Effect of hot water fibre treatment on the properties of kenaf/polyester composites

The work was undertaken to evaluate the efficacy of hot water treatment of kenaf fibres on the properties of 36 volume % kenaf/polyester composites. Two hot water treatment temperatures were examined, 75˚C and 100˚C. Both involved soaking for 4 hours. The 75˚C treatment was supplemented by ultrasonic agitation. No ultrasonic agitation was used for the 100˚C treatment but some agitation was present due to the boiling action of the water. Untreated fibres were also examined for comparison.The hot water treatments were found to have a substantial effect on the appearance of the surface of the kenaf technical fibre bundles, with the coating seen on the untreated fibres being substantially removed by the hot water treatments. The 100˚C treatment was the most effective, indicating that temperature was more important than agitation. FTIR analysis indicated that the products removed were pectins and waxes. A lower amount of the carbonyl volatile fractions was emitted from the treated fibres during TGA, also consistent with the removal of pectin. The hot water treatments also increased the coarseness of the technical fibre bundles, with the increase being greatest for the 100˚C treatment. The tensile strength of single technical fibres was 182-245 MPa, the Young’s modulus was 13.0-19.2 GPa while the strain to failure was 1.3-1.4%. Because of the wide scatter in the data, no significant differences were detected between the different treatments when the data was analysed statistically. A Weibull analysis of the strength data gave Weibull modulus values of 1.7-2.0.The interfacial shear strength determined from the fragmentation test was 40.7 MPa for the fibres treated in 100˚C water, 13.3 MPa for the fibres treated in 75˚C water and 9.1 MPa for the untreated fibres. The improvement of interfacial shear strength with temperature of hot water treatment is attributed to the progressive removal of pectins and waxes from the surface of the fibres resulting in improved fibre matrix bonding. The tensile strength of the composites ranged from 91-100 MPa, with the modulus ranging from 13.1 to 14.6 and the strain to failure ranging from 1.5- 2.0%, while the flexural strength and modulus ranged from 112-138 MPa and from 14.7-17.2 GPa, respectively, and the impact strength ranged from 20.9-28.9 KJ/m2. The differences between the different treatments in tensile and impact properties proved not to be statistically significant, but the flexural properties were 20% lower for the composites made with the 100˚C water treated fibres than for the composites made with the other fibres