Thermo-oxidative aging of natural rubber: experimental study and a thermodynamically consistent mechanical-chemical-diffusion model

Elastomers have diverse properties that make them suitable for use in many industrial applications. Natural Rubber, in particular, is an attractive elastomer due to its desirable mechanical properties as well as lightweight compared to metals. However, due to the natural rubber structure, these elastomers are susceptible to heat, oxidation, and chemical compounds, which limits their potential use. In this paper, in order to study the behavior of natural rubber under thermo-oxidative aging, experiments, including continuous stress relaxation, creep, and intermittent tensile tests, are carried out on the samples. Based on the experimental results and using dynamic-network model, a mechanical-chemical-diffusion model is proposed to predict the changes in natural rubber properties during thermo-oxidative aging considering the effect of the natural rubber curing system. In the chemical part of the model, the two main process of aging, including chain scission and crosslinking, are modeled by using two internal variables. The proposed model is implemented using the finite element method to simulate experimental tests for the model verification. The comparisons demonstrate the proposed model ability to accurately simulate the various loading states under thermo-oxidative aging of natural rubber.