Reprocessing of wood fibre reinforced polypropylene composites. Part II: Hygrothermal ageing and its effects

In this paper, hygrothermal ageing behaviour of virgin and reprocessed composites based on radiata pine (Pinus Radiata) wood fibre with a polypropylene (PP) matrix were investigated. Composites were produced with 40 wt% fibre and 4 wt% maleated polypropylene (MAPP) coupling agent using extrusion followed by injection moulding. Composites reprocessing was carried out using repeated pelletising and injection moulding for up to eight times. Hygrothermal ageing was carried out by immersing specimens in distilled water at 50 °C over a 9 month period. The diffusion coefficient of moisture absorption was obtained for composites by measuring water uptake of specimens at regular time intervals. It was found that the diffusion coefficient and the equilibrium moisture contents of composites decreased with increased number of times the materials were reprocessed. After hygrothermal ageing, tensile strength (TS), Young’s modulus (YM) and hardness of both virgin and reprocessed composites were found to decrease, but impact strength (IS) and failure strain (FS) increased. The thermal stability of both virgin and reprocessed composites was found to decrease after hygrothermal ageing.