The properties of OPW fibres make them suitable for the manufacture of composite biopolymers (e. g. plastics). The pores on fibre surface have an average diameter of 0.07 m which gives it a better mechanical interlocking with matrix resin in compos­ite fabrication (Sreekala et al. 1997) . Also, the high cellulose content and high toughness value of OPW make it suitable as composite materials. Lignocellulosic materials such as OPW have the potential to replace synthetic fibres such as aramid and glass fibres in the field of composite material. Though the fibres of lignocellulosic materials have lower density (1.25-1.50 g/cm3) compared to that of fibre glass (2.6 g/cm3), they have high tensile strength similar to those in plastic materials and durable compared to synthetic fibre glass (Agrawal et al. 2000). Also, the high car­bon and nitrogen contents of palm oil liquid wastes make them suitable for the production of biopolymers for composite materials. Nowadays, fibre-reinforced plastic composites (bioplastics) find many applications in the aerospace and auto­motive industries, sports and recreation equipment, boats, office products, machin­ery, etc. (Sreekala et al. 2002).

Polyhydroxyalkanoates (PHA) made from OPW are green biodegradable materi­als widely used as packaging materials though the cost of production is found to be high. However, through improved process technology (Purushothaman et al. 2001), PHA have been synthesised from OPW by various means using different kinds of bacteria and have many applications in the polymer industry. A two-stage process for the production of PHA from POME has been proposed by some authors in which organic acids (such as acetic and propionic acids) were anaerobically pro­duced (Nor’Aini et al. 1999; Phang et al. 2003; Sim et al. 2009) and converted to PHA by a phototrophic bacterium, Rhodobacter sphaeroides IF0 12203 (Hassan et al. 1996) and Comamonas sp. EB 172 (Mumtaz et al. 2010; Zakaria et al. 2008). Other authors have reported the synthesis of PHA from EFB (Dovi et al. 2009).

Polyhydroxybutyrate (PHB) and polylactate (PLA) are other bioplastics that can be synthesised from both the solid and liquid residues of the OPW. During PHB pro­duction, the OPW is fermented to produce acid which is further fermented to produce the polymer using various enzymes. In PLA technology, sugar is produced from the OPW and fermented into l-lactic acids which are polymerised into PLA resins.

OPWs have also been used in many composite materials including OPW/natural rub­ber (NR) composites, OPW/polyvinyl chloride composites, OPW/polypropylene (PP) composites, OPW/polyurethane (PU) composites, OPW/polyester composites, OPW/ phenol formaldehyde (PF) composites, OPW/polystyrene (PS) composites and OPW/ epoxy composites. Polyurethane (PU) composites filled with EFB were prepared using molasses and glycerol-based polyols (Tay et al. 2011) and diphenylmethane diisocya­nate and polyethylene glycol (Rozman et al. 2004) matrices. Both reports concluded that good quality PU composites were produced with higher tensile and flexural properties.

The chemical resistance, void content and tensile properties of EFB/jute (natural rubber) composite have been investigated by Jawaid et al. (2011) to be good. The tensile strength of PPF/natural rubber composites as reported by Joseph et al. (2006) and Jacob et al. (2004) is in accordance to the ASTM D 412-68 Standards. It is inferred from their reports that the tensile strength of PPF/NR composite was higher (7.28 MPa) compared to that of PPF/Sisal/NR composites (3.25 MPa).

Lignin obtained from EFB was used as curing agent in green epoxy composites (Kalam et al. 2005) with the conclusion that the EFB/epoxy composite with 25% EFB-based lignin content gave the optimum properties (Abdul Khalil et al. 2011). Synthesis and physico-mechanical properties of OPW fibre-reinforced epoxy composites have been reported by various studies (Kalam et al. 2005; Bakar et al. 2007; Hariharan and Khalil 2005) with conclusions that they possess better charac­teristics compared to pure epoxy materials.

Benzene diazonium salt has been used in treating OPW fibre to be used as OPW fibre/polypropylene composites (Haque et al. 2009) whose properties are almost similar to coir fibre/polypropylene composites. Other potential applications of PP hybrid composites with OPW include EFB/glass fiber/PU composites (Rozman et al. 2001); EFB/PU, oil palm cellulose/PU composites (Khalid et al. 2008); PPF/ PU composite in which the addition of coupling agent in the makes it a promising bio-product as the addition of fibers to the matrix improved the flexural strength and modulus compared to the pure PP (Goulart et al. 2011); PPF/kaolinite/PU composite (Amin and Badri 2007) and EFB/PU composite (Rozman et al. 2007).

The mechanical properties of benzoylated EFB reinforced poly(vinyl chloride) composites have been studied by Bakar et al. (2007) with improved EFB/PVC matrix interfacial adhesion. Thevy et al. (2008) have reported that the thermogravi­metric analysis (TGA) have not shown any significant changes in the thermal stabil­ity of the composite.

Saline — and alkali-treated PPFs have been used in the synthesis of green compos­ites (PPF/phenol formaldehyde composite) in which the pretreatments increased the thermal stability of the composites compared to untreated PPF (Agrawal et al. 2000). Other authors (Sreekala et al. 2002) have also investigated into the mechani­cal properties of OPW fibre-reinforced phenol formaldehyde composites. Dynamic mechanical analysis of OPW fibre/PF composite carried out by Sreekala et al. (2002) showed that the incorporation of OPW fibre increased the modulus and damping characteristics of the pure sample.

The tensile strength of OPF/glass fibre-reinforced polyester composites increased up to total fibre content of 45% (Abdul Khalil et al. 2007). The weight loss on abra­sion of pure polyester resin is reduced (by 50-60%) by the reinforcement with OPW fibre, whilst the friction coefficient of OPF/polyester composite is reduced by about 23% compared to that of neat polyester (Yousif and Tayeb 2007). The tensile stress of OPF/polyester composites increased slightly upon both acetylation and saline treatments and decreased with titanate treatment (Hill and Khalil 2000).

The modulus of OPW fibre/PS composite is assessed to increase with increase in fibre loading up to 30% whereas the maximum strain and flexural strength decreased (Zakaria and Poh 2002).

Biopolymers such as poly(3-hydroxybutyrate-co-3-hydroxyvalerate) from EFB (Salim et al. 2011) and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) from spent palm oil using Cupriavidus necator (Rao et al. 2010) have also been synthesised using various treatment methods. Alkali treatment is the commonest pretreatment of OPW fibres which is able to improve the fibre-matrix interfacial adhesion.