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INJECTION MOLDED SILANE CROSSLINKABLE RICE STRAW/HIGH
DENSITY POLYETHYLENE BIOCOMPOSITE
NURNADIA BT ANDENAN
UNIVERSITI TEKNOLOGI MALAYSIA
INJECTION MOLDED SILANE CROSSLINKABLE RICE STRAW/HIGH
DENSITY POLYETHYLENE BIOCOMPOSITE
NURNADIA BT ANDENAN
A thesis submitted in fullfilment of the
requirements for the award of the degree of
Master of Engineering (Polymer)
Faculty of Chemical Engineering
Universiti Teknologi Malaysia
OCTOBER 2010
iii
“Dedicated to my beloved husband Haritz Khan, parents, brothers and sister for all
their love, encouragement and support...”
iv
ACKNOWLEDGEMENT
First and foremost, I would like to express my heartfelt appreciation and
gratitude to my supervisor, Associate Professor Dr Wan Aizan Bt Wan Abdul
Rahman for her continous encouragement and support throughout the course of this
thesis: I greatly appreciate the importance and positive contributions that she has
made to the career that I enjoy so much. She has been en excellent example to me.
The assistance and technical support from material processing to testing stage
at Laboratory Polymer Engineering Department, FKKKSA, UTM and are greatly
appreciated.
I also wish to thank all the lecturers, technicians and colleagues from the
Laboratory of Polymer Engineering at University Technology Malaysia for their
assistance. Thanks to all the assistance and services from the library and the
computer facilities in UTM.
I am grateful to FRGS Vote 78133 and School of Graduate Studies UTM for
the generous financial assistance.
Finally, I would to express my gratitude to my husband, parents, brothers,
sister and Biopolymer Research Group for their encouragement, understanding and
care as well as those who have directly and indirectly assisted me in the preparation
of this thesis. Thank You.
v
ABSTRACT
A formulation was designed to produce silane crosslinked rice straw/High
Density Polyethylene (RSPE) compound suitable for injection molding process. The
formulation consist of HDPE as the base polymer, rice straw as the filler, processing
aids and a mixture of crosslink chemicals. Crosslink chemicals consist of
vinyltrimethoxysilane (VTMO) as crosslinking agent, dicumyl peroxide (DCP) as the
initiator and dibutyltin dilaurate (DBTL) as the condensation catalyst. The rice straw
was oven dried at 70ºC for 24 hours, grinded and followed by sieved. A counter
rotating twin shaft high speed mixer was utilized to mix the rice straw, HDPE and
the processing aids. The blends were then compounded on twin screw extruder. Test
specimens were prepared via injection molding process followed by oven cured at
90ºC. Fourier Transform Infra Red (FTIR) was used to determine the chemical
functional group involved in the crosslinking reaction. Degree of crosslinking in the
silane crosslinked compounds was measured by determining the gel content. Thermal
properties were analyzed on the Differential Scanning Calorimetry (DSC) for the
melt temperature whereas Thermogravimetry Analysis (TGA) for its thermal stability
behavior. The degree of crosslinking in RSPE increased with an increased in VTMO
and DCP concentration. The results from FTIR showed the presence of Si-O-Si bond
and Si-O-C indicative of crosslinks formation. Thermal stability of the compound
illustrated that the crosslinked RSPE was more stable than the uncrosslinked RSPE
while the melting point was unchanged. Tensile strength and flexural strength
improved after crosslinking and increased with the amount of VTMO and DCP,
whilst impact strength showed an optimum value with respect to crosslink chemicals
composition. The concentration of 3 phr VTMO, 0.5 PHR dcp AND 0.015 phr
DBTL was the optimum crosslinked chemical composition to produce the
crosslinked RSPE, significant properties enhancement.
vi
ABSTRAK
Formulasi telah direkabentuk untuk menghasilkan sebatian silane terpaut
silang jerami padi/Polietilina berketumpatan tinggi (RSPE) yang sesuai untuk proses
pengacuan suntikan. Formulasi ini mengandungi HDPE sebagai polimer asas, pengisi
jerami padi, bahan bantu pemprosesan dan campuran kimia pemaut silang.
