dimension of specimens for tear test...67

Figure 3.4 Changes of sample thickness as function of time for compression set testing ...68

Figure 3.5 Device for compression set under constant deflection...69

(13)

Figure 4.1 (a) Tensile strength, (b) Elongation at break of control and different types of fillers; maerogel and NS filled in NR composites with various filler loadings from 1 to 5 phr ...77 Figure 4.1 (c) Modulus at 100 elongation (M100) and (d) Modulus at 300 elongation (M300) of control and different types of fillers; maerogel and NS filled in NR composites with various filler loadings from 1 to 5 phr .78 Figure 4.2 Tear strength of control and different types of fillers; maerogel and NS filled in NR composites with various filler loadings from 1 to 5 phr ...79 Figure 4.3 Compression set of control and different types of fillers; maerogel and NS filled in NR composites with various filler loadings from 1 to 5 phr ...80 Figure 4.4 Hardness measurement of control and different types of fillers;

maerogel and NS filled in NR composites with various filler loadings from 1 to 5 phr ...81 Figure 4.5 SEM ensile fracture specimens with maerogel filler: a (control), b (2 phr), c (5phr) at Mag 50X, and d(5phr at Mag 300X) ...82 Figure 4.6 Tensile fracture specimens with nanosilica filler: (a): control, (b) 1 phr, (c) 2 phr, (d) 3 phr, (e) 4 ph, and (f) 5 phr at mag 25X...83 Figure 4.7 FTIR spectrum; (a) NR/NS, (b) NR/Maerogel with different fillers loadings: a (control), b (1phr), c (2phr), d (3phr), e (4phr), and e (5phr) under reflectance mode...85 Figure 4.8 The effect of maerogel and nanosilica on thermal properties of NR composites, (a) TGA and (b) DTG curves. ...87 Figure 4.9(a) Tensile strength, (b) Elongation at break of control and different fillers; maerogel and NS filled in NR composites with various fillers loadings from 1 to 5 phr ...91 Figure 4.9 (c) Modulus at 100 elongation (M100) and (d) Modulus at 300 elongation (M300) of control and different fillers; maerogel and NS filled in NR composites with various fillers loadings from 1 to 5 phr...92 Figure 4.10 Compression set of NR/NS composites with different silane coupling agents loadings 1.5, 3, 4.5phr of Si-69 and APTES ...93 Figure 4.11 Hardness measurement of NR/NS with various different silane coupling agents loadings 1.5, 3, 4.5phr of Si-69 and APTES ...94

(14)

Figure 4.12 SEM tensile fracture specimens of NR/NS with silane coupling agents: (a): control, (b)1.5 phr, (b) 3 phr and (d) 4.5 phr of APTES, mag. 300X ...96 Figure 4.12 SEM tensile fracture specimens of NR/NS with different silane coupling agents: (e) 1.5 phr, (f) 3 phr and (g) 4.5 phr of Si-69, mag.

300X...97 Figure 4.13 FTIR spectrum of NR/NS with different silane coupling agents (a) n (e) control, (b)1.5 phr, (c) 3 phr, (d) 4.5 phr of APTES, (f) 1.5 phr, (g) 3 phr and (h) 4.5 phr of Si-69 ...99 Figure4.14 Tensile properties of different curing systems; CV and Semi-EV at 0 day and 3 days ageing at 100 °C : (a) Tensile Strength , (b) Elongation at break and (c) M100 ...102 Figure 4.15 Compression set of different curing system; CV and Semi-EV on NR/NS/APTES composites and gum rubber...103 Figure 4.16 Hardness measurement of different curing systems; CV and Semi-EV on NR/NS/APTES composites and gum rubber...104 Figure 4.17 Crosslink density measurement of different curing systems; CV and Semi-EV on NR/NS/APTES composites and gum rubber...105 Figure 4.18 (a) Tensile strength, (b) Elongation at break of the effect of hybrid fillers; NS/ CaCO3, NS/china clay and NS/mica with ratios of 0/20, 1/19, 2/18, 3/17 and 3/17 with 1.5 phr of APTES on mechanical properties of NR composites ...109 Figure 4.18 (c) Modulus at 100 elongation (M100) and (d) Modulus at 300 elongation (M300) of the effect of hybrid fillers; NS/ CaCO3, NS/china clay and NS/mica with ratios of 0/20, 1/19, 2/18, 3/17 and 3/17 with 1.5 phr of APTES on cure characteristic of NR composites ...110 Figure 4.19 Compression set of the effect of hybrid fillers; NS/ CaCO3, NS/china clay and NS/mica with ratios of 0/20, 1/19, 2/18, 3/17 and 3/17 with 1.5 phr of APTES on NR composites ...111 Figure 4.20 Hardness measurement of the effect of hybrid fillers; NS/ CaCO3, NS/china clay and NS/mica with ratios of 0/20, 1/19, 2/18, 3/17 and 3/17 with 1.5 phr of APTES on NR composites...112 Figure 4.21 SEM hybrid fillers: NS/CaCO3 (a) 0/20phr, (b) 1/19phr, (c) 2/18phr, (d) 3/17 phr and (e) 3/17phr and 1.5phr of APTES, mag. 100X ...114

(15)

Figure 4.22 SEM hybrid fillers; NS/china clay (a) 0/20phr, (b) 1/19phr, (c) 2/18phr, (d) 3/17 phr and (e) 3/17phr and 1.5phr of APTES mag.

