Evaluation of the aging coefficient and the aging lifetime of carbon black-filled styrene-isoprene-butadiene rubber after thermal-oxidative aging

We investigated the changes in the mechanical properties of carbon-black-filled styrene-isoprene-butadiene rubber (SIBR-CB) during a thermal-oxidative aging process at 90–130 °C. By tracking the changes in the mechanical properties of SIBR-CB over time at different temperatures, we estimated the aging temperature coefficient and aging lifetime of the rubber. Using the same methods, we directly compared the aging behavior of SIBR-CB to that of carbon black filled solution–polymerized styrene-butadiene rubber and carbon-black-filled neodymium-catalyzed isoprene rubber. The SIBR-CB sample exhibited the highest aging temperature coefficient, with values spread over a wider range compared to those of the other two rubbers. We attributed this to the presence of polybutadiene and polyisoprene chains within the macromolecular structure of SIBR-CB, which were susceptible to cross-linking and chain scission, respectively, during the thermal-oxidative aging process. These two reactions competed with each other and, in the case of SIBR-CB, the cross-linking was the dominant reaction. Consequently, the SIBR-CB sample exhibited the longest aging lifetime among the three rubbers. In addition, we established a relationship between the aging temperature and the aging lifetime and derived an equation that enables the calculation of the aging lifetime depending on the aging conditions.