CHAPTER ONE

1.0     INTRODUCTION

1.1     BACKGROUND OF STUDY

Composite is the combination of a matrix and a reinforcement, which when combined gives properties superior to those of the individual components (Ashori & Nourbakhsh 2009a). Wood plastic composite (WPC) is therefore a combination of wood and plastic with the plastic as the matrix and the wood as the reinforcement. Wood plastic composite, (WPC), can be made from virgin materials as well as recycled ones. In Nigeria, plastic waste is enormous and its disposal has always been a challenge. In using recycled plastic of WPC, the advantages are that; raw materials are readily available, control the plastic waste menace and also save some virgin and natural products. Substantial increase in human population and the consequential strain on natural resources such as forests and the associated harmful results as well as the plastic menace challenging the nation are some of the challenges that make the study of WPC important. The green mentality and the shift in attitude are favouring environmentally-friendly products such as WPC (Azadeh et al., 2011). WPCs can be used in several applications such as profiles, sheathing, Decking, Roof tiles, Window trim, automotive parts, stepping stones etc. Natural fibers such as wood are considered environmentally friendly and sustainable due to their renewability and biodegradability. Natural fillers have other added advantages over artificial fibers in the sense that they have low specific weight, high specific strength and stiffness, safer handling and working conditions; they are also non-abrasive to the processing equipment (Tong et al., 2014).

Development of the oil sorbents made of organic waste materials was initiated in order to provide resources for marine oil spill response with less environmental load and cost (Masaki Saito et al., 2003). Sorbents of the oil spill in water are materials that soak up the oil. They can be used to recover oil through the mechanisms of absorption and adsorption, or both. Absorbents allow oil to penetrate into pore spaces in the material they are made of, while adsorbents attract oil to their surfaces but do not allow it to penetrate into the material. Once sorbents have been used to recover oil, they must be removed from the water and properly disposed of on land or cleaned for reuse. Any oil that is removed from the sorbent materials must also be disposed of or recycled. Sorbents can be divided into three basic categories: natural organic, natural inorganic and synthetic. The first category includes peatmoss, straw, hay, sawdust, ground corncobs, feathers, and other carbon-based products. They are relatively inexpensive and generally readily available. Organic sorbents can absorb 3 to 15 times their weight of oil, but they do present some disadvantages. Some organic sorbents tend to absorb water as well as oil, causing them to sink. Many organic sorbents are loose particles, such as sawdust, and are difficult to collect after they are spread on the water (Ghalambor, 1995).

Natural inorganic sorbents include clay, perlite, vermiculite, glass, wool, sand, and volcanic ash. They can absorb from 4 to 20 times their weight of oil. Inorganic substances, like organic substances, are inexpensive and readily available. Most organic materials can only be used on land and are not adaptable to water use for oil spill clean-up. Synthetic sorbents includes man-made materials that are similar to plastics, such as polyurethane, polyethylene, polypropylene, and nylon fibers. Most synthetic sorbents can absorb as much as 70 times their weight of oil. Synthetic sorbents that cannot be cleaned after use can present difficulties because they must be stored temporarily until they can be disposed of properly. They are best suited to absorb lighter viscosity oils that can perpetrate or wick into its fibre. Sorbents work by either absorption or adsorption (Ghalambor, A. 1995). Absorbents operate like sponges and collect oil by capillary action or suction. Adsorbents rely on the large surface area, the chemical affinity of the sorbents for the spilled oil, and chemical constituents including their porosity, molecular structure and change in volume. Absorbents work best on light, less viscous oils, while adsorbents work best on heavy, sticky, more viscous oils. In some cases, a sorbent material may utilize both techniques for oil recovery.

Walkup et al., 1969 reported that an oil spill clean-up is a question of options and not solutions. Even though no oil spill clean-up system is likely to be completely effective. Sorbents are one of the most widely used methods for compacted oil spills in the sea.

This study looks at WPC made from recycled plastic and wood waste and its absorption capacity

1.2     Problem statement

Plastic waste is a huge challenge confronting this nation; due to the large volumes used and discarded every day and their non-degradable nature. Landfilling has usually been used to dispose of plastic waste but has proved ineffective since it fills up the site quickly. Incineration of the plastic waste can also cause pollution. The need for effective and sustainable method to manage the menace is urgent. Recycling has proven to be the best way to solve the plastic waste problem. Other recycling methods have been used to manage the situation and this work offers an alternative mode of recycling plastic waste, which is the formation of Wood Plastic Composite. Some of the advantages of using WPC in the auto industry are: reduction in material weight and energy consumption, enhancement of acoustic performance and processing time, lowering production cost, improving safety and shatterproof performance under extreme temperature changes, and improving biodegradability of the auto interior parts (Thompson et al., 2010). WPC are used as trim parts in dashboards, parcel shelves, seat cushions, backrests, door panels and cabin linings.

At sawmills, unless reprocessed into particleboard, burned in a sawdust burner or used to make heat for other milling operations, sawdust may collect in piles and add harmful leachates into local water systems, creating an environmental hazard.

Airborne sawdust and sawdust accumulations present a number of health and safety hazards. Wood dust becomes a potential health problem when, for example, the wood particles, from processes such as sanding, become airborne and are inhaled. Wood dust is a known human carcinogen. Certain woods and their dust contain toxins that can produce severe allergic reactions.

This work involves the formation of a composite using low density polyethylene wastes, white sand and sawdust. This composite formed can be used as a sorbent in absorption of crude oil so as to reduce oil spillage.

1.3     Aim of study

• Reduction of oil spillage in Niger Delta using wood plastic composite from saw dust, white sand and low density polyethylene waste.

Objectives of study

• Prepare wood plastic composite from sawdust, white sand and low density polyethylene plastic.
• Calculating the rate of absorption of crude oil, water and crude oil in water using composite.

1.4     Justification of study

Economically, viable recycling and value addition to the plastic waste is of great urgency due to the increasing amount being generated each day. Composite formation is one of the many ways by which plastic waste can be recycled.

WPC products are gaining popularity around the world.  Several works have been done on WPC with different plastics and wood waste at different percentages (Santos et al., 2013). But little has been published on the wood specie used and its effects on the properties of products formed. Producing composite materials from recycled plastics of low density polyethylene and sawdust will help Nigeria solve the problem of plastic waste. A look around towns, on the streets, market places, gutters, and even dump sites in Nigeria tells the story better. Some people resort to burning of the plastic which releases toxic substances such as dioxins, mercury and furan. When these toxins gets into the body leads to serious health implications, example is heart disease and can also aggravate respiratory ailments such as Asthma (WEFCF, 2012).

