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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 (h) 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 thermooxidative aging.

An artificial neural network (ANN) was developed to estimate the relaxation property of diene rubber. Regularization was introduced into the ANN and the average prediction accuracy was 98.72%. The sensitivity analysis shows that compressive strain is the crucial influence on the relaxation property. Diene rubber shows a higher relaxation at low compressive strain than at high compressive strain. Molecular simulations show that rubber at low compressive strain possesses high fractional free volume, molecular chain movement, and ozone permeability. The chemical characterization of cross-link density and 2D-FTIR correlation analysis show that the rubber network at low compressive strain is seriously degraded by random scission and the generation rate of the carbonyl group is faster than that of ozonide group, indicating chain scission predominates in ozonation. These fundamental studies are expected to provide a comprehensive understanding of the relaxation property of deformed rubber and guidance for the design of antiaging materials.

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