Demand for wood/plastic compounds is rising worldwide, though European demand has lagged. This appears set to change, with interest high in applications that replace existing fillers or reduce costly plastics’ use by adding natural fibers.

The path forward is not without obstacles though, with Peter Sauerwein, director of the Association of German Wood Industries, noting prices for wood flour have jumped by 30% in the last year. But Machael Carus, area manager for renewable resources at the Nova Institute (Hürth, Germany), which late last year organized the second Wood Plastics Composites (WPC) Congress in Cologne, Germany with more than 350 participants, says WPC demand is on the rise in Europe. Just three years ago Germany produced only 5000 tonnes/yr of WPC; last year Europe was expected to produce 100,000 tonnes, of which 20,000 tonnes came from Germany. By contrast, he says North American WPC production in 2005 was more than 700,000 tonnes and is expected to reach 1.6 million tonnes by 2010.

One reason for slower growth in Europe has been that quality standards only now are being put into place, he says. European compounders mostly use virgin-pine wood flour rather than lower-cost and -quality recycled wood, which can contain creosote or other impurities. Kersten Kurda from the South German Plastics Center (SKZ; Würzburg, Germany) says European WPCs typically use polypropylene (PP) as the WPC matrix rather than high-density polyethylene (HDPE), traditionally used in North America, or PVC in Asia. Kurda says European WPC processors want to substitute their traditional glass-fiber, talc, and chalk fillers with wood flour in PP applications. PP matrices make up 82% of the total European WPC market today, reports the SKZ.

The sector is seeing new developments that could help speed WPC growth. Agrolinz Melamine International (AMI; Linz, Austria), part of the Borealis Group, introduced what it says is the first extrudable modified melamine resin, HIPE®ESIN MPER, for use on conventional extruders.

The thermoset can include up to 70% wood fibers/flour. The company claims this mix overcomes some of the shortcomings of conventional thermoplastic-based WPCs, such as low thermal stability, by combining thermoplastic processing behavior with thermosets’ product performance. The material can be processed on conical counter-rotating twin screws, but with an inverse temperature profile; extruded profiles cure and crosslink while passing through a heated die. Andreas Endesfelder from AMI says end products have higher scratch resistance than thermoplastic WPC parts, plus good mechanical properties and dimensional stability at high temperatures.

PVC supplier Wacker Polymers (Burghausen, Germany) now markets a Vinnex-brand vinyl acetate/ethylene resin powder that can be extruded with wood flour to produce flexible profiles for furniture or for adhesive-backed wall baseboards. This binding resin/natural-fiber extruded material has a wood look, and processes on existing extruders without major changes.

Also, Holland Colours (Apeldoorn, Netherlands) has developed specialty dust-free natural colorants for pigmenting thermoplastic WPC profiles. The additives reduce edge tear, and the company says they permit faster color changes compared to traditional masterbatches.

On the equipment side, underwater pelletizer manufacturer Gala Kunststoff und Kautschukmaschinen (Xanten, Germany) offers a system that avoids moisture absorption during underwater pelletizing of WPC granulate. Gala developed a WPC two-phase flow pelletizing process, i-heat, that reduces the water contact time of the WPC pellet, and through a hot-air injection system strips the moisture from the pellet surface to produce dust-free pellets with no surface tack. The system permits a broad range of base polymers to be used with natural filler content up to 75%.