Monitoring the degradation of stabilization systems in polypropylene during accelerated aging tests by liquid chromatography combined with atmospheric pressure chemical ionization mass spectrometry

Degradation pathways of three commonly used antioxidants were successfully studied by using accelerated aging tests for polymers. Additionally, thermal stability and resistance to discoloration of seven stabilizers were investigated by aging pure stabilizers dissolved in the polymer-mimicking solvent squalane. Methods based on high-performance liquid chromatography hyphenated with highly sensitive tandem mass spectrometric detection (HPLC-MS) were developed for structural elucidation of degradation products. Subsequent quantification was done using UV-detection. While Irganox 1330, Irganox 3114 and Cyanox 1790 showed a similar degradation mechanism with highly colored decomposition products, no corresponding oxidized species could be found for other stabilizers and less discoloration was observed. For Irganox 1010, hydrolysis was the preferred degradation mechanism, leading to products with an increased solubility in water. Therefore this stabilizer is less suitable for materials intended for water applications. In the aged materials previously unknown degradation mechanisms were observed for Irganox 1010 and Irgafos 168 which also contribute to the inhibition of autoxidation of the polymer.