Synergistic effect of eugenol and antioxidant 4020 on enhancing the thermo-oxidative aging resistance of silica/NR composites

This study investigates eugenol as an alternative to mitigate environmental pollution and worker hazards associated with antioxidant N-(1,3-dimethyl)butyl-N′-phenyl-p-phenylenediamine (4020) while aligning with trends toward sustainable additives. Silica/natural rubber (NR) composites with varying ratios of eugenol and 4020 were prepared to assess their aging resistance, mechanical properties, and the synergistic antioxidant effects. Thermogravimetric analysis, cross-linking density experiments, thermo-oxidative aging tests, and oxidation induction tests revealed the highest thermo-oxidative aging resistance when 0.5 phr of 4020 was substituted with eugenol. When 1.0 phr of 4020 was replaced by eugenol, the antioxidant properties of the composites matched those containing 2.0 phr of 4020. However, when eugenol exceeded 1 phr, the antioxidant properties gradually decreased. DIN wear tests showed optimal wear resistance when 1 phr of 4020 was replaced with eugenol. These findings suggest that 50% of conventional antioxidants can be substituted with eugenol without compromising material properties. The partial substitution of eugenol in silica/NR composites proves eugenol can act as a sustainable alternative, providing comparable antioxidant capacity while reducing environmental impact.