Extrude profiles using wet sawdust.

Extruding profiles of recycled PP with up to 85% wood flour is a tough job. It's even harder using unsieved sawdust direct from a sawmill that contains 50% moisture. One machine that's up to the task is the conical-rotor Conex extruder developed in the 1990s by Nokia Maillefer in Finland. As the grooved rotor turns, steam vents out the top, and water runs out the bottom. Residence time for mixing is short, and the fibers orient in the machine direction. Test runs on a 380-mm (rear diameter) Conex machine with 44-lb/hr capacity produced a hollow rectangular profile, 60 x 40 mm with 8 mm thick walls, using 2% acid amide lubricant and 2% maleic anhydride-grafted polyolefin coupling agent.

The tests were conducted by Conenor Ltd., Lahti, Finland, which builds the Conex, and VTT Processes, a research group in Tampere, Finland. They reported the results last month at the Woodfibre-Plastic Composites Conference in Toronto, sponsored by the U.S.D.A.'s Forest Products Laboratory in Madison, Wis., and the University of Toronto. Conenor: [phone]/PTDirect. 612FD * VTT Processes: [phone], www.vtt.fi