Composites have been prepared with polypropylene (PP) as a matrix and pine flours, either thermally treated (W-tr) or not (W), as fillers resulting in wood plastic composites (WPCs). The treatment by retification at 280 degrees mainly elevates the hydrophobicity of wood. The WPCs were fabricated with a co-rotating twin-screw extruder with the screw speeds of 500 and 1200 rpm and specimens were prepared by injection molding. Viscoelastic behavior, tensile test and Charpy impact test of WtrPC were compared with PP and WPC. WtrPC has a better dispersion and highest tensile modulus. As expected, a decrease in elongation at break and impact strength was observed for all composites. Processing at 1200 rpm improved by 60% the Young modulus of the WPC compared to 500 rpm, whereas 500 rpm was enough to obtain the highest modulus for WtrPC.