Chemiluminescence as a probe of polymer oxidation

Many oxidation reactions of organic materials, including polymers, are accompanied by the emission of weak chemiluminescence (CL). From a study of the mechanism of this weak CL, it is shown that the time development of the CL intensity may provide the kinetics of the oxidation reaction and is thus a sensitive probe of the degradation of the material. The intensity of emission reflects the concentration of peroxidic species in the material. Whereas the kinetics of the oxidation may be described by a series of elementary, homogeneous free radical reactions, the use of imaging techniques has shown that the oxidation of polymers such as polypropylene is highly heterogeneous. A model that describes the oxidation as spreading through the material as an infection from a number of initiating sites is able to rationalize these observations and provide a new approach to the prediction of the useful lifetime of a polymeric material.