Campuran kimia pemaut silang terdiri daripada vinyltrimethoxysilane (VTMO)
sebagai agen pemaut silangan, dicumyl peroxide (DCP) sebagai bahan pemula dan
dibutyltin dilaurate (DBTL) sebagai pemangkin kondensasi. Jerami padi dikeringkan
pada suhu 70ºC selama 24 jam dan seterusnya dihancurkan dan diayak. Pencampur
berkelajuan tinggi digunakan untuk mencampurkan jerami padi, HDPE, bahan
penyuai dan bahan bantu pemprosesan. Campuran kemudian disebatikan
menggunakan penyemperitan skru berkembar. Spesimen-spesimen ujian disediakan
melalui proses pengacuan suntikan dan seterusnya dimasukkan ke dalam ketuhar
pada suhu 90ºC untuk diawet. Fourier Transform Infra Red (FTIR) digunakan untuk
mengenal pasti kumpulan berfungsi yang terlibat dalam tindakbalas pemaut silangan.
Darjah pemaut silangan pada sebatian silane terpaut silang dapat diukur berdasarkan
kandungan gel. Sifat haba bagi sampel berangkai silang dianalisa menggunakan
Differential Scanning Calorimetry (DSC) untuk menguji takat lebur sebaliknya
Thermogravimetry Analysis (TGA) untuk kelakuan kestabilan haba. Darjah pemaut
silangan RSPE meningkat dengan pertambahan kepekatan VTMO, DBTL dan DCP.
Keputusan FTIR menunjukkan kehadiran ikatan Si-O-Si dan Si-O-C membuktikan
berlakunya pembentukan pemaut silang. Kestabilan sebatian menggambarkan terpaut
silang RSPE yang telah berangkai silang lebih stabil daripada tidak terpaut silang
RSPE manakala takat lebur tidak menunjukkan perubahan yang ketara. Kekuatan
regangan dan kekuatan lenturan menunjukkan peningkatan selepas pemaut silangan
dan semakin meningkat dengan pertambahan VTMO dan DCP manakala kekuatan
hentaman menunjukkan nilai optimum dengan pertambahan komposisi kimia pemaut
silang. Kepekatan yang bersesuaian, berdasarkan 100 bahagian polimer asas, untuk
VTMO ialah 3.0 phr , DCP ialah 0.5 dan DBTL 0.015 untuk menjadikan terpaut
silang RSPE mempunyai sifat yang baik.
vii
TABLE OF CONTENT CHAPTER TITLE PAGE TITLE PAGE
DECLARATION
DEDICATION
ACKNOWLEDGEMENT
ABSTRACT
ABSTRAK
TABLE OF CONTENTS
LIST OF TABLES
LIST OF FIGURES
LIST OF ABBREVIATION AND SYMBOLS
I INTRODUCTION
1.1 Introduction of study 1
1.2 Problem Statement 4
1.3 Objectives of study 6
1.4 Scopes of study 7
2 LITERATURE REVIEW
2.1 Biocomposite 9 2.2 PE/Natural Fiber Biocomposite 11
2.2.1 PE/Empty Fruit Bunch 11
2.2.2 PE/Wood Flour 12
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2.2.3 PE/Kenaf Fiber 13
2.2.4 PE/Straw 14
2.3 Crosslinked HDPE/Natural Fiber 14
2.4 Polyethylene 18
2.4.1 The Chemistry of High Density 20
Polyethylene
2.5 Crosslinked Polyethylene
Technologies 21 2.5.1 Introduction 21 2.5.2 Method of Crosslinking 22
Polyethylene
2.5.2.1 Physical Crosslinking 23 2.5.2.2 Chemical Crosslinking 25 2.6 Natural Fiber 28 2.6.1 Properties of Natural Fibers 31 2.6.2 Application of Natural Fibers 33 2.6.3 Stalk Fibers (Rice Straw) 36 2.7 Market Survey 39
3 METHODOLOGY 3.1 Introduction 43
3.2 Raw Materials 43
3.2.1 Resin 43
3.2.2 Filler 44
3.2.3 Dispersing Agent 46
3.2.4 Binding Agent Compatibilizer 46
ix
3.2.5 Organosilane Crosslinker 47