100X and (f) 3/17phr and 1.5phr of APTES mag. 500X ...115 Figure 4.23 SEM hybrid fillers; NS/Mica (a) 0/20phr, (b) 1/19phr, (c) 2/18phr, (d) 3/17 phr and (e) 3/17phr and 1.5phr of APTES, mag. 100X...116 Figure 4.24 FTIR spectrum of the effect of hybrid fillers: (a) NS/ CaCO3 and (b) NS/China clay with ratio 0/20, 1/19, 2/18, 3/17 and 3/17 with 1.5 phr of APTES on NR composites in range of 4000 – 550cm^-1 under reflectance mode ...118 Figure 4.24 (c) FTIR spectrum of the effect of hybrid fillers; NS/Mica with ratios of 0/20, 1/19, 2/18, 3/17 and 3/17 with 1.5 phr of APTES on NR composites in range of 4000 – 550cm^-1under reflectance mode ...119 Figure 4.25 Effect of hybrid fillers; NS/Mica with ratios of 0/20, 1/19, 2/18, 3/17 and 3/17 with 1.5 phr of APTES on thermal properties of NR composites, (a) TGA and (b) DTG curves ...120

(16)

LIST OF ABBREVIATIONS

APTES (3-aminopropyl)triethoxysilane

A/S Accelerators/Sulphur

ASTM American Standard for Testing and Materials

CB Carbon black

CBS N-cyclohexyl-2-benzothiazole sulfonamide

CNT Carbon nanotube

CRI Cure Rate Index

CRRI Cambodia Rubber Research Institute (CRRI) CV Conventional vulcanization

DSC Different Scanning Calorimetry DTA Different Thermal Analysis DTG Derivative Thermogravimetry

Eb Elongation at break

EV Efficient vulcanization FTIR Fourier Transform Infrared GDR General Department of Rubber

Ha Hectare

IPPD N-isopropyl-N’-phenyl-p-phenylenediamine JIS Japan Industrial Standard

KBr Potassium Bromide

MAFF Ministry of Agriculture, Forestry and Fisheries

MDR Monsanto Moving Die Rheometer

NR Natural rubber

NS Nanosilica

(17)

Phr Part per hundred of rubber Psi Pounds per square inch

SCRL Standard Cambodian Rubber grade L SEM Scanning Electron Microscopy Semi-EV Semi efficiency vulcanization SMR Standard Malaysian Rubber SVR Standard Vietnamese Rubber

TCPTS 3-Thiocyanatopropyl-triethoxysilane TEM Transmission Electron Micrographs TGA Thermogravimetric Analysis

TS Tensile Strength

TSR Technically Specified Rubber

(18)

LIST OF SYMBOLS

% Per centage

C Compression set

d Thickness

F Force

g gram

min minutes

nm nanometer

M100 Tensile modulus at 100% elongation M300 Tensile modulus at 300% elongation

MH Maximum torque

ML Minimum torque

MPa Mega Pascal

Si-69 Bis[3-(triethoxysilyl)propyl] tetrasulfide TESPT Bis(triethoxysilylpropyl)tetrasulfide

t90 Cure time

ti Final thickness of specimen tn Thickness of the spacer bar to Original thickness of specimen ts Thickness of the spacer bar

ts2 Scorch time

[X] Crosslink Density

Vr Volume fraction or rubber Vs Molecular volume of toluene WA Weight of unswollen rubber (g)

(19)

WB Weight of swollen rubber (g)

 Interaction parameter

_r Density of rubber (g/cm³)

_s Density of toluene (g/cm³)

(20)

KESAN PENGISI NANOSILIKA KE ATAS SIFAT-SIFAT PEMATANGAN, MEKANIKAL DAN MORPOLOGIKAL BAGI NANOKOMPOSIT PIAWAI

GETAH ASLI KEMBOJA ABSTRAK

Nanosilika (NS) dan maerogel adalah bahan mesoporous yang ringan, ketumpatan pukal yang rendah, terma konduktiviti yang rendah dan luas permukaan yang tinggi dengan rangkaian mikrostruktur yang terdiri daripada liang bersaiz nano.

NS telah digunakan sebagai pengisi dalam nanokomposit piawai getah asli kemboja (PGAK). 3 bsg bahan pengisi NS telah menunjukkan CRI yang pendek dengan kekuatan tensil dan pemanjangan takat putus yang baik berbanding pengisi maerogel.

