The wood flour used in wood-plastic composites (WPCs) can biologically deteriorate and thus the overall mechanical performance of WPCs decrease when exposed to moisture and fungal decay. Protecting the wood flour by chemical modification can improve the durability of the wood in a nontoxic way so it is not harmful to the environment. WPCs were made with modified wood flour and then evaluated for moisture sorption, fungal resistance and mechanical performance. Two different chemical modifications at 2 different levels were used: organosilicate (OS, 1% and 2.5%) and cobalt sulfate (CoS, 2.5% and 5%). All modifications had less weight loss than the unmodified controls with the 2.5% OS blend showing no weight loss from decay by either brown or white rot fungi. Water soaking for 1-week at elevated temperature (70°C) was more aggressive for laboratory decay and mechanical testing as shown by higher weight loss and lower mechanical properties compared to 2-week water soaking at room temperature (23°C). Moisture exposure decreased the mechanical properties, but 2.5% OS, 2.5% CoS and 5% CoS had better performance than the unmodified controls and 1% OS after 70°C conditioning and decay.

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