Thermal oxidative degradation of styrene-butadiene rubber (SBR) studied by 2D correlation analysis and kinetic analysis

The thermal oxidation degradation of styrene–butadiene rubber (SBR) was investigated by in situ FTIR, 2D-FTIR, and programming heating DSC. The results of analyses suggest that the degradation reaction is an autocatalytic process and mainly occurs on the aliphatic part instead of benzene pendants. Based on the results of in situ FTIR and 2D-FTIR, the oxidation process can be divided into three stages. In stage one, just two carbonyl peaks appear, namely 1,697 cm^?1 (conjugate carbonyls) and 1,727 cm^?1 (saturated carbonyls), and the generation speed is 1,697 > 1,727 cm^?1. Yet the peaks appearing at 1,777 cm^?1 belonged to peresters and anhydrides generating in stages two and three. The generation sequences are: 1,698 > 1,727 > 1,777 cm^?1 for stage two; and 1,698 < 1,727 < 1,777 cm^?1 for stage three. According to DSC results, the thermal oxidation of SBR contains four steps. The first step is the generation of alkyl radicals and the accumulation of hydroperoxide species. The second step is initial oxidation stage mainly producing conjugate carbonyls. The third step is deep oxidation process generating diverse carbonyls. The fourth is chain termination reaction, in which step the generation rates of anhydrides and peresters are the fastest due to bi-radical termination of alkoxy radicals and the consumption of conjugate carbonyl. Furthermore, crosslinking reactions occur during the whole thermal oxidation.