Influence of Moisture Absorption on Mechanical Properties of Wood Flour-Polypropylene Composites

Wood-plastic composites are being examined for a greater number of structural-type applications that may be exposed to different environments, some of them adverse. This paper discusses the influence of moisture absorption on the mechanical properties of wood flour-polypropylene composites. Composites filled with 20% or 40% wood flour (by weight) were placed in different environments, removed periodically, and tested for moisture content and mechanical properties. The composites filled with 20% wood flour (20%WF) absorbed moisture in all the environmental exposures, but no significant degradation of properties was observed. The 40%WF composites absorbed more moisture than did the 20%WF composites. The flexural properties of composites subjected to a water bath and to 90% relative humidity were lower than the flexural properties of the other composites. Tensile properties and notched impact strengths decreased only for composites placed in a water bath. Unnotched impact strengths did not change significantly with absorption of moisture.