Effect of deep eutectic solvents on vulcanization kinetics and strain-softening behavior of natural rubber/styrene-butadiene rubber

Natural rubber/styrene-butadiene rubber (NR/SBR) blends are widely used as tyre sidewall compounds; however, discrepancies in vulcanization rates and the selective distribution of vulcanization additives in SBR and NR contribute to suboptimal dynamic properties. In this study, we propose a straightforward strategy to modulate the multi-scale structure in NR/SBR blends by incorporating an ionic liquid-like deep eutectic solvent (DES) as a novel reactive vulcanization agent. The addition of DES substantially enhances the dispersion of ZnO within NR/SBR blends, accelerates the vulcanization process of SBR and the NR/SBR blend and increases their crosslinking densities. Furthermore, DES interacts with the non-rubber components of NR, facilitating the vulcanization of NR. The impact of DES on the linear and non-linear rheological behavior of NR, SBR and NR/SBR vulcanizates is minimal, except for an enhancement in weak strain overshooting. The distribution of DES within NR/SBR blends can be manipulated by varying the mixing sequence of DES with NR and SBR, while selectively positioning DES within the SBR phase may synchronise the vulcanization rates of the NR/SBR blend, thereby improving tensile strength and reducing mechanical hysteresis. This approach may provide a viable method for producing NR/SBR blend products characterised by high strength and low hysteresis energy.