Effect of repeated cycles of wetting and drying on mechanical properties of wood–polypropylene composites

Abstract

Wood plastic composites (WPCs) are being used for many outdoor applications such as fencing, railing and decking. In outdoor conditions, composites are exposed to varying atmospheric conditions which may influence its mechanical properties. Among the various effects, most predominant one is the moisture absorption due to rainfall. It is necessary to evaluate the effect of moisture absorption/desorption on mechanical properties of WPC. In the present investigation, Melia dubia wood fibre-reinforced polypropylene composites were prepared with and without coupling agent at 40 and 60% fibre loading. Composites were also prepared with three different wood fibre sizes. The composites were exposed to 25 cycles of wetting and drying. During each cycle, the samples were immersed in water for a period of 100 h followed by drying in atmospheric condition for 100 h. Samples were weighed after wetting and drying in each cycle, and mechanical properties were evaluated at 0, 5, 10 and 25 cycles. The results indicated that the composites with higher wood content and fine particle size exhibited higher water absorption and increased loss in mechanical properties. Composites prepared with coupling agent exhibited relative lower moisture absorption and smaller loss in mechanical properties compared to uncoupled composites.