This project propose a key measure to prevent indiscriminate disposal of these principal wastes and absorption of crude oil in water, apart from punitive enforcement of legislature. This is to develop technological solutions by providing alternative use for these waste materials which will place a value on them. Identifying the potential use of waste to create job and inadvertently help in shaping public attitude towards its disposal and create job in the long term.

Saw dust wastes are not normally properly disposed of and therefore end up in landfills. To help put this by-product to good use, it is being incorporated into the project as one of the reinforcements.

1.5                        LITERATURE REVIEW

COMPOSITES AND COMPOSITE MATERIAL

Varieties of cellulose fibers that can be used to reinforce thermoplastic include wood fibers, coir, pineapple leaf (palf), rice husk, and sugarcane bagasse. These fibers are abundantly available throughout the world.

1.5.1    Cellulose fibers for reinforced composites

Cellulose fiber, often referred to as vegetable fibers come from a renewable resource. The production of these fibers requires little energy with the consumption of CO₂; oxygen is given back to the environment. The fibers are light in weight which results in higher specific strength and stiffness than glass. Production is at low cost, which makes the material an interesting product for low-wage countries. Its processing is not harsh on the tooling equipment thus resulting in little wear, no skin irritation and also that thermal recycling is possible. These fibers are now used to reinforce plastic waste composites (Mukherjee et al., 1986).

1.5.1.1 Pineapple leaf (Palf)

Pineapple is a tropical plant. Its leaf fiber is rich in cellulose, relatively inexpensive and abundantly available. Furthermore, it exhibits excellent mechanical properties. These fibers are extracted from the leaf of the plant, Ananas cosomus belonging to Bromeliaceae family. Physical properties, mechanical and dielectric properties, tensile behaviour, surface, and fracture morphology of palf have been reported by many researchers (Muherjee et al., 1986 and Bhattacharrya et al., 1986). It has the potential for polymer reinforcement. At present pineapple leaf fibers which are waste product of pineapple cultivation and therefore relatively inexpensive can be obtained for industrial purposes.

1.5.1.2 Rice husk

Rice is one of the large groups of cereal grains that can be used to produce hull fibers. Currently, wheat, corn, husk, oats and other cereal crops are used to produce fibers and investigations carried out in the area of reinforced composites. Ismail et al., 2001 studied the mechanical properties of rice husk filled polymer composites and their relation to fiber loading, coupling agent, processability, hygrothermal aging, and hybridization effect. Other studies have focused on: flame retardant properties of rice husk and polyethylene composites (Zhao et al., 2009 and Kim et al., 2004).   

1.5.1.3 Coconut fiber (Coir)

Coconut fiber is a by-product obtained from the husk of the fruit of the coconut palm. It is found between the hard, internal shell and the outer coat of a coconut. The individual fiber cells are narrow and hollow, with thick walls made of cellulose. They are pale when immature, but later become hardened and yellowed as a layer of lignin is deposited on their walls. Each cell is about 1mm long and 10 to 20 µm. Fibers are typically 10 to 30 cm long (Hindu, 2009). The two varieties of coir are brown and white. Brown coir harvested from fully ripened coconuts is thick, strong and has high abrasion resistance. It is typically used in mats, brushes and sacking. Mature brown coir fiber contain more lignin and less cellulose than fiber such as flax and cotton. They are also stronger but less flexible. Coir has also been tested as a filler or a reinforcement in different composite materials (Choudhbury et al., 2007).

1.5.1.4 Sugar cane fiber (Bagasse)

Bagasse is the fibrous residue which remains after sugarcane stalks are crushed to extract their juice. It is currently used as a renewable cellulose fiber for the manufacture of composites materials. Monteiro et al., (1998) studied the possible uses of bagasse waste as reinforcement in polyester matrix composites. Preliminary results have attested to this possibility. Composites with homogeneous microstructures can be fabricated and enhance the levels of their mechanical properties to enable them have practical applications. Vazquez et al., (1999) reported processing and properties of bagasse fiber-polypropylene composites. Vegetable fibers were with the thermoplastic matrix. The fibers were washed with alkaline solution. The effects of the treatment reactions on the chemical structure of the fibers were analysed by infrared spectroscopy.

1.5.1.5 Saw dust from ceiba pentandra

Wood fiber is a plant fiber composed of elongated cells oriented in the longitudinal direction of the stem. The stem consists of cellulose, hemicellulose, and lignin. Cellulose comprises of crystalline structure, while hemicelluloses has a semi crystalline structure. The lignin is an amorphous polymer. The use of wood-based material, such as sawdust and wood fibers, as reinforcement for thermoplastics has gained significant interest. Wood fibers offer a number of advantages over conventional reinforcing materials in the form of abundancy, renewability, low specific gravity, high specific strength stiffness, and relatively low cost (Zadorecki, 1989 and Bledzki et al., 1998).

According to Hagan, (1999) the activities of the timber and wood processing industries generate an estimated 61,000 metric tonnes of wood waste annually. These wastes are not normally properly disposed of and therefore end up in landfills. To help put this by-product to good use, it is being incorporated into the project as one of the reinforcements.

Ceiba pentandra is native to the American tropics, Mexico, Peru, Bolivia and Brazil, and West Africa. It is however known by these other common names such as Pochota, Yaxché (Mexico), Bonga, Ceiba de lana (Colombia), Sumaúma (Brazil), Toborochi (Bolivia) (Martin, 1980). The wood is soft and very light varying in colour from white to light brown. The components of wood are cellulose 40-55 %, lignin 15-35 %, and hemicelluloses 20-35 % (Kenneth, 2002).

The hemicelluloses of wood consist of several types of amorphous polymeric carbohydrates that occur through the woody structure of plants (Word, 1973). The lignin gives the structural rigidity, stiffening and holding the fibers together. Currently, the main use of Ceiba pentandra is as a source of timber as well as for plywood manufacture, packaging composites, and lightweight construction materials.

It is also used locally for carving canoes.

