ABSTRACT
The aim of this research is to develop a value-added product from a renewable resource, investigate the effect of its loadings on the mechanical and thermal properties of PS, as well as, to investigate the interaction between PS and plasticiser (ENO). Neem oil has high contents of unsaturated fatty acids which can be converted to epoxy fatty acids. The vegetable oil-based epoxy materials are sustainable, renewable and biodegradable materials replacing petrochemical-based epoxy materials in some applications. Neem oil was epoxidised at 600C and one atmospheric pressure for 5 hours. Fourier transform infrared (FTIR) spectroscopy was used to identify the unsaturation and epoxy group in the neem oil (NO) and epoxidised neem oil (ENO). Disappearance of the absorption band around 3011.7 cm-1 shows that the C=C has been used up and the appearance of a band around 943 cm-1 which is not seen in the spectrum of the raw neem oil confirm the success of epoxidation. ENO was used as a green plasticiser and added to PS. ENO was added to PS at different contents using solution casting method. Different compositions of PS/ENO blends; (95/5, 85/15, 75/25, 65/35, 45/55, and 35/65) were tested for mechanical performance, thermal behaviour, morphological arrangement and miscibility. Comparison of mechanical properties such as elongation at break, tensile strength and tensile modulus revealed apparent compatibility domain for 95/5 PS/ENO (8.70±0.08, 24.40±0.02 and 37.0±1.0). The miscibility of the two components (PS/ENO) in solution phase was investigated by reduced as well as relative viscosities. The viscosity measurements revealed that miscibility occurs between the compositions 95/5, 85/15, 45/55 and 35/65 wt% PS/ENO while phase inversion and phase separation occur at compositions 65/35 and 75/25 wt% showing immiscibility and incompatibility. Morphological arrangements of the blends were examined by scanning electron microscopy (SEM). The SEM micrographs of the blends showed a two-phase system appearing bright (epoxy phase) and the other appearing black (PS phase) in virtually all the micrographs, even though the heterogeneity due to phase inversions (phase changes) was relevant for some compositions. For other compositions, a domain distribution showed considerable miscibility within the range of compositions. But blends composition of 95/5, 85/15. 65/35 wt% show better morphology. However, blend composition of 35/65 forms another region within the morphology leading to phase separation. The thermal study reported that plasticisation of the PS with ENO at certain compositions lowers the glass-transition temperature (Tg), crystallisation temperature (Tc) as well as melting temperature (Tm) revealing the level of miscibility of PS with ENO. From the results obtained, this value added product which is potentially biodegradable has great potentials as alternative to the conventional use plasticisers such as phthalates, which can be used to enhance structure-property relationship in polymers.
TABLE OF CONTENTS
Declaration……………………………………………………………………………………………………………. 3
Certification ………………………………………………………………………………………………………….. 4
Acknowledgements ………………………………………………………………………………………………… 5
Dedication …………………………………………………………………………………………………………….. 6
List of Tables ………………………………………………………………………………………………………. 10
List of Figures ……………………………………………………………………………………………………… 11
List of Plates ……………………………………………………………………………………………………….. 12
Abbreviations and Symbol …………………………………………………………………………………….. 13
Abstract ……………………………………………………………………………………………………………… 15
CHAPTER ONE ………………………………………………………………………………………………… 16
1.0 INTRODUCTION …………………………………………………………………………………………. 16
1.1 Background of the Study …………………………………………………………………………… 16
1.2 Vegetable Oils ………………………………………………………………………………………….. 18
1.3 Epoxidation of Vegetable Oil (EVO)…………………………………………………………… 19
1.4 Polystyrene ………………………………………………………………………………………………. 21
1.5 Neem Seed (Azadirachta Indica) Oil ……………………………………………………………. 25
1.6 Plasticiser as Additive to Polymers …………………………………………………………… 271
1.7 Fourier Transform Infrared (FTIR) Spectroscopy ………………………………………. 29
1.8 Tensile Properties …………………………………………………………………………………… 303
1.9 Thermal Properties…………………………………………………………………………………… 31
1.10 Morphological Study ………………………………………………………………………………. 32
1.11 Viscosity Measurement ……………………………………………………………………………. 32
1.12 Research Problem Statement …………………………………………………………………… 32
1.13 Aim of the Study …………………………………………………………………………………….. 33
1.14 Objectives of the Study ……………………………………………………………………………. 33
