RECURRING VULCANIZATES .2. EFFECT OF ADDED ACCELERATORS

Vulcanizates, to which more accelerator has been added by swelling, were recured to study the interaction between the accelerator and the sulfur crosslinks. The addition of benzothiazole, or dithiocarbamyl sulfenamides, to SBR, SBR/BR, or NR vulcanizates caused more crosslinks to form on recuring. A typical induction period was also noted. The results were essentially the same in all rubbers. Crosslink formation, as measured by modulus development or rheometer torque, increased with increasing loadings of accelerator. Similarly, at a given accelerator loading, crosslink formation increased with increasing length of the polysulfide crosslink. These results indicate that an equilibrium exists between the zinc salt of the accelerator and the polysulfide crosslinks.