3.2.6 Dibutyl Dilaurate 47
3.2.7 Dicumyl Peroxide 48
3.2.8 Decayhydronapthlene 48 3.3 Formulation Development Process 49
3.3.1 Rice Straw/HDPE Biocomposite Formulations 49
3.3.2 Crosslinked Rice Straw/HDPE Biocomposite Formulations 51
3.3.3 Preparation of Silane Liquid Mixture 53
3.3.4 Compounding of RSPE Formulation 53
3.3.5 Compounding of Crosslinkable RSPE Formulation 53
3.3.6 Curing 54
3.4 Material and Product Characterization Testing 54
3.4.1 Fourier Transform Infra-Red 54 (FTIR)
3.4.2 Differential Scanning Calorimetry 55 (DSC)
3.4.3 Thermogravimetry Analysis (TGA) 55
3.4.4 Melt Flow Index (MFI) 55
3.4.5 Water Absorption Characteristic 56
3.4.6 Degree of Crosslinking-Gel 56 Content Test 3.4.7 Scanning Electron Microscopy (SEM) 58
3.5 Material and Product Performance Test 58
3.5.1 Impact Testing 58
x
3.5.2 Flexural Test 59 3.5.3 Tensile Test 60 3.5.4 Experimental Procedures 61
4 RESULTS AND DISCUSSION
4.1 Introduction 62
4.2 Filler Characterization 62 4.2.1 Rice Straw Characteristic 62 4.2.2 Thermal Effect on Rice Straw (RS) 63 4.3 The RSPE Composite for Injection Molding 65 4.3.1 Effect of Filler Size 66 4.3.2 Effect of Filler Loading 67 4.4.1.1 Flowability 67 4.4.1.2 Tensile strength 68 4.4.1.3 Young’s Modulus 70 4.4.1.4 Flexural Strength 71 4.4.2 Thermal Characteristic 73 4.4.2.1 Differential Scanning Calorimetry (DSC) 73 4.4.2.2 Thermogravimetry Analysis (TGA) 75 4.4.2.3 Water Absorption Characteristic 77
4.4.3 Characteristic of RSPE Biocomposite 82
4.5 Introduction 83
4.6 Effect of VTMO Silane Crosslinker 85
4.6.1 Gel Content Test 85 4.6.2 Differential Scanning Calorimetric (DSC) 86
xi
4.6.3 Thermogravimetry Analysis (TGA) 88 4.6.4 Water Absorption Analysis 90 4.6.5 Tensile Strength 92
4.6.6 Impact Strength 93 4.6.7 Flexural Strength 94
4.7 Effect of DCP initiator 96
4.7.1 Gel Content Test 96
4.7.2 Differential Scanning Calorimetric (DSC) 98
Analysis
4.7.3 Thermogravimetry Analysis (TGA) 99 4.7.4 Water Absorption Analysis 101 4.7.5 Tensile Strength 102 4.7.6 Impact Strength 103 4.7.7 Flexural Strength 105
4.8 Effect of DBTL Catalysts 106 4.8.1 Gel Content Test 106 4.8.2 Differential Scanning Calorimetric (DSC) 107 4.8.3 Thermogravimetry Analysis (TGA) 108 4.8.4 Water Absorption Analysis 109 4.8.5 Tensile Strength 111
4.8.6 Impact Strength 112
4.8.7 Flexural Strength 113
4.9 FTIR Analysis 115 4.9.1 Uncrosslinked RSPE 115 4.9.2 Crosslinked RSPE 115 4.10 Mechanism of Crosslinking 118
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4.11 Scanning Electron Microscopy 122 5 CONCLUSSIONS AND RECOMMENDATION 5.1 Overall Conclussions 125 5.2 Future Work 127 REFFERENCES 129
PUBLICATION 141
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LIST OF TABLE
TABLE TITLE PAGE
2.1 Type of Polyethylene 18
2.2 Changes in properties of polyethylene after 22
crosslinking
2.3 Comparison of several crosslinking methods 28
2.4 Natural Fiber Properties and Comparison with E-glass 32
2.5 Mechanical properties of different types of potential 33
natural fibers for composite applications.
