Influence of Al 2 O 3 nanoparticles and eggshell powder on epoxy hybrid composite properties

This study examines the influence of aluminium oxide (Al 2 O 3 ) nanoparticles and bio-derived eggshell powder, in both raw (ESP) and heat-treated (HTES, 120°C for 1 h) forms, on the mechanical, tribological, thermal, and flammability properties of epoxy LY556 composites. Five formulations were prepared by hand layup and characterised for tensile strength, flexural modulus, specific wear rate, thermal conductivity, limiting oxygen index (LOI), and vertical burn behaviour in accordance with ASTM D3801. Among all formulations, the hybrid composite containing 3 wt% Al 2 O 3 and 3 wt% HTES achieved the highest tensile and flexural performance, which is attributed to improved filler-matrix interfacial adhesion resulting from the removal of surface organic matter during thermal treatment. The binary composite reinforced with 3 wt% Al 2 O 3 recorded the lowest specific wear rate, due to a third-body abrasion mechanism at the sliding interface. Thermal conductivity increased monotonically with Al 2 O 3 loading, reaching a maximum at 6 wt%. Flammability testing revealed that raw ESP promoted char formation and suppressed flame propagation more effectively than HTES, indicating a trade-off between surface thermal treatment and flame-retardant contribution. These findings establish the multifunctional potential of bio-waste hybrid fillers as sustainable reinforcements in epoxy polymer composites.