Influence of hybrid lignocellulosic fillers on processing, microstructure, mechanical and thermal behavior of kenaf/epoxy composites

Abstract

The large-scale generation of agricultural residues such as pine needle (PN) and citrus peel waste poses environmental and disposal challenges. This study investigates the valorization of these lignocellulosic wastes as hybrid bio-fillers in kenaf fiber-reinforced epoxy composites, establishing a sustainable waste-to-material conversion pathway. PN and citrus limetta peel (CLP) particulates were incorporated individually and in hybrid configurations to evaluate their influence on mechanical and thermal performance, flammability behavior, and moisture-related dimensional stability. Mechanical characterization showed that both single and hybrid PN/CLP filler configurations improved the mechanical performance relative to the unfilled kenaf/epoxy reference, with the magnitude of improvement depending on filler type and the PN:CLP ratio. Among the investigated formulations, the KE-CLP10 composite exhibited an increase of approximately 47% in tensile strength, 26% in tensile modulus, and 80% in impact strength relative to the reference composite. Thermogravimetric analysis indicated enhanced thermal stability, with the hybrid composites exhibiting residual char contents of approximately 13% to 18%. Water absorption studies showed composition-dependent moisture uptake, with selected hybrid formulations exhibiting lower water absorption and improved dimensional stability relative to the neat kenaf/epoxy reference. The findings demonstrate that underutilized PN and citrus peel residues can be effectively converted into value-added reinforcing materials, improving composite durability while contributing to resource circularity and sustainable materials engineering.