1.15 Scope and Limitation ………………………………………………………………………………. 33
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1.16 Significance of the study……………………………………………………………………………..17
CHAPTER TWO ……………………………………………………………………………………………….. 35
2.0 LITERATURE REVIEW ………………………………………………………………………………. 35
2.1 Review of the Past Related Works ……………………………………………………………… 35
CHAPTER THREE ……………………………………………………………………………………………. 63
3.0 MATERIALS AND METHODS …………………………………………………………………….. 63
3.1 Materials …………………………………………………………………………………………………. 63
3.2 Methods …………………………………………………………………………………………………… 64
3.2.1 Modification of oil sample via epoxidation ……………………………………………………………. 64
3.2.2 Characterisation of raw and epoxidised neem oil samples via FTIR spectroscopy ………… 64
3.2.3 Preparation of PS/ENO blends…………………………………………………………………………….. 64
3.2.4 Casting of PS/ENO films ………………………………………………………………………… 65
3.3 Determination of Mechanical Properties …………………………………………………….. 65
3.3.1 Sample preparation …………………………………………………………………………………………… 65
3.3.2 Tensile properties measurement…………………………………………………………………………… 66
3.4.Determination of Thermal Properties…………………………………………………………. 66
3.4.1. Differential scanning calorimetry (DSC)………………………………………………………………. 66
3.5. Determination of Morphological Properties ……………………………………………….. 66
3.5.1. Scanning electron microscopy (SEM) ………………………………………………………………….. 66
3.6 Viscosity Measurements ……………………………………………………………………………. 67
CHAPTER FOUR ………………………………………………………………………………………………. 68
4.0 RESULTS AND DISCUSSION ………………………………………………………………….. 68
4.1 Fourier Transform Infrared Analysis of the Neem and Epoxidised Neem Oil samples …………………………………………………………………………………………………………. 70
4.2 Effect of ENO loading on the Tensile Properties of PS. ………………………………… 73
4.2.1 Percentage elongation ……………………………………………………………………………………….. 74
4.2.2 Tensile strength ………………………………………………………………………………………………. 758
4.2.3 Tensile modulus…………………………………………………………………………………………………….60
4.3 Thermal Property Study of PS/ENO Films ………….. Error! Bookmark not defined.2
4.4 Morphological Property Study of PS/ENO Films ………………………………………. 934
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4.5 Miscibility Study of PS/ENO Films …………………………………………………………. 1012
CHAPTER FIVE…………………………………………………………………………………………….. 1056
5.0 CONCLUSION AND RECOMMENDATIONS ……………………………………………. 1056
5.1 Conclusion……………………………………………………………………………………………. 1056
5.2 Recommendations …………………………………………………………………………………. 1067
REFERENCES………………………………………………………………………………………………………..89
CHAPTER ONE
1.0 INTRODUCTION
1.1 Background of the Study
Polymers are widely used due to their ease of production, light weight, design flexibility and processability. However, polymers are of lower modulus and strength compared to metals and ceramics. One way to modify their properties is to reinforce them with additives; most common of which being embedding of inclusions in the polymer. The resulting material will contain desirable properties not achieved by either phase alone. Hence, polymer properties can be improved while maintaining their light weight and ductile nature and such modifications could be done at relatively low filler content. Plasticisation, in general, refers to a change in the thermal and mechanical properties of a given polymer which involves lowering of its rigidity at room temperature, lowering of temperature, at which substantial deformations can be effected with not too large forces, increase in the elongation to break at room temperature and increase in the toughness (impact strength) down to the lowest temperature of serviceability. These effects can be achieved through compounding the given polymer with a low molecular weight compound or with another polymer and also by introducing into the original polymer a comonomer which reduces crystallisability and increases chain flexibility.
The formulation of polymer blends has been an area of research interest for the past three decades owing to the enhancement in physical and mechanical properties of blends achieved via
17
synergism (Coleman et al., 1991; Utracki, 1998; Ashraf et al., 2007). The physical as well as chemical properties of the blends depend on the degree of miscibility of the components in the blends. Although even immiscible or partially miscible blends have found commercial applications, complete miscibility of the components in the blend is desirable because mixing on molecular scale results in superior physical as well as mechanical properties with change in composition (Zaccaria and Utrack, 2003).