1.5.2    Plastics

Plastic materials are the most widely used group of synthetic polymers. They include the following: polyethylene, polypropylene, poly (vinyl chloride), polystyrene, fluorocarbons, epoxy, phenolics, and polyesters but the most extensively used in Nigeria are polyethylene, polypropylene, polystyrene, nylon, and polyesters. Plastics are organic polymers of high molecular mass, but contain other substances. They are usually synthetic and are most commonly derived from petrochemicals. Plastics are durable and degrade very slowly because they have chemical bonds that make plastics resistant to the cellulose processes of degradation. There are two types of plastics: thermoplastics and thermosetting polymers. Thermoplastics are the plastics that do not undergo chemical change in their composition when heated and can be recycled. Examples include polyethylene, polypropylene, polystyrene, polyvinyl chloride, and polytetrafluoroethylene (PTFE) (Alan, 2010). Thermoplastics are made up of many repeating molecular units, known as repeat units, derived from monomers. Thermoplastic polymers are distinguished by their ability to be reshaped upon the addition of heat (above the glass transition temperature of the amorphous phase or the melting temperature of the crystalline phase). This cycle can be carried out repeatedly. Most linear polymers are thermoplastics.

Thermosetting polymers, on the other hand, undergo chemical reactions during curing which crosslink the polymer molecules. Once crosslinked, thermosets become permanently hard and simply undergo chemical decomposition under the application of excessive heat. Thermosetting polymers typically have greater abrasion resistance and dimensional stability over that of thermoplastic polymers, which typically have better flexural strength properties. Thermoset polymers are generally harder and stronger than thermoplastics and have better dimensional stability. Most of the crosslinked and network polymers, which include vulcanized rubbers, epoxies, phenolics and polyester resins, are thermosetting in nature (Callister, 2007).

1.5.2.1 Polyethylene

Polyethylene or polythene (abbreviated PE; IUPAC name polyethene or poly(methylene)) is the most common plastic. The annual global production is around 80 million tonnes.(baner, 2008) Its primary use is in packaging (plastic bags, plastic films, geomembranes, containers including bottles, etc.). Many kinds of polyethylene are known, with most having the chemical formula (C₂H₄)_n. PE is usually a mixture of similar polymers of ethylene with various values of n.

1.5.2.1.1          Properties

   The properties of polyethylene can be divided into mechanical, chemical, electrical, optical, and thermal properties. (Piringer, 2008)

• Mechanical properties

Polyethylene is of low strength, hardness and rigidity, but has a high ductility and impact strength as well as low friction. It shows strong creep under persistent force, which can be reduced by addition of short fibers. It feels waxy when touched.

• Thermal properties

The usefulness of polyethylene is limited by its melting point of 80 °C (176 °F) (HDPE). For common commercial grades of medium- and high-density polyethylene the melting point is typically in the range 120 to 180 °C (248 to 356 °F). The melting point for average, commercial, low-density polyethylene is typically 105 to 115 °C (221 to 239 °F). These temperatures vary strongly with the type of polyethylene.

• Chemical properties

Polyethylene consists of nonpolar, saturated, high molecular weight hydrocarbons. Therefore, its chemical behavior is similar to paraffin. The individual macromolecules are not covalently linked. Because of their symmetric molecular structure, they tend to crystallize; overall polyethylene is partially crystalline. Higher crystallinity increases density and mechanical and chemical stability.

Most LDPE, MDPE, and HDPE grades have excellent chemical resistance, meaning they are not attacked by strong acids or strong bases, and are resistant to gentle oxidants and reducing agents. Crystalline samples do not dissolve at room temperature. Polyethylene (other than cross-linked polyethylene) usually can be dissolved at elevated temperatures in aromatic hydrocarbons such as toluene or xylene, or in chlorinated solvents such as trichloroethane or trichlorobenzene. (Kenneth et al., 2005)

Polyethylene absorbs almost no water. The gas and water vapor permeability (only polar gases) is lower than for most plastics; oxygen, carbon dioxide and flavorings on the other hand can pass it easily.

PE can become brittle when exposed to sunlight, carbon black is usually used as a UV stabilizer.

Polyethylene burns slowly with a blue flame having a yellow tip and gives off an odour of paraffin (similar to candle flame). The material continues burning on removal of the flame source and produces a drip.

Polyethylene cannot be imprinted or stuck together without pre-treatment.

• Electrical properties

Polyethylene is a good electrical insulator. It offers good tracking resistance; however, it becomes easily electrostatically charged (which can be reduced by additions of graphite, carbon black or antistatic agents).

• Optical properties                         

 Depending on thermal history and film thickness PE can vary between almost clear (transparent), milky-opaque (translucent) or opaque. LDPE thereby owns the greatest, LLDPE slightly less and HDPE the least transparency. Transparency is reduced by crystallites if they are larger than the wavelength of visible light. (Chung, 2010)

1.5.2.1.2          Molecular structure of different PE types

The diverse material behaviour of different types of polyethylene can be explained by their molecular structure. Molecular weight and crystallinity are having the biggest impact, the crystallinity in turn depends on molecular weight and degree of branching. The less the polymer chains are branched, and the smaller the molecular weight, the higher the crystallinity of polyethylene. The crystallinity is between 35% (PE-LD/PE-LLD) and 80% (PE-HD). Within crystallites polyethylene has a density of 1.0 g·cm⁻³, in the amorphous regions of 0.86 g·cm⁻³. Thus, an almost linear relationship exists between density and crystallinity. (Kaiser and Wolfgang, 2011)

1.5.2.1.3          Classification

Polyethylene is classified by its density and branching. Its mechanical properties depend significantly on variables such as the extent and type of branching, the crystal structure, and the molecular weight. There are several types of polyethylene:

• Ultra-high-molecular-weight polyethylene (UHMWPE)
• Ultra-low-molecular-weight polyethylene (ULMWPE or PE-WAX)
• High-molecular-weight polyethylene (HMWPE)
• High-density polyethylene (HDPE)
• High-density cross-linked polyethylene (HDXLPE)
• Cross-linked polyethylene (PEX or XLPE)
• Medium-density polyethylene (MDPE)
• Linear low-density polyethylene (LLDPE)
• Low-density polyethylene (LDPE)
• Very-low-density polyethylene (VLDPE)
• Chlorinated polyethylene (CPE)

With regard to sold volumes, the most important polyethylene grades are HDPE, LLDPE, and LDPE.

Low-density polyethylene (LDPE)

LDPE is defined by a density range of 0.910–0.940 g/cm³. LDPE has a high degree of short- and long-chain branching, which means that the chains do not pack into the crystal structure as well. It has, therefore, less strong intermolecular forces as the instantaneous-dipole induced-dipole attraction is less. This results in a lower tensile strength and increased ductility. LDPE is created by free-radical polymerization. The high degree of branching with long chains gives molten LDPE unique and desirable flow properties. LDPE is used for both rigid containers and plastic film applications such as plastic bags and film wrap. In 2013, the global LDPE market had a volume of almost US$33 billion.

