Indicator products: A new tool for lifetime prediction of polymeric materials

The possible correlation between the degree of degradation in the polymer matrix and the release of indicator products was investigated. The degree of degradation was measured by following the molar mass changes by size exclusion chromatography, while indicator products were analyzed by gas chromatography -mass spectrometry. The degree of degradation in polyethylene and polyethylene vinyl acetate matrix after thermooxidation was found to be in correlation with the amount of dicarboxylic acids and lactones formed during aging, while the degree of degradation in photooxidized polyethylene could be predicted from the amount of dicarboxylic acids. The relative amount of lactones compared to the relative amount of dicarboxylic acids increased if the oxidation temperature was increased. However, the total amount of indicator products was in correlation with the remaining number average molar mass and the number of chain scissions caused by oxidation. The amount of butanedioic acid and butyrolactone correlated well with the total amount of dicarboxylic acids and lactones, respectively. Thus, instead of the whole compound classes, butanedioic acid or butyrolactone alone could be used as indicators of oxidation. The detected correlation offers a novel tool for making lifetime predictions and studying the long-term properties of polymeric materials.