Modification of the composition of the structural units represents one of the main approaches to the modification of polymer behaviour. In addition to the chemical nature and composition of the structural units that constitute the polymer backbone, molecular architecture also contributes to the ultimate properties of the polymeric products (Ebewele, 2000). The improvement in the toughness, flexibility and tensile strength of a polymer of high molar mass can also be achieved by blending it with an additive of low molar mass. Low molar mass from vegetable resource like lactose (Fan et al, 2001) and starch cinnamate (Thakore et al., 2001; Thakore et al., 1999) have been used to modify the properties of poly(methyl-methacrylate) and other polymers. Development of consumer products from renewable agricultural raw materials is an area of great interest for researchers in academia, industry and government (Kaplan, 1998). The materials provide renewable and low cost source of raw material for various applications. In addition, these materials can be used and disposed without negatively impacting the environment or the health of people associated with their use, and disposal. These properties make agricultural products the preferred raw materials over the petroleum resource for the manufacture of consumer products. Nearly all agricultural raw materials have the potential to be used in the manufacture of consumer products ranging from automobile to utensils. Some of the agricultural–based raw materials being pursued for various applications include vegetable oils
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(Biresaw et al., 2002) (e.g. lubricants), fibre (Mohanty et al., 2000) (e.g. composite for automobile), starches (Doane et al., 1992) (e.g. biodegradable polymers), and cellulose (Edgar et al., 2001) (e.g. bio-plastics).
1.2 Vegetable Oils
Vegetable or plant oils are the fats and lipids containing triglyceride molecules and represent a renewable resource that can be used as starting material to access new products with a wide array of structural and functional variations. For a long time, plant oils and their derivatives have been used by polymer chemist due to their renewability nature and relatively low prices, and their wide application possibilities. In recent years, there has been a great demand for plant oils as an alternative resource for production of additive for various applications such as polymer, coating, adhesive and nanocomposite (Wool and Sun, 2005). The necessity of releasing the polymer industry from its dependence on depleting resources represent a major concern, and consequently deemed necessary the search for industrially applicable renewable alternatives. Fortunately, plant oils offer many advantages which make them industrially attractive and feasible, as daily demonstrated by oleo chemistry. Their availability and relatively low prices make them industrially attractive and feasible, as daily demonstrated by 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 perennial plants such as the palm, olive, coconut or neem (Hui, 1995). The application of modified natural fats and oils in the chemical industries is becoming more and more interesting because of their availability from renewable resources (Ikhuoria and Dadson, 2007). Naturally occurring plant oils and fatty acids are mostly 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).
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At low temperature (below -100C), vegetable oils undergo various physical changes like
cloudiness, precipitation, poor flow and solidification (Schuster et al., 2008) in sharp contrast to
mineral oil-based fluids. Thus successful conversion of vegetable oils into viable and consumer
products require overcoming these and other shortcomings. The unsaturation present in vegetable
oils can be chemically modified to a value added product by epoxidation.
1.3 Epoxidation of Vegetable Oil (EVO)
Epoxidation increases the polarity and the stability of vegetable oil by improving their
compatibility with polymers. Hence, epoxidised vegetable oils can be used as plasticizers,
stabilisers, lubricants, composite, etc, in the polymer industry (Padmasiri et al., 2009). The
reason why vegetable oils are widely used as plasticisers is because the high numbers of carboncarbon
double bonds present in the vegetable oils make them a good target for manipulation into
some other useful products e.g. soybean oil into epoxidised soybean oil (Hosler, 2008). Usually,
a peroxide or per acid is used to add an atom of oxygen and convert the -C=C- bond to an
oxirane group which is more reactive than double bond. An example of the conventional method
of preparing epoxidised vegetable oils (Hill, 2000) is displayed in the scheme below.
H2O2 + R C
O
OH
R C
O
O
HO
+ H2O
Hydrogen peroxide Simple carboxylic acid Peracid Water
CH3(CH2)nCH CH C
H
CH(CH2)nC
O
OH R C
O
O
HO
Peracid
CH3(CH2)nCH C
H
C
H
CH(CH2)nC
O
OH
O O
+ R C
O
OH
Unsaturated fatty acid from oil Simple carboxylic acid Epoxy fatty acid
+ 2 2 (2)
(1)
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Scheme 1.1: Conventional method of producing epoxidised vegetable oil. These EVO from biological origin substrates could bring along numerous advantages and new beneficial properties, which may not be derived from petroleum-based epoxy resins. EVO have been evaluated as ecological and environment friendly alternative for petroleum-based epoxy resins since they are neutral in carbon (IV) oxide cycle and are readily biodegradable. Other advantages of the EVO include cost effectiveness, renewability and availability. EVO or polymerisable monomers (Ikhuoria and Dadson, 2007) possesses epoxy ring in their backbone chain and produces flexibility and elasticity when it is treated with thermoplastic or thermosetting polymer along with suitable curing agents (Tayde et al., 2011). Because of these special kinds of properties, EVO can easily replace phthalates which are petroleum base. Many plants oils such as soybean oil, rubber seed oil, Karajan seed oil, linseed oil, castor oil, African bean seed oil, e.t.c., (Ikhuoria and Dadson, 2007; Okiemen et al., 2005; Vaibhav et al., 2007; Akpan et al., 2006) have been modified in various forms to improve their industrial potentials.