The radical polymerization process used to make LDPE does not include a catalyst that “supervises” the radical sites on the growing PE chains. (In HDPE synthesis, the radical sites are at the ends of the PE chains, because the catalyst stabilizes their formation at the ends.) Secondary radicals (in the middle of a chain) are more stable than primary radicals (at the end of the chain), and tertiary radicals (at a branch point) are more stable yet. Each time an ethylene monomer is added, it creates a primary radical, but often these will rearrange to form more stable secondary or tertiary radicals. Addition of ethylene monomers to the secondary or tertiary sites creates branching.

Fig 1.1     A schematic representation of the chemical structure of a low density polyethylene polymer showing a more extended branching leading to low density property

Waste LDPE can provide a suitable matrix for making composites with saw dust and coir fiber. This is one of the most abundant plastics worldwide due to its low cost, ease at processing and other desirable properties (Gómez et al., 2005). Since it is used mainly for disposable packaging, it often finds itself in waste streams. This makes it a good candidate for recycling.

Low-density polyethylene (LDPE) is a thermoplastic polymer made from the monomer ethylene. It was the first grade of polyethylene, produced in 1933 by Imperial Chemical Industries (ICI) using a high pressure process through free radical polymerization (Dennis, 2010) It is defined by a density range of 0.910 -0.940 g/cm³.

It has a high degree of short and long chain branching as shown in Figure 1.1 which means that the chains do not pack in a crystal-like structure. It has therefore, weaker intermolecular bonds compared to HDPE and MDPE. Though more new polymers are competing with it, LDPE continues to be an important plastic grade.

LDPE has more branching of carbon atoms than HDPE, so its intermolecular forces (instantaneous–dipole induced–dipole attraction) are weaker, its tensile strength is lower, and its resilience is higher. Also, its density is lower since its molecules are less tightly packed and less crystalline. LDPE possesses the following characteristics: very tough, weatherproof, good chemical resistance, low water absorption, semi-rigid and translucent (Ratzlaff, 2004).

Table 1.1: Properties of LDPE

Polyethylene is a plastic material of choice for the composites It is one of the urban wastes which are non-degradable.

1.5.2.2 Polystyrene

Polystyrene is a hard, rigid transparent thermoplastic which has a chemical formula (C₈H₈). It contains the chemical elements carbon and hydrogen and it is one of the most widely used plastics. The scale of its production is several billion kilograms per year (Maul et al., 2007). As a thermoplastic polymer, polystyrene is in a solid glassy state at room temperature but flows when heated above its glass transition temperature (about 100^oC). It becomes rigid again when cooled. It is free from odour and taste and burns with a sooty flame. Other valuable qualities are that it is low cost, has good mouldability, low moisture absorption, good dimensional stability, good electric insulation properties, colourability and reasonable chemical resistance. It is widely used as an injection moulding and vacuum forming material (Brydson, 1999). The principal limitations of the polymer are its brittleness and inability to withstand the temperature of boiling water. Discarded polystyrene does not biodegrade for hundreds of years and is resistant to photolysis (Bandyopadhyay et al., 2007). The mechanical properties of polystyrene depend on the nature of the polymer (e.g. its molecular weight), on the method of preparation of the sample for testing and on the method of test, as is the case with all plastic materials.

1.5.2.3 Polyethylene terephthalate

Polyethylene terephthalate includes naturally occurring chemicals, such as in the cutin of plant cuticles, as well as synthetics prepared through step–growth polymerization. Depending on the chemical structure, polyester can be a thermoplastic or thermoset; however, the most common polyesters are thermoplastics (Rosato, 2004).

They are highly crystalline and exhibit high toughness, strength, abrasion resistance, low friction, chemical resistance and low moisture absorption. PET has been available for many years but mainly as a fiber (e.g. Terylene). As a moulding material it was less attractive, due to processing difficulties but these were overcome with the introduction of polybutylene terephthalate (PBT). PET is now renowned for its success as a replacement for glass in beverage bottles (Crawdford, 1998). The polar nature of the ester group leads to the resin having a higher power factor and dielectric constant than the hydrocarbon polymers and this limits their use as high frequency electrical insulators. Many mechanical properties are dependent on the density of cross-links and on the rigidity of the molecules between cross-links.

1.5.2.4 Polyamides (Nylon)

Polyamides, or nylon polymer compose of long, multiple-unit molecules in which the repeating units in the molecular chain are linked together by amide groups. Amide groups have the general chemical formula CO-NH. There are several different types of nylon (e.g. nylon 6, nylon 66, and nylon 11) but as a family their characteristics of strength, stiffness and toughness have earned them a reputation as engineering plastics (Crawdford, 1998). Typical applications for nylon include small gears, bearings, bushings, sprockets, housing for power tools, terminal blocks and slide roller. Another major application of nylon is in fiber which is strong (Crawdford, 1998).

An important design consideration is that nylon absorbs moisture which can affect its properties and dimensional stability. Glass reinforcement reduces this problem and produces an extremely strong, impact resistant material. Another major application of nylon is in fibers which are notoriously strong (Callister, 2007).

1.5.3    Coupling agent

Most polymers, especially thermoplastics, are non-polar and therefore hydrophobic substances, which are not compatible with polar (hydrophilic) substances such as wood fibers.  This therefore results in poor adhesion between the polymer and wood fiber in the wood fiber plastic composite (WFPC) (Geottler, 1983, Klason et al., 1984). In order to improve the affinity and adhesion between wood fibers and thermoplastic matrices, chemical coupling agents have been employed (Chun et al., 1984, Woodhams et al., 1984).

According to Dalväg et al., (1985), Schneider et al., (1985) coupling agents are substances that are used in small quantities to treat a surface so that bonding occurs between it and other surfaces. Coupling agents are classified into organic, inorganic, and organic-inorganic groups. Organic agents include isocyanates, anhydrides, amides, imides, acrylates, chlorotriazines, epoxides, and organic acids. Only a few inorganic coupling agents, such as silicates, are used in WFPC. Organic-inorganic agents include silanes and titanates. Coupling agents can be directly mixed with wood fiber and polymer in the melt-blending formation, such as injection moulding, extrusion, and transfer moulding. They can also be coated or grafted on the surface of wood fiber and polymer or both. Then the pre-treated and untreated wood fiber and polymer are kneaded. Usually, pre-treatment of wood fiber and polymer is by coating or grafting to enhance the mechanical properties.

