Chemiluminescence from oxidized polypropylene during temperature cycling

The chemiluminescence measured during temperature cycling over some temperature range reveals the complexity of the oxidation of polypropylene much better than isothermal or ramp experiments. It enables the characterization of the stages of oxidation within one temperature cycle by corresponding values of apparent activation energy and pre-exponential factor. The independence of the rate constant of oxidation on the extent of oxidation within certain limits is thus demonstrated. It is shown that the Arrhenius plot for the increase of temperature in the first cycle of decomposition of polypropylene hydroperoxides in nitrogen covers the rate constants of so-called faster decomposing hydroperoxides while that for subsequent cycles approaches the rate constants of so-called slower decomposing hydroperoxides. The bimolecular decomposition of hydroperoxides in initiation of oxidation provides a unified approach to the “heterogeneous’ and “homogeneous’ interpretation of polypropylene oxidation.