Monitoring Thermal Oxidation of Sulfur Crosslinks in SBR-Elastomers by Quantitative Analysis of Sulfur K-Edge XANES-Spectra

This paper presents a quantitative description of the processes occurring at the sulfur crosslinks of vulcanized rubber during thermo-oxidative aging. To extract this information in a nondestructive way, sulfur K-edge X-ray absorption near-edge structure (XANES) spectra have been analyzed quantitatively. We find that reversion takes place before the onset of oxidative processes at the sulfur bridges. Parallel to the oxidative processes, the production of cyclic sulfanes takes place. Both the relative and absolute contributions of the different reactions involving the sulfur crosslinks vary strongly with sample composition. Whereas antidegradants delay the thermo-oxidative aging without actually changing the aging resistance of the sulfur bonds, both the amount of S8/TBBS (N-tert-butylbenzothiazole-2-sulfenamide) and the presence of carbon black in the sample enhance this parameter considerably.