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New options in natural-fiber reinforced composites. (Keeping Up with Composites).

Two new developments in natural-fiber reinforced polypropylene composites could expand their range of applications in automotive parts.

Improved wood fibers

Rayonier in Jesup, Ga., has developed a high-purity cellulose fiber derived from local hard and soft woods. What makes the 1- to 2.2-mm-long, 20- to 40-micron-diam. TerraCel wood fibers different is their high (95% or above) content of pure alpha-cellulose. Generally, wood contains less than 50% alpha-cellulose together with lignin and other components that impair the fibers' physical and thermal properties.

John Underwood, Rayonier's market-development manager, says a 30%-reinforced PP composite using these wood fibers can achieve stiffiness exceeding that of mineral-filled PP and approaching short-glass reinforced compounds. In Europe, TerraCel composites are in advanced testing by independent compounders for automotive OEMs. The fibers have a density of 1.25 to 1.5 g/cc, which typically is more than 50% lighter than glass or mineral reinforcements. In addition, the fibers are non-abrasive, resistant to breakage in numerous reuse cycles, and free of residual ash when incinerated.

Equally important, the high cellulose level in Rayonier fibers boosts their ability to resist degradation up to around 527 F. Conventional wood flours and fibers typically withstand no more than 392 F. Consequently, conventional wood reinforcement has been largely restricted to PP matrix materials.

Rayonier's wood fiber is being used at 30% levels in nylon 6, which has a melting point of around 437 F. A modified screw design keeps peak temperatures below the fibers' degradation point. "Nylon 6 broadens the potential of fiber-reinforced compounds in more severe end-uses," Underwood claims. He says compounders are also developing 30% wood/mineral-filled nylon 6 hybrid compounds as potential replacements for mineral- and short-glass reinforced compounds in under-the-hood and semi-structural applications. Tel: (912) 427-5000,

Mold decorative panels

Meanwhile, Cannon Tecnos in Milan, Italy, has manufactured a complete production system (photo) for compression molding decorative auto-interior parts using a flax-reinforced PP sheet. Tecnos proposes this material as an alternative to conventional GMT sheet. Initial commercial use is a six-piece trunk liner molded in a single shot for Audi in Germany.

Carlos Ortenzi, Tecnos' market manager, says the sheet is a sandwich of a PP core and flax-reinforced PP skins. Tecnos' system introduces the preheated flax/PP sheet into the press simultaneously with two outer layers of a printable polyester non-woven rollstock that is cold-fed into the system without contacting the PP sheet prior to molding.

The double-acting press has movable upper and lower platens to improve the balance of flow in the mold. Tecnos supplies the press, preheating oven, automatic sheet-feeding and centering equipment, unwinding stations, and automatic roll-change systems for the decorative rollstock. The line produces six parts a minute. Tel: +39 331 406811,
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Publication:Plastics Technology
Date:Apr 1, 2002
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