Bio-oil engineered epoxy matrix for abaca fiber-reinforced composites: Assessment of thermo-mechanical and interfacial strengthening attributes

This work presents a mechanistic investigation of bio-oil-engineered epoxy matrix reinforced with natural fibers, focusing on the role of cross-link density and interfacial strengthening in governing multiscale composite performance. Epoxy matrices were modified using bio-derived oils at varying concentrations and reinforced with alkali-treated natural fibers to fabricate composite laminates via hand lay-up processing. Comprehensive characterization spanning Molecular (FTIR), Microstructural (SEM), Thermal (TGA), and Mechanical (Tensile, Flexural, Impact, ILSS) scales was performed to establish structure–property relationships. The results reveal that controlled bio-oil incorporation significantly alters the epoxy compositional architecture, leading to an optimal balance between cross-link density and molecular mobility. At intermediate bio-oil content, enhanced cross-linking and improved fiber–matrix interfacial adhesion result in substantial improvements in Tensile (80%), Interlaminar Shear (130%), and Impact Strength (350%) compared to the unmodified system. At higher bio-oil concentrations, a reduction in cross-link density promotes increased ductility but compromises stiffness and load-bearing capacity, indicating a clear stiffness–toughness trade-off. Fractographic analysis confirms a transition from interfacial debonding to cohesive fracture and matrix yielding, highlighting the role of engineered interfaces in damage resistance. The findings demonstrate that bio-oil engineering provides a tunable strategy for designing sustainable, high-performance natural fiber composites with tailored mechanical and thermal characteristics.