Accelerated weathering of natural fiber-filled polyethylene composites

The resistance of natural fiber-filled high-density polyethylene composite specimens to ultraviolet- (UV) and moisture-induced degradation was evaluated by measuring changes to flexural properties. High-density polyethylene (HDPE) served as the polymer matrix for four formulations: two formulations without fiber filler and two formulations one containing wood flour and the other containing kenaf fiber, each added at 50% by weight. Specimens were exposed for 4,000 h to UV radiation and moisture cycling in a laboratory weathering device to simulate the effects of exposure to sunlight and rain. Modulus of elasticity and modulus of rupture were measured prior to and after specific exposure periods. The flexural modulus and strength decreased significantly with increasing exposure for both natural fiber-filled HDPEs, but these composites still outperformed composites without filler. To explore a practical means to predict the changes in flexural properties to observed physical changes, a two-layer elementary mechanics model consisting of a degraded surface layer and an unaffected core layer was considered. The model was only partially successful-it provided reasonable predictions of flexural strength but did not accurately predict modulus of elasticity.