Synergistic Nano-SiC/EPDMModification of Wood Fiber/PolypropyleneComposites for Enhanced Strength, Toughness, and Thermal Properties

Abstract Polymer composites reinforced with renewable plant fibers are attractive for sustainable materials development, but their practical application is often limited by the persistent tradeoff between strength and toughness. To address this issue, a cost-effective synergistic modification strategy combining nanosilicon carbide (nano-SiC) as a rigid reinforcing phase and ethylene–propylene–diene rubber (EPDM) as an elastic toughening phase was developed for wood-fiber/polypropylene (WF/PP) composites. The composites were fabricated by injection molding, and their mechanical and thermal behaviors were systematically investigated through mechanical testing, thermal characterization, fracture-surface observation, and single-fiber representative volume element (RVE) simulations. The results show that 3–4 wt% nano-SiC significantly improved crystallinity, flexural modulus, and flexural strength, whereas EPDM markedly enhanced toughness. At 20 wt% EPDM, the impact strength and elongation at break reached 10.89 kJ/m2 and 13.76%, respectively. Among all formulations, the composite containing 3 wt% nano-SiC and 15 wt% EPDM achieved the best balance between strength and toughness. RVE simulations revealed that nano-SiC promotes local stress concentration to facilitate load sharing with fibers, while EPDM homogenizes the stress field through deformation and cavitation, thereby suppressing crack propagation. This work provides a practical route for overcoming the strength–toughness tradeoff in WF/PP composites and offers mechanistic guidance for designing high-performance sustainable plant-fiber composites.