Strategic purification and activation of waste-tire-derived pyrolytic carbon black for enhanced natural rubber reinforcement: Mechanistic insights and practical considerations

This study systematically investigated the reinforcement mechanisms of waste-tire-derived pyrolytic carbon black (CBp) in natural rubber (NR) composites at the component level through controlled demineralization strategies and modification treatments. This study identifies three main findings. First, SiO₂ acts as a rigid structural skeleton that improves filler polarity and interfacial bonding, increasing the tensile strength by 16.8% (21.39 MPa) and the modulus M300 by 9.77 MPa. Second, ZnS negatively impacts composite performance by inducing stress concentration and weakening adhesion; its removal markedly improves the mechanical strength. Third, KOH activation increases the mesopore surface area from 36.27 to 45.69 m²/g, but this benefit is realized only when KOH activation is combined with SiO₂ retention, resulting in optimal mechanical properties (22.17 MPa tensile, 10.48 MPa M300). This work delineates component-level reinforcement contributions, demonstrating that purified CBp with retained SiO₂ exhibits performance comparable to that of fossil-derived carbon black (CB), whereas ZnS-free CBp-ZK shows superior dynamic mechanical properties (e.g., a reduced Payne effect). These findings advance the high-value utilization of CBp as a sustainable reinforcing filler, addressing critical gaps in waste tire pyrolysis product applications. This study further highlights the dual role of inorganic components, with SiO₂ enhancing compatibility and ZnS impairing interfacial bonding, providing a foundation for industrial-scale CBp modification strategies.