Thermo-oxidative aging and its influence on the performance of silica, carbon black, and silica/carbon black hybrid fillers -filled tire tread compounds

Silica and carbon black fillers in Solution-based Styrene butadiene rubber (S-SBR) are investigated to improve tire performance for rolling resistance and traction under the influence of thermo-oxidative aging. This study provides a detailed analysis of the thermo-oxidative aging behavior in solution-styrene-butadiene rubber (S-SBR) compounds, a material extensively utilized in passenger car radial (PCR) tires. The performance of silica (Si), carbon black (CB), and Si/CB hybrid filler systems was investigated to assess their influence on aging resistance and mechanical durability. Comprehensive tensile testing, coupled with entanglement and crosslinking density analysis, revealed that silica-filled S-SBR compounds exhibit superior aging resistance compared to their carbon black and hybrid counterparts. Specifically, the Si-filled rubber (70 phr) demonstrated a significantly higher reinforcement index and a notably lower aging coefficient, suggesting enhanced retention of mechanical properties post-aging. Crosslink density increased markedly across all systems during thermo-oxidative aging, with Si-filled compounds outperforming CB and Si/CB-filled systems. The evolution of crosslink density and physical entanglements from polymer–filler, and filler-filler interaction was assessed using the Mooney-Rivlin model, which indicated that the Si-filled rubber showed the highest physical entanglement density upon aging. Interestingly, the Si-filled system also displayed a reverse stress-softening effect during aging, suggesting a complex interplay between filler–polymer interactions and entanglement dynamics. This behavior contrasts with the increased stress relaxation observed in CB-filled compounds, likely attributable to enhanced chain mobility and entanglement evolution. A schematic of polymer chain kinetics was proposed to elucidate the molecular-level interactions between the polymer matrix and filler systems during aging. Si-filled compounds exhibited elevated hysteresis and stress-softening resistance, confirming the superior aging performance attributed to silane coupling in silica-filled rubbers. These results underscore the potential of silica as a highly effective filler for improving the thermo-oxidative aging resistance of tire tread compounds, thereby offering valuable insights for developing high-performance, durable tire materials.