Wood-plastics composites | applications The latest research in wood-plastic
composites (WPCs) encompasses the entire range of the industry, from alternative materials to new applications. Lou Reade reports
Putting wood to good use: WPCs
Wood-plastic composites (WPCs) have come a long way since they were introduced to the US decking market in the 1990s, and are now the subject of intensive research and development across the board – in materials, machinery, tools and processing. In Europe, Battenfeld-Cincinnati and the Kompeten- zzentrum Holz (Wood K plus) research institute are to extend their WPCs co-operation agreement that stretches back to 2008. The agreement, part of the Comet program organ- ised by the Austrian Research Promotion Agency FFG, will now be extended for another eight years. Battenfeld-Cincinnati has overhauled the FiberEx 38
WPC extrusion line used by Wood K plus, allowing more fl exible methods of processing materials with natural fi bre content to be realised – in both one- and two-step processes. The latest line has an optimised screw geometry and a new degassing unit. The degassing unit prevents the release of dust particles from the process chamber. Many projects have already been implemented under
the agreement, including: research into alternative fi bre materials – such as cork, bamboo, hemp and straw; testing of innovative processes such as WPC foaming; and investigating whether conventional fi breboard could be replaced by WPCs.
Die improvements Researchers at the Institute for Polymers and Composites at the University of Minho in Portugal have used numeri-
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cal research to improve the fl ow balance of a die – in this case for extruding wood-plastic composites (WPCs). “Minimising dependence on the designer requires
fully automatic design schemes in which optimisation software makes the most important process decisions and corrects the geometry without any user interven- tion,” said the researchers, whose work was published in Polymer Engineering & Science. “Such design of profi le extrusion dies is still in its infancy stages.” The researchers built two extrusion dies – a trial die and an optimised die. This was done for two reasons: fi rstly, two experimental case studies allowed more extensive validation of the numerical code; and secondly, it allowed better evaluation of the benefi ts obtained from a properly designed extrusion die. They then extruded a WPC profi le with four hollow zones – which were created using four ‘torpedoes’ in the die. A WPC formulation using 50% wood particles was run through the die at 190˚C. The researchers used a numerical modelling code based on the fi nite volume method (FVM) to model the process. For optimisation reasons, the geometry of the
parallel zone was divided into 15 elemental sections (ESs), so that local average velocity could be monitored. The aim was to achieve the correct fl ow rate in each section. Modifi cations to the die parallel zones were made by changing the dimensions of the torpedo cross sections – so the external contour of the fl ow channel was not modifi ed.
June 2016 | COMPOUNDING WORLD 69
Main image: The link-up between
Battenfeld- Cincinnati and Wood K plus has investi- gated many concepts in WPC
processing and production
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