Some of the important considerations in choosing coupling treatments are concentration and chemical structure of coupling agents, choice of wood fiber and matrix (e.g. shape, size and species), ratio of wood fiber to total matrix weight, formation methods, and end-user requirements of the finished product.

Coconut oil as coupling agent in composites.

Coconut oil is an oil extracted from the kernel or meat of matured coconuts fruit. Melting Point is at 25ºC. Smoking Point is at 177ºC and it is insoluble in water at room temperature and has a density of 0 924.27 g/cm.3 Chemical properties of coconut oil is predominantly composed of saturated fatty acids and a high proportion of glycerides of lower chain fatty acids. The oil is highly stable towards atmospheric oxidation. It is characterized by a low iodine value, high saponification value, and high saturated fatty acids content and is a liquid at room temperatures of 27^oC. It has various applications in food, medicine, and industry.

Figure 1.2: The chemical structure of a typical triglyceride showing the polar and non-polar moiety in the same structure.

Figure 1.3: Schematic representation of the coupling effect of a triglyceride molecule with cellulose fiber and plastic matrix

Coconut oil contains a high percentage of glycerides which chemical structure consists of a polar and non-polar end as shown in Figure 1.2 just like other coupling agents. This characteristic makes it possible to blend with the fibers which are polar and the LDPE plastics which are non-polar.

Table 1.2 Chemical Composition of coconut oil

Izyan et al., (2008) have worked on the effect of coconut oil as a coupling agent on the physical properties, swelling behaviour and morphology of silica-filled polypropylene composites. The incorporation of coconut oil coupling agent (COCA) in silica-filled polypropylene (PP) composites gave positive effect by improving tensile strength, elongation at break and Young’s modulus but reduced the water absorption resistance. Micrographs of tensile fracture surfaces of silica filled with PP exhibit that silica was covered by PP matrix as a result of better adhesion.

1.5.4    Cellulose fiber-reinforced plastic waste composites.

This section outlines some of the recent reports published in literature on the mechanical behaviour of some common plastics reinforced with cellulose fibers (wood dust and coir) to form composites through the action of coupling agents. Cellulose fiber-reinforced waste plastic composites have been used to develop new value-added products such as floor carpets, flower vases, waste paper baskets, park benches, picnic tables and plastic lumber as a way of recycling wastes.

Generally, cellulose fiber-reinforced waste plastic composites are made of a blend of plastics (high density polyethylene and polypropylene) and wood fiber, coir or other agricultural wastes as reinforcing filler. Many researchers like Chen et al., (2006),and Lee et al., (2010), have worked on various wood-plastic ratios which typically range between 50 to 80 % of sawdust or fiber either as filler or reinforcements (Clemons, 2002). The higher strength and aspect ratio of natural fibers offers good reinforcing potential in composite matrix compared to the artificial fibers (Abdul et al., 2014 and Clemons, 2008).

The interface between the non-polar plastics and the polar cellulose fiber waste is improved to ensure the transfer of stress between the two phases when loaded by a coupling agent. Typical coupling agents used in the process include anhydrides or organic acids. Fibrous composite materials typically have two or more distinct phases, which include high strength/stiffness reinforcing fibers and the encapsulating matrix material. Fibers can be either discontinuous (chopped) or continuous. Polymer matrices typically fall into two categories: thermoplastic and thermosetting polymers.

