Composite Materials from Natural Resources: Recent Trends and Future Potentials

Composites are combinations of two or more than two materials in which one of the materials, is reinforcing phase (fibres, sheets or particles) and the other is matrix phase (polymer, metal or ceramic). Composite materials are usually classified by type of reinforcement such as polymer composites, cement and metal-matrix composites (Chemical and Materials Engineering Department, home Page 2011; About.com, home page, 2011). Polymer matrix composites are mostly commercially produced composites in which resin is used as matrix with different reinforcing materials. Polymer (resin) is classified in two types thermoplastics (polyethylene (PE), polypropylene (PP), polyether ether ketone (PEEK), polyvinyl chloride (PVC), polystyrene (PS), polyolefin etc.) and thermosets (epoxy, polyester, and phenol-formaldehyde resin, etc.) which reinforces different type of fibre like natural (plant, animal, mineral) and man-made fibre for different application. In metal matrix composites, metal is one of important part of element and other part may be metal, ceramic or organic compounds. Cement matrix composites are made up of cement and with aggregate and basically used in building applications. Due to increase in population, natural resources are being exploited substantially as an alternative to synthetic materials. Due to this, the utilization of natural fibres for the reinforcement of the composites has received increasing attention. Natural fibres have many remarkable advantages over synthetic fibres. Nowadays, various types of natural fibres Natural fibres are largely divided into three categories depending on their origin: Mineral based, Plant based, and Animal based. In general, a mineral based composite is asbestos and is only a naturally occurring mineral fibre (silicate based mineral). In 2006, 2.3 million tones of asbestos were mined worldwide. Russia was the largest producer with about 40.2% world share followed by China (19.9%), Kazakhstan www.intechopen.com Advances in Composite Materials -Analysis of Natural and Man-Made Materials 122 (13.0%), Canada (10.3%), and Brazil (9.9%) (Wikipedia, home page, 2010). The main properties of asbestos fibres are their thermal, electrical, and sound insulation; inflammability; matrix reinforcement (cement, plastic, and resins), adsorption capacity, wear and friction properties (friction materials), brake linings and chemical inertness (except in acids). Asbestos fibres are often mixed with cement or woven into fabric or mats/ sheets (Britannica home page, 2011; Plant-based natural fibres are ligno-cellulosic in nature composed of cellulose, hemicellulose, and lignin, whereas animal based fibres are of proteins, e.g., silk and wool. Natural fibre-reinforced polymer composites have attracted more and more research interests owing to their potential as an alternative for synthetic fibre composites such as glass or carbon fibre composites Natural fibre composites posses the advantages such as easy availability, renewability of raw materials, low cost, light weight and high specific strength, and stiffness. It is expected that in the near future biodegradable polymers will replace synthetic polymers, at least in some specific applications where a short life of the product will be more desirable. Natural polymers are considered suitable to replace synthetic ones in some specific applications where a long span life is not required. Natural fibre thermoplastic composites are relatively new family of composite materials. In such composites, a natural fibre/filler (such as kenaf fibre, wood fibre, hemp, sisal etc.) is mixed with a thermoplastic (e.g., polyethylene, polypropylene, PVC etc.) to produce the composite. In the last few years, thermoplastics as well as thermosetbased natural fibre composites (NFCs) have experienced a tremendous growth in the auto industry due to environmentally friendliness, renewability of these fibres, good sound abatement capability, and improved fuel efficiency resulted from the reduced weight of the components. These composite materials have received much commercial success in the semi-structural as well as structural applications. For example, interior parts such as door trim panels from natural fibre polypropylene (PP) and exterior parts such as engine and transmission covers from natural fibre-polyester resins are already in use in auto industry. Advantages of thermoplastic NFC over thermoset-based NFC include the greater design freedom as they are suitable for injection molding and extrusion processing in addition to the recycling possibilities.

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