Penambahan agen-agen pengganding silana Bis[3- (trietokxisilil)propil] tetrasulfida (Si69) dan (3-aminopropil)trietokxisilana (APTES) dengan 3 bsg NS telah mengurangkan kumpulan silanol semasa proses pencampuran seperti yang ditunjukkan dalam spektrum FTIR. Ianya memberikan masa pematangan yang pendek kerana kehadiran kumpulan amina di dalam APTES. Pembebanan optimum 1.5 bsg APTES dan 3 bsg NS telah dijalankan dengan sistem-sistem pematangan yang berbeza (CV dan semi-EV). Sebelum penuaan, sistem CV menunjukkan kekuatan tensil yang tinggi dengan penurunan yang signifikan ke atas kekuatan tensil selepas penuaan berbanding sistem semi-EV. Sistem semi-EV menunjukkan masa pematangan yang lebih pendek dan mempunyai kestabilan terma yang lebih baik berbanding sistem CV kerana amaun pencepat yang tinggi dengan sambung silang yang lebih stabil. Pengisi hibrid NS/mika dengan 1.5 bsg APTES telah meningkatkan sifat-sifat mekanikal komposit PGAK berbanding pengisi-pengisi hibrid NS/CaCO3

dan NS/china clay disebabkan keupayaan semulajadi mika untuk meningkatkan modulus dan kekuatan tensil komposit.

(21)

THE EFFECT OF NANOSILICA FILLER ON CURING CHARACTERISTICS, MECHANICAL AND MORPHOLOGICAL PROPERTIES OF STANDARD CAMBODIAN NATURAL RUBBER

NANOCOMPOSITES

ABSTRACT

Nanosilica (NS) and maerogel, which are mesoporous light solid materials, low bulk density, low thermal conductivity, and high surface area with microstructure network consists of nano sized pore. NS was used as filler in Standard Cambodian Rubber (SCRL) nanocomposites. 3 phr of NS filler showed a shorter CRI with higher tensile strength and Elongation at break than maerogel filler. The addition of silane coupling agents; Bis[3-(triethoxysilyl)propyl] tetrasulfide (Si69) and (3-aminopropy)triethoxysilane (APTES) with 3 phr of NS reduced silanol group during mixing process as observed from FTIR spectrum. Its provided short cured time due to the presence of amine groups in APTES. The optimum loading of 1.5 phr of APTES and 3 phr of NS were carried out with different curing systems (CV and Semi-EV). Before ageing, CV system showed higher tensile strength with significant decrease in tensile strength after ageing compared to Semi-EV system. Semi-EV system exhibited shorter cured time and better thermal stability compared to CV system due to high amount of accelerator with stable crosslinking. The hybrid filler of NS/mica with 1.5 phr of APTES gave the enhancement on mechanical properties of SCRL composites than hybrid fillers of NS/CaCO3and NS/china clay due to the nature ability of mica to enhance modulus and tensile strength of SCRL composites.

(22)

CHAPTER 1 INTRODUCTION

1.1 Research Background

Natural rubber (NR) is one of the most commercial polymers. Polymer chains in rubber are long and flexible with a coiled and kinked nature. The unique physical and chemical properties of NR are low hardness, high elasticity, high elongation at break, and swell more than double its size in organic solvents but it is impermeable to water (Thomas and Stephen, 2010). The nature of NR is sticky when it warm and brittle when it cold. These properties are limitation of many rubber products for certain applications. The discovery of vulcanization technology by Charles Goodyear and Thomas Hancock plays a significant role in rubber industries with more than 1000 of rubber products such as tires, hoses, belts, gaskets, seals, bearing, bushings, mounts and also there are applications in automotive industries, especially in the modern passenger car.

Beside the vulcanization process, fillers are the most important things to improve the properties of end used applications of rubber. Carbon Black (CB) has been used as a filler to enhance overall properties of NR behavior. Both CB and NR are organic materials which gives good interaction between filler-rubber compounds.

CB is widely used in rubber industry, especially in tyre industries and seal products.

However, it is limited for some specific applications due to its black color. Hence, mineral fillers such as silica, calcium carbonate (CaCO3), talc, mica and so on, which

(23)

are inexpensive, natural and abundant materials are used as fillers in NR especially for light colour products (Heinrich, 2011, Dick, 2003).

Polymer/ nano-filler composites have received an intense attention and become a core focus of nanoscience and nanotechnology today (Bhattacharyya et al., 2008, Sarawade et al., 2010). The automotive manufactures are planning to build the 150,000 mile car which can be driven reliably with low maintenance for more than ten years. For realizing this vision, rubber parts manufacturers need to improve the quality of their parts with significant reduction in dimensional variation. Effective test methods are essential to achieve this goal (Dick, 2003). Development of new tyre requires high performing elastomeric materials. Hence, the choice of fillers is crucial.

There are 3 main factors of a filler that determine it reinforcement abilities. They are particle size, structure and characteristics of surface (Leblanc, 2002). Usage of nanoparticles such as layered silicates, carbon nanotube and nanosilica (NS) were used to achieve products with improved properties for end use application. Compare with microfiller-reinforced rubber, nanofiller-reinforced rubber exhibits high hardness, modulus, anti-aging, gas barrier properties flammability and good rubber compatibility (Thomas and Stephen, 2010, Shanmugharaj et al., 2007).

