Physico-mechanical response of curauá and sisal composites to short-term hygrothermal exposure: A comparison between synthetic and bio-based systems

The rising demand for sustainable materials is driving research into natural fibre-reinforced composites. Due to their high specific strength, non-toxicity, and cost-benefit advantage, these materials are ideal candidates for lightweight structural applications. However, sensitivity to moisture and heat, as well as limited interfacial adhesion to polymeric matrices, remain critical challenges to their long-term reliability. This study investigates the influence of short-term hygrothermal ageing on the physico-mechanical behaviour of sisal and curaua fibre-reinforced composites. A full factorial design is employed to evaluate the effects of synthetic (epoxy) and bio-based (castor oil polyurethane) systems on the density, water absorption, and the tensile, flexural, and impact properties of laminates aged under both water vapour and immersed conditions. Results indicate that while the curaua/epoxy system offers superior structural durability, the sisal/castor oil variant is distinguished by its enhanced impact performance. Castor-oil polymer offers lower density and reduced water uptake, along with higher bending stiffness compared to composites manufactured with epoxy systems. To achieve an optimal balance of properties, future strategies should focus on fibre surface treatments to mitigate moisture sensitivity and improve interfacial bonding.