Water absorption behaviour and its effect on the mechanical properties of hybrid interwoven cellulosic fibre composites

Abstract

With aim to fulfill the public need that eager for ‘green product’, natural based fibres started to receive attention to substitute synthetic fibres as reinforcement in composites. Natural fibres is relatively cheap, easy to get, non-toxic, non-abrasive, less harmful to human health and possessed high specific strength and modulus which make them the perfect choice to reduce the dependence towards the petroleum based fibres. As the extension to the research involving woven and natural fibre hybrid composites, this study investigated the water absorption behaviour and its effect on the mechanical properties of hybrid cellulosic fibre composites. Hybrid composites consists of interwoven kenaf/jute and kenaf/hemp yarns were prepared by infusion process using epoxy as the matrix. Woven kenaf, jute and hemp composites were also prepared for comparison. Water absorption test were conducted according to ASTM D590 standard by immersing the composite samples in tap water at room temperature until the water content reach saturation. Dry and water immersed samples of both woven and interwoven hybrid composites then were subjected to tensile and flexural tests according to ASTM D638 and ASTM D790, respectively. Fractured portion of the samples were examined using field emission scanning electron microscope (FESEM) to observe the effect of water absorption towards the fiber/matrix interface. Water uptake was rapidly increased at the beginning and getting slower until reach saturation at 1400 hours of immersion time. Among individual woven composites, woven kenaf composite had the highest water uptake and through hybridization with jute and hemp fibres, water resistance properties of kenaf fibre were improved by 46 and 64%. At both, dry and wet condition, mechanical properties of interwoven hybrid composites was found to be greater than their individual woven composites. In dry condition, tensile and flexural strength of interwoven kenaf/jute hybrid composite were 11 and 22% higher than woven kenaf composite and 16 and 39% greater than woven jute composite. For dry samples of interwoven kenaf/hemp hybrid composite, increment of 4 and 17% over woven kenaf composite and 9 and 33% over woven hemp composite were recorded for their tensile and flexural strength. Similar as the dry samples, increase of tensile and flexural strength was also observed for the water immersed samples of the interwoven hybrid composites. Amount of water uptake increased as the immersion time increased and reduced the strength and modulus (tensile and flexural) of the water immersed samples. Tensile strength of woven kenaf, jute, hemp, interwoven kenaf/jute and kenaf/hemp hybrid composites at their saturation state were reduced by 75, 69, 67, 72 and 69% over their strength at dry condition. Following the similar sequence, flexural strength of the saturated samples also reduced by 73, 64, 57, 69 and 67% than the dry condition samples. Those reductions attributed by debonding, matrix cracking, and delamination as shown through the FESEM images.