Effects of moisture and temperature cycling on material properties of a wood/plastic composite

Wood/plastic composites tend to be more resistant to moisture uptake and are promoted as being immune to moisture. Laboratory studies, however, have shown that small samples experience substantial losses in bending strength after wetting and drying. The potential for this same effect to occur in larger samples was investigated by subjecting a commercial wood/plastic composite to repeating moisture and freeze/thaw cycling. The materials were then tested to failure in third-point loading. Moisture sorption was generally low in all samples, but tended to increase with the number of wet/dry cycles. None of the cycles, however, were associated with significant reduction in either modulus of elasticity or modulus of rupture. The lack of effect probably reflects the limited ability of moisture to penetrate for substantial distances into the wood to disrupt the wood/plastic interface and thereby reduce properties.