2.6 The ranges of the chemical constituent in cell wall 38
3.1 Physical properties of HDPE grade HD6070UA 44
3.2 Particle of Rice Straw 45
3.3 Physical properties of the dispersing agent and binding 46
agent
3.4 Specification for Dynasylan® VTMO 47
3.5 Specification for Dibutylin Dilaurate 48
3.6 Properties of Decayhydronapthlene 49
3.7 Formulation for the effect of rice straw particle 50
3.8 Formulations for the effect of rice straw composition 50
3.9 Selection of optimal Vinyltrimethoxysilane 51
(VTMO) composition
3.10 Selection of optimal Dibutyltin Dilaurate 52
(DBTL) composition
3.11 Selection of optimal Dicumyl Peroxide 52
(DCP) composition
4.1 Summary of RSPE biocomposites thermal degradation 77
at various rice straw content.
xiv
4.2 Water absorption test result of RSPE biocomposite 80
4.3 Percentage of water absorbed of RSPE biocomposite 81
compared to commercial wood.
4.4 Summary properties of RSPE biocomposite. 83
xv
LIST OF FIGURES
FIGURE NO. TITLE PAGE 2.1 Bonding between a silane coupling agent, cellulose, 17
and polymeric resin
2.2 Polyethylene chain and molecule 19
2.3 Schematic representation of the different classes of 20
Polyethylene
2.4 Beta irradiation crosslinking technique 24
2.5 Peroxide crosslinking technique 26
2.6 Silane crosslinking technique 27
2.7 Various type and sources for biofibers 29
2.8 Schematic representation of reinforcing 30
natural/biofibers classification
2.9 Schematic drawing of cellulose molecules including the 31
intramolecular and intermolecular hydrogen bonds
2.10 Top of the range automotive vehicles incorporate 35
many components made from natural fibers for the
Mercedes “E"
2.11 Small house developed from rice husk/polyethylene build 36
at MTDC, UTM
2.12 Malaysia Rice, Milled Production by year 1960-2009 37.
2.13 Total consumption of natural fiber composites in 41
North America
2.14 Total consumption of wood fiber composites in North 42
America
3.1 Gel content testing apparatus 57
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3.2 Izod Impact Tester 59
3.3 Tensile Tester 60
3.4 The flow of research work 61
4.1 SEM micrograph of the rice straw surface at Mag x 500 63
and Mag x 1000
4.2 Thermograms and derivative thermograms of rice straw 64
4.3 The tensile strength of RSPE biocomposites with 66
different filler size
4.4 Effect of rice straw loading on the MFI of RSPE 67
Biocomposite
4.5 Effect of rice straw loading on the tensile 69
strength of RSPE biocomposite.
4.6 Effect of rice straw loading on the Young’s Modulus 71
of RSPE biocomposite
4.7 Effect of rice straw loading on the Flexural Modulus 72
of RSPE biocomposite
4.8 Effect of rice straw loading on the Flexural Strength 73
of RSPE biocomposite
4.9 Effect of rice straw loading on the melting point 74
of RSPE biocomposite
4.10 TGA curves of RSPE biocomposites 76
4.11 Change in weight of RSPE biocomposite after 79
water absorption test
4.12 Percentage of Water Absorbed by RSPE biocomposite 80
4.13 Percentage of water absorbed of RSPE biocomposite 81
compared to commercial wood.
4.14 The Effect of the VTMO concentration on gel content 86
of RSPE biocomposite.
4.15 DSC thermogram of of crosslinked RSPE at various 88
VTMO concentration (S0) 2.0phr, (S2) 1.5phr, (S3) 2.5phr,
(S4) 3.0 phr
4.16 TGA thermogram of decomposition temperature of 90
crosslinked RSPE biocomposite at various VTMO
concentration (S0) 2.0phr, (S4) 3.0 phr.
xvii
4.17 The Effect of the VTMO concentration on percentage 91
of water absorbed by RSPE biocomposite.
4.18 Effect of VTMO concentration on tensile strength 93
of RSPE biocomposite.
4.19 Effect of VTMO concentration on impact strength 94
of RSPE biocomposite.
4.20 Effect of VTMO concentration on flexural strength 96
of RSPE biocomposite
4.21 The Effect of the DCP concentration on gel content 97
of RSPE biocomposite.
4.22 DSC thermogram of of crosslinked RSPE at various DCP 99
concentration (S10) 0.4phr, (S11) 0.5phr.
4.23 TGA thermogram of decomposition temperature 100
of crosslinked RSPE at various DCP concentration.
(S0) 0.2phr, (S8) 0.1phr, (S) 0.3phr.
4.24 The Effect of the DCP concentration on percentage water 102
absorbed by RSPE biocomposite.
