Abstract
A tendency for zinc and sulfur to reagglomerate, along with wax, has been observed in oil extended SBR and natural rubber tires. In high concentrations these relatively brittle reagglomeration areas are associated with poor resistance to groove cracking. The pigment-polymer environment has a significant effect on the occurrence of non-carbon reagglomeration. An increase in reagglomeration in oil extended SBR treads is favored by: 1. Poor initial dispersion of the non-carbon components. 2. Fine particle size and low structure carbon blacks. 3. Excessive zinc and wax. Conversely, reagglomeration can be reduced or eliminated by good dispersion of all compound ingredients, the use of higher structure or larger particle size carbon blacks, and through blending with polybutadiene.