The epoxidised soybean oils are used as plasticisers for poly(vinyl chloride) resins to improve its quality in terms of flexibility, elasticity and toughness and to impart stability to the polymer towards heat and UV radiation (Vaibhav et al., 2007). Due to high reactivity of the oxirane ring, epoxides can also be used as starting materials for a variety of chemicals such as alcohols, glycols, alkanol-amines, carbonyl compounds, olefin compounds and polymers like polyesters, polyurethanes and epoxy resins (Carlson and Chang, 1985). Today, one of the most important epoxidised vegetable oils is the epoxidised soybean oil (ESO) and its worldwide production is about 200,000 tonnes per year (Rusch et al., 1999). Epoxidation of vegetable oil on an industrial
21
scale is most frequently carried out with per-oxo-acetic acid and per-oxo-formic acid due to low cost. Those per-acids are generated in the reaction mixture `in situ` reacting the relevant acid with hydrogen peroxide, under pre-selected conditions. In general, olefins can be epoxidised with various per-acids, of which m-chloro-per-benzoic acid has been most often used (March, 1992). Other per acids especially per-acetic acid and per-benzoic acid have also been used (trifluoroperacetic acid and 3, 5–dinitroperoxybenzoic acid) as reported by Vijayagopalan and Gopalakrishnan, (1971).
1.4 Polystyrene
Polystyrene is brittle, rigid, transparent, easy to process (shrinkage is low), free from odour and taste polymer. It is thermally stable, with excellent electrical properties. All these properties are responsible for its commercial success. Polystyrene is sometimes referred to as crystal polystyrene, which refers to the clarity of the finished product and does not imply that the molecular structure responsible for many of the good properties of polystyrene such as clarity of products, the low energy input required for processing and eases of processing with low shrinkage. Polystyrene is used in a wide range of products due to its versatile properties. Some of these properties are listed below. i. General
Polystyrene is an amorphous thermoplastic with a density of 1.05 g/cm3 with extremely low moisture absorption (0.05%). Styrene polymers have some unique properties which make them useful in a wide range of products. The single most important characteristic of general purpose
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polystyrene is that it is a glass-like solid below 100°C. Above this temperature, commonly called the glass-transition temperature, the polymer chain (on a molecular level) has rotational freedom which allows large-chain-segment mobility. The polymer is thus fluid enough to be easily shaped into useful forms. Below the glass-transition temperature, polystyrene possesses considerable mechanical strength, allowing it to be used in load-bearing tasks in many applications. Rubber-modified polystyrene is a two-phase system consisting of a dispersed rubber phase and a continuous polystyrene phase. The dispersed rubber particles initiated large numbers of crazes without crack formation, thus contributing to the development of very tough products. In addition to toughening, the rubber particles also increase the environmental stress-crack resistance because the microscopic rubber particles are placed in tension as they are cooled after fabrication, compressing the rigid phase. The particles try to shrink more than the rigid phase because rubber has a greater coefficient of expansion than polystyrene. Modern micrographic and analytical tools have been developed to measure and predict the complex interactions of these two-phase systems. Styrene readily copolymerises with a variety of other monomers. The first well known copolymer was styrene-butadiene synthetic rubber. Other significant copolymers include tough, solvent-resistant copolymers with acrylonitrile; heat resistant polymers with maleic anhydride; and rubber-modified, transparent systems with methyl methacrylase. Although there have been many studies concerning multiple (more than two) comonomers, few significant commercial products exist.
