Wood plastic composites, WPCs, are rapidly taking shares from preservative treated wood on the decking market. However, the long term performance of the WPC products in this application is uncertain. Therefore, in an attempt to increase the long term performance and durability, the substitution of the unmodified wood component with modified wood has been studied in the work presented in this paper. WPCs, with 70% wood content, from modified wood were successfully produced in semi-industrial scale. The wood component originated from acetylated and heat treated wood. WPCs from unmodified wood were also produced and used as references. Both acetylated wood and heat treated wood exhibits high durability and dimensional stability. Using modified wood in the WPC would not only increase the long time durability, but also enable a higher wood content, in high quality WPC products for exterior applications. The moisture sorption was significantly reduced for WPC with acetylated wood compared with WPC with unmodified wood. Also, for the WPC samples from heat treated wood, a reduced moisture sorption was observed. Microscope analysis clearly demonstrated the formation of cracks in the interface between unmodified wood and polymer matrix after water soaking and drying. No cracks were formed in the acetylated WPC samples. Improvements were also observed for the WPC samples from heat treated wood.

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