1.2 Problem Statements

Rubber plantation in Cambodia grew significantly in vast lands from 60, 406 ha in 2005 until 213, 104 ha in 2011 and keep on growing. The Cambodia Government has estimated that the rubber trees will continue to be planted to cover 300, 000 ha of land with an average production of 290, 000 tons by 2020. However, Cambodia still has limited knowledge of natural rubber composites when most of dry

(24)

rubber product is exported to nearby countries such as China, Vietnam, Malaysia, and Singapore. Phanny (2011) has studied SCR 10 and SCR L composites with addition of 30 phr of CB filler. He compared SCR 10 and SCRL with Standard Malaysian Rubber (SMR) and Standard Vietnamese Rubber (SVR 3L). Both SCRL and SCR 10 gave better tensile, tear and tensile modulus properties of compound than SMR and SVR 3L. However, SCRL gives higher tensile strength than SCR 10.

In this research, SCRL was used as a matrix to produce natural rubber (NR) nanocomposites with different types of fillers (maerogel and NS) and hybrid fillers (NS/CaCO3, NS/china clay and NS/mica). This work is expected to be very useful for future rubber composite in Cambodia.

The small amount of maerogel and nanosilica (NS); 1 – 5 phr were used as fillers instead of high amount of silica due to their low thermal conductivity, high surface area, small particle size (10 – 20 nm) with more ability to reduce the heat transfer and improve mechanical properties of NR composites. Although they improve overall material performance there are still challenge in handling because nanoparticles tend to aggregate due to silanol group (Si-OH) content in maerogel and NS fillers which lead to strong filler-filler interaction (Sae-oui et al., 2004, Sae-oui et al., 2006). During processing, particle aggregation resulted in reduction of thermal and mechanical properties of nanocomposites. Silane coupling agents were extensively used to improve good filler-matrix interaction where the silanol group needs to be reduced. Two functional groups, hydrolyzable alkoxy group (-OCH3or – OC2H5) and the organo-functional group composed in silane coupling agent which react with silanol group to form siloxane linkages. They can couple with non-polar materials (natural rubber). It is known that natural rubber is organic materials and

(25)

minerals fillers are inorganic materials. Hence, incompatibility between rubber and fillers exists. However, the maximum properties of its components can only be attained through modification of fillers. Hence, interaction between hydrophobic (rubber) and hydrophilic (fillers) need to be improved in order to obtain good physical and chemical properties in NR matrix.

Sae-oui et al. (2004) have compared the different types of silane coupling agents; 3-thiocyanatopropyl triethoxy silane (Si-264) and Bis[3- triethoxysilyl)propyl] tetrasulfide (Si-69) in NR composites. The results revealed that, Si-69 performs better than Si-264 by providing rubber vulcanizates with lower heat build-up. In this study, (3-aminopropy)triethoxysilane (APTES), which composed of a silane moiety and amine group (NH2) is used to compare with Si-69.

The amine group accelerated the reaction in NR composites hence will gives shorter curing time than Si-69.

Hybrid fillers composites can improve the performance of rubber product which single fillers loadings cannot be attained with reduction in cost of the final products. Silica/CB hybrid filler with ratio of 0/50, 10/40, 20/30, 30/20, 40/10 and 50/0 were carried out by Rattanasom et al. (2007). 20 phr of silica and 30 phr of CB give better overall mechanical properties. Especially, the compound containing 20 phr of silica is more practical than the compound containing 30 phr of silica due to high amount of CB which can easily incorporated into NR than silica. Hybrid of CB/Maerogel filers with ratio of 20/0, 19/1, 18/2, 17/3, and 17/3 with 0.5phr of Si-69 filled in NR composites has been carried out by Siti Rohana (2011). The results revealed that 17/3 phr of CB/Maerogel loadings in NR composites improved the

(26)

mechanical properties, solvent transport and heat ageing properties which attributed from the partial replacement of CB by maerogel which reduced the amount of oxidation catalysts.

This work focused on NS/CaCO3, NS/china clay and NS/mica hybrid fillers in SCRL composites. The presence of CaCO3, china clay and mica in NR can improve the compression set and hardness which normally attributed from the large particles of fillers while retaining the good tensile strength, tear, tensile modulus and elongation at break from small NS particles (Thomas and Stephen, 2010).

1.3 Objectives of the study

The main aim of this study was to investigate the effect of nanofillers to improve overall properties of Cambodian standard natural rubber (SCRL) nanocomposites. The specific objectives of this research are as follows:

i. To determine the effect of maerogel and nanosilica fillers on properties of SCRL nanocomposites.

ii. To compare the effect of fillers modification with Si-69 and APTES coupling agents on mechanical properties of SCRL nanocomposites.

iii. To compare the effect of different curing systems (CV and Semi-EV) on the properties of Cambodian natural rubber nanocomposites.

iv. To determine the effect of hybrid fillers (NS/CaCO3, NS/china clay and NS/mica) on mechanical properties of SCRL nanocomposites.