Since styrene polymers are non-polar, chemically inert, resistant to water, and easy to fabricate, they are the products of choice for electronic, medical, food packaging, appliance and
23
automotive applications. Recent manufacturing trends provide improved processability and further decrease trace impurities. High-speed, efficient fabrication equipment is both reducing the cost of manufacturing and increasing the strength of the fabricated parts. Polystyrene molecules can be oriented during fabrication. Modern processing equipment uses controlled orientation to produce tougher fabricated parts. Tensile strengths may double and elongation may increase by up to two orders of magnitude, resulting in tremendous increase in toughness. Toughening by orientation contributes to the success of polystyrene foam, now widely used in both insulation and as foam sheet in food packaging, and to the success of clear, thermoformed, biaxially oriented polystyrene. Pure polystyrene does not absorb ultra violet light in the terrestrial sunlight spectrum and would apparently have better ultraviolet stability if it were not for the presence of ultraviolet absorbing trace impurities. The presence of rubber tends to decrease the outdoor stability; this is countered by incorporating special rubbers and stabilisers. Anionic polymerisation produces a more thermally stable polymer which can be made even more stable by proper selection of the end group, because most degradation begins at chain ends. Because of the commercial interest in polystyrene, its polymerisation ease, and its relatively simple linear structure, polystyrene is one of the most thoroughly investigated polymer systems in the world (Wool and Sun, 2005).
Several attempts have been made to enhance the mechanical properties and stability of polystyrene during loading conditions in recent years. Unmodified, unblended or virgin polystyrene is a brittle, inflexible material with limited commercial possibilities and usefulness. Its utilisation is based on the compounding of the base polymer with additives. With the addition
24
of additive such as plasticisers, heat stabilisers, lubricants, fillers and copolymerisation with other monomers; the poor properties of polystyrene can be improved (Xiea et al., 2004). Fracture resistance of polystyrene can be enhanced by blending it with elastomers like natural rubber (Shaws and Singh, 1989), polyurethane (Siddaramaiah and Somashekar, 1998), ethylene polypropylene rubber (Shaws and Singh, 1989), polybutadiene (Ivankova et al., 2003), polyethylene (Gao et al., 2003), poly(acrylic acid) (Zhang and Eisenberg, 1999). The morphology, miscibility and mechanical properties of these blends are well documented. In these blends, however, the problem of immiscibility and phase separation is overwhelmingly encountered that ultimately hamper the synergism in the physico-mechanical properties of the blend (Gao et al., 2003). ii. Mechanical properties Mechanical properties of any material is essentially defined as those properties that determine the response of the material to applied stresses or strain during service (Bello, 2001). Polystyrene is hard, stiff and dimensionally stable but relatively inextensible material with high tensile strength (55 – 80 NM/m2) and low elongation at break (<10%). The mechanical strength is affected to a large degree by the processing conditions. The highest value can be obtained with free flowing materials at a low processing temperature. iii. Chemical resistance Polystyrene has good chemical resistance. It is resistant to alkalis, dilute mineral acids, water and aqueous solution at room temperature. iv. Resistance to stress-cracking
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Polystyrene is susceptible to stress-cracking with internal stresses which can form stress cracks even in the resistance. It is therefore advisable to produce injection-moulded parts with a few internal stresses as possible. v. Advantages and limitations Polystyrene has good chemical properties, low cost, easy to process, low shrinkage, however, it has limitations, which include negligible mechanical properties above 70°C, brittle at room temperature and degrade rapidly in outdoor use due to ultraviolet light.
1.5 Neem Seed (Azadirachta indica) Oil
Neem (Azadirachta indica) belongs to Meliceae family and grows rapidly in the tropics and semi-tropic climates. It is also observed that this tree could survive in very dry and arid conditions. Neem tree is an evergreen related to mahogany, growing in almost every part of the world like India, Saudi Arabia, East Asia and West Africa, etc (Muthu et al., 2010). In Nigeria, neem forms about 90% of the trees in the forestry plantations established in the 12 states within the savannah zone under the afforestation programme (Ogbuewe et al., 2011).
