The tearing energy threshold of crack growth in rubber exposed to ozone: an experimental–numerical approach

The global rubber industry is seeking alternatives to the widely-used antiozonant, N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD), due to its environmental toxicity concerns when used in automobile tires. These substantial research and development efforts on new antiozonants for rubber are hindered by a general inability to characterize the fundamental physical parameter of ozone-induced tearing energy threshold for crack growth, which underlies the practical ozone resistance of rubber products. Therefore, this paper presents, for the first time, a novel experimental–numerical combined approach to determine the tearing energy threshold in rubber exposed to ozone, which is a key criterion for assessing the resistance of rubber to ozone crack growth. The approach is based on in-situ optical analysis of ozone crack growth on the rubber surface and the determination of the crack growth rate when the rubber is stretched. Subsequently, the growth rates form the basis for calculating the energy release rates at the crack tips using the finite element method in Ansys software. By comparing the calculated energy release rates and experimentally measured crack growth rates, the energy release rate interval corresponding to the threshold tearing energy is determined. Based on this approach, the tearing energy threshold for carbon black reinforced natural rubber exposed to ozone was found to be a maximum of 2.12 J/m². This value is 96% lower than the threshold for the non-ozone-exposed specimens. In conclusion, this novel methodology was able to determine the ozone threshold tearing energy and represents a powerful, unique tool for an efficient future development of environmentally friendly antiozonants.