Tailoring fiber–matrix interfaces in coconut fiber-reinforced epoxidized vegetable oil-based bio-composites

The quest for sustainable polymer composites is growing; however, issues such as fiber hydrophilicity and poor interfacial adhesion persist. This study explores the development of bio-based polymer composites, employing Methacrylic Anhydride modified Epoxidized Linseed Soybean Oil (MAELSO) as the resin and surface modified Coconut Fibers (CF) as the reinforcing agent. Fiber treatments included alkali (5 wt%), alkali (5 wt%) + Glycidyl Methacrylate (GMA, 2–4 wt%) and alkali (5 wt%) + 3-aminopropyltriethoxysilane (APTES, 2–4 wt%) to increase interfacial interaction. Spectroscopic analysis confirmed successful chemical modifications, while thermal evaluations indicated improved stability in the optimally treated systems. Alkali treated composites exhibited the highest tensile and flexural strengths of 21.72 MPa and 39.90 MPa, respectively. In contrast, alkali + GMA-treated composites demonstrated superior impact strength (73.11 J/m) with reduced porosity (~2–3%), indicating improved structural integrity. SEM analysis verified enhanced interfacial adhesion and reduced microvoid formation. Alkali + GMA treatment significantly mitigated water uptake and enhanced chemical resistance, whereas alkali + silane treatment augmented flame retardancy, reaching a maximum limiting oxygen index of 66%. Environmental evaluations, including UV and soil burial tests, confirmed improved durability. Overall, this study demonstrates a sustainable strategy for developing bio-composites for light-duty applications.