Structure-property relationship of eggshell-derived bio-filler reinforced flax fiber/ epoxy composites

This study examines the impact of eggshell powder as a sustainable, bio-derived filler on the structural and property features of flax-fiber-reinforced epoxy composites designed for lightweight structural applications. Composite laminates incorporating 0, 5, 10, and 15 wt% eggshell powder were produced via the hand lay-up method, subsequently undergoing post-curing. The influence of filler loading on physical, mechanical, and microstructural properties was methodically assessed via density, void fraction, tensile strength, flexural strength, interlaminar shear strength (ILSS), impact resistance, and water absorption tests, adhering to ASTM standards. The composite with 15 wt% eggshell powder demonstrated enhanced mechanical properties, achieving a tensile strength of 54.53 MPa, a flexural strength of 89.77 MPa, and an interlaminar shear strength (ILSS) of 6.076 MPa, in addition to increased impact resistance. The void fraction diminished to 1.24%, signifying augmented matrix densification and enhanced structural integrity. Scanning electron microscopy demonstrated enhanced fiber-matrix interfacial adhesion, reduced fiber pull-out, and consistent filler distribution at elevated filler concentrations. Despite the increase in water absorption with filler content, the composites exhibited consistent moisture behavior in distilled, normal, and saline conditions. The novelty of this study lies in the utilization of eggshell-derived bio-waste as a sustainable filler in flax fiber reinforced epoxy composites, along with the optimization of filler loading and the establishment of a clear structure-property relationship linking filler content with density, void fraction, and mechanical performance. The findings validate that the regulated integration of eggshell powder improves load transfer efficiency and structural performance, indicating the viability of eggshell-filled flax fiber/epoxy composites as sustainable lightweight materials for engineering applications.