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CHARACTERIZATION OF THERMOSET BIOPOLYMER IN THERMOPLASTIC
OF LOW AND HIGH DENSITY POLYETHYLENE UPON UV IRRADIATION
NURUL SYAMIMI BINTI MOHD SALIM
UNIVERSITI TUN HUSSEIN ONN MALAYSIA
CHARACTERIZATION OF THERMOSET BIOPOLYMER IN
THERMOPLASTIC OF LOW AND HIGH DENSITY POLYETHYLENE UPON
UV IRRADIATION
NURUL SYAMIMI BINTI MOHD SALIM
A thesis submitted in fulfilment 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
JULY 2017
iii
DEDICATION
Special dedicated to:
my mummy ; Robiah Ismail
my daddy ; Mohd Salim Hj Kamari
Not to forget : my brother and my sisters
Mohd Nor Fazly
Erliananiza
Nor Farah Atikah
the only one:
my husband ;Mohamad Nazrin Abd Malek
and my precious baby:
my daughter: Cinta Nur Mikayla
iv
ACKNOWLEDGEMENT
First and foremost, I would like to express grateful thanks to my respectful
supervisor, Assoc. Prof. Dr Anika Zafiah Binti Mohd Rus whose encouragement,
patience, guidance, and support from the initial till final level enabled me to
develop an understanding of the subject. Her willingness to motivate me
contributed tremendously to the project.
Thank you to Mr. Shahrul Mahadi Bin Samsudin and Mr. Fazlannuddin
Hanur bin Harith form Polymer and Ceramics Laboratory, who help me during
specimen fabrication stage and also during the mechanical testing.
I would not forget to thank to my beloved family, my husband, my
lecturers, my fellow friends and Sustainable Polymer Engineering group (E1) for
their concern and support and helps when I faced difficulty in the research.
Finally, I wish to extend my gratitude to University Tun Hussein Onn
Malaysia (UTHM) for supporting and providing students with the training and
education for a brighter future. At the end I also place on record, my sense of
gratitude to one and all, who directly or indirectly, have lent their hand in this
study. Last but not least, thank you God for making the project successful.
v
ABSTRACT
As the economy achieves global status, many factors regarding the competitiveness
of a nation come under investigation. More recently, together with important areas
such as technology advancement and technology transfer, issues related to
sustainable development and environment preservation are receiving increasing
attention from the world community. Blends of BioPolymer (BP) and
thermoplastic polyethylene (LDPE and HDPE) may contribute to make recycling
more economically attractive. In this study, the monomer is mixed with flexible
isocynate as a crosslinker, known as BioPolymer (BP). The BP were hand mixed
with LDPE or HDPE with propotion ratio of 5%, 10%, 15%, 20%, 25% and 30%.
wt/wt of thermoplastic. The melt flow index (MFI) were indicated that the
processing temperature is the same for both blends which is 190 °C. The aim of
this work is to fabricate and study the processibility of BP/LDPE and BP/HDPE
blends using injection molding. Futhermore, Ultra-violet (UV) Accelerated
weathering test up were conducted at 500 hours, 1000 hours, 1500 hours, 2000
hours, 2500 hours and 3000 hours. The blends yielded tensile strength, percentage
of elongation at break and young’s modulus is very dependent on their
composition ratio of BP with thermoplastic. The tensile strength increased at 500
hours UV irradiation exposure with BP/LDPE is 10.55 Mpa. This is attributed
from further crosslink between BP and thermoplastic LDPE. With the BP/LDPE is
67.64 % which diferent from BP/HDPE with the highest elongation of 53.09 % on
virgin HDPE. While elongation at break and young’s modulus is found to decrease
with increases of UV irradiation hours. The decrement of tensile strength and
young’s modulus after UV exposure is due to the occurrence of the chain breaking
process (chain scission) of carbon-carbon backbone as a result of photo-oxidation.
In conclusion, BP content and UV irradiation time play significant roles in
controlling mechanical properties of the BP-blended with LDPE and HDPE
synthetic polymer, thus providing the opportunity to modulate polymer properties.
vi
ABSTRAK
Pada ekonomi globalisasi, banyak faktor mengenai daya saing negara yang berada
di bawah penyelidikaan. Baru-baru ini, bersama-sama dengan bahagian teknologi
seperti kemajuan teknologi dan pemindahan teknologi, isu-isu yang berkaitan
dengan pembangunan mampan dan pemuliharaan alam sekitar menerima perhatian
daripada masyarakat dunia. Menggabungkan Biopolimer (BP) dan polietilena
termoplastik (LDPE dan HDPE) boleh menyumbang untuk membuat kitar semula
lebih menjimatkan. Dalam kajian ini, monomer bercampur dengan isocynate
fleksibel sebagai crosslinker, yang dikenali sebagai Biopolimer (BP). Kemudian,
BP dicampur secara manual dengan LDPE atau HDPE dengan nisbah peratusan
yang berbeza sebanyak 5%, 10%, 15%, 20%, 25% dan 30%. wt / wt termoplastik.
Indeks aliran leburan (MFI) telah menunjukkan bahawa suhu pemprosesan adalah
sama untuk kedua-dua jenis campuran iaitu 190 ° C. Tujuan kerja ini adalah untuk
menghasilkan dan mengkaji proses hasil campuran BP/LDPE dan BP/HDPE
dengan menggunakan acuan suntikan. Tambahan pula, sampel kemudian
didedahkan kepada pendedahan sinaran ultra-ungu (UV) dengan menggunakan alat
pecutan luluhawa. Ujian ke atas sinaran ultra-ungu telah dijalankan pada 500 jam,
1000 jam, 1500 jam, 2000 jam, 2500 jam dan 3000 jam. Campuran menghasilkan
kekuatan tegangan, kekuatan pemanjangan dan modulus pukal adalah bergantung
kepada nisbah komposisi BP dengan termoplastik. Kekuatan tegangan meningkat
pada 500 jam pendedahan sinaran UV untuk campuran BP/LDPE iaitu 10.55 Mpa.
Ini adalah hasil daripada silang lanjut antara BP dan LDPE termoplastik. Kekuatan
pemanjangan untuk campuran BP/LDPE adalah 67.64% , manakala, campuran
BP/HDPE dengan pemanjangan tertinggi iaitu sebanyak 53,09% berbeza daripada
HDPE. Walaupun pemanjangan pada takat putus dan modulus pukal didapati
berkurangan dengan kenaikan jam penyinaran UV. Selepas pendedahan UV,
penyusutan kekuatan tegangan dan modulus pukal adalah disebabkan oleh
berlakunya proses rantaian berbuka (rantaian scission) pada tulang belakang
vii
karbon-karbon yang mengakibatkan foto-pengoksidaan. Kesimpulannya,
kandungan BP dan masa penyinaran UV memainkan peranan yang penting dalam
mengawal sifat-sifat mekanik campuran BP dengan LDPE dan polimer sintetik
HDPE, dengan itu menyediakan peluang untuk memodulasi sifat polimer.
