JEC COMPOSITES MAGAZINE - Issue #46 - January/February 2009 - 39

Additives Jazz up your WPC: additives improve WPC mechanically and visually Modifying polymers with additives and colorants has always been an important innovation issue in the plastics industry. In fibre-reinforced plastics, conventional inorganic fillers such as chalk, talcum, glass, aramid, and carbon, as well as natural fibres were used initially. Then, following decades of falling material prices and the wider availability of technical reinforcing fibres, natural materials were relegated to second place. However, in view of the increasing environmental awareness and the search for resource-saving alternatives, the situation has now changed fundamentally. The demand for natural fibres as a reinforcement for composites is on the rise. thereof, are the most commonly used for wood fibres in Europe. In other regions of the world, rice hulls and peanut shells, aloe hemp, cotton, rubber tree, oak, and maple are used. The wood content of wood fibre-reinforced plastics ranges between at least 50% to a maximum of 90%. WPC are processed using standardised thermoplastic moulding methods, such as extrusion, injection moulding, or hot pressing, all of which require minor adjustments to fit the properties of each material. The standard methods must undergo several technological changes to suit WPC, for several reasons: the very low bulk density of the wood chips, which are incorporated into the polymer matrix in large quantities; large amounts of water vapour forming in the process because of the high equilibrium moisture content of wood (10%); and, last but not least, the difficulty of filling the highly viscous molten mass evenly into the profile tools. BEATE TREFFLER, TECHNICAL MANAGER WAXES, CLARIANT PRODUKTE (DEUTSCHLAND) GMBH ood Plastic Composites (WPC) are a special type of natural fibre-reinforced composite. Using wood fibres offers ecological, economic, and technological benefits. Compared to wood, WPC give designers more flexibility because the parts can be shaped three-dimensionally, and they also have better moisture resistance. Compared to plastics, WPC offer superior stiffness, and a significantly lower thermal expansion coefficient. Wood, like any other organic material, has only limited thermal resistance. This makes polymers with a melting/processing temperature of under 200°C the best choice for WPC. In the case of a polymer with a higher melting temperature, the wood fibres would undergo thermal decomposition, even with short processing times. This rules out the use of many polyamide, polycarbonate and polymethyl methacrylate materials as a matrix for WPC. Worldwide, the matrix materials used are almost exclusively thermoplastics, such as polyethylene (65%), polyvinylchloride (16%), polypropylene (14%) and polystyrene (5%). In Europe, polypropylene is by far the most commonly used matrix material for WPC, at 82%. For more convenient dosing, the wood component is often added in the form of pellets. Different types of loose fibres are also available on the market, differing in their fibre geometry and type of wood. Due to their ample availability and reasonable price, soft woods such as pine, spruce or cedar, or mixtures W Economics and applications The WPC market has developed rapidly over the recent years, especially in the United States and Japan, where it recorded an annual growth rate of more than 25%. With an annual production of 70,000 metric tons, the European market is considerably smaller than the North American one, which accounts for over 700,000 metric tons annually. WPC applications with a very large market volume in the United States, such as decks, are still underdeveloped in Europe, including Germany. However, the European WPC industry is becoming more and more successful in finding suitable applications for WPC. Applications such as injection-moulded furniture or automotive components will give the production volume a tremendous boost. To fulfil the high requirements of these applications, WPC needs to be improved on different levels. Improved impact resistance No46 January-February 2009 / jec composites magazine 39

JEC COMPOSITES MAGAZINE - Issue #46 - January/February 2009

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #46 - January/February 2009