Construction of the Reactive Primary-Secondary Antioxidant Synergistic System with Multi-Mechanisms for Enhancing Thermo-Oxidative Aging Resistance of NBR

In this study, the reactive primary-secondary antioxidant covulcanized MC@AB/NBR composites were successfully prepared for the first time to address the issues of thermo-oxidative aging susceptibility and migration of antioxidant in NBR. The primary-secondary antioxidants, featuring unsaturated double bonds and sulfide ether structures, optimize the NBR cross-link network, promote vulcanization, and enhance mechanical properties. Specifically, the vulcanization rate increases from 10.6 min^-1 to 12.6 min^-1, and the elongation at break improves from 386.51% to 600.86%. The synergistic effect between the aniline structure of the primary antioxidant and the sulfide structure of the secondary antioxidant enhances thermo-oxidative aging resistance, with the aging coefficient increasing from 0.095 ± 0.004 to 0.774 ± 0.027 after aging at 121 °C for 120 h, superior to many commercial antioxidant systems. Concurrently, characterization methods including oxidation induction time (OIT), temperature of oxidative exothermic peak (<i>T</i> _o), thermo-oxidative degradation kinetics and SEM of fractured cross-section have demonstrated the remarkable thermo-oxidative aging and degradation resistance of the reactive antioxidant MC@AB system. The mechanism reveal that the primary antioxidant MC releases hydrogen radicals to scavenge carbon-chain and peroxyl radicals, while the sulfide ether structure of secondary antioxidant AB degrades generated unstable hydroperoxides into stable alcohols, thereby terminating the thermo-oxidative aging chain reaction. The MC@AB system enhances aging resistance of NBR composites by reducing molecular chain unsaturation to strengthen stability and inhibiting aging via scavenging free radical and degrading hydroperoxide. This strategy offers a novel approach for designing long-term high-temperature-resistant rubber materials.