viii
TABLE OF CONTENTS
CONTENTS PAGE
TITLE i
DECLARATION ii
DEDICATION iii
ACKNOWLEDGEMENT iv
ABSTRACT v
ABSTRAK vi
TABLE OF CONTENTS vii
LIST OF TABLES xi
LIST OF FIGURES xiii
LIST OF SYMBOLS xviii
LIST OF ABBREVIATIONS xix
LIST OF APPENDICES xx
CHAPTER 1 INTRODUCTION 1
1.1 Background of study 1
1.2 Objective of research 2
1.3 Scope of research 3
1.4 Problem Statement 3
CHAPTER 2 LITERATURE REVIEW 6
2.1 Biopolymer 6
2.2 Biopolymer from vegetable oils 8
2.3 Cross-linker for thermoset polymer 9
2.4 Monomer 11
ix
2.5 Polymer 12
2.6 Thermoplastic Polymer 15
2.6.1 Polyethylene 17
2.6.2 Low Density Polyethylene (LDPE) 20
2.6.3 High density polyethylene (HDPE) 21
2.7 Thermoset Polymer 22
2.8 Degradation of polymer 24
2.9 Melt flow index (MFI) 28
2.10 Thermogravimetric (TGA) 30
2.11 Injection molding in polymer manufacturing 33
2.12 Tensile test of dumbbell test specimens 35
2.13 Artificial Weathering Ultraviolet (UV) irradiated 37
2.13.1 Working principle 40
2.14 Density 41
2.15 Scanning electron microscopy (SEM) 42
CHAPTER 3 RESEARCH METHODOLOGY 44
3.1 Introduction 44
3.2 Materials 46
3.3 Composition ratio of polymer blends 47
3.4 Sample preparation – blending process 48
3.5 Melt flow index (MFI) 50
3.6 Thermogravimetric analysis (TGA) 50
3.7 Injection molding (IM) machine for tensile test
preparation
50
3.8 Ultra-violet accelerated weatherometer 52
3.8.1 Sample preparation for UV irradiated 53
3.8.2 UV Accelerated weatherometer
parameter setting
53
3.9. Tensile test 55
3.10 Density test 57
3.11 Scanning electron microscopy (SEM) 57
x
CHAPTER 4 RESULTS AND DISCUSSION 58
4.1 Introduction 58
4.2 Thermogravimetric analysis (TGA) 58
4.3 Flow characteristic – Melt Flow Index (MFI) 65
4.4 Injection moulding parameters 67
4.5 Mechanical characterization of HDPE/BP and
LDPE/BP blended before UV exposed
68
4.6 Mechanical properties LDPE/BP blended after UV
exposed
73
4.7 Mechanical properties HDPE/BP blended after UV
exposed
77
4.8 Density 81
4.9 Fracture analysis 84
CHAPTER 5 CONCLUSION AND RECOMMENDATION 89
5.1 Conclusions 89
5.2 Recommendation 90
REFERENCES 91
APPENDICS 100
LIST OF PUBLICATION 133
xi
LIST OF TABLES
2.1 Types of natural monomer and it forming. 11
2.2 Structure parameters effecting polymers mechanical properties 15
2.3 Advantaged and disadvantaged of thermoplastic 17
2.4 Classification of polyethylene by density according to ASTM
standard
21
2.5 The advantages and disadvantages of thermoset 23
2.6 Type of Flat Test Specimen 36
3.1 List of materials used. 47
3.2 Composition ratios for BP/LDPE blends 47
3.3 Composition ratios for BP/HDPE blends 48
3.4 Standard for thermoplastic for MFI 50
3.5 Injection molding parameters for thermoplastic/BP blends 51
3.6 Types of sample size based on thickness 52
3.7 UV exposure time 55
4.1 Thermal property of BP,LDPE and HDPE sample 59
4.2 Temperature degradation of BP/LDPE blends 62
4.3 Temperature degradation of BP/HDPE blends 64
4.4 Comparison of Melt Flow Index (MFI) of BP/LDPE and
BP/HDPE blends
66
4.5 The injection molding parameters used for BP/LDPE and
BP/HDPE blended
67
4.6 The mechanical properties for the BP/LDPE and BP/HDPE
injected samples
69
4.7 Tensile strength of BP/LDPE blends after UV exposure. 73
xii
4.8 Percentage of elongation at break of BP/LDPE blends after UV
exposure
74
4.9 Young’s Modules of BP/LDPE blends after UV exposure 75
4.10 Tensile strength of BP/HDPE blends after UV exposure 78
4.11 Percentage of elongation at break of BP/HDPE blends after UV
exposure
79
4.12 Young’s Modules of BP/HDPE blends after UV exposure 80
4.13 Density of BP/LDPE and BP/HDPE blended before UV
irradiation
82
4.14 Density of BP/LDPE blends after UV irradiation exposure 83
4.15 Density of BP/HDPE blends after UV irradiation exposure 84
xiii
LIST OF FIGURES
2.1 Classification of Biodegradable. 7
2.2 Types of isocyanate MDI. Monomers structure of different
polymers
10
2.3 Polymerization by Ethylene molecules. 11
2.4 Model of step-growth polymerization showing two type of
reaction occurring, (a) n-mer attaching a single monomer to
form (n+1)-mer and (b) n1-mer combining with n2-mer to
form (n1 + n2)-mer.
14
2.5 Sequence is shown by (1) and (2)Model of chain-growth
polymerization; (1) initiation, (2) rapid addition of the
monomers and (3) resulting long chain polymer molecule
with mers at termination of the reaction.
