Moisture absorption studies of sisal fibre reinforced polypropylene composites

In this research, sisal fibre reinforced polypropylene (SF/PP) composites were prepared by injection moulding using a pre-coating technique that we have developed earlier. The composite specimens were subjected to hot water immersion treatment at 90 °C for different durations. The effects of the immersion treatment on the tensile and impact fracture characteristics were investigated. The apparent weight gain and weight loss curves were constructed. From the weight loss curves for the individual composites, the weight loss within the induction period was negligible. At the end of the induction period, the weight loss increased sharply. Due to the weight loss and the formation of additional moisture diffusion paths as immersion treatment proceeds, the apparent weight gain was non-Fickian. Both the tensile modulus and tensile strength of the SF/PP composites decreased continuously with increasing water immersion time. On the contrary, the Izod impact strength increased initially with immersion treatment. After reaching the maximum impact strength, the impact strength was found to decrease with further increase in immersion time. These contradictory behaviours between the tensile and impact properties were explained by the plasticization of the SF/PP interface and the swelling of the reinforcing sisal fibres.