1.5.5    Natural fibre reinforced composite

Several bio based fibres such as wood, sisal, jute, flax, abaca, banana, oil palm, pineapple leaf, bamboo etc. have been studied as reinforcements for the preparation of composites. Natural fibres in composites materials act as load carrying material (reinforcement) imbedded in matrix. Reinforcement provides strength and rigidity, helping to support the structural load. The matrix or binder (organic or inorganic) maintains the position and orientation of the reinforcement. The constituents of the composites retain their individual, physical and chemical properties. In the past decade mechanical properties, processing technologies and the interfacial compatibility of cellulose fibre reinforced composites were investigated extensively. Use of natural fibres as reinforcement in thermoplastics and thermosetting matrix has a number of technological and environmental benefits. Natural fibre reinforced composites have been used in various fields such as aerospace, automotive, marine, infrastructure, military, etc. Natural fibres have certain advantages over traditional reinforcing materials such as synthetic fibres (glass fibre, carbon fibre, etc.) Natural fibre reinforced composite have specific properties such as easy availability, light weight, ease of separation, enhanced energy recovery, high toughness, non-corrosive nature, low density, low cost, good thermal properties, reduced tool wear, and respiratory irritation, cause less abrasion to processing equipment, renewability and minimize the environmental pollution. The tensile properties of composites have been improved by adding fibres to a polymer matrix. The mechanical properties such as elastic modulus and ductility of bio-composites increased substantially as compared to the neat polymers matrix. The mechanical properties of most of fibre reinforced composites increased with the increase in the amount of fibre in the polymer matrix. The fire performance of composite material has been improved by using additive type fire retardants. Additive type flame retardants are added to the composite material during processing. Flame retardants are present in many forms, although most suitable are particles or powders (Deo et al., 2008). Fibre reinforced composite materials not only act as effective insulators, but also provide mechanical support for field carrying conductors. Composite materials are increasingly used for dielectric applications. The electrical applications of composite materials have been determined in terms of dielectric constant, volume resistivity and loss factor. The composite materials find extensive applications in different areas, like in electrical industry as electrical insulation, encapsulation, multilayer ceramic chip and capacitors and for piezoelectric, ferroelectric, and pyroelectric devices that provide sensing, actuation, terminals, connectors, industrials and house hold plugs, switches, printed circuit boards etc. The incorporation of fibre to the polymer matrices is suitable for electrical applications. Jayamol et al., (1997) have investigated the electric properties of pineapple reinforced polyethylene composites. The increase in the dielectric constant of composite with fibre loading was due to increased orientation and interfacial polarization of cellulosic fibre. Thwe and Liao (2003) have studied the durability of bamboo fibre reinforced in polypropylene polymer matrix. The improvement in properties such as tensile strength and elastic modulus of bamboo fibre was observed. Rice husk was reinforced with polypropylene matrix and the flame retarding effect was studied (Sain et al., 2004; Deo et al., 2008). It was observed that magnesium hydroxide increased the flame retardancy of composites. Joseph and Thomas (2008) have investigated the electric properties of banana fibre and glass fibres reinforced phenol formaldehyde matrix. It has been observed that banana fibre reinforced phenol formaldehyde composite showed good electric properties as compared to treated and glass fibres. Arbelaiz et al., (2005) have studied the mechanical properties of flax fibre reinforced polypropylene composites. It was reported that the tensile strength and modulus of fibre reinforced composites depend on the fibre and matrix ratio. Jute fibre reinforced polypropylene matrix composites have been developed by hot compression moulding technique by varying parameters, such as fibre condition (untreated and alkali treated), fibre sizes (1, 2 and 4 mm) and percentages (5%, 10% and 15% by weight). The improvement in mechanical properties was observed with alkali treated fibres loading of 10% (Rashed et al., 2006). The water absorption and dielectric behaviour of polyester matrix composite of glass and jute fibre was investigated. The dielectric constant of jute fibre reinforced composite was found to be higher than glass fibre due of higher water uptake (Fraga et al., 2006). Panthapulakkal and Sain (2007) reported the mechanical and thermal properties of hemp and glass fibre reinforced polypropylene (PP) composite materials. It was observed that the hybrid composite material enhanced the flexural and impact properties. The addition of glass fibre into hemp-PP composites resulted in improved thermal properties as well as the water resistance. The tensile strengths of hardwood fibres reinforced with high density polyethylene (HDPE) composites increased gradually with fibre loading and reached to maximum at 25% (Facca et al., 2007). Singha and Thakur (2008) have synthesised the urea formaldehyde matrix reinforced with Hibiscus Sabdariffa fibres. Mechanical properties such as tensile strength, compressive strength, flexural strength, and wear resistance of the natural fibre reinforced composite increased with fibre loading. Li et al., (2009) reported the flax fibres (10% to 30% by mass) reinforced in high density polyethylene (HDPE) by extrusion and injection moulding to produce bio-composites. The results showed that increasing fibre content resulted in increased tensile properties. Kalia and Kaith (2008) synthesized the flax-g-copolymers reinforced phenol formaldehyde composites. The mechanical properties such as wear resistance, modulus of rupture (MOR), modulus of elasticity (MOE) and stress at the limit of proportionality (SP) were enhanced. The mechanical properties of microwave induced flax-g-copolymers reinforced composite was compared with flax-gcopolymer reinforced composites. Saleem et al., (2008) investigated the effect of pectinase treatment on hemp (Cannabissativa L.) fibres and studied their properties with polypropylene matrix based composites. The improved tensile and flexural property of these thermoplastic composites was recorded after treatment. The effect of hemp fibre content has been examined on the basis of tensile properties of the composite materials (Hajnalka et al., 2008). Khoathane et al., (2008) have reported the mechanical properties of bleached hemp fibre reinforced with 1-pentene-polypropylene (PP1) composite. The increase in the amount of hemp fibre resulted in the increase in the tensile strength of the composite. Mechanical and thermal properties of hemp fibres reinforced with polypropylene matrix were enhanced with the fibre loading (Kechaou et al., 2010). Sisal fibres reinforced polypropylene composites of different weight percent sisal fibre with or without maleic anhydride have been developed. Mechanical and dielectric properties of composites with and without MA-g-PP have been determined. The improvement in the mechanical and dielectric properties of composites was observed (Chand et al., 2008).Saccaharum cilliare and Grewia optiva fibre have been reinforced with urea formaldehyde resin. Mechanical properties such as tensile strength, compressive strength and wear resistance of urea formaldehyde composite was found higher. It has been observed that the particle reinforcement was more effective as compared to short and long fibre reinforcement (Singha and Thakur, 2009a; Singha and Thakur, 2009b). Long discontinuous natural fibres of kenaf and jute have been reinforced in polypropylene (PP) matrix with fibre weight fraction varying from 10% to 70% (Lee et al., 2009) . It has been observed that the tensile and modulus strength of both kenaf and jute fibre reinforced PP composites increased with fibre loading and found maximum at 30%. Oxygen index and cone calorimeter tests has been used to characterize the fire performance of wood polyethylene composites, and compared with the unfilled polyethylene and solid wood. Fire reardent such as magnesium hydroxide and ammonium polyphosphate improved the fire performance of wood polyethylene composites (Stark et al., 2010). Singha et al., (2011) have synthesized the Cannabis indica fibre reinforced composites. The Tensile properties of polyhydroxybutyrate (PHB) matrix and composite reinforced with sunn hemp (SH) fibre have been found to be 56 and 199 MPa, respectively. In case of fibre reinforcement with SH-g-poly(EA), SH-gploy(EA+MMA), SH-g-poly(EA+AA), the tensile strength of composites was found to be 315, 318, and 295 MPa, respectively (Kalia et al., 2011). Mechanical properties such as tensile strength (TS), bending strength (BS) and bending elongation (BE) of jute fibre reinforced low density polyethylene (LDPE) composites prepared by compression moulding of (10-30% fibre, by weight) was found more as compare to LDPE (Miah et al., 2011). Flame retardancy of urea formaldehyde (UF) board made from saw dust fibres has been investigated. Flame retardant chemicals such as boric acid (BA) and borax (BX) were incorporated with saw dust fibres. It has been observed that the highest concentration of BA+BX enhanced the fire retardancy of composites (Nagieb et al., 2011). Sisal-jute-glass fibre reinforced polyester composites was developed and their mechanical properties such as tensile strength, flexural strength and impact strength was evaluated (Ramesh et al., 2013). It was observed that the incorporation of sisaljute fibre with glass-fibre reinforced polymers (GFRP) improved the mechanical properties and used as an alternate material for glass fibre reinforced polymer composites. Brown grass flower broom fibre reinforced epoxy composites have been prepared (Dhal and Mishra, 2013). The dielectric properties (relative permittivity and loss factor) of pure epoxy resin and composites with different amount of broom fibre reinforced polymer composite have been studied in the frequency range from 100 MHz to 1 MHz. The results indicated that the dielectric constant and dielectric loss factor decreased with frequency. It may be due to the orientation polarization. The increase in temperature was due to greater movement of polar molecular dipole which appears to be beneficial in electronic industry.