14
2.6 Structure of amorphous, crystal and lamellar 16
2.7 Schematic illustration of spherulite, lamella and amorphous
phase structure
18
2.8 Structure of lamella; (a) the regularly folded chain model
for semi-crystalline polymer; (b) non-regularly folded chain
model for semi-crystalline polymer
18
2.9 Branch structure of polyethylene 19
2.10 Schematic, two-dimensional representation of thermoset
cure. For simplicity difunctional and trifunctional co-
reactants are considered. Cure starts with A-stage or
uncured monomers and oligomers(a); proceeds via
simultaneous linear growth and branching to an
increasingly more viscous B-stage material below the gel
24
xiv
point (b); continues with formation of a gelled but
incompletely cross-linked network(c); and ends with the
fully cured, C-stage thermoset(d)
2.11 Tensile strength (a) and Young‟s modulus (b) versus
degradation time for various polymer compositions:
poly(L-lactide) filled triangles, poly(D-lactide), copolymer
poly( dl -lactide), and blend polymer poly(L/D-lactide)
26
2.12 Photograph and schematic cross-section of MFI. 28
2.13 Melt flow index of polypropylene/starch blends at different
composition
30
2.14 A schematic thermobalance instrumentation 31
2.15 (a) TGA of purified SWCNTs; 3 specimens sampled from
the same batch. (b) Graph illustrating the ambiguity in
determined Tonset
32
2.16 TGA curves of (a) HP, (b) XHP, (c) HP35 and (d) XHP35 33
2.17 Typical injection molding 34
2.18 Cycle of operation for injection molding 34
2.19 Typical Stress-Strain Diagram for Tensile Test 36
2.20 Condensation cycle for fluorescent UV device 38
2.21 Example of Accelerated UV ageing using Polypropylene
0.5 mm films in Q-Sun exposure chamber at temperatures
40, 50, 60 and 70 oC
40
2.22 Example of Tensile stress–strain curves for non-irradiated
(NI) neat HDPE, non-irradiated (NI) HDPE/piassava fibre
composites (COMP), and for irradiated and non-irradiated
HDPE/piassava fibre composites with 2.5% of GMA
(COMP1)
40
2.23 Working principle of UV wheaterrometer 41
2.24 Basic constructionScanning Electron Microscope (SEM) 43
3.1 Flow Chart of Methodology 45
3.2 Monomer was heated into oven 49
3.3 Monomer and Methyldiphenyldiisocyanate is stirred in a
bowl
49
xv
3.4 Thermoplastic and biopolymer is mixed until BP solidify 49
3.5 Thermoplastic/BP blends 49
3.6 Injection Moulding Nissei Horizontal Screw Type Injection
Moulding NP7 Real Mini
51
3.7 Sample size for standard ISO 527-2 52
3.8 Ultra – Violet Accelerated Weathering Tester 53
3.9 Specimens mounted on the sample holder 54
3.10 Sampler holder on the UV Accelerated Weatherometer 54
3.11 Instron Universal Tensile Machine AG-I located at
Polymer Ceramic Laboratory
56
3.12 Tensile test specimen based on the ISO 527-2 standard (all
measurement in mm unit)
56
3.13 Sample clamped at the Instron Universal Tensile Machine
clamping system
56
3.14 Mettler Toledo located at Polymer Ceramic Laboratory 58
4.1 Thermogram (TG) and Derivative weight loss (DTG) of BP
samples
59
4.2 Thermogram TGA and derivative weight loss of LDPE 60
4.3 Thermogram TGA and derivative weight loss of HDPE 60
4.4 Percentage of mass loss of BP/LDPE blends 62
4.5 Thermogram TGA and derivative weight loss of LB15 62
4.6 Percentage of mass loss of BP/HDPE blends 63
4.7 Thermogram TGA and derivative weight loss of HB25 64
4.8 Melt Flow Index (MFI) of LDPE/BP and HDPE/BP blends 66
4.9 Tensile strengths for all injected specimens with respective
compositions
70
4.10 Percentage elongation at break for all injected specimens
with respective compositions
71
4.11 Young’s Modulus for all injected specimens with
respective compositions.
72
4.12 Tensile strength of LDPE / BP blends after UV exposure 74
4.13 Percentage of elongation at break of LDPE/BP blends after
UV exposure.
75
xvi
4.14 Young’s Modules of BP/LDPE blends after UV exposure. 76
4.15 Tensile Strength of HDPE/BP Blends after UV Exposure 78
4.16 Percentage of elongation at break for HDPE/BP Blends
after UV Exposure
79
4.17 Young’s Modules of BP/HDPE blends after UV exposure. 80
4.18 Density of LDPE/BP and HDPE/BP blended before UV
irradiation
82
4.19 Density of LDPE/BP blended after UV irradiation 83
4.20 Density of HDPE/BP blended after UV irradiation 84
4.21 SEM image for HB20 85
4.22 SEM image for LB5 85
4.23 SEM images for LDPE 86
4.24 SEM image for LB15 at 3000 hours UV irradiation
exposure
87
4.25 SEM image for HB10 at 2000hours UV irradiation
exposure
87
xviii
LIST OF SYMBOLS
g - gram
s - second
h - hour
W, M, m - Total mass or total riding mass
MPa - Mega pascal
oC - Degree celcius
% - Percentage
g/ 10min - Gram per 10minutes
m3 - volume
L - LowDensity Polyethylen
H - High Density Polyethylene
B - Biopolymer
LB5 - 5% of biopolymer, 95% low density polyethylene
LB10 - 10% of biopolymer, 90% low density polyethylene
LB15 - 15% of biopolymer, 85% low density polyethylene
LB20 - 20% of biopolymer, 80% low density polyethylene
LB25 - 25% of biopolymer, 75% low density polyethylene
LB30 - 30% of biopolymer, 70% low density polyethylene
HB5 - 5% of biopolymer, 95% high density polyethylene
HB10 - 10% of biopolymer, 90% high density polyethylene
HB15 - 15% of biopolymer, 85% high density polyethylene
HB20 - 20% of biopolymer, 80% high density polyethylene
HB25 - 25% of biopolymer, 75% high density polyethylene
HB30 - 30% of biopolymer, 70% high density polyethylene
xix
LIST OF ABBREVIATIONS
UV - Ultraviolet
BP - BioPolymer
wt. - weight
UTHM - UniversitiTun Hussein Onn Malaysia
WCO - Waste Cooking Oil
ASTM - American Society for Testing and Materials
MDI - Methylene DiphenylDiisocyanate
EFB - Empty Fruit Bunch
PLA - Polylacticasid
N - Nitrogen
BP - Biodegradable polymer
CO2 - Carbon Dioxide
TAG - Triacylglycerol
C - Carbon
NHCOO - Carbamate
OH - Hydroxide
O - Oxygen
PGA - Polyglycolide
PHB - Polyhydroxybutyrate
CH2-CH2 - Polyethylene
PE - Polyethylene
LLDPE - Low linear density polyethylene
LDPE - Low density polyethylene
HDPE - High density polyethylene
MDPE - Medium density polyethylene
xx
LB5 - 5% of biopolymer, 95% low density polyethylene
LB10 - 10% of biopolymer, 90% low density polyethylene
LB15 - 15% of biopolymer, 85% low density polyethylene
LB20 - 20% of biopolymer, 80% low density polyethylene
LB25 - 25% of biopolymer, 75% low density polyethylene
LB30 - 30% of biopolymer, 70% low density polyethylene
HB5 - 5% of biopolymer, 95% high density polyethylene
HB10 - 10% of biopolymer, 90% high density polyethylene
HB15 - 15% of biopolymer, 85% high density polyethylene
HB20 - 20% of biopolymer, 80% high density polyethylene
HB25 - 25% of biopolymer, 75% high density polyethylene
HB30 - 30% of biopolymer, 70% high density polyethylene
TGA - Thermogravimetric analysis
DTG - Derivative thermogravity
MFI - Melt flow index
IM - Injection moulding
xx
LIST OF APPENDICES
A Sample 100
Sample after tensile test 101
B Thermogravity analysis graph forBP/LDPE and
BP/HDPE
108
C SEM image for all BP/thermoplastic blends before
UV irradiated
114
SEM image for all BP/LDPE blends after UV
irradiated.
115
SEM image for all BP/HDPE blends after UV
irradiated.
118
D Tensile test before UV irradiation. 121
Tensile test after UV irradiation 125
E The steps for parameter setting for the UV
Accelerated Weatherometer machine
127
Steps for Mettler Toledo machine 129
Procedure of Scanning Electron Microscope
machine
131
CHAPTER 1
INTRODUCTION
1.1 Background of study
Polymer is a long and large material that plays an essential and important molecule
in everyday life. Polymer can be divide into two properties that is synthetic and
natural polymer created via polymerization of many monomers. Polymer in form
of plastic make most of the product that we use in our daily life such as knobs,
containers, jugs, pipes and so on. Nowadays, most of consuming industries only
take polymer that synthesized from petroleum sources or natural gas raw materials
such as polyethylene, polypropylene, polystyrene and polyvinyl chloride.