(27)

1.4 Scope of the study

This research focused on the morphology, structure, properties and application of Cambodian NR nanocomposites with unmodified and modified nanofillers. It investigated the effect of fillers/natural rubber interaction, compatibility between matrix and fillers using modified and unmodified nanofillers.

Moreover, it also studied the effect of nanosilica hybrid fillers (NS/CaCO3, NS/china clay and NS/mica) on properties of Cambodian NR with CV systems. Tensile, tear, hardness, compression set, SEM, FTIR and TGA were done to support this research study.

1.5 Organization thesis

This thesis is divided into five chapters which explained and discussed the entire research work in detail.

 Chapter 1 covers the general introduction of the research background, problem statement and the objectives of study and scope of studies.

 Chapter 2 contains the literature reviews on some fundamental concepts of rubber composites together with some review of related work reported in the literature.

 Chapter 3 explains the material specifications, sample preparation and research methodology carried out in this study.

 Chapter 4 focused on the results and discussion, with all the data and observations presented in graphs, tables, and figures. This is followed by a discussion of the results and data obtained from the tests conducted. All the points of discussion are according to the objectives of this study.

(28)

 Chapter 5 includes the conclusion and summary of the entire research work and findings. This chapter also includes the proposal for the future work recommendations and improvements to be done on this project in the future.

(29)

CHAPTER 2 LITERATURE REVIEW

2.1 Natural Rubber

Natural Rubber found in the liquid of a tree named Hevea braziliensis. The origin of Hevea braziliensis tree is in the southern equatorial region of America, especially in the Amazon valley. It can grow up to 30 m in height with a main trunk of about 50 cm in diameter (Kothandaraman, 2008, Dick, 2001). For the past hundred years, it was planted conversely in many tropical areas around the world. In 1876, Sir Henry Wickham gathered 70,000 Hevea rubber seeds in Brazil and also rubber seeds were grown in Southeast Asia, especially in Malaysia, Sri Lanka, and Indonesia while synthetic rubber was a product of industrialized countries like the United States, Japan and Europe.

Tyre products account for approximately 60% of the synthetic rubber and 75% of natural rubber is used, and this industry employs about half a million workers worldwide (Chaiear, 2001). Since 2005, more than 14 million acres, containing more than 2 million rubber trees, have been cleared out of dense jungles and rain forests in Southeast Asia. The basic conditions for commercial growth were temperatures at 70 to 90 °F, heavy rainfall over the year, and elevations preferably not higher than a thousand feet above sea level. NR was the most resourceful for fabrication into rubber products and accounted for practically 100% of all rubber usage before World War II. Two-thirds of this total usage is for tyres. However, NR did not become an important industrial commodity until the discovery of sulfur vulcanization in 1839

(30)

and the invention of the pneumatic tyre in 1888 by John Dunlop. Table 2.1 shows properties of NR and synthetic rubber and their common use. Figures 2.1 and 2.2 show a rapid growth of world rubber production and rubber consumption. World rubber production and consumption were increased from 2000s until early 2008.

However, early the last quarter of 2008, both world rubber production and consumption were heading into recession and continue to drop down dramatically in 2009 due to economic crisis (MacGregor, 2005, Board, 2012).

Table 2.1 Some important Natural rubber and synthetic rubber, its properties and common uses (Chaiear, 2001).

Type of

rubber/elastomer Properties Common uses

Natural rubber General purpose; not oil resistant, swollen by solvents;

deteriorates when exposed to oxygen, ozone, and UV light

Tyres, shock mounts, seals, couplings, bridge and building bearing, footwear, hoses, conveyor belts, moulded products, linings, rolls, gloves, condoms, medical devices, adhesives, carpet backing, thread, foam

Polyisoprene (IR) General purpose; synthetic natural rubber, similar properties

Same as natural rubber above

Styrene-

butadiene General purpose: Second World War natural rubber substitute; poor oil/solvent resistance

Tyres (75%), conveyor belts, sponges, moulded goods, footwear, hoses, roll coverings, adhesives, waterproofing, latex carpet backing, foam products

Polybutadiene

(BR) Poor oil/solvent resistance;

subject to weathering; high resilience, abrasion resistance and low temperature flexibility

Tyres, shoes, conveyor belts, transmission belts, toy super balls

(31)

Figure 2.1 World Rubber production (Board, 2012)

Figure 2.2 World Rubber comsumption 2000-2012 (Board, 2012)

(32)

2.1.1 Properties of Natural Rubber

NR is a high-molecular-weight polymer of isoprene with chemical structure is cis-1,4-polyisoprene (Figure 2.3). Two carbon atoms are joined together by a double bond and locked in a rigid structure. Due to the presence of an asymmetric carbon atom, cis (two similar groups attached to each carbon in the same sides) and trans (two similar groups attached to each carbon in the opposite sides) formation are possible (Simpson, 2002). There are at least 200 different species of plants such as goldenrod and dandelion (Table 2.2). Molecular chain of NR is basically composed of hydrogen and carbon which molecular weight is 200, 000 – 500, 000 g.mol^-1, wallace plasticity (Po=0.30 min), density(_r=0.9055 g/cm³). It is known that, the unique physical and chemical properties of NR are low hardness, elongation at break, and swell more than double its size in organic solvents. The resistance to heat, oxygen and ozone is poor because of highly carbon-carbon double bonds content in its chemical structure. However NR has extremely high resilience, high tensile strength, good tear resistance and high fatigue to failure in cured state (MacGregor, 2005, Thomas and Stephen, 2010).