4.25 Effect of DCP concentration on tensile strength 103
of RSPE biocomposite.
4.26 Effect of DCP concentration on impact strength 104
of RSPE biocomposite.
4.27 Effect of DCP concentration on flexural strength 105
of RSPE biocomposite.
4.28 The Effect of the DBTL concentration on gel content 106
of RSPE biocomposite.
4.29 DSC thermogram of of crosslinked RSPE at 108
various DBTL concentration, (S5) 0.005phr, (S6)
0.015phr, (S0) 0.01phr.
4.30 TGA thermogram of decomposition temperature of 109
crosslinked RSPE at various DBTL concentration.
(S5) 0.005phr, (S0) 0.01phr, (S) 0.015phr.
4.31 The Effect of the DBTL concentration on water 110
absorption rate of RSPE biocomposite.
xviii
4.32 Effect of DBTL concentration on tensile strength 111
of RSPE biocomposite.
4.33 Effect of DBTL concentration on impact strength 113
of RSPE biocomposite.
4.34 Effect of DBTL concentration on flexural strength 114
of RSPE biocomposite.
4.35 FTIR spectra of uncrosslinked and crosslinked RSPE 117
containing 3.0phr VTMO, 0.4 phr DCP and
0.015phr DBTL.
4.36 (a) The reaction mechanism during peroxide induced melt 119
grafting of vinyltrimethoxysilane onto polyethylene
4.36(b) Radical induced crosslinking of polyethylene 119
4.37 The hydrolysis step (1) and condensation step (2) during 120
silane crosslinking
4.38 Bonding between silane, fiber and polyethylene. 121
4.39 SEM analysis of the fracture surface of the uncrosslinked 123
RSPE biocomposite at Mag x 100.
4.40 SEM analysis of the fracture surface of the crosslinked 123
RSPE (at 2.0 phr VTMO) biocomposite at Mag x 100
4.41 SEM analysis of the fracture surface of the crosslinked 124
RSPE (at 0.2 phr DCP) biocomposite at Mag x 100.
xix
LIST OF ABBREVIATIONS AND SYMBOLS
NFRC - Natural Fiber Reinforce Composite
WPC Wood/Natural Fiber Plastic Composites
HDPE - High Density Polyethylene
VTMO - Vinyltrimethoxysilane
DCP - Dicumyl Peroxide
DBTL - Dibutyltin Dilaurate
PE - Polyethylene
PP - Polypropylene
ASTM - American Standard Testing Method
RSPE - Rice Straw Polyethylene
phr - Parts per hundred
DSC - Differential Scanning Calorimetry
MFI - Melt Flow Index
TGA - Thermogravimetry Analysis
FTIR - Fourier Transform Infra-Red
ρ - Density
m - Mass
CHAPTER 1
INTRODUCTION
1.1 Introduction of study
Polymer composite have been subjected to increasing interest, study, and
utilization for some decades. The depletion of petroleum resources coupled with
increasing environmental regulations are acting synergistically to provide the impetus
for new materials and products that are compatible with the environment and
independent of fossil fuels. Waste minimization is one of the problems that we need
to overcome. All these issues have induced to look for alternatives. Recent advances
in genetic engineering, natural fiber development, and composite science offer
significant opportunities for new, improved materials from renewable resources,
which can biodegradable and recyclable but also obtained from sustainable sources at
the same time as reported by Amar et al., (2005) and Hoi-Yan Cheung et al., (2009).
Composite materials are attractive because they combine material properties in ways
not found in nature.
Recently, natural fibers have been investigated as filler materials capable of
serving as localized tensile reinforcement and volume fillers within several types of
polymer matrices. Current conventional fillers include wood flour, talc, calcium
2
carbonate, fiberglass and nylon. Natural fillers have several advantages over
conventional fillers in improving the general characteristics of plastics for example
polyethylene. Natural fillers- plastic composite have several advantages include
reduce processing temperatures thereby which is less than 200°C thus reducing
energy costs during production. In comparison to other mineral filled plastics, natural
filler have a lower specific gravity resulting in both material savings during
production and shipping costs after production and increased life span of the molds
and extruder due to abrasion by the filler as report by Johnson et al., (1997). A
number of natural fillers have been under continued investigation for use in natural
filler reinforced polymer composites (NFRC); including wood fiber, jute, sisal,
kenaf, flax, wheat straw and bamboo. These natural fillers are especially being
sought since the production of composites using natural substances as reinforcing
fillers is not only inexpensive but also able to minimize the environmental pollution
caused by the characteristic biodegradability, enabling these composites to play an
important role in resolving future environmental problems (Hang-Seung Yang et al.,
2004a). More than that, these fillers often contribute greatly to the structural
performance when used in plastic composites.