Meanwhile, low density polyethylene (LDPE) is one of the most widely
used plastics, especially in making bottles. LDPE is known for its relatively low
density due to minor branching in the molecule. These LDPE can be obtained from
polymerization of ethylene. Ethylene comes from a non-renewable source which is
petroleum and does not undergo the process of biodegradation.
On the other hand, high density polyethylene (HDPE) has a vast application
as it is known for its high strength to density ratio. However, this polymer is
generally detrimental and has drawbacks as it does not undergo the process of
biodegradation and is highly dependent on a limited source; petroleum gas (Rus,
2010).
Due to the detrimental effects and dependency towards this limited source,
there must be methods to replace or improve these plastics (Rus et al., 2009; Rus,
2
2010). There have been many researches being done using waste vegetable oil as
an alternative feedstock for sustainable monomer (Rus et al, 2013).
The term of waste vegetable oils includes all vegetable oil such as soybean
oil, peanut oil, sunflower oil, linseed oil, coconut oil, cottonseed oil, canola oil,
corn oil, safflower oil, walnut oil, castor oil, tung oil, etc. The main components
existing in waste vegetable oil are triglycerides with saturated and unsaturated fatty
acids useful in many synthesis transformations and become new polyol sources
(Clark et al., 2008). In polymer industry, waste vegetable oils which represent a
major potential source of chemicals have been utilized as an alternative feedstock
for bio monomers (Rus et al., 2009) and solidify as bio polymer (BP).
Therefore, bio monomer which is synthesize in lab scale was used to blend
with thermoplastic (LDPE and HDPE). The process by using injection molding
due to injection molding is the most common, easy and commercial method for
processing or manufacturing of plastic parts into various products or even for
material testing. An important advantage of injection molding is that complex
geometries can be made easily in one production step in an automated process (Eva
et al., 2009). Currently, there are extensive researches that are being done to
accommodate the world’s vision in growing to a more sustainable and
environmental friendly future. This lead to a series of studies in producing
sustainable plastics.
Since injection molding is one of the most widely used method for
processing thermoplastics, this study aims to determine and understand the
processing conditions of the LDPE/BP and HDPE/BP blends by injection molding.
Besides that, the resulting mechanical and physical properties of the injected
samples were analyzed.
1.2 Objective of research
1. To fabricate different composition ratios of biopolymer/thermoplastics
granulate which were injected by using injection molding machine.
2. To study the mechanical and physical properties of polymer blended of
(LDPE/BP and HDPE/BP).
3. To investigate the mechanical and physical properties of polymer blended
of (LDPE/BP and HDPE/BP) upon ultra violet (UV) irradiated samples.
3
1.3 Scope of research
1. To prepare BP with correct proportion ratio such as 1:0.5 for monomer and
cross-linker.
2. To study and prepare manually the polymer blends with different ratio of
LDPE and HDPE with (5%, 10%, 15%, 20%, 25% and 30%) loading of BP
(wt. %).
3. To run MFI to study the flow rate of plastic materials.
4. To study the injection molding machine (Nissei Horizontal Screw Type
Injection Molding NP7 Real Mini from Japan) based on ISO 527 (5A) for
the preparation of tensile dumb bell samples.
5. To understand the UV irradiation of the specimens for 500h, 1000h, 1500h,
2000h, 2500h and 3000h by using Accelerated UV Weatherometer
machine.
6. To measure the mechanical properties based on ISO 527 (5A) by using
Universal Tensile Machine (UTM) AG-I, Shimadzu.
7. To study the density of LDPE/BP and HDPE/BP by using Mettler Toledo
density test machine.
8. To study fracture surface morphology of LDPE/BP and HDPE/BP by
scanning electron microscope (SEM).
1.4 Problem statement
Vegetables or plant oils represent a renewable and sustainability resource that can
be used as reliable starting material to access new products with a wide array of
structural and functional variations. The ample availability and the relatively low
cost make plant oils an industrially attractive raw material for the plastics industry.
Already for a long time, plant oils and their derivatives have been used by
polymer chemists due to their sustainability nature, world wide availability at
relatively low price, and their wide application possibilities. In recent year, there
has been a large amount of demand for plant oils as an alternative resource for the
production of additive for various applications such as polymer, coating, adhesive
and nanocomposite (Belgacem et al., 2008, Xia et al., 2010). The necessity of
4
releasing the polymer industry from its dependence on depleting resources
represents a major concern, pushing the search for industrially applicable
sustainability alternatives. In this case, plant oils offer many advantages apart from
their sustainability. Their worldwide availability and relatively low prices make
them industrially attractive and feasible, as daily demonstrated with industrial oleo
chemistry. The largest sources of vegetable oils are annual plants such as soybean,
corn, linseed, cottonseed or peanuts. However, other sources are oil-bearing
perennials such as the palm, olive or coconut (Hui, 1995).
Naturally occurring plant oils and fatty acids derived mostly are considered
to be the most important renewable feedstock processed in the chemical industry
and in the preparation of bio-based functional polymers and polymeric materials
(Guner et al., 2006, Montero et al., 2011).
Vegetable oils with high viscosity indices, low volatility and a high flash
point have been applied in a series of applications as lubricants and additives in
polymer, coatings and resins (Guner et al., 2006). For example, epoxidized
vegetable oil not only improves the stability of the oil, but also provides adequate
reactivity to form chemical linkages with other polymer chains. For example,
vernonia oil, in conjunction with other epoxidized plant oils, has been used as a
plasticizer and stabilizer to modify the properties of plastic resins or to act as a
reactive modifier (diluents or toughener) in epoxy resins (Muturi et al., 1994).
In general, today it is possible for researcher to chemically modify and
transform the triglyceride into reactive group via epoxidation, epoxidation &
metathesis of double bond, acrylation of epoxies reaction with maleic anhydride or
tran- sesterification. Because of functional epoxies group on the structure of
epoxidized vegetable oil and relatively high oxirane content of linseed and soybean
oil, presently it is used in appropriate curing agents in order to produce bio-based
epoxies system with satisfactory properties (Monhanty et al., 2005). Vegetable oils
were commonly used as poly(vinyl chloride) plasticizers, stabilizers, lubricants and
starting materials to produce polyols, pre-polymers in surface coating formulations
and to synthesize of polyurethane foams (Rosli et al., 2003, Klass et al., 1999).
Also, modified vegetable oils could be used to improve the efficiency of the
fabrication process of linoleum floor cloth, to modify other thermoset polymers
and to synthesize new polymers that were appropriate for liquid molding (Xu et al.,
2002, Hilker et al., 2001).
5
Research on development of vegetable oil based polymeric materials,
including additives, biocomposites and nanocomposites, has attracted increasing
attention in recent years. In this review, our motivation is to provide a perspective
on how vegetable oil based materials is used for polymer in a great number of
applications like polymeric additive, coating and composite application.
The purpose of this study has been made to determine evaluation of
mechanical and physical properties of LDPE/BP and HDPE/BP blends. Other than
that, to investigate the composition range for better mechanical performance and
also to define the impact of ultra violet (UV) irradiated at prolonged exposure.
