JEC COMPOSITES MAGAZINE - Issue #46 - January/February 2009 - 40

FEATURE “Natural fibres” bond between the wood fibres and the polymer matrix, the coupling agents significantly increase the flexural strength and stiffness, dimensional stability and impact resistance of woodplastic composites. Bonding agents also reduce material creep and water absorption. Under the trade name Licocene®, Clariant offers highperformance waxes produced with metallocene catalysts. The sandwich-like molecular structure of the metallocene catalysts can be modified as needed, making it possible to synthesise waxes that are perfectly tailored to a particular application. A newly launched product is the top-of-the-line Licocene® PP MA 7452 TP a bonding agent grafted with MAH that generates , excellent results in polypropylene compounds in terms of mechanical properties, water absorption, and processing behaviour. An economical alternative is Licocene® PP MA 6452 TP which has a lower drop point than Licocene PP MA 7452 TP , while also offering good results in polypropylene compounds. In polyethylene composites, Licocene® PE MA 4351 TP a MAH, grafted polyethylene wax with high polarity, provides outstanding results. Its low melting viscosity, producing optimal wetting of the natural fibres with the coupling agent, supports the high effectiveness of the product. g…/… Jazz up your WPC: additives improve WPC mechanically and visually and UV stability, reduced water absorption and improved dimensional stability are just a few of the goals that the WPC industry is pursuing. Additives amount to only 2-4% of the total weight in a typical composite. However, it is the judicious selection of additives that gives WPC their superior profile. Depending on the individual application, almost all additives established in the plastics industry are also used as additives in WPC, including UV stabilisers, lubricants, impact modifiers, pigments, coupling agents, and odour absorbers. The Pigments & Additives Division of Clariant offers a comprehensive portfolio of special additives for WPC, which are continuously developed in close cooperation with WPC processors. Tailored lubricants Waxes or wax-like products used as lubricants are also crucial WPC additives. These additives usually consist of fatty acid derivatives, montanic wax esters, polar and non-polar polyolefin waxes, or amide wax, and fulfil diverse functions. Adding suitable lubricants has a positive impact on the surface quality of WPC components. Among other things, lubricants facilitate mould release, influence the flowability of the plastic molten mass, and serve as a compatibiliser between the fibre and the plastic. The use of an appropriate lubricant, such as a Licomont® ET 141, Licolub® H 12 or Licolub FA 6 TP gives natural fibre, reinforced composites a smooth, high-quality surface. The products also reduce the tool cavity pressure, which increases the throughput. And, finally, materials to which these additives have been added absorb less water and show less swell. To protect WPC components from exterior influences, light stabilisers and flame retardants are also usually added. Additional high-quality additives, such as pigments for attractive colouring and odour absorbers, make it possible to combine two highly different materials - wood and polymers - into a firstclass material with an excellent property profile. Current applications include outdoor flooring and stairway railing, furniture and high-quality automotive products. Continuous product improvements will open additional markets worldwide, help WPC become established as a material using mainly renewable resources, and open up new and interesting perspectives and unexpected possibilities. More information: www.clariant.com Contact: beate.treffler@clariant.com The demand for natural fibres as reinforcement for composites is on the rise. Coupling agents and compatibilisers Interface adhesion is of special importance in natural fibrereinforced plastics, because only a limited fibre length is available in the composite for stress transmission. To maximise stress transmission between wood fibres and the plastic matrix, it is indispensable to add agents that improve bonding and compatibility, also referred to as “coupling agents”. Stress is transferred as shearing stress from the matrix to the fibres. If the fibre-matrix bond is weak, it will cause sliding friction of the fibre composite at the interface. This will lead to a shift between fibre and matrix, and eventually, under increasing stress, to fibre pullout and a premature failure of the composite. The quality of the fibre-matrix bond depends on the formation of both chemical and physical bonds (Van-der-Waal forces and entanglements). Comprehensive tests have demonstrated that maleic anhydride (MAH)-functionalised polyolefins significantly improve the mechanical and physical properties of WPC. Polypropylenes grafted with MAH have non-polar areas and polar functional groups that react with the hydroxyl group of the wood, forming covalent ester bonds. The newly formed carboxyl groups (-COOH) can form hydrogen bonds with the free OH groups of the wood. The non-polar areas have a strong affinity with the hydrocarbons of the polyolefin chain. Acting as a connecting 40 jec composites magazine / No46 January-February 2009

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

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