Effect of extractives on the flexural properties of wood/plastic composites

This study investigated the effect of extractives in wood flour on the mechanical propertied,: of wood-polypropylene (PP) composites. Three different solvents, acetone/water, dioxane/water and benzene/ethanol, were used to remove extractives in both pine and Douglas fir wood flour. X-ray photoelectron spectroscopy (XPS) confirmed that extraction resulted in a change in the surface composition of the wood flour. Differential scanning calorimetry showed no changes in the percent crystallinity of the PP matrix in the wood-PP composites and optical microscopy showed no detectable changes in PP spherulite size or shape between filled PP containing extracted and unextracted wood flour. A large increase in the strength of pine flour-PP composites was observed upon removal of extractives from pine flour. The Douglas fir flour-PP composites showed a smaller, but statistically significant. increase in strength upon removal of extractives. with the exception of the dioxane/water extracted Douglas fir. Significant differences were also observed in stiffness between extracted wood-PP and unextracted wood-PP composites with the exception of the dioxane/water extracted Douglas fir, which was not significantly different from the control.