CHAPTER 2
LITERATURE REVIEW
2.1 Biopolymer (BP)
Biopolymer is material that uses natural polymer or living organism as based
material. It forms larger structures by monomeric units that bonded each other. The
characteristic of biopolymer that can be degradable make it use useful material
because of the awareness of the environment. The differentiation of biopolymer
that been produce according to polymer type, degree of polymerization, type and
concentration of additives or filler. The various type of biopolymer may produce
such as polylactide (PLA), polyglycolide (PGA) and polyhydroxybutyrate (PHB).
Biopolymer was derived by the atmospheric CO2 that can be absorbed vegetal
biomass which means biopolymer contribute less to the global warming compare
to the petroleum based polymers (Fenouillot et al, 2010). Because of that, the
polymer that based on the available biomass should be developed in order to
replace the existing synthetic polymer.
Biopolymer can be blend with the synthetic polymer to produced
biodegradable polymer which is more environmental friendly and can become a
green product. Monomers from the natural resources have been used for the
synthetic polymer development in order to produce biodegradable polymer. One of
the most important polymer that can ensure this matter is polylactic acid (PLA)
because it is made from agricultural product and already biodegradable (Yu et al,
2006).
Another renewable resource that have been intensively studied is the
vegetables oil, this is because vegetables oil have the ability to synthesis the
7
renewable polymer which almost the same as synthetic polymers. Usually,
polymer that produced from the fatty- acid will show limited thermo-mechanical
properties because of aliphatic structure (Alam et al, 2014). All these natural
resources have been studied in order to produce renewable polymer that can bring
benefits to the human beings and to the world.
The different between polymer and biopolymer can be found in their
structure. As we known, polymer and biopolymer made of repetitive units called
monomers. Most of biopolymer characteristic is in the compact shapes which
determine their biological function and their primary structure. Biopolymer has 4
different categories that consist of biomass product, microorganism, biotechnology
and petrochemical (Ramarad, 2008).The classification of biodegradable polymer
shown in Figure 2.1.
Figure 2.1: Classification of Biodegradable Polymer. (Chandra, 1998)
Most structure of synthetic polymer much simpler and more random which is lead
to molecular mass distribution that is missing in biopolymer. In fact,
monodispersity phenomenon exist which their synthesis is controlled by a template
directed process in most vivo system contain the similar sequences and numbers of
8
monomers and thus all have the same mass. This phenomenon in contrast to the
polydispersity encountered in synthetic polymer has result index of 1 (Halaka &
Virtane, 1997).
2.2 Biopolymer from vegetable oils
Vegetable oil is fats or oil that extract from variety of plant or seed such as palm
oil, olive oil, soy oil and corn oil. Cooking, cosmetic, paint and biodiesel was an
application that using vegetable oil. It shows that vegetable oil was multipurpose
oil that our industry used to make a good quality product that solves the economic
problem in our country. Vegetable oils such as linseed and Tung oil are drying
oils, which can self-crosslink under atmospheric oxygen. This type of drying oil
has long been used in the coating industry (Sharma et al., 2006). Soy bean oil is
one example of semi-drying oils that are of plentiful supply and therefore of
relatively low cost, have also attracted great interest for the preparation of
polymers or resins (Pfister, 2011).
In China, 5 million tons of waste cooking oil (WCO) was produced each
year in the catering of large and medium cities, and create the increasing demand
to its rational disposal and reutilization. In the past, the dominant technology is to
convert WCO into bio-diesel by transesterification (Kumaran et al, 2011), since the
main composition of WCO resulting from vegetable oils and animal fats is
triglycerin (Chen et al, 2014).
According from Hanna & Raimo, (2011), although vegetables oils are not
naturally present as polymer, they are precursors for monomer chains that can be
used to synthesize various polymers including polyurethane, polyester, polyether
and polyolefin. Therefore, vegetable oils biopolymer structures can be easily tuned
by converting vegetable oil to different monomers.
Vegetable oils are suitable for producing monomers with structures similar
to petroleum-based monomers. At present all the raw materials are derived from
petrochemicals, and the toxicity and volatility of starting materials such as
formaldehyde require careful environmental, health and safety monitoring (Shida
et al, 2014). But there could soon be a new, greener alternative on the market
based on a new generation of 'bio-resins' – thermoset resins derived principally
from the vegetable oils such as rapeseed (Gerard et al, 2013).
9
Palm oil industry generates vast amount of oil palm biomass mainly from
milling and crushing palm kernel. Oil palm (Elaesis guineensis) empty fruit bunch
(EFB) was a lignocellulosic waste generated during palm oil extraction process is a
good source of cellulose, lignin and hemicellulose which can used in many
industrial processes. Over 15 million tons of (EFB) waste residue is generated
annually in Malaysia. This waste is mostly disposed through combustion or land
filling, creating considerable pollution and economical problems. Therefore,
utilization of this organic waste in any industrial process would be of immense
environmental and economical benefits to society (Khalil et al, 2010)
2.3 Cross-linker for thermoset polymer
Cross-linkers are either homo- or hetero bi-functional reagents with identical or
non-identical reactive groups, respectively, permitting the establishment of inter-
as well as intra molecular cross-linkages (Kapoor, 1996). Crosslinking is the
process of joining two or more molecules by a covalent bond chemically. Cross-
linkers also are commonly used to modify nucleic acids, drugs and solid surfaces.
Crosslinking reagents have been used to assist in determination of near-
neighbour relationships, three-dimensional structures of proteins, solid-phase
immobilization, hapten-carrier protein conjugation and molecular associations in
cell membranes. They also are useful for preparing antibody-enzyme conjugates,
immunotoxins and other labeled protein reagents (Thermo, 2009).
Example of crosslinking reagents are isocyanate. Isocyanate are a group of
highly reactive, low molecular weight compounds that contain the isocyanate
group, -N-C-O. They react exothermically (producing heat) with the hydroxyl (-
OH) groups in alcohols, to produce compounds containing the carbarmate (-
NHCOO-) group, which is commonly referred to as urethane (Cherie, 2013).
The main effect of the isocyanate groups (NCO) in the 2 and 4 positions is
on reactivity. The isocyanate group in 2 (ortho) – position is three times less
reactive than the isocyanate group in 4 (para) – position. Pure 4,4’ – MDI is solid
at room temperature, melts at 38oC and is a major raw material for adhesive and
coating applications where high reactivity and linearity is required (Frans et al,
2014).
10
Meanwhile, the 2,4’ – MDI isomer is not readily available in 100 per cent
purity. Concentrations of up to 50 per cent are commercially available. The so-
called mixed isomer 50 (MI 50), with a melting point of 18 oC, exhibits a good
compromise between lower reactivity and liquidity. Above their melting point,
both isomers and their mixtures have very low viscosities.
Methylene diphenyl diisocyanate (MDI) is an aromatic diidocyante with the
chemical formula C15H10N2O2 where the two aromatic rings are connected by a
methylene group. Three isomers -2,2’-MDI (Diphenylmethan-2,2’-diisyocyanate /
2,2’-Diphenylmethan-diisocyanat), 2,4’-MDI (Diphenylmethan-2,4’-diisocyanate /
2,4’-Diphenylmethan-diisocyanat / 2,4’-diisocyanatodiphenylmethan) and 4,4’-
MDI (Diphenylmethan-4,4’-diisocyanate / 4,4’-Diphenylmethan-diisocyanat / p,p’-
Diphenylmethan-diisocyanat) exist (Frans et al, 2014). These are indicated as
“pure MDIs” in Figure 2.2.
