Recycled leather–epoxy hybrid composites exhibiting novel fracture behavior identified through multimodal characterization

This study investigates the mechanical behavior and fracture mechanisms of recycled leather-epoxy composites fabricated via resin infusion and evaluated under quasi-static three-point bending. The work employs industrial post-consumer leather waste, mechanically processed into fibrous form, as a sustainable reinforcement alternative to conventional natural fibers. At a fiber volume fraction of approximately 0.3, the composites achieved a flexural strength of 100.8 ± 1.92 MPa and a modulus of 18.64 ± 0.38 GPa, showing favorable performance relative to reported jute-epoxy and flax-epoxy systems under comparable testing conditions. The bilinear viscoelastic-softening model captured the composite stress-strain response and an estimated critical energy release rate (Gc ≈ 8.89 × 10^-3 J/m²) reflected the onset of progressive delamination. Micro-voids and resin-deficient zones associated with collagen-based fiber morphology acted as stress concentrators that shaped local failure events. This exploratory study advances understanding of micromechanical toughening in bio-derived composites and indicates that processed post-consumer leather fibers exhibit promising flexural behavior and damage tolerance, suggesting potential for semi-structural or moderately loaded lightweight applications pending further durability and service-level validation.