1.5.5    Mechanical properties of cellulose fiber-plastic composites

Chtourou et al., (2009) have evaluated the mechanical properties of wood fiber–waste plastic composites. They have investigated the use of saw dust–waste thermoplastic composites for guard-rail posts on highways. Miller et al., (1998) have assessed the tensile strength of wood fiber–waste plastic composites with particular emphasis on coupling agents. Their results have shown that plastic wastes reinforced with cellulose fiber and appropriate coupling agents can be used to make composite materials with good mechanical strength. Lu et al., (2000) recently reviewed work done by some researchers who examined the mechanical properties of the composites and the effects of various coupling agents on the interfacial bonding between the fiber and the polymer; they have stated that the presence of a suitable coupling agent is crucial for the achievement of significant gains in the mechanical properties of these composites. Recently, bio-based wood polymer composites (WPC) have been receiving considerable attention due to their low processing cost, problem-free biodegradation, and improved physical, mechanical, and biological performance. Wood is mainly composed of three polymers, namely cellulose, hemicellulose, and lignin, with a minor proportion of extractives that is subject to biodegradation.

Monteiro et al., (2008) worked on reinforced coir fiber with polyester to form a composite and determined the structural characteristics and mechanical properties of the coir fiber/polyester composites.  Individually loose coir fibers were used in two distinct forms: tangled or pressed in mats with a thickness of 1.0 cm. The fibers were used untreated, except that they were dried at 50^oC for 24 h. Two kinds of coir fibers, tangled mass and pressed mats were used in this work. A commercially available unsaturated orthoftalic polyester resin with 1 wt % of methyl-ethyl-ketone as catalyst was used as matrix for the composites. After being thoroughly mixed, the resin was poured into the cavity of a steel mould, which was previously filled with a suitable amount of coir fiber. Composites with amounts of coir fibers ranging from 10 to 80 wt% were manufactured at two pressure levels, namely: 2.6 and 5.2 MPa. The cure was done under pressure at room temperature. As the fibers in any of the two configurations (tangled or mat) did not have a preferred orientation, the composites fabricated in the present work are considered as randomly oriented. Rectangular specimens 122 mm long, 25 mm wide and 10 mm thick were bend tested using the three-point bending procedure. The span-to-depth ratio was maintained constant at 9, and the minimum number of specimens used for each of the test conditions and coir fiber arrangements was 6. Before their incorporation in the composites, the coir fibers were analysed by scanning electron microscopy (SEM). The analysis was performed on gold-sputtered samples in a microscope, coupled with EDS, operating at a beam voltage of 15 kV.

Their results show that random oriented coir fiber–polyester composites have flexural strengths that enable their use as non-structural building elements. The low modulus of elasticity is attributed to their lack of an efficient reinforcement by the coir fibers, in comparison with that of the bare polyester resin.

1.5.6    Sawdust-polyethylene composite

Jae-Pil et al., (2012) experimented on sawdust–reinforced polyethylene (PE) (1:1) composites with ethylene–vinyl alcohol copolymer (EVAL) as adhesion promoter to improve mechanical strength. Linear low density polyethylene (LLDPE, Tm 122^oC; melt index 5 g/10 min; density 0.9 g/cm³) was used as matrix material. The saw dust used as wood filler was of the following particle size range and weight: 20–30 mesh

10 wt %, 30–60 mesh 80 wt % and 60–100 mesh 10 wt %. This wood was dried at 105⁰C for 12 hr. Ethylene–vinyl alcohol (EVAL) and vinyl-acetate (VA) was of the following content: 2, 8, 15 and 30 mol % were prepared from hydrolysis of ethylene vinyl acetate (EVAcs). Saw dust (50 wt % of composite with the exception of EVAL) was placed in a blender. EVAL (1–10 wt % of wood) was added and mixed at 60 rpm for 5 min at 160^oC. LLDPE was charged into the blender and mixed continuously for 10 min at the same temperature. The kneaded samples were moulded into films by hot-pressing with Carver Hot-Press. The samples were placed between a pair of Teflon films with a thin spacer. The temperature of the hot press was set at 160^oC. After heating for 5 min, the samples were sustained to 3.5 MPa pressing and allowed to stand at this pressure for 5 min. The samples were cooled to room temperature after subsequent cold pressing at the same pressure for 1 min.

The tensile properties of the composites were measured according to ASTM S 638 using an Instron tensile testing machine, model 4201 at room temperature and 50% relative humidity. The standard General Tensile Test Program method was used to evaluate the mechanical properties. The cross head speed was 10 mm/min and the reported properties were measured at yield point. The results were obtained from average of ten repeated measurements.

The EVAL copolymers containing various VA were found to be adhesion promoters for wood plastic composite. The EVAL coated saw dust–LLDPE composites had the improved mechanical strength as compared to the composites of uncoated saw dust. The results indicated that EVAL played an important role in improving the mechanical properties of LLDPE composites containing saw dust. The WPC prepared from EVAL coated saw dust and LLDPE had a good mechanical strength improved by hydrogen bonding between hydroxyl groups of saw dust and hydroxyl groups of EVAL. The fracture surface of EVAL-coated saw dust–LLDPE composites showed good adhesion.

1.5.7    Coir reinforced polyethylene composite

Arrakhiz et al., (2012) worked on HDPE with coir fibers of 20 cm length as reinforcement. Before use, the fibers were ground into small 2–3 mm length pieces, treated with sodium hydroxide (NaOH), acetic acid (CH₃COOH), dodecane bromide, and 3-(trimethoxysilyl) propylamine (C₉H₂₃NO₃Si). The crushed coir fibers were first washed with water and then kept for 48 h in a 1.6 mol/L sodium hydroxide aqueous solution. After removal of the fibers from the NaOH solution, they were treated with acetic acid (100 mL) to neutralize the remaining hydroxide after which they were air-dried for 24 h. 3 ml dodecane bromide was added to 5g of coir fibers and 20 ml of NaOH in isopropanol. The solution was vigorously stirred at room temperature for 12 h. The coir fibers were recovered by filtration, washed thoroughly with isopropanol and ethyl ether and then dried for 12 h at 50 ^oC.

A solution of 0.5 wt. % silane coupling agent 3-(trimethoxysilyl) propylamine was prepared in acetone. The pH of the solution was adjusted to 3.5 with acetic acid, after which the solution was stirred continuously for an additional 5 min. Fibers were immersed in the resulting solution for 45 min, after which they were dried at 65^oC for 12 h to initiate the chemical reaction between the fibers and silane coupling agent. The fibers were then thoroughly washed with water to remove chemical residues until a pH value of 7 was measured. The last step involved drying the fibers at 80 ^oC for 48 h.