Figure 2.2: Types of isocyanate MDI (Frans et al, 2013).
In general, two components systems consist of polyol or polyol mixtures and an
isocyanate crosslinker. The two components are mixed together at the application
site in various ratios and after mixing, applied onto the substrate to be bound or
coated. Two component systems have the advantage of fast reaction time or cure
speed, in comparison to typical one component systems. The main curing
mechanism of two component systems is the formation of urethane linkages,
resulting from the reaction of the isocyanate with the hydroxyl function of the
polyol (Frans et al, 2013).
4,4’
2,4’
2,2’
11
2.4 Monomer
A monomer from greek mono meaning “one” and meros means “part” is an atom
that binds chemically to other monomer to form a repeating chain molecule called
polymer. In other words, monomer is a substance that able to forming covalent
bond with a sequence of additional molecules via polymerization reaction that is
repeating unit of the polymer sequence. There are a few types of monomer shows
in Table 2.1. Most of the monomer term is refers to organic molecules to form
synthetic polymer such as vinyl chloride to produce polymer polyvinyl chloride
(PVC). Glucose is also one of the common natural monomer which is linked by
glycosides bonds into polymer such as cellulose and starch.
Table 2.1: Types of natural monomer and its origin forming.
Type of Natural monomer Forming
Amino acid protein
Nucleotides Nucleic acid (DNA/RNA)
Glucose Starches, glycogen, cellulose
Xylose Xylan
Isoprene Natural rubber
All the monomers will have carbon-to-carbon bond. Monomers link together by
two basic methods which are addition polymerization and condensation
polymerization. For the addition polymerization, a monomer will mix up with
another monomer and bond to each other to form a long chain as shown in Figure
2.3. Because of that, polymer formed by the process will have every atom of the
starting monomers. The polymerization can be represented by the reaction of a few
monomer units (Groover, 2002).
12
Figure 2.3: Polymerization by Ethylene molecules (Groover, 2002).
(Monomer) x (number of links) = polymer
As a simple analogy, consider a pearl necklace. It is made up of a number of pearl
beads joined together to form chain. Each single bead represents the monomer, the
string represents the chemical link and the complete necklace represents the
polymer itself.
Different type of monomers will have different type of formations. For
examples, Amino Acids are natural monomers that will be polymerizing at
ribosome to form proteins while glucose monomers can polymerize to form
starches, glycogen or cellulose. Monomer that polymerized and form natural
rubber is known as Isoprene and it is one of the natural monomers.
Polyfunctionality was the essential feature of monomer because the
capacity to form chemical bonds to at least two other monomer molecules.
Biofunctional polymer can form only linear, chainlike polymers but monomers of
higher functionality yield cross-linked, network polymeric products (Xanthos,
2010).
2.5 Polymer
The term polymer comes from the Greek word; poly means many and meros
means parts. In a scientific term, polymer can be defined as materials having many
units of small molecules chemically joined or linked by normal covalent bonds to
form long chain molecules (Spelling, 2001). The starting material is known as a
13
monomer. Carbon and hydrogen are the most common atoms in monomers, but
oxygen, nitrogen, chlorine, fluorine, silicon and sulfur may also be present.
Think of a polymer as a chain in which the monomers are linked
(polymerized) together to make a chain with at least 1000 atoms in a row (Azemi,
2009). It is this feature of large size that gives polymers their special properties. A
polymer has a high molecular weight as a consequent of its long chain molecules.
The molecular weight of polymers varies from 25,000 – 1,000,000 g/mol or greater
(Azemi, 2009). Their molecules are 100 – 100,000 times larger than ordinary
molecules.
Macromolecules or polymers are found in the human body, animals, plants,
minerals and manufactured products. Substances like the following contain
polymers; diamond, concrete, quartz, glass, nylon, plastics, DNA, tires, cotton,
hair, bread and paint. The polymers can have different end units, branches in the
chain, variations in the sequence of the monomers and different monomers
repeated in the same chain which leads to the large number of manufactured
polymers as well as all of the natural polymers. The double bond in the monomer
is broken or water is eliminated in the polymerization process.
Rubbers, plastics, fibers and cellulose are examples of a few materials
classified as polymers. However, they behave differently. A vulcanized rubber
undergoes long range reversible extensibility while plastic flows when pressure is
applied. If the plastic is semi-crystalline, it is tough and hard. If it is amorphous, it
is glassy and brittle. Plastic can be grouped into either thermoplastic or
thermosetting. Thermoplastic can be fabricated by heating. In contrast,
thermosetting undergoes irreversible, thermally induced reactions when heated. A
fiber is capable of being drawn into filaments.
Step-growth polymerization and chain-growth polymerization are the two
general categories of synthetic lab method (Stamm, 2006). Step polymerization
happens when two reacting monomers are brought together in order to form a new
molecule of the desired compound. As the reactions happens continuously, more
reactant molecules will combined with the molecule first synthesized to form
polymers of length n=2 and the continue to form polymers of length n=3 and so on.
Some of the examples of the polymers produced by step-growth polymerization are
nylon, polycarbonate and phenol formaldehyde. In the other case, for chain-growth
polymerization exemplified by polyethylene, the double bonds the carbon atoms in
14
the ethylene will be induced to open so that the atoms can be joined with other
monomers. The most common polymers that were produced by chain-growth
polymerization are polyethylene and polypropylene (Groover, 2002). The
examples of the polymerization process are as shown in Figure 2.4 and Figure 2.5.
Figure 2.4: Model of step-growth polymerization showing two type of reaction
occurring, (a) n-mer attaching a single monomer to form (n+1)-mer and (b) n1-
mer combining with n2-mer to form (n1 + n2)-mer. Sequence is shown by (1) and
(2) (Groover, 2002).
Figure 2.5: Model of chain-growth polymerization; (1) initiation, (2) rapid addition
of the monomers and (3) resulting long chain polymer molecule with mers at
termination of the reaction (Groover, 2002).
Polymer properties are broadly divided into several classes based on the scale at
which the property is defined as well as upon its physical basis (Monteiro, 2010).
The constituent monomer structure of polymer will determine the polymer basics
15
mechanical property. Table 2.2 shows the parameters that can affect polymer
mechanical properties.
Table 2.2: Structure parameters effecting polymers mechanical properties
(Monteiro, 2010).
Generally, polymer will have properties such as low density relative to metal and
ceramics, good strength to weight ratios for certain polymers, high corrosion
resistance and low electrical and thermal conductivity. However, instead of having
advantages such as light in weight and easy to shape, polymer also have
advantages such as low strength relative to metals and ceramics, low stiffness,
service temperatures are limited to only few hundred of degrees. Furthermore,
some polymer will be degraded when subjected to the sunlight or some other
forms of irradiation (Groover, 2002).
2.6 Thermoplastic polymer
Thermoplastic materials are those materials that are made of polymers linked by
intermolecular interactions or van der Waals forces, forming linear or branched
structures (Sperling, 2001).