Figure 2.3 Repeat unit for NR (polyisoprene) (Simpson, 2002)

(33)

Table 2.2 Some Common Rubber-Bearing Plant Species (MacGregor, 2005)

Name Countries

Funtumia elastica Africa

Landolphia Africa

Castilloa elastic Mexico

Manihot glaziovii(ceara) South America

Ficus elastic India, Burma

Taraxacum koksagys Russia

Parthenium argentatum(Guayule) Mexico, United States (California) Cryptostegia grandiflora United States (Florida)

2.2 Cambodian Rubber

2.2.1 History of Cambodian rubber plantation

In early 1910s, rubber plantations had been cultivated in Veal Rinh district (Shihanouk Province) in Cambodia by Mr. Bouillard. By 1914, rubber plantation was established over an area of 150 ha. It was apparently increased during the early 1920s on the vast scale in Chup and Chamcar Loeu plateau to European plantations following the granting of concession. Even though overproduction of rubber all over the world impaired the international rubber price during the early 1930s, concerted efforts and agreements among producers managed to stabilize prices. Approximately 20 per cent of the total rubber plantations in Indochina come from Cambodia’s rubber plantation in 1937s. After the independence from French in 1953, there were around 30,000 ha of rubber plantation, which had emerged extensively in basaltic red

(34)

plateau region in Kampong Cham and Kratie Provinces by private estate plantations.

At the end of the 1960s, the area cultivated with rubber reached 62,000 ha, where 48,000 ha belonged to private companies and the rest was belonged to village plantations. Total production was about 52,000 tons of rubber. Figure 2.4 shows the brief history of NR production in Cambodia, 1921 – 2011 (Jecelyne Delarue and Noel, 2008).

Unfortunately, Cambodia’s rubber production was declined as a result of declaring a conflict between North Viet Nam and United States –backed Government of South Viet Nam along the Cambodian-Vietnamese border adjacent to the rubber growing areas between 1970 and 1979 and was take overed by Khmer rouge (1975- 1979) subsequently. The production had plummeted to fewer than 10,000 tons.

Following the Socialist regime, rubber plantations revived through village plantations to the Provinces and their productions had been risen to 43,000 tons. By 1991, the Cambodia Rubber Research Institute (CRRI) was established with the objective to upgrade the rubber yields and production (Jecelyne Delarue and Noel, 2008, Hang, 2009, Raya et al., 2012).

(35)

2.2.2 Current development of the Cambodian rubber

In the past two years, the development of the Cambodian rubber sector has been significantly noticeable with the rise in prices of both natural and synthetic rubber, which accelerated smallholders, private companies, and state-run estates to expand their harvested areas. By 2007, total rubber plantations area was 82, 059 ha, in which 48% was dominated by state-owned plantations, 44% followed by smallholders, 6% came from private companies. The expansion of rubber plantations in 2008 rose nonstop approximately 30% from 2007, which had six state-run plantations as illustrated in Table 2.3. Moreover, beside traditional areas located in Kampong Cham, Kraie and Mondul Kiri, new areas emerged in Siem Reap, Preah

Figure 2.4 Natural rubber production in Cambodia 1921-2011 (MAFF, 2011)

Production (tons)

Year

(36)

Vihear, Kampong Thom, Ratanakiri and potential areas located in Battambang, Pailin and Pursat as shown in Figure 2.5 (Gergely, 2007).

Table 2.3 Natural rubber plantation situaion, 2007-2008 (Hang, 2009)

2007 2008

Mature Immature Total Mature Immature Total

Rubber estates

16,740 22,731 39,471 16,378 22,073 38,451

Chup 5,722 8,625 14,347 5,884 5,814 11,698

Peam Cheang 2,064 1,400 3,464 2,000 2,030 4,030

Krek 2,639 1,764 4,403 2,290 2,140 4,430

Memot 1,778 2,755 4,533 1,900 3,000 4,900

Snuol 1,082 1,782 2,864 1,000 1,870 2,870

Chamcar Andong

1,810 3,396 5,206 1,720 4,200 5,920

Boeung Ket 1,310 2,560 3,870 1,300 2,500 3,800

CRRI 335 449 784 284 519 803

Private 3,353 2,883 6,236 5,036 12,126 17,162

Tapao 1,053 1,053 2,106 1,050 1,253 2,303

Labansiek 2,300 90 2,390 3,500 90 3,590

New investment

1,740 1,740 486 10,783 11,269

Smallholders 10,398 25,953 36,351 12,900 40,144 53,044

Total 30,491 51,567 82,058 34,314 74,343 108,657

(37)

According to General Department of Rubber (GDR) in Ministry of Agriculture, Forestry and Fisheries (MAFF, 2011), total cultivation in Cambodia in 2011 was more than 200,000 ha, which about 45,000 ha can be tapped to producing more than 51,000 tons of NR. About 168,000 ha were used for maintenance either for replanting rubber trees on existing orchards, or for planting new trees. The estimation of Cambodian rubber production next few years will be greatly higher than today because of the strong current re-planting. Therefore, the government targets a total rubber planted area of 300,000 ha, of which 235,000 ha for harvesting, yielding and also target an average production of 290,000 tons by 2020 as shown in Table 2.4.

