Mechanical, morphological, and sustainability assessment of bio hybrid composites reinforced with sodium-acetate-treated and steam exploded banana fibers with coconut and walnut shell fillers

This study investigates the development of bio hybrid epoxy composites reinforced with sodium acetate treated and steam exploded banana fibers in combination with coconut shell powder (CSP) and walnut shell powder (WSP) fillers, aiming to enhance mechanical performance through eco-friendly fiber/filler modification. Banana fibers underwent non acidic alkali salt treatment followed by steam explosion, resulting in improved fibrillation and surface activation, while CSP and WSP provided micro scale reinforcement. The composites were fabricated using a wooden mold hand layup process, and mechanical, physical, and morphological properties were evaluated. The optimized formulation, BECW3, exhibited a tensile strength of 20.16 MPa, flexural strength of 97.85 MPa, hardness of 46 Shore D, density of 1.082 g/cm 3 , void content of 5.65%, and stable impact energy of 0.2–0.4 J, representing a 13.4% increase in tensile strength and approximately 156% increase in flexural strength compared with untreated banana epoxy composites. SEM analysis confirmed improved fiber–matrix adhesion, reduced pull out, and more uniform filler dispersion due to synergistic effects of treatment and hybrid filler inclusion. These findings demonstrate a viable pathway for converting agricultural wastes banana pseudo stem, coconut shell, and walnut shell into high performance, sustainable polymer bio composites suitable for structural, packaging, and automotive interior applications.