Seawater immersion effects on the tensile, flexural, and low-energy impact properties of a basalt/flax hybrid reinforced bio-epoxy

Abstract This study presents a novel hybrid eco-composite comprising a single ply of basalt fibre on the outer layers of a flax-woven fabric-reinforced bio-epoxy laminate. Mechanical performance was assessed via tensile, flexural, and low-energy impact tests, while long-term real seawater immersion experiments evaluated degradation in marine environments. The role of basalt fibre in enhancing mechanical properties and reducing water uptake by flax fibres was investigated. Tensile testing showed that basalt fibre improved stiffness, strength, and elongation at break by 8%, 67%, and 19%, respectively. Additionally, the outer basalt layer acted as a moisture barrier, reducing water absorption and limiting stiffness degradation to 11%. Flexural properties exhibited even greater enhancement, with increases exceeding 100% in both modulus and strength. However, under seawater immersion, the barrier effect was less pronounced, as flexural property losses in basalt–flax hybrid reinforced bio-epoxy (BFRB) composites were comparable to those of pure flax fibre-reinforced bio-epoxy (FFRB) composites. In terms of impact resistance, basalt fibre hybridisation significantly increased penetration and perforation energy thresholds by 140% and 123%, respectively. Notably, seawater immersion did not impair energy dissipation, with BFRB composites maintaining stable impact performance in wet conditions. These findings highlight the potential of BFRB composites as sustainable materials for semi-structural marine applications. Further research is recommended to optimise laminate thickness and stacking sequences for improved structural performance.