Influence of moisture absorption on mechanical properties of wood flour-polypropylene composites

Wood-plastic composites are being examined for a greater number of structur al-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. Composit es filled with 20% or 40% wood flour (by weight) were placed in different e nvironments, removed periodically, and tested for moisture content and mech anical properties. The composites filled with 20% wood flour (20%WF) absorb ed moisture in all the environmental exposures, but no significant degradat ion of properties was observed. The 40%WF composites absorbed more moisture than did the 20%WF composites. The flexural properties of composites subje cted to a water bath and to 90% relative humidity were lower than the flexu ral properties of the other composites. Tensile properties and notched impa ct strengths decreased only for composites placed in a water bath. Unnotche d impact strengths did not change significantly with absorption of moisture .