Increased technical innovations, identifications of new applications,
continuing political and environmental pressures, and government investment in new
methods for fiber harvesting and processing are leading to projections of continued
growth in the use of natural fillers in composite. One of the largest areas of recent
growth in natural filler composites is the automotive industry, where natural fillers
are advantageously used as a result of their low density and increasing environmental
pressures. Most of the composites currently made with natural fillers are press
molded, although a wide range of processes have been investigated (Craig and
Danial, 2005). The automobile industry has begun to apply NFRC in a variety of
exterior and interior panel applications. The significant weight savings and the ease
and low cost of the raw constituent materials have made NFRC an attractive
alternative material compare to glass and carbon fiber reinforced polymer
composites. However, further research needs to address significant material and
production obstacles before commercially available NFRC are widely used in
architectural and civil works.
3
An increasing amount of interest has developed over the past few years for
NFRC because of their ease of production, subsequent increase in productivity, cost
reduction, lower density and weight, enhanced biodegradability, combustibility, ease
of recyclability, non toxic and use of renewable resources. Composite materials (or
composites for short) are engineered materials made from two or more constituent
materials with significantly different physical or chemical properties and which
remain separate and distinct on a macroscopic level within the finished structure.
Recently, these natural fillers especially plant fibers have been coupled in a matrix
primarily composed of two commodity thermoplastic matrix materials such as
polyethylene (PE) and polypropylene (PP) which melt or soften relatively at low
temperatures (Prachayawarakorn and Yaembunying, 2005). Natural fillers have
gained their importance especially for load bearing application while specific
mechanical properties of natural fillers vary according to the particular filler, the
overall performance of natural fillers lies within a relatively tight range as a result of
similar molecular composition. These advantages place the natural fillers composites
among high performance composites having economical and environmental
advantages, with good physical properties (Mehta and Parsania, 2006). Wood-plastic
composites are currently one of the dominating natural filler composite markets in
North America, as these composite materials are being accepted widely in to the
building and construction industry (Suhara and Mohini, 2007). The composite
industry always looks into alternative low cost lignocellulosic sources, which can
decrease overall manufacturing costs and increase stiffness of the materials.
4
1.2 Problem Statement
Industries are developing and manufacturing “greener” materials; government
is encouraging biobased product research while the academicians are searching for
eco-friendly materials; and the public is coming to value the benefit of environment
friendly products and processes, but at affordable prices. Previously, most
researchers have used wheat straw, wood flour, rice husk and empty fruit bunch as
reinforcement in the various polymers such as polyethylene, polyvinyl chloride and
polypropylene for making a new type of environmentally-friendly composites (Bakar
et al., 2005; Nak et al., 2006; Cheng et al., 2009; Ming Zhu et al., 2009). The use of
natural fillers in polymer matrix is highly beneficial because the strength and
toughness of resulting composites are greater than those of unreinforced materials.
Even though a very large quantity of work has been published on various
natural fillers and its composites, an effort has been made in the present work to
introduce new filler which is rice straw in the development of new composite
materials for lightweight structures. Some studies were already reported on the
exploration and extraction of rice straw which is also comparable with established
filler as reported by Kiran et al., (2000), Mohammad et al., (2004) and Fei et al.,
(2008). Previous work on rice husk polyolefin biocomposite has been done and
shows that these filler posses good mechanical properties that make them suitable to
compound with plastics (Naurah, 2005; Han-Seung Yang et al., 2004b). Nowadays,
rice straw is abundantly available and renewable in nature. As open-field burning of
rice straw is being phased out in Malaysia, rice growers and government agencies are
looking for new rice straw uses. This economical source compared to other natural
sources is still underutilized and not yet established especially in Malaysia.
