materials feature | Wood-plastic composites
Liquid compatibilisation A Finnish PhD student has discovered that liquid by-products from the wood industry could be used as additives in the manufacture of wood-plastic compos- ites (WPCs). Taneli Väisänen, of the department of applied physics at the University of Eastern Finland, has also devised a way in which the liquids can be incorporated into the material. Additives are an important factor in WPCs, and help
Liquid by-prod- ucts from the wood industry could be used as compatibi- lisers in the manufacture of WPCs
into profiles – including siding profiles. The team also compounded a number of formula- tions using the rice husks, which was used to make thick insulating board and trialled at Beologic’s facilities in Belgium. “Complete testing of siding profiles, including construction, is now underway,” he said.
Laser focus Starrett-Bytewise, a specialist in dimension measure- ment technology, said that in-process inspection of WPC profiles could help to boost quality. Jim Williams, sales director, said there were a number of concerns with current periodic measure- ment techniques such as callipers, fixtures and off-line comparators. These included: whether they truly describe the process; whether they capture out-of-spec parts; whether they are operator dependent; and, whether they are capable of capturing area and embossing depth. “In an off-line operation, 10 operators will typically take
10 different measurements with a calliper,” said Williams. This, he says, has a huge effect on repeatability.
Using callipers, four parts that each require two or three critical measurements will mean 21 measure- ments being taken – seven each, by three different operators. In comparison, a laser measurement system such as Starrett-Bytewise’s Profile360 will take 25 identical measurements in each place. While the callipers will have an average measure-
ment range of 0.0129in, that of the laser measurement system is 0.0013in. “This is an improvement by a factor of 10,” he said. By allowing producers to run much closer to
specifications helps them save on materials costs, he said – estimating that a typical WPC decking board running at 12ft/min would be made around $1,100/day more cheaply, or more than $385,000 in a whole year. “Payback time is around one month,” said Williams.
14 PIPE & PROFILE EXTRUSION | November/December 2016
to enhance the compatibility of the wood and plastic constituents. Additives are also used to improve water-absorbing and weather resistance properties, among other things. However, some additives are expensive and they are
difficult to incorporate into WPCs – which is why Väisänen has been looking for new additives based on renewable resources. In his study, liquid by-products from biochar
production and heat treatment of wood were added to WPCs, and their effects analysed. The findings show that the liquids can be added to
WPC granulates using a method developed by Väisänen. Material samples were very homogeneous. Further- more, addition of the liquids reduced the water absorption of the composites and in some cases improved mechanical properties. The study also discovered that adding the liquids
increased the amount of volatile organic compounds (VOCs) released from WPCs – though the emission levels of harmful compounds did not increase to a level that would be hazardous, said Väisänen. He also identified that proton-transfer-reaction
mass-spectrometry (PTR-MS) was a suitable method for measuring the VOC levels released. The advantages of the method include a short analysis time and the opportunity to monitor the release of VOCs in real time.
Graphic detail Researchers at the University of Minho in Portugal have used graphics processing units (GPUs) to improve the process of designing complex profile extrusion dies – including ones for WPCs. The time needed for this type of calculation is
normally long, but the researchers parallelised the numerical code in the GPU using a simple programming approach, that required no complex memory manipula- tion. To verify the method, simulations were performed in three benchmark problems. The code was used to design two real-life extrusion dies – to make a medical catheter and a wood-plastic composite decking profile. One of the main challenges in extrusion die design is to achieve balanced flow at the flow channel outlet, said
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