Mechanical and physical performance of kenaf-banyan hybrid epoxy composites incorporating calcium-rich bio-waste fillers

The development of natural fiber-reinforced polymer (NFRP) composites as competitive substitutes for traditional synthetic composites has accelerated due to the shift toward sustainable engineering materials. This study investigates the impact of bio-derived fillers, specifically eggshell and snail shell powders, on the mechanical and water absorption characteristics of hybrid epoxy composites reinforced with handwoven kenaf and banyan fibers. Eggshell and snail shell powders were added to six different types of composite samples in accordance with the ASTM standard at filler contents of 1, 2, and 3 wt%, respectively. The incorporation of 2 wt% snail shell powder achieved a maximum tensile strength of 54.00 MPa, representing a 69.63% improvement over the 1 wt% baseline (31.84 MPa). Eggshell-reinforced composites attained the highest flexural strength of 82.52 MPa at 3 wt% loading, a 14.6% increase compared to the 1 wt% eggshell sample (72.01 MPa). Hardness values increased consistently with filler content, reaching 75 Shore D at 3 wt% snail shell powder, demonstrating a 13.07% improvement over the 1% baseline. Impact strength peaked at 38.46 kJ/m² with 1 wt% snail shell loading. Most significantly, water absorption was substantially reduced from 9.05% (1 wt% snail shell) to 6.58% (3 wt% snail shell), a 27.3% reduction, indicating improved matrix densification and reduced micro-void content. Scanning Electron Microscopy confirmed that snail shell powder promotes superior fiber-matrix wetting and void reduction, whereas eggshell-filled systems exhibited more prominent brittle fracture morphologies. These results underscore the potential of utilizing bio-wastes as functional fillers to engineer high-performance, eco-friendly composites for structural applications in the automotive and construction sectors.