Thermoplastic polymer is a polymer which normally produced in one step
and can be made into product with subsequence process. Thermoplastic will be
solid material in room temperature but will become viscous liquid when heated to
Parameters Effects
Increase of the chain length Increase of tensile strength and
stiffness
Increase of number and length of side
chains
Increase of tensile strength and
stiffness
Introduction of large monomers in
molecules Increase of stiffness
Increase of number and strength of
cross-links.
Increase of tensile strength and
stiffness
16
temperature of a few hundred degrees. Due to this characteristic, thermoplastic can
be easily and economically manufacture into products. Thermoplastic can be
recycled because it can be subjected to heating and cooling cycles without
experience any significant degradation. Polyethylene, polypropylene and
polystyrene are the examples of thermoplastic polymer (Mohsin, 2012)
Depending on the degree of the intermolecular interactions that occurs
between the polymer chains, the polymer can take two different types of structure
as shown in Figure 2.6, amorphous and crystalline structure, being possible the
existence of both structure in the same thermoplastic materials (Scheirs, 2000).
Amorphous structure is a polymer chains acquire a bundled structure, like a
ball of thread disordered, amorphous structure that is directly responsible for the
elastic properties of thermoplastic materials. For crystalline structure, polymer
chains acquire in ordered and compacted structure, it can be distinguished mainly
lamellar structure and micellar form (Minnesota, 2003).
This crystal structure is directly responsible for the mechanical properties
of the resistance to stresses or loads and the temperature resistance of
thermoplastic materials (Alvarado, 2007). If the thermoplastic material has a high
concentration of polymers with amorphous structures, the material will have a poor
resistance to loads but it will have an excellent elasticity. But on the contrary, if the
thermoplastic material has high concentration of polymers with a crystalline
structure, the material will be very strong and even stronger than thermoset
materials, but with a little elasticity that provides the characteristic fragility of
these materials (Cheng, 2008).
Figure 2.6: Structure of amorphous, crystal and lamellar (Scheirs, 2008).
Recently, there were so many studies have been carried out in order to study and
improve the mechanical properties of synthetics thermoplastic polymer. Some
other material such as starch and vegetables oil have been used in the studies as the
17
demand of decreasing the use of petroleum based polymer has increased in the
present days (Van De Velde & Kiekens 2002). All the results and knowledge
gathered from the studies will be used and shared for the future studies.
Often some additives or fillers are added to the thermoplastic to improve
specific properties such as thermal or chemical stability, UV resistance
(Minnesota, 2003).
Table 2.3: Advantaged and disadvantaged of thermoplastic (Minnesota, 2003).
Advantages Disadvantages
The softening or melting by heating allows
welding and thermoforming.
The processing cycles are very short because
of the absence of the chemical reaction of
crosslinking.
Processing is easier to monitor because there is
only a physical transformation.
Thermoplastics do not release gases on water
vapour if they are correctly dried before
processing.
The wastes are partially reusable as virgin
matter because of the reversibility of the
physical softening or melting.
When the temperature rises, the
modulus retention decreases due to
absence of chemical links between
macromolecules.
For the same reason, the creep and
relaxation behaviours are not as good as
for the thermosets.
During a fire, fusibility favours
dripping and annihilates final residual
physical cohesion.
2.6.1 Polyethylene
Polyethylene is a chemically simple polymer with the basic repeating unit (-CH2-
CH2-). It is a semicrystalline polymeric material with crystalline and amorphous
phases. The crystalline lamellae provide polyethylene with structural integrity
while amorphous parts provide polyethylene with its elastic properties. The
semicrystalline nature of polyethylene allowed it to become one of the most widely
used polymers worldwide. In practical applications polyethylene is usually
crystallized from a melt.
Meanwhile, melt-crystallized polyethylene has a spherulite morphology,
where lamellae made up of spherulites are embedded in a matrix of amorphous
material (Lin et al, 1994). The spherulites are made up of thin flat lamellae as
shown in Figure 2.7. The structure of lamellae generally consists of regular chain-
18
folding arrangements with the molecular chains perpendicularly aligned to the
lateral lamellar surfaces in Figure 2.8.
Figure 2.7: Schematic illustration of spherulite, lamella and amorphous phase
structure (Cheng, 2008).
Figure 2.8: Structure of lamella; (a) the regularly folded chain model for semi-
crystalline polymer; (b) non-regularly folded chain model for semi-crystalline
polymer (Cheng, 2008).
For the amorphous phase of polyethylene, there are three types of inter-crystalline
material. The first type, cilia, begins as a crystalline chain and ends as an
amorphous chain. The second type begins ands in lamellae with its mid-section in
the amorphous phase, thus forming a loose loop. The third type consists of inter-
lamellar links that connect two adjacent lamellae. There are two types of inter-
lamellar links; the first are tie-molecules that are chains crystallized in two or more
lamellae at the same time (Lu et al, 1995). The second type of inter-lamellar links
19
consists of physical chain entanglements that can be made up by the entanglements
of cilia, loose loop and even tie-molecules.
Polyethylene can have linear and branched chains. Short chain branching
can be introduced into polyethylene through the use of comonomer (like 1-
hexene). Short chain branches interfere with the formation of lamellae, and
therefore affect crystallinity and density of semicrystalline polymer.
Linear low density polyethylene (LLDPE) and high density polyethylene
(HDPE) have a lamellar and spherulite morphology, while plastomer and elastomer
have bundle-like crystals embedded in amorphous material. An increase in
crystallinity, hence an increase in density, of polyethylene increases the stiffness
and tensile yield strength of the material (Lu et al, 1995).
Branching in polyethylene chains affects material density and other
properties. There are two types branching, short chain branching mostly due to
introduction of comonomer and long chain branching formed from side reactions
during polymerization.
High density polyethylene is generally linear with low short chain
branching content. Linear low polyethylene has higher short chain branching
content than high density polyethylene with few or no long chain branches. Low
density polyethylene on the other hand is known to have both high short chain
branching and long chain branching contents. Presence of short chain branches
interferes with formation of lamellae, hence linear low density polyethylene and
low density polyethylene with higher short chain branching content have lower
density as shown in Figure 2.9 (Cheng, 2008).
Figure 2.9: Branch structure of polyethylene (Cheng, 2008).
(a) HDPE
(b) LLDPE
(c) LDPE
20
2.6.2 Low Density Polyethylene (LDPE)
Low-density polyethylene (LDPE) is a branch of the polymer chains and with
polyethylene most major compounds are amorphous. The density of (LDPE) is a
approximately 0.92 and it has a melting temperature 115º C. LDPE has a low cost
of merit, and it is more suitable or flexibility at low temperatures of -120 ºC. LDPE
has the inner strength of a chemical in a variety of physical forms of liquid or solid
(Xanthos, 2010).
LDPE is part of the polyolefins family. The LDPE and LLDPE volumes in
2007 account for 35% (roughly 7.8 million tonnes per year) of Western Europe’s
total polyolefins production which is 22.1 million tonnes/year. Polyolefins
represent 40% of total plastics production in Western Europe, which is 55 million
tonnes/year (PlasticEurope, 2016).
The main technique which is used for the production of LDPE is autoclave
and tubular high pressure technology: When the monomer is held at high pressures
of up to 300MPa and temperatures above the polymer melting point of up to
300°C, the monomer/polymer mixture can act as a polymerisation medium
(Cornelia, 2005). This technology is typical for LDPE and LDPE co-polymers
production. The obtained polymer can be mixed with additives and is extruded into
pellets.
