Effect of Partial Silica Replacement with Carbon Black, Graphene, and Carbon Nanotubes on the Fatigue Performance and Ageing Behaviour of SBR Compounds

This study investigated the effect of the partial replacement of silica with carbon fillers, namely carbon black (CB), graphene, and carbon nanotubes (CNTs), on the curing behaviour, thermo-mechanical properties, ageing resistance, and degradation of styrene-butadiene rubber (SBR) vulcanizates. The aim was to determine whether small amounts of carbon fillers could improve the durability-related properties of silica-filled SBR compounds. Graphene and CNTs reduced the maximum curing torque compared with the CB-filled compound while maintaining satisfactory curing characteristics. Thermal conductivity increased with temperature for all materials and reached 0.126 W·m−1·K−1 for the graphene-filled vulcanizate at 40 °C, compared with 0.109 and 0.107 W·m−1·K−1 for the CNT- and CB-filled compounds, respectively. Dynamic ageing tests revealed significant differences in self-heating behaviour. After 10,000 De Mattia cycles, the graphene-filled compound exhibited the lowest temperature increase (1.5 °C), whereas the CB5/Sil15 formulation showed the highest value (4.5 °C). GC-IMS analysis confirmed the formation of volatile degradation products during cyclic ageing, while increasing carbon filler content reduced the intensity of the characteristic VOC signals. Analysis of the crosslink structure indicated that CNT-containing compounds exhibited the highest resistance to ageing-induced structural changes, whereas graphene promoted an increase in the proportion of monosulfidic and carbon–carbon crosslinks. Overall, the results demonstrate that partial replacement of silica with carbon nanofillers improves the thermo-mechanical stability of SBR vulcanizates. Graphene provided the greatest enhancement in thermal conductivity and the lowest heat build-up, while CNTs showed the highest resistance to structural changes during dynamic ageing.