Constructing ‘Molecular Bridges’ Between Aramid Pulp and Rubber for Significantly Enhanced Reinforcement

Aramid pulp (AP), a short fiber reinforcement with excellent mechanical properties, is highly promising for weight reduction and reinforcement in rubber transmission belts, tires, and sealing products. However, its smooth and chemically inert surface leads to weak interfacial adhesion with the rubber matrix, severely limiting its reinforcing efficiency. In this study, a two-step surface grafting strategy combining alkaline treatment, isocyanate activation, and thiol functionalization was proposed, through which thiol groups capable of co-vulcanization with nitrile butadiene rubber (NBR) were successfully introduced onto the aramid pulp surface. The effects of AP at different treatment stages on the mechanical properties and dynamic service behavior of NBR composites were systematically evaluated. The results demonstrated that, compared with the unmodified AP, the NBR composite reinforced with the two-step modified AP exhibited a significantly higher tensile modulus, improved abrasion resistance, a greatly prolonged tensile fatigue life at 50% strain, and reduced compression heat build-up. This work demonstrates that the interfacial co-crosslinking strategy is effective in enhancing the performance of aramid pulp-reinforced rubber and provides experimental evidence and new insights for the interfacial design of high-performance aramid fiber/rubber composites.