Dsc combined with chemiluminescence for studying polymer oxidation

A DSC instrument modified to incorporate a chemiluminescence (CL) detector has been used to make simultaneous measurements of heat flow and light emission for oxidising polymer samples. Comparison of heat flow and light emission from unstabilised polypropylene shows a linear relation between heat flow and square root of intensity, giving indirect confirmation of the Russell mechanism for CL emission. Measurements of oxidation induction times (OIT) for stabilised samples show excellent correlation of the two techniques. The advantage of the CL method in being insensitive to thermal transitions in the sample is illustrated by a study of poly(ethylene terephthalate), whilst the very high sensitivity of CL detection is illustrated by its ability to detect peroxides at levels which are not detected by DSC. Finally, the limitations of the OIT approach in lifetime prediction by Arrhenius extrapolation are emphasised.