The importance of the neem tree has been recognized by U S National Academy of Sciences, which published a report in 1992 entitled `Neem a tree for solving global problems` (Biswas et al., 2002). Neem has been in a global context today because it offers answers to the major concerns facing mankind. Neem (Azadirachta indica) is considered harmless to human, animals, birds, beneficial insects and earthworms and has been approved by the U S Environmental Protection Agency for use on food crops (Debjit et al., 2010; Sharma et al., 2011). A matured neem tree produces 30 to 50 kg of fruits every year and has a productive life span of 150 to 200
26
years (Ragit et al., 2011). Neem oil comprises mainly of triglycerides and large amount of triterpenoid compounds. It contains four significant saturated fatty acids, of which two are palmitic acid and two are stearic acid. It also contains polyunsaturated fatty acids such as oleic acid and linoleic acid (Muthu et al., 2010). The quality of oil in terms of its fatty acids composition is very important. All parts of neem plant such as leaves, bark, flower, fruit, seed and root have advantages in medical treatment and industrial products. Its leaves can be used as drug for diabetes, eczema and reduce fever. Bark of neem tree can be used to make toothbrush. Neem root has an ability to heal diseases and is used against insect bites (Puri, 1999; Ragasa et al., 1997). Neem seed is a part of neem tree which has high concentration of oil. Neem oil is widely used as insecticides, lubricant, drugs for variety of diseases such as diabetes and tuberculosis (Puri, 1999; Ragasa et al., 1997 and Johnson et al., 1996). There are several methods to obtain neem oil from the seed like mechanical pressing, supercritical fluid extraction and solvent extraction (Puri, 1999). Mechanical extraction is the most widely used method to extract neem oil from its seed. However, the oil produced with this method usually has low price, since it turbid and contains a significant amount of water and metal contents. In extraction using supercritical fluid, the oil produced has very high purity; however, the operating and investment cost is high. Extraction using solvent has several advantages. It gives higher yield and less turbid oil than mechanical extraction and relatively low operating cost compared with supercritical fluid extraction (Maria et al., 2008). In order to increase the application potential of neem oil, the side-chain olefinic groups are converted to epoxide. The table below shows the physicochemical properties and fatty acid composition (%) of NO. Table 1.1: Physico-chemical Properties and Fatty acid composition (%) of NO
27
Physico-chemical property /Fatty acid (g / 100 g)
Neem oil
Specific gravity
0.915 – 0.920 / 300 C
Saponification value (mg / g KOH)
175 – 200
Iodine value (mg / g I2)
65 – 80
Palmitic acid (C16)
13.6 – 16.2
Stearic acid (C18)
14.4 – 24.0
Oleic acid (C18:1)
49 – 62
Linoleic acid (C18:2)
2.3 – 15.8
Linolenic acid (C18: 3)
―
Total unsaturated acid
64.55
Total saturated acid
34.10
Source: Uko et al., 2008, ― = not determined.
1.6 Plasticiser as Additive to Polymers
Polymer additives are substances compounded into a resin to enhance or improve specific resin characteristics. They function by contributing to the quality, life and usefulness of the resin. Based on chemical profiles and overall functions, additives are commonly divided into categories. In order to improve the processing, performance and elasticity of plastic materials, the polar and non-polar additives (plasticisers) are added. In 1951, the International Union of Pure and Applied Chemistry (IUPAC) developed a universally accepted definition of a plasticiser as a substance or a material incorporated in a material (usually a plastic or elastomers) to increase its flexibility, workability, or extensibility (Krauskopf and Godwin, 2005).
Plasticiser is typically present in between 1% to 10% by weight of polymeric material. Below 1%, the plasticiser may not effectively plasticise the polymeric material and above, it tends to leach out of the material (Hu et al., 2013). The interactions of plasticiser molecules with polymer chains cause disruption of secondary valence bond or van der Waals force between polymer
28
molecules. As a consequence, a decrease in molecular interactions and thus an increase in mobility of the polymer chains are observed. As a result, the materials are characterised by lower moduli, stiffness, glass-transition temperature (Tg) and hardness. The elongation of material and chain flexibility significantly also increases (Adelia et al., 2013). The most generally applied plasticisers are low molecular mass organic compounds characterised by low volatility in order to prevent their rapid evaporation from manufactured products. Among commercial applied plasticisers for polystyrene are phthalate esters such as dimethyl, diethyl, dipropyl, dibutyl, diheptyl, dioctyl, diisodecyl or dibenzylbutylphthalate commonly used (Etchenique and Weisz, 1999; Mills et al., 1998). In addition, the application of adipate and glutarate esters as plasticisers for expanded polystyrene and the liquid paraffin and zinc stearate as internal plasticisers is reported (Garder et al., 1999; Usui et al., 2002). In the last decade, the worldwide production of plasticisers was around 5 million tonnes per year. These were applied to around 60 polymers and more than 30 groups of products (Bialecka-Florjanczyk and Floranczyk, 2007). The use of plasticisers for plastic products manufacture