Figure 2.5 Rubber production areas (Gergely, 2007)

(38)

The main processed products are SCR L and SCR 5. However, SCR 10 and SCR 20 are produced for world demand especially for tyre industry where high grade rubber is not required. Both SCRL and SCR 5 are similar to the SMR, which accordance with technically specified rubber (TSR) as shown in Table 2.5 (Fulton and Thorpe, 1996).

Table 2.4 Cambodia’s cultivation, production and exports of natural rubber (MAFF, 2011).

Year Total

planted (ha)

Immature area (ha)

Mature area (ha)

Production (tons)

Yield (kg/ha)

Exports (tons)

1922 1,224 1,224 0 0 0 …

1930 22,959 21,159 1,800 482 268 …

1940 27,977 1,970 26,007 19,988 768 …

1950 30,386 8,207 22,179 15,295 690 …

1960 41,644 13,220 28,424 37,109 1,306 40,466

1967 64,054 24,907 39,147 53,716 1,372 47,655

1980 5,000 0 5,000 1,300 260 1,454

1990 51,160 38 51,122 34,700 680 25,563

2000 53,722 11,024 42,698 42,007 980 40,066

(…) - - - -

2005 60,406 30,004 30,402 29,464 960 28,950

2006 69,994 37,604 32,390 32,077 990 31,184

2007 82,059 51,568 30,491 32,975 1,080 33,121

2008 108,510 74,197 34,313 37,050 1,080 36,000

2009 129,920 95,785 34,135 37,380 1,095 36,500

2010 181,433 143,027 38,406 42,466 1,100 45,000

2011 213,104 167,942 45,162 51,339 1,137 44,969

2020 (estimate)

300,000 65,000 235,000 290,000 1,235 -

(39)

Table 2.5 Grades classification of SMR L and SMR 10 (Fulton and Thorpe, 1996).

Parameters SMR L SMR 10

Dirt content (max, % wt) 0.02 0.08

Ash content (max, % wt) 0.50 0.75

Volatile matter content (max, % wt) 0.80 0.80

Nitrogen content (max, % wt) 0.60 0.60

Po (min) 35.0 30.0

PRI (min, %) 60.0 50.0

Color Lovibond scale (max) 6.00 ---

2.3 Fillers

A filler broadly can be defined as finely divided particles that are frequently used to enhance the performance and various attractive properties of the host matrix, depending on a specific application. Many researchers have contributed to the development and the use of different fillers with dimensions of nanometer level.

Especially in rubber technology, the term nanoscale is not unfamiliar to a rubber specialist. Since the beginning of the twentieth century, carbon black (CB) and silica with primary particle sizes of these fillers remained in the nanometer range have been used as effective reinforcing agents in various rubber formulations for a variety of applications. Nevertheless, with these conventional fillers, the dispersion towards individual primary particles was extensively difficult to realize (Heinrich, 2011).

Normally, fillers such as CB , precipitated silica, nanosilica, maerogel, silicates, calcium silicate, clays, magnesium silicate (talc), calcium carbonate, calcium sulphate and so on (Simpson, 2002, Daniel et al., 2003) were used to improve properties of NR such as mechanical properties, thermal stability, curing

(40)

characteristics and to reduce the cost of final product (Chen et al., 2009, Lazzara and Milioto, 2010, Zhu et al., 2008). The amount of reinforcement fillers upon filling in NR depends on their particle sizes, shape, and structure.

The advantages of nanofillers are not only to reinforce the rubber matrix but also to impart a number of other properties such as barrier properties, flammability resistance, electrical/electronic and membrane properties and polymer blend compatibility. During the last two decades, tremendous research work had been done on the field of polymer nanocomposites at stage of infancy as far as their application was concerned. The major challenge in this regard is to replace carbon black and silica, which are mostly used in bulk amounts in rubber compositions, by small amount of nanofillers (Heinrich, 2011, Bhattacharyya et al., 2008).

However, the non-reinforcing white fillers such as talc, calcium carbonate, frequently used as extenders to reduce the cost of the final compound, do not greatly increase the levels of measured adhesion; these are generally inert materials where they reduce the elongation and produce an increase in the compound modulus. They do not reinforce the compound and do not significantly increase the tear strength (Wootton, 2001).