Meanwhile, the benefits of LDPE is its versatility (large range of density,
molecular weight (MW) and MW distribution, and chemical inertness), LDPE
remains a popular plastic in use today. LDPE resins can be tailored to be used in
many applications such as film applications (e.g. collation shrink film, carrier bags,
agricultural film), pharmaceutical packaging, liquid paper board coatings, electrical
cable coatings, injection moulding parts, pipes, etc.
For responsible end-of-life management, Plastics Europe recommends
recycling (whether mechanical or feedstock) as far as economically feasible and
environmentally sensible (Plastic Europe, 2008). Alternatively, for residual streams
energy recovery can be conducted in special designed plants.
Due to its unique properties, LDPE is used in critical applications where
stress cracking resistance is an issue, such as wire and cable. LDPE has a high
intrinsic thermal stability and therefore requires a minimum amount or even no
21
stabilizers at all. LDPE maintains its physical and mechanical properties after
recycling and is increasingly being recycled in several European schemes.
2.6.3 High Density Polyethylene (HDPE)
Polyethylene is a thermoplastic made from the petroleum waste. It is known for its
toughness and has a large strength to the density ratio. Polyethylene can be divided
into four common types which is High Density Polyethylene (HDPE), Medium
Density Polyethylene (MDPE), Low Density Polyethylene (LDPE) and High
Density Homo-polymer (Cheng, 2008). Classification of polyethylene is shown in
Table 2.4.
Table 2.4: Classification of polyethylene by density according to ASTM strandard
(Cheng, 2008).
PE types Density (g/cm3)
Low 0.910 – 0.925
Medium 0.926 – 0.940
High 0.940 – 0.959
High Density Homo-Polymer 0.96 and above
Polyethylene was classified based on the density because the changes in its density
will associate with the changes of its crystallinity and morphology. The stiffness
and yield strain of the material will increase when the density of polyethylene
increased (Wu et al. 1999).
HDPE is a recyclable polymer that has makes it widely used in the plastic
industries. Products such as plastic bottle, plastic jugs and pipes were made from
the HDPE polymer. HDPE polymer is composed from carbon and hydrogen which
joined together to produced high molecular weight products (Gabriel, 1995).
High density polyethylene (HDPE) is a linear thermoplastic polymer that
widely used in various industries especially in packaging industry. The most
application of HDPE are plastic bag, banner, plastic lumber, water pipes and more.
High density polyethylene is one of the most commonly used materials in the
22
world. Product that produces by it was labeled as #2 plastic usually found in
packaging product such as milk jug, plastic bags and refillable plastic bag.
Consumption of polymer in global has increase in the last several decades
from 5 million tons to 100 million tons in current decade. Approximately 42% of
this volume for manufacture of packaging material made of low density
polyethylene (LDPE) and high density polyethylene (HDPE) (John et al, 2003).
It unique properties such as excellent mechanical properties, ozone
resistance, good electrical properties, chemical resistance and ease of processing
make it widely used in many industries (Canevarolo, 2006). Moreover, it
advantages in low cost material and its little branching give tensile strength than
low density polyethylene makes it as chosen material than other material.
Although, HDPE is an expensive polymer, but it has poor stress crack resistance in
some engineering application. So, crosslinking process will be taken to improve its
properties (Xanthos, 2010).
HDPE is linear thermoplastic polymers which have so many advantages
such as balance mechanical properties, chemical resistance, low cost and easy to
process. The mechanical and physical properties of the end products of HDPE
mostly determined by its molecular weight, molecular weight distribution and the
amount of branching. To make have a good performance, HDPE have been
composed with natural fibres (Lu et al, 2006). Based on (Ferreira et al, 2013),
cross-linking HDPE of 3 dimensional networks can improve its tensile strength,
chemical resistance and thermal characteristic. However, all this modification of
properties is based on the ionizing radiation treatment approach.
2.7 Thermoset Polymer
Differ from thermoplastic polymer, thermoset polymer cannot tolerate with the
repeated heating and cooling cycles which made thermoset polymer not recyclable.
This is because, when thermoset polymer is reheated, it will degrade and thus char
rather than soften. Thermosets are network-forming polymers. Unlike
thermoplastics, the use of thermoset involves chemical reaction. These reactions
have caused the materials first increase in viscosity and eventually cross-link and
become set, and as a result they can no longer flow or dissolve.
23
Cure is most often thermally activated, which gives rise to the term thermoset, but
network-forming materials whose cure is light activated are also considered to be
thermosets. Some thermosetting adhesives cross-link by a dual cure mechanism
that is by either heat or light activation (Prime, 2009). Examples of thermoset
polymer are phenolics, epoxy and certain polyester (Hamerton, 2010).
Generally, thermoset polymer will have the properties such as rigid, brittle,
low soluble than thermoplastic polymer in common solvent and capable of higher
service temperature than thermoplastic polymer (Mohsin, 2012). Similar with the
thermoplastics polymer, thermoset polymer had also been used widely in the
previous and current study for the benefits of the mankind.
There were so many experiments and researches have been done to
improve the use of current polymer and in order to find the solution for the issues
of using the petroleum based polymers. Table 2.5 showed the advantaged and
disadvantaged of thermosetting.
Table 2.5: The advantages and disadvantages of thermoset (Minnesato, 2003).
Advantages Disadvantages
Infusibility : thermosets are degraded by
heat without passing through the liquid
state. This improves some aspects of fire
behavior: except for particular cases, they
do not drip during a fire.
When the temperature increases the
modulus rentention is better.
Better general creep behaviour.
The chemical reaction crosslinking
takes a considerable time that lengthens
the production cycles and often requires
heating.
The processing is often more difficult to
monitoring
Certain polymers release gases, in
particular water vapour.
The wastes are not reusable as virgin
matter because of the irreversibility of
the hardening reaction. At best, they can
be used like fillers after grinding.
The infusibility prevents assembly by
welding.
Thermosets are mixtures of small reactive molecules, often monomers in the
uncured state. Catalysts are often added to accelerate cure. Most thermosets
incorporate particulate fillers or fiber reinforcement to reduce cost, to modify
physical properties, to reduce shrinkage during cure, or to improve flame
24
retardance. Thermosets generally possess good dimensional stability, thermal
stability, chemical resistance and electrical properties. Unlike thermoplastic
polymers, chemical reaction of cure needed in processing thermoset. As illustrated
in Figure 2.10 cure begins by the growth and branching of chains.
Figure 2.10: Schematic, two-dimensional representations of thermoset cure.For
simplicity difunctional and trifunctional co-reactants are considered. Cure starts
with A-stage or uncured monomers and oligomers(a); proceeds via simultaneous
linear growth and branching to an increasingly more viscous B-stage material
below the gel point (b); continues with formation of a gelled but incompletely
cross-linked network(c); and ends with the fully cured, C-stage thermoset(d)
(Prime, 2009).
2.8 Degradation of polymer
Polymer degradation can be defined as changes of the polymer based on its
strength, color and shape by specific process. Degradation of mechanical, optical
or electrical characteristics was called as changes in material properties that change
91
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