AbstractThe effect of unmodified talc particles on the mechanical and thermal expansion performance of talc-filled high density polyethylene (HDPE) and co-extruded wood plastic composite (WPC) with talc-filled shells was studied. The use of talc in HDPE helped enhance its tensile, bending, and dynamic modulus, but lowered its tensile and impact strength. The selected models for composite modulus and tensile strength fit the data well after adjusting the model parameters. Talc-filled HDPE had lower linear coefficient of thermal expansion (LCTE) values in comparison with the neat HDPE values, and the LCTE reduction rate increased after the talc loading levels increased above the 30 wt%. Extruding a relatively thick, less-stiff HDPE shell with a large LCTE value over a stiff and thermally stable WPC core decreased overall composite modulus and increased the LCTE values. The composite modulus and strength increased and LCTE values decreased with increase of the talc loading levels in the shell. The impact strength of co-extruded WPC was greatly enhanced with unfilled- and filled HDPE shells.