is well known. Its application to modify polymer characteristics began in the 1800s. In these early days, manufacturers of colloid or colloid lacquers used camphor and castor oil for plasticisation purposes, but these were unsatisfactory for many end uses. Later, in 1912, triphenyl phosphate was tested to substitute camphor oil, representing the beginning of the ester plasticisers‟ era. Phthalic acid esters found applications as plasticisers for the first time in 1920 and continue to be the largest class of plasticisers in the 21st century (Rahman and Brazel, 2004). Di(2-ethylhexyl)phthalate (DEHP), also known as dictoylphthalate (DOP), was introduced in 1930 and has been the most widely used plasticiser since 1930s. However, most of the phthalates have toxic properties for human. Due to this, the intensive studies on the new, non-toxic and biodegradable materials that could replace harmful
29
plasticisers are developed (Hendorf et al., 2007; Yang et al., 2006). Nowadays, there is increasing interest in the use of natural- based plasticisers that are characterised by low toxicity and low migration. This group includes epoxidised triglycerides vegetable oils from soybean oil, linseed oil, castor oil, sunflower oil and fatty acid esters (FAEs) (Baltacioglu and Balkose, 1999). Several theories have been proposed to explain the mechanism and action of plasticisers on polymers. Among those theories, lubricity theory and gel theory have been widely accepted to describe the effect of plasticisers on polymeric networks. Lubricity theory proposes that the plasticiser acts as a lubricant to reduce friction and facilitates polymer chain mobility past one another and consequently lowering deformation. Gel theory extends the lubricity theory and suggests that plasticiser disrupts and replaces polymer-polymer interactions (hydrogen bonds, van der Waals or ionic forces etc) that hold polymer chains together resulting in reduction of the polymer gel structure and increase flexibility.
1.7 Fourier Transform Infrared (FTIR) Spectroscopy
FTIR spectroscopy is a technique that is sensitive to intermolecular interactions. Infrared spectrum helps to reveal the structure of a new compound by telling us what groups are present or absent from the molecule. A particular group of atoms give rise to characteristic absorption bands; that is a particular group absorbs light of certain frequencies that are much the same from compound to compound. In this research, FTIR spectroscopy is used to monitor the absorption peak shift in specific region to determine the functional groups in raw neem oil and epoxidised neem oil.
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1.8 Tensile Properties
Tensile testing instruments are widely used to study mechanical properties of the plastic material. These properties which include, tensile stress, % elongation and Young`s modulus all depend on the basic properties of the polymer chain molecule and other factors such as processing and environmental conditions. Mechanical properties of polymer blends normally determine its applicability. Tensile measurement is employed to investigate the influence of EVO on the mechanical properties of the sample at different compositions. The response of a polymer to applied stresses would depend upon its gross morphology and molecular behaviour (Bello, 2001). One of the most accessible ways of determining mechanical properties of polymeric materials is by the stress-strain curve experiment and Instron tensile tester is the most common instrument being used. The results from the tensile test are commonly used to select a material for an application, for quality control, and to predict how a material will react under other types of forces. Properties that can be measured from tensile test are tensile stress, percentage elongation, tensile modulus, e.t.c. (Czichos, 2006). Tensile strength is the stressed state caused by an applied load that tends to elongate the material in the axis of the applied load, in other words, the stress caused by pulling the material. Tensile strength is the most often specified property of plastic materials used to indicate the inherent strength of the material. Tensile strength is dependent on molecular structure and the orientation of the polymer within a particular sample, as well as any filler or reinforcements that may be incorporated in the polymer (Shah, 1984). The strength of any material relies on three different types of analytical methods: strength, stiffness and stability, where strength means load carrying capacity, stiffness means deformation and stability means ability to maintain the initial configuration of the material. Stress (δ) is expressed by:
31
δ = 𝐹𝐴…………………….. (1.1); where F is the force (N) acting on A (m2) (Beer and John, 2006).
Tensile stress (N/m2) = 𝐵𝑟𝑒𝑎𝑘𝑖𝑛𝑑 𝑙𝑜𝑎𝑑(𝑁)𝐶𝑟𝑜𝑠𝑠 𝑠𝑒𝑐𝑡𝑖𝑜𝑛𝑎𝑙 𝑎𝑟𝑒𝑎(m2) ….. (1.2); (Beer and John, 2006). Elongation is a measure of the permanent extension of a length of the polymer specimen after failure and it can be obtained by the expression shown below:
% Elongation = 𝐸𝑥𝑡𝑒𝑛𝑠𝑖𝑜𝑛 𝑋 100𝐼𝑛𝑖𝑡𝑖𝑎𝑙 𝑙𝑒𝑛𝑔𝑡……………..(1.3) dimensionless. (Beer and John, 2006) It is sometimes referred to as the `strain percent`. It`s a measure of ductility and can be related to toughness in plastic materials. Modulus of elasticity (E), also called tensile modulus or Young`s modulus, is the ratio of stress to the strain, below the elastic limit. It is a measure of material`s stiffness. The modulus is calculated using the equation below. The value is recorded as the E value.
