Empirical Study of the Effect of Fibre Hybridisation on the Water Absorption and Dimensional Stability of Natural Fibre-Reinforced Polyester Composites for Outdoor Applications

Water absorption is a critical durability limitation of natural fibre-reinforced polymer composites destined for outdoor structural applications, driving research into hybridisation strategies that mitigate moisture uptake while retaining the sustainability benefits of natural reinforcements. This study empirically evaluates the effect of hybridising kenaf and glass fibres on water absorption behaviour and dimensional stability of unsaturated polyester composites, targeting outdoor applications in North East Nigerian construction environments. Hybrid composites with kenaf-to-glass ratios of 100:0, 75:25, 50:50, 25:75, and 0:100 at 35 percent total fibre volume fraction were produced by hand lay-up. Water absorption tests were conducted by immersion in distilled water, synthetic seawater, and dilute acidic solution at 23 and 50 degrees Celsius over 30 days, monitoring mass gain, thickness swelling, and mechanical property retention. Fickian diffusion coefficients were determined from absorption kinetics. Results demonstrate that increasing glass fibre proportion progressively reduced water absorption coefficient, with 50:50 kenaf/glass hybrid achieving equilibrium water uptake of 3.2 percent, compared to 8.7 percent for all-kenaf composites, representing a 63 percent reduction. Thickness swelling after 30-day immersion declined from 4.1 percent for all-kenaf to 1.4 percent for 50:50 hybrid. Tensile strength retention after 30-day immersion was 71 percent for all-kenaf composites and improved to 88 percent for 50:50 hybrid. The Fickian diffusion model provided an adequate fit to absorption data for all compositions. The study recommends 50:50 kenaf/glass hybrid composites as an optimised formulation balancing outdoor durability with cost efficiency for roofing and cladding applications in North East Nigeria. Keywords: hybrid composite, kenaf, glass fibre, water absorption, dimensional stability