2.3.1 Type of particulate fillers

There are three core groups of fillers included reinforcing fillers, semi- reinforcing fillers, and non-reinforcing fillers. CB and precipitated silica are the most significant commercial reinforcing fillers when high strength is needed. CB plays an important role on improving mechanical and electrical properties in rubber materials

(41)

(Herman. F, 2005). It mainly attributes to two effects: (i) the formation of a physically bonded flexible filler network and (ii) strong polymer filler couplings which depend on a high surface activity and specific surface of the filler particles (James, 2007). The use of precipitated silica is slightly reduced MH, ML due to high viscosity and slow cure rate but it has ability to attribute of tear, heat resistance and linkage to fabrics and metal in NR compounds; especially for reduction of tyre rolling resistance (Hewitt, 2007).

On the other hand, for some applications where high mechanical properties is not an important role, semi or non-reinforcing fillers such as clay, calcium carbonate, talc, and calcium silicate which improved stiffness and adhesion of vulcanizates are used strongly. However, non-reinforcing fillers are used to increase hardness and tensile strength and also they are used to decrease resilience, resistance to abrasion and tear properties; especially to reduce the cost of final product of NR composites (Sae-oui et al., 2009, Poompradub et al., 2008).

2.3.1 (a) Nanosilica

The technology of nanostructural materials is developing at an astonishing speed and is being applied extensively into many materials (Choolaei et al., 2012).

Polymer/ nano-fillers composites have received intense attention hence they have become a core focus of nanoscience and nanotechnology. In this study, NS used as a filler in natural rubber to reinforce its mechanical properties and morphological behaviors. NS is produced in industrial scale to support a growing number of commercial products. It is a high porous material and has a large surface area with microstructural network (Sarawade et al., 2010, Zhu et al., 2008, Pal et al., 2010).

(42)

Figure 2.6 shows SEM image of silica nanoparticles and Figures 2.7 (a) and (b) show TEM image of silica nanoparticles without and with surface treatment. The large surface area and size of silica particle have played a key role in enhancement of the mechanical properties due to embedded silica in the polymer matrix (Rahim et al., 2011, Lazzara and Milioto, 2010, Tang and Wang, 2005).

Figure 2.6 SEM image of silica nanoparticles measurements (Rahim et al., 2011)

(43)

(b) (a)

2.3.1 (b) Maerogel

Aerogel was invented in 1932 by Kistler, an American scientist. He designated gels in which the liquid was replaced with a gas without collapsing the gel solid network. Wet gels were previously dried by evaporation and new supercritical drying technique was applied after gels being transformed to a supercritical fluid. In practice, supercritical drying includes heating a gel in an autoclave until the pressure and temperature exceed the critical temperature Tc and

Figure 2.7 TEM image of silica nanoparticles (a): without surface treatment with high agglomeration and (b): with surface treatment with reduced agglomeration where the nanosilica particles are relatively in nanodispersed (Rahim et al., 2011)

(44)

pressure Pc of the liquid entraps in the gel pores to prevent the formation of liquid- vapor. Aerogel designated dry gels with a very high relative or specific pore volume depend on the nature of the solid (Michel et., 2011). The most frequently studied silica aerogels with 90 % of pore volume significantly lower in other types of aerogels. Figure 2.8 illustrates TEM micropgraphs of this aerogel and of a SiO2

aerogel. In Figure 2.8 A, aerogel dried by the CO2 supercritical method while Figure 2.8 B shows TEM micrograph of the aerogel in Figure 2.8 A. C. TEM micrograph of a SiO2 aerogel made from 80% TMOS and 40% methyltrimethoxylsilane, dried by CO2supercritic method. Figure 2.8 D shows technical modeling of a local domain in an oxide aerogel, inspired from local zones in the TEM micrographs in Figures 2.8 B and C.

Silica aerogel is a mesoporous light solid material (Hrubesh, 1998, Schmidt and Schwertfeger, 1998), lightest and low bulk density (Obrey et al., 2011), low thermal conductivity, and high surface area with microstructure network consists of nano sized pore, superior insulating capabilities, particle with nanoscale size averaging (20 – 50 nm) (Tang and Wang, 2005, Parmenter and Milstein, 1998, Li and Wang, 2008, Soleimani Dorcheh and Abbasi, 2008, Sarawade et al., 2010).

Maerogel, stand for Malaysian aerogel discovered by Malaysian researcher, Prof. Dr Halimaton Hamdan. It is a silica aerogel produced from rice husk ash which is an agricultural waste content 90 to 97% of Silicone dioxide (SiO2) with trace amounts of CaO, MgO, K2O, and Na2O. Maerogel is the most suitable material to replace the conventional materials for silica aerogel production due to its high surface area, more superiority and low cost (80%) compared to current commercial aerogel. It is also non-toxic and an environmentally amorphous material which has simpler preparation

(45)

technique (Figure 2.9) and it possesses established physic-chemical properties which can be modified for specific applications (Halimation, 2009). Based on its properties (Table 2.6), maerogel can improve the mechanical properties of natural rubber composites (Tang and Wang, 2005).

Figure 2.8 Micropgraphs of this aerogel and of a SiO2aerogel; (Michel et al., 2011)