Consumption and reaction mechanisms of antioxidants during thermal oxidative aging

The consumption, the efficiency depending on the molecular structure, the generation of active intermediates and the fate of p-phenylenediamines during thermal-oxidative aging were investigated in rubbers and model systems. By means of OIT determinations, a high correlation could be shown between the effectiveness of the antioxidants and the type of substituents at the nitrogen atom. Activation energies and rate constants of the antioxidant consumption were determined. Dependent on aging-time the identification of the reaction product results in aldehyde adducts of the corresponding PPD. Investigations on 6PPD/squalenebased model systems by means of chemiluminescence, FT-IR, GC-MS and LC-MS led to hydroxylated squalene derivatives and aldehyde adducts. CL is useful for short term characterization of thermal-oxidative aging processes.