Effect of Pretreated CZ/S on the Vulcanization and Rheological Behaviors of Isoprene Rubber Vulcanizates

N-Cyclohexyl-2-benzothiazolesulfenamide (CZ) is commonly used in the rubber industry as a vulcanization accelerator, while the mechanism for promoting vulcanization is not clear. Herein, CZ was mixed with sulfur (S) at high temperatures to study the structure of mixtures and their effects on the vulcanization and rheological responses of isoprene rubber (IR). It is shown that polysulfides and residual S existed in the pretreated CZ/S mixtures, and the mixtures could adjust the crosslinking density (vc) of vulcanizates by the modulation of mixing temperature and time. Furthermore, pretreated CZ/S affects the nonlinear rheological and thermo-oxidative aging behaviors of IR vulcanizates. The pretreated CZ/S mixed for 10 min can improve the vc and mechanical properties, weaken the Payne effect and the Mullins effect, and delay the thermo-oxidative aging of IR vulcanizates in comparison with the CZ/S mixture without being pretreated. This work provides a way to modulate the cross-linking network to prepare rubber products with high strengths and low hysteresis energies at lower vulcanization temperatures and ZnO amounts.