Tearing of Carbon Black-Filled Natural Rubber Vulcanizate Cured With Dicumyl Peroxide

The strength of rubber cured with dicumyl peroxide (DCP) has been studied previously. First, a brief introduction of fillers types, fracture mechanics and peroxide vulcanization basics will be discussed. An empirical equation is proposed to calculate the DCP levels that are needed to match the crosslink densities of the corresponding sulfur-cured vulcanizates with the same black levels. Observation and discussion of fracture for DCP-cured NR with different filler levels will follow. A percolation threshold was detected where 100% modulus, the Payne effect plateau G’ and curing torque show upturns as black concentration increases. Crack branching behavior and reinforcement effect had their onset at this black level. A detailed discussion of this structure-property relationship will be given. The tearing behavior of DCP-cured compositions will be compared with corresponding S vulcanizates. Finally, tearing/tensile behavior was studied with gum NR cured with different levels of DCP. The tensile/tearing strength of the gum rubbers increase, then pass through maxima, and finally decrease with increasing DCP levels.