Studies on thermal and thermo-oxidative degradation of poly(ethylene terephthalate) and poly(butylene terephthalate)

A comparative study was conducted into the thermo-oxidative degradation of poly(ethylene terephthalate) (PET) and poly (butylene terephthalate) (PBT). Degradation of the polymer films and model compounds, ethylene dibenzoate (EDB) and butylene dibenzoate (BDB), was carried out in an oxygen atmosphere at 160 degreesC. On the basis of the compounds identified by GC-MS a mechanism is proposed for the degradation of the model compounds that involves the oxidation at the alpha -methylene carbon with formation of unstable peroxides and carboxylic acids. From the studies performed under N-2 at 160 degreesC it could be concluded that benzoic acid and esters are products of the thermal degradation, while benzoic and aliphatic acids, anhydride and alcohols are due to thermo-oxidative degradation. In contrast to the thermo-oxidative degradation of other polymers, for PET and PBT, especially at the beginning, thermal degradation plays an important role. The results clearly showed that PET is more stable towards degradation than PBT. (C) 2001 Elsevier Science Ltd. All rights reserved.