The Effects of Carbon Black-Vulcanization System Interactions on Natural Rubber Network Structures and Properties

Abstract

Abstract We have studied the interaction of the vulcanization system (conventional and EV) and filler (HAF black, N330) concentration on the technical properties and network structure of NR vulcanizates. At lower loadings of filler, a marked difference in values of resilience, hardness, tear strength, elongation at break and tensile strength was observed between the vulcanizates of the two systems; whereas, this difference is minimized at higher loadings of filler. At all loadings, modulus, flex cracking resistance, dynamic set, and compression set are higher for the conventional system than for the EV one. But irrespective of filler concentration, heat buildup is higher for the EV system than for the conventional system. At lower loadings of filler, abrasion loss is independent of the vulcanization system, but at higher loadings, abrasion loss for the EV system is more than for that of the conventional one. Addition of HAF black at 5 phr loading increases total crosslink density and the proportion of polysulfidic crosslinks in the conventional system, and higher loadings of filler do not have any further effect on the network structure. That is why the vulcanizates of the conventional system yield higher resilience, hardness, tear strength, elongation at break, tensile strength, modulus, flexcracking resistance, and set properties as well as less heat buildup. But at higher loadings of filler, some of the above properties tend to become independent of the vulcanization system. This implies that at higher loadings of filler, rubber-filler attachment overshadows the network structure, and the properties become independent of vulcanization system and are governed by the filler concentration. We have also calculated the vulcanization rate parameters with the help of Goran's model for understanding higher polysulfidic crosslinks in the presence of HAF black and in conventional systems.