other wood-based panel structure. HPL has high perfor- mance characteristics, but it may be over-engineered in some applications and is currently difficult to recycle, says Arne Schirp, Project Leader at WKI. A structure of plywood topped with the bio-composite sheet, however, could be easily recycled by grinding and reusing in a wood-plastic composite, for example. There would be no need to separate the top sheet from the plywood core prior to material recycling. Schirp says the group is experimenting with between 20 and 50% (by weight) wood particle fillers compounded into PLA along with a flame retardant. The main challenge has been to integrate high levels of wood filler and sufficient flame retardant for good fire performance while maintaining processability. “If the total filler level gets too high, com- pounding becomes difficult,” says Schirp. The wood filler is usually not dried before compounding,


but appropriate compounding conditions and vacuum degassing in the twin-screw extruder have been used successfully without triggering hydrolysis of PLA. PLA was chosen as a readily available and affordable bio-based plastic, but the researchers have also worked with other polymer matrices. Polyamides, HDPE, or PP — all available from bio-based sources — are potential options when higher heat resistance is needed, says Schirp. One of the next steps for the project is to experiment with colorants and ways to customise the appearance of the top layer. Research carried out by a number of Norwegian compa- nies in partnership with the RISE PFI research institute is finding some success in compounding of wood thermo-me- chanical pulp (TMP) fibres into thermoplastic composites for flooring and other products. Some of the findings are covered HERE in the May 2023 edition of Compounding World. Wood fibres are also being used as fillers in what some are calling biocomposite materials to indicate their bio-based composition. These materials are finding use in a wide range of applications beyond building and construction, including packaging and single-use as well as durable products. Activity is greatest in Europe, where European Union and country-specific regulations are driving change in plastic use. For example, Finland’s Sulapac says its materials are


WPC-capped


plywood produced by Fraunhofer WKI


as part of the Basajaun project www.compoundingworld.com


info@fineorganics.com www.fineorganics.com


IMAGE: FRAUNHOFER WKI


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