Weathering performance of plant-fiber/thermoplastic composites

Natural fiber/thermoplastic composites were made using aspen fiber and poly propylene. Several different levels of aspen fiber (30 to 60% by weight) we re used with and without the addition of a compatibilizer (maleic anhydride grafted polypropylene, MAPP). These composites were tested for strength pr operties, exposed to boiling and cyclic liquid water and oven drying tests, and evaluated in an accelerated weathering test for 2000 hours. As the lev el of fiber increases without MAPP, flexural strength, flexural modulus, te nsile strength and tensile modulus increases but notched and unnotched impa ct strength decrease as compared to pure polypropylene. The presence of MAP P has a very large positive effect on flexural strength, flexural modulus, tensile strength and tensile modulus as compared to composites made without MAPP. As the level of fiber increased in the composites, the rate and exte nt of thickness swelling and moisture sorption increased as compared to pur e polypropylene. The presence of MAPP decreased the extent of swelling and moisture pickup. Weathering of composites under accelerated weathering cond itions (water sprayed for 18 minutes followed by 102 minutes without water spray of UV radiation produced by a 6500-watt xenon are light source) was r estricted to the outer 0.5 mm of the surface. Weathering gave rise to the d evelopment of a white chalky surface layer which started at about 150-200 h ours of weathering. After 2000 hours of accelerated weathering, weight loss increased with increasing fiber content and there was more weight loss in specimens containing MAPP as compared to specimens without the addition of MAPP. After scraping off the chalky white layer after 2000 hours of weather ing, weight loss was greatest in specimens containing no fiber.