MATERIALS | WPCs
transition to WPC can be passed on to the market”. For wood content above 40-60%, respondents said the decrease in performance and cost advan- tage was greater than any increase in sustainability benefits. An average wood proportion of 50% was seen as the optimum for efficiency, he said. In addition, moisture resistance of WPC was a major concern for the industry. This lowered the ‘acceptable’ wood content – which would have been higher had colour resist- ance been seen as more important. “To fully exploit the eco-potential of WPCs,
future developments should optimise hydrophobic properties rather than colour stability,” said Friedrich.
Above: The moisture resistance of WPC is seen as a key
advantage over traditional
timber decking
the International University of Applied Sciences in Mainz in Germany, says that users of WPCs are generally prepared to accept lower material performance compared to pure plastics, knowing that they can gain a sustainability benefit. “The fibre content makes WPCs ecological, but
also more expensive and susceptible to colour change and water absorption,” he said. His study surveyed 167 German “industry
experts”, asking them if WPC could increase the sustainability of their products and applications, and what maximum wood content they would accept – if it delivered sustainability. In all, 85% of respondents agreed with the benefit of using WPCs. About 19% would accept cost increases for sustainability, while a majority (nearly 49%) preferred to renounce colour stability rather than moisture resistance (18%). However, if higher moisture absorption was tolerated, the experts tended towards lower maximum wood contents. A limitation of the study was that respondents
were put in a hypothetical decision-making situation, without any consequences. However, it took place in a company environment, so results would be more reliable than in a consumer survey, he said. And, while respondents were all based in Germany, Friedrich said the “cultural and economic closeness” of central European countries meant that results could serve as a ‘template’ for other studies. The paper reached a number of conclusions. For
one, WPC was not generally seen to be more advantageous than ‘pure’ plastics – with around 15% of applications rated as ‘non-substitutable’. Secondly, using WPCs may well lead to higher substitution costs for material performance to be maintained. However, he added that because “most consumers are willing to pay more for biobased products, additional costs from the
28 PIPE & PROFILE EXTRUSION | Winter 2024
Building a future In addition, researchers from Chaoyang University of Technology in Taiwan prepared a WPC that – as well as wood flour – incorporated recycled protec- tive clothing (which contained Tyvek), brewery waste and aluminium hydroxide powder from waste artificial marble. In this case, the researchers took HDPE from
discarded milk bottles and crushed into into pellets smaller than 1cm. The recycled protective clothing was cut into pieces about 1cm square. The waste artificial marble powder underwent thermal treatment in a high-temperature furnace at 300, 400 and 500°C, each for a duration of 2 h. WPC test samples were prepared by compres- sion moulding at 175°C at varying pressures. HDPE content ranged from 32 to 34%, while wood flour content was 40-48%, and aluminium hydroxide was 0-20%. The researchers carried out tests including TGA analysis, tensile strength testing and sunlight exposure. The resultant material had a processing tem-
perature of 175°C, and a tensile strength around 28% higher than a ‘standard’ WPC. The aluminium hydroxide powder increased thermal conductivity, leading to an 8.5°C lower surface temperature. “Therefore, they can be applied to outdoor cool WPCs to reduce the risk of foot burns – or used as roof heat-insulating layers to reduce indoor air conditioning usage, achieving energy-saving and carbon reduction,” said the researchers, whose research was published this year in the journal Buildings.
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IMAGE: SHUTTERSTOCK
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