Composites of high density polyethylene (HDPE) with 20 wt % of chemically treated coir fibers were blended using a heated rolls mill. Compounding of each 30 g composite batch was performed at 200^oC with the roll mill operating at 60 RPM for 3 min. Under these conditions, a homogeneous dispersion and distribution of the fibers was achieved in the HDPE matrix. The neat HDPE matrix was first filled in the heated mixing cavity while the mills were under constant rotational speed. After 30 s, the fibers were carefully added onto the melted HDPE and mixed for 3 min. At that point, the measured torque was found to be constant. The rolls were then stopped and the composite removed from the heated rolls before being cut into small pieces for hot press moulding. Hot press moulding was performed using a semi-automatic press with both platens heated to 190^oC. The sample being moulded was held for 30 s at that temperature under compression before being cooled to room temperature. The mould used was shaped according to (ISO 527-1 1993) for mechanical testing.

1.5.8    Oil Spill Clean-up.

Oil is the life wire of our today’s world. Oil is used to fuel vehicles, lubricate machinery, make plastics, heat homes, make plastics, inks, fertilizers, vanishes, paints, etc. The environment, however, has borne the brunt of oil exploration and transportation for several decades as oil spills have contaminated coastal waters and lands. Oil spill, though, usually applied to marine oil spills in which oil is released into ocean and coaster waters, it may also be on land. Oil spill may be due to releases of oil crude oil from tankers, offshore platforms, drilling rigs and wells, as well as spills of refined petroleum products (such as gasoline, diesel, etc.) and their by-products, heavier fuels, or the spill of any other refuse or waste oil. Oil and water do not mix. Upon spillage, the oil forms a thin and often a large layer on the surface of the water. Oil spills harm aquatic life. Fishes, birds, mammals and reptiles which consume the oil suffer serious health problems and furred animals exposed to the oil have their mobility and body temperatures affected (Teal et al., 1995). Most birds that are coated in oil would not survive if not cleaned. Plants growing in or near the water can be destroyed as the sunlight required for photosynthesis is blocked. This kills plant growing in the water. Thus, pollution resulting from oil spill adversely affects the economy, leisure and tourism (Hussein et al., 2008).

1.5.8.1 Current Methods of Oil Spill Clean-up

• Containment with Oil Booms
• Chemical Dispersant
• Bioremediation
• Mechanical Recovery

1. Skimmers
2. Burning

• Sorbents

Sorbents

Sorbents are solid porous materials obtained from organic and synthetic sources employed for recovering oil in preference to water. Sorbent materials can act either by adsorption or by absorption. In adsorption, the oil is preferably attached to the surface of the adsorbent while in absorption, the oil incorporated into the body of the material. The sorbent is required to attract oil in preference to water i.e. it should be oleophilic and hydrophobic. This research centers on the synthesis of a porous material for oil spill remediation. As such, much effort would be devoted to the review of previous works on the synthesis and characterization of sorbents for oil spill clean-up.

1.5.8.2 Porous Materials for Oil Spill Remediation

The application of sorbent materials is of interest due to the possibility of complete collection of oil from the spill site. These porous materials have an added advantage of possible recycling. Properties of good absorbent materials include hydrophobicity and olephilicity, high uptake capacity, high rate of uptake, retention time, oil recovery from absorbents and the reusability and biodegrability of the absorbents (Adebajo et al., 2003). Therefore, to combat environmental pollution resulting from oil spill, there is a need to deepen research in the area of developing effective sorbent materials for oil spill remediation.

1.5.8.3 Oil Sorption Phenomenon

Sorption is commonly used for both absorption and adsorption. Absorption is the incorporation of a substance from one state into another (e.g. liquid being absorbed by a solid or gases absorbed by water). Adsorption is the physical adherence or bonding of ions and molecules into the surface of another molecule. An adsorbent is a porous solid material that is coated by a liquid on (Placeholder2) (Kenneth, Geoffrey, Hartmut, Ralph, & Wolfgang, 2005) (Chung, 2010) (Kaiser & Wolfgang, 2011) (Jayamol, Bhagwans, & Thomas, 1997)its surface including pores and capillaries without more than 50% in excess fluid (Karan et al., 2011). In the process of adsorption, the adsorbate diffuses from the bulk stream to the external surface of the adsorbent, from where it migrates to the pore and finally adheres to the pore sites via van der Waals forces through physical adsorption or by chemical adsorption which is due to electron exchange among adsorbate and surface of adsorbent. In absorption, the adsorbate permeates the body of the adsorbents. The driving force in this case is the capillary pressure gradient between the adsorbate and the adsorbent.

1.5.8.4 Classification of Oil Sorbents

According to Adebajo et al., (2003), porous absorbents for oil spill remediation can be categorized into three major class namely inorganic mineral products, synthetic organic products and organic vegetable products. Many organic or natural sorbents have been investigated for their possible use as adsorbents. Examples include barley straw (Hussein et al., 2009), cotton (Hussein et al., 2011), kappok, milk weed, rice straw and peat (Choi, H.M and Kwon, H. 2009). Researches have shown that these natural sorbents are biodegradable, economical but have poor buoyancy, low hydrophobicity and relatively low sorption capacity (Adebajo et al., 2003). However, it has been reported that some of these natural sorbents such as kapok fibre, milkweed, cotton fiber and kenaf core have shown to sorb more oil than polypropylene materials that are normally used commercially (Radetic et al., 2008). Synthetic organic products are the most commonly used commercial sorbents in oil spill clean-up application. Examples include polypropylene and polyurethane. Polyurethane is said to have a sorption capacity of about100 times its weight of oil from oil-water mixture (Adebajo et al., 2003). They are highly oleophilic and hydrophobic. Polypropylene non-woven sorbents have high oil sorption capacity and low water uptake (Karan et al., 2011). The limitation of synthetic organic sorbents is their non-biodegradability. As such, disposing them in landfills and through incineration causes another form of pollution or is too expensive. The mineral products employed as oil sorbents include silica aerogels, organoclays, exfoliated graphite, zeolite, pertite, vermiculites and diatomites. CF3-modified silica aerogel, which, according to Reynold and co-workers (2001), is very hydrophobic, completely absorbs oil at oil/aerogel ratio of up to 3.5. Hydrophobic pure-silica zeolite has equally given a good sorption of oil (Adebajo et al., 2003). Poor biodegradability, poor buoyancy and oil sorption capacity are the limitations of mineral sorbents (Karan et al., 2011). However, Adebajo et al., (2003) suggested the blending of these mineral products with other materials like cotton wool and activated carbon to enhance their performance.

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