E = 𝑇𝑒𝑛𝑠𝑖𝑙𝑒 𝑠𝑡𝑟𝑒𝑠𝑠𝑇𝑒𝑛𝑠𝑖𝑙𝑒 𝑠𝑡𝑟𝑎𝑖𝑛 = 𝐹𝐴 𝑒𝑙 ………………………………. (1.4); Pa. where F is the force, A is the cross sectional area, e is the extension and l is the initial length of the polymer film. Materials with high E values are rigid stiff materials while materials with low E values are rubber-like. Plastics that behave like rubbers have high elongation (change in length to low stress or force applied).
1.9 Thermal Properties
Differential scanning calorimetry (DSC) measures the amount of heat energy absorbed or released when a material is heated or cooled. For polymeric materials that undergo important property changes near thermal transition, DSC is a very useful technique to study glass-transition
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temperature (Tg), crystallisation temperature (Tc) and melting behaviour (Tm), in addition to the associated enthalpy (ΔH) for each process.
1.10 Morphological Study
Scanning electron microscopy (SEM) is normally employed to study the surface morphology of the fractured tensile specimens of polymeric material and qualitatively illustrate the state of dispersion of the additives in the polymer matrix. SEM is used to study the morphologies of the plasticised polymeric films and examine the contrast difference between phases of varying composition in the blends.
1.11 Viscosity Measurement
Viscometry is a simple and effective technique for monitoring the interactions in solutions of polymer blends. The miscibility studies of polyblends in solution phase could be determined by viscometric measurements. The viscosity method is found to be more sensitive and accurately reflects the changes in compatibility of the polyblends. Low viscous polymeric fluids are more miscible than higher viscous ones.
1.12 Research Problem Statement
The existing plasticiser (phthalate) obtained from non-renewable resource (petroleum) is highly toxic and expensive. Polystyrene is highly brittle and have limited mechanical applications. Hence the need to modify its structure for enhanced mechanical properties. This study is to see the viability of applications of the oil sample (ENO) towards improving the structure-property
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relationships in the polyblends. It is in this vein that various researches like this are embarked upon to produce polystyrene system that has enhanced and stabilised mechanical and thermal properties under a variety of loading conditions when blended with a value-added product derived from a renewable resource (EVO).
1.13 Aim of the Study
The study is aimed at investigating the effect of ENO (plasticiser) loading on the mechanical and thermal properties of polystyrene, as well as the interaction between polystyrene and (epoxidised neem oil).
1.14 Objectives of the Study
The aim will be achieved through the following objectives:
I. To improve industrial potential of the neem oil sample via epoxidation.
II. To establish the effectiveness of ENO loading in enhancing the mechanical property of polystyrene under a variety of loading conditions.
III. To establish the effectives of ENO loading on the thermal behaviour of polystyrene.
IV. To investigate the molecular interaction between PS and ENO at different wt % compositions.
1.15 Scope and Limitation
This research is focused on the chemical modification of virgin oil sample (raw neem oil) via conventional epoxidation method and analysis of the modified neem oil through FTIR spectroscopy. Investigating the effect of ENO loading on the mechanical properties of the PS.
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Investigation of the thermal behaviour of PS and PS/ENO blends samples at different compositions. Examination of the morphologies of the cross-section of the film samples of different compositions by scanning electron microscope (SEM). 1.16 Significance of the Study The unique high biodegradability, low toxicity, renewability and excellent lubricating performance of vegetable oils make them a viable alternative to petroleum based oils. Owing to these properties and potentials, environmentalists and engineers have made attempts to explore the possibilities of using vegetable oils as environmental friendly lubricants for range of applications. In this vein, significance of this research is to develop a value-added product (ENO) from locally available and economically viable vegetable oil (neem oil) and establish whether the epoxidised oil sample can be used to enhance the mechanical and thermal properties of polystyrene and its stability under a variety of loading conditions which can serve as substitute for phthalates used as plasticisers in polymer industry. The analysis derived from this research will reveal the quality and sustainability of this epoxidised oil for many industrial applications. Finally, this study will serve as a means to create awareness on the economic potentials and industrial applications of vegetable oils especially the non-edible vegetable oils.
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