Environmental effects on the degradation behaviour of sisal fibre reinforced polypropylene composites

The environmental degradation behaviour on the physical and mechanical properties of short sisal/PP composites has been studied with special reference to the influence of ageing conditions like treatment with water and UV radiation. The dependence of water uptake on the sorption characteristics of sisal/PP composites was evaluated by immersion in distilled water with respect to fibre loading, temperature and chemical treatment. It is found that water uptake increases with increase of fibre loading due to the increase in cellulose content. The raise of temperature up to 70 degreesC is accompanied by an increase of the rate and extent of sorption. Chemical treatments such as urethane derivative of PPG, PMPPIC and MAPP were given to sisal fibre. All chemically modified fibre composites showed lower uptake than the unmodified composites. This is because all chemical treatments given to sisal fibre reduce its hydrophilicity thereby favouring strong interfacial adhesion between the fibre and PP matrix. The influence of water uptake on the tensile properties of sisal/PP composites was studied. Tensile properties decreased with water uptake, time of immersion and fibre loading. The behaviour was strongly dependent on the chemical treatment and fibre orientation. The influence of the tensile properties of sisal/PP composites exposed to UV radiation was studied. The tensile properties were found to decrease with increase in the time of exposure to UV radiation. The reduction in properties is due to chain scission and degradation occurring to PP molecules as a result of photooxidation promoted by ultraviolet radiation. As a result of UV irradiation, surface cracks can be seen on neat PP and PP composites which can be evidenced from SEM photos. The retention of tensile properties increased with increase of fibre loading. (C) 2002 Published by Elsevier Science Ltd.