Compressive stress relaxation modeling of butadiene rubber under thermo-oxidative aging

The compressive stress relaxation tests of butadiene rubber (BR) at different thermo-oxidative aging temperatures were carried out. Fourier transform infrared spectroscopy with attenuated total reflectance (FTIR-ATR) was used to observe the variations of internal groups before and after the thermo-oxidative aging. Magnetic resonance-crosslink density (MR-XLD) spectroscopy was used to measure the crosslink densities. The results showed the compressive stress relaxation of BR during thermo-oxidative aging was dominated by chemical reactions: crosslinking, chain scission, and oxidation. Then an empirical model and an amendatory standard linear solid (SLS) model were put forward to describe the compressive stress relaxation behavior of BR. Both models fitted the data well. The SLS model, based on the aging mechanism of BR, not only made up the disadvantages of the empirical model, but also considered the changes of intrinsic viscosity (η) during the thermo-oxidative aging of BR. The SLS model showed that the thermo-oxidative aging of BR was mainly dominated by the crosslinking and oxidation reactions. This research proposes the amendatory SLS model and has important significance for study the stress relaxation behavior of crosslinked rubbers during thermo-oxidative aging.