5
In spite of all the advantages mentioned about natural filler, there are also
drawbacks in using natural filler as reinforcement in thermoplastics. One difficulty
that has prevented the use of natural filler is the lack of good adhesion between the
hydrophilic filler and the hydrophobic polymer (Magnus and Kristina, 2006). The
adhesion between the reinforcement fillers and the composite and the matrix in
composite plays an important role in the final mechanical properties since the stress
transfer between matrix and fillers determines reinforcement efficiency (Ahmad et
al., 2009). It is well known that chemical treatments applied onto filler surface may
affect the mechanical properties of the final material as reported by Kostic et al.,
(2008) who did chemical treatment on hemp fibers. The surface of fillers is usually
modified using various types of chemical modification and has been carried out
previously by using maleic anhydride, maleated polypropylene and titanate
treatments in order to improve the filler surface wettability with the matrix and to
create a strong bond at the filler-matrix interface (Han-Seung Yang et al., 2007;
Byung Dae et al., 2004; Ferran et al., 2007). Poor adhesion leads to composites with
rather poor durability and toughness.
This is the main reason of using silane technology in crosslinking
polyethylene-rice straw composites. Silane was used as coupling agents to adhere
fillers to a polymer matrix, stabilizing the composite material. In general, the use of
this coupling agent significantly improves the mechanical properties of the
composites (Soo Jin et al., 2009). Previous research by Magnus and Kristina (2005)
has succesfully produced silane crosslinked polyethylene/wood flour composites in a
one step process via extrusion. The crosslinked biocomposites showed significantly
higher impact strength compared to uncrosslinked. This study was carried out to
develop an optimum formulation for the silane crosslinkable rice straw/HDPE
compound grade for injection molding. By doing so, the production of the
biocomposites is more economical and also believed to be more industrially friendly.
6
List of problems statement:
(i) Which size of rice straw is suitable for the rice straw/HDPE
biocomposite manufacturing on injection molding process?
ii) What is the optimum composition of rice straw as filler for the HDPE
biocomposite with respect to strength and processability for injection
molding?
iii) Is silane able to crosslink HDPE with rice straw biocomposite for
properties improvement and still processable by injection moulding
technique?
1.3 Objectives of the Study
The main objective of this study is to develop crosslinkable rice straw/HDPE
compound formulation that are processable by injection molding technique. This
main objective is further subdivided into:
i) To categorize the appropriate size of rice straw suitable as a filler in
HDPE with respect to tensile strength.
ii) To study the effect of rice straw composition based on mechanical
properties and flowability of uncrosslinked rice straw/HDPE
biocomposite on the injection molding process.
iii) To investigate the potential of silane as crosslinker in injection
molded rice straw/HDPE biocomposite.
7
iv) To determine the characteristics and properties of crosslinkable rice
straw/HDPE biocomposite and analyze its suitability for injection
molding process.
1.4 Scope of the study
The scope of study involved the following stages:
(i) Filler preparation.
• Rice straw used as filler undergoes preparatory stages prior to
compounding. The rice straw was grinded and sieved into three
ranges of sizes. The rice straw powder was dried before
compounding.
ii) Formulation development of unrosslinked rice straw/HDPE biocomposite.
• HDPE resin was used as base polymer fill with grinded rice straw as
filler. Compounding of rice straw with HDPE and standard additive
on twin screw extruder. Injection molding process was used to
prepared the test specimen
• Tensile test was used as the basic test for following investigations:
a) Effect of rice straw particle size on uncrosslinked rice
straw/HDPE.
b) Effect of rice straw composition uncrosslinked rice
straw/HDPE.
c) Crosslinking of rice straw/HDPE biocomposite with silane
chemicals.
• Silane chemicals formulation
8
a) Premixing of silane chemicals with rice straw/HDPE
biocomposite in the high speed mixer for preparing the
crosslinked rice straw/HDPE.
b) Injection molding processability study.
c) Curing
(iii) Rice Straw/HDPE characterizations.
d) FTIR, to analyze the crosslink.
e) Thermal analysis for thermal properties determination.
f) Water absorption test
g) MFI, to determine its injection molding processability.
h) Gel content test to determine the degree of crosslinking.
(iv) Mechanical properties determination
i) Flexural Test
j) Izod Impact Test
128
REFERENCES
Abdel M, Boufi S, Belgacem MN, Duarte AP, Salah AB, Gandini A. (2004).
Modification of Cellulosic Fibres with Functionalized Silanes:Development
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