Influence of Water Absorption on the Interlaminar Shear Strength and Fracture Toughness of Hybrid Hemp–Banana Fiber-Reinforced Composites

This study investigates the impact of water absorption on the interlaminar shear strength (ILSS) and fracture toughness of hybrid hemp-banana/epoxy composites, in comparison to pure hemp/epoxy and banana/epoxy systems. Building on previous work under dry conditions, this research focuses on moisture-induced degradation to simulate humid service environments. Composite laminates were fabricated via compression molding and subjected to water immersion tests. Hemp/epoxy composite exhibits the highest water absorption (22%), followed by banana/epoxy (18%) and hybrid composites (15%), reflecting cellulose content and fiber–matrix interfacial bonding differences. Under dry conditions, hybrid composites achieved superior ILSS (18.17 MPa) and fracture toughness (7.66 MPa·m1/2), attributed to synergistic fiber interactions that improved the stress transfer and crack deflection. Post-immersion, ILSS declined by 47%, 40%, and 36% for hemp, banana, and hybrid composites, respectively, while fracture toughness dropped by 62%, 48%, and 39%. Statistical analysis (paired t-tests) confirmed that these property reductions were highly significant, with the hybrid composite showing the least severe degradation. SEM micrographs revealed matrix plasticization, fiber swelling, and interfacial debonding as a dominant degradation mechanism. This work highlights the synergetic effects of hemp-banana hybridization in mitigating moisture-induced mechanical degradation, offering insights into optimizing natural fiber composites for sustainable applications in humid environments.