Toward Greener Rubber: Impact of Resin Type and Amount on Curing, Network Structure, and Viscoelastic Properties in SBR compounds

In the pursuit of more sustainable tire technologies, the replacement of petroleum-derived additives with bio-based alternatives has become a key research focus. Tackifying resins, which contribute significantly to tread performance and viscoelastic behavior, are among the additives under evaluation for substitution. In this study, several complementary techniques were applied to styrene–butadiene rubber (SBR) compounds, containing either a natural rosin-based resin (Dertoline) or a petroleum-derived resin (Kristalex) at concentrations ranging from 15 to 45 phr, to investigate the effect of resin on the curing process and on compound properties before and after curing. Solid-state NMR spectroscopy and differential scanning calorimetry revealed intimate mixing between polymer and resin at all concentrations and a slowdown in dynamics with increasing resin content that was more pronounced for Kristalex. Dertoline appeared to hinder effective interactions between carbon black, used as a filler, and SBR, leading to a strong suppression of bound rubber, as evidenced by swelling experiments. Vulcanization kinetics, monitored by moving die rheometer experiments, was affected by the two resins in different manners: Kristalex slowed down curing, while Dertoline accelerated it. Moreover, a marching phenomenon was observed at long curing time for high Dertoline concentrations. Cross-link density, determined by equilibrium swelling, decreased with increasing resin loading. Final mechanical and viscoelastic properties of vulcanized compounds, evaluated by dynamic mechanical analysis and tensile tests, were influenced by both resin type and concentration, showing mechanical plasticization effects and changes in both the elastic and anelastic response. Importantly, the two resins appeared to influence wet grip and rolling resistance differently, highlighting their distinct impact on key performance parameters. These results support the tailored use of bio-based tackifiers in sustainable SBR formulations.