Effects of water absorption on creep behavior of wood-plastic composites

The effects of filler loading and immersion in water on the creep/ recovery behavior of composites made from MDF (medium density fiberboard) flour (as natural fiber) and recycled HDPE (high density polyethylene) (as resin) were studied (at 60, 70, and 80% by weight fiber loadings). Nominal density and dimensions of the manufactured panels were 1 g/cm(3) and 35 x 35 x 1 cm(3), respectively. Maximum values of flexural modulus and strength of panels were obtained at 70 and 60% fiber content, respectively. The creep strain decreased as the lignocellulosic flour level increased. Water absorption has negative effect on creep behavior of MDF flour/HDPE composites. For all filler contents, it can be seen that the creep strain increases when the immersion time increases. This is believed to occur as a result of the cumulative effect of absorbed water on fiber matrix debonding and easier relaxation of the molecules at higher moisture contents leading to larger deformations at longer times.