Creep resistance of wood-filled polystyrene/high-density polyethylene blends

Abstract

Creep, the deformation over time of a material under stress, is one characteristic of wood-filled polymer composites that has resulted in poor performance in certain applications. This project was undertaken to investigate the advantages of blending a plastic of lower-creep polystyrene (PS) with high-density polyethylene (HDPE) at ratios of 100:0, 75:25, 50:50, 25:75, and 0:100. These various PS-HDPE blends were then melt blended with a short fiber-length wood flour (WF). Extruded bars of each blend were examined to measure modulus of elasticity and ultimate stress. Increasing the ratio of WF increased modulus of elasticity in all composites, except between 30 and 40% WF, whereas the effect of WF on ultimate stress was variable, depending on the composite. Scanning electron microscopic images and thermal analysis indicated that the wood particles interacted with the PS phase, although the interactions were weak. Finally, creep speed was calculated by using a three-point bending geometry with a load of 50% of the ultimate stress. Creep decreased only slightly with increasing WF content but more significantly with increasing PS content, except at pure PS. The WF/75PS-25HDPE blend showed the least creep.