Poly (ethylene terephthalate) thermo-mechanical and thermo-oxidativedegradation mechanisms

摘要

1H NMR and MALDI-TOF MS measurements were used to study the thermo-mechanical and thermo-oxidative degradation mechanisms of bottle-grade PET (btg-PET). In the thermo-oxidative degradation, theconcentration of low molar mass compounds increased with time and the main products were cyclic andlinear di-acid oligomers. In the thermo-mechanical degradation, the main-chain scission reactions affect thestability of the cyclic oligomers. One of the most important bottle-grade PET co-monomers is diethyleneglycol (DEG), which is a "reactive site" in the thermal degradation of btg-PET. The DEG co-monomer wasshown to be the precursor to colour changes in btg-PET, owing to the attack by molecular oxygen on themethylenic protons adjacent to the ether oxygen atoms of DEG. This behaviour was observed in the thermo-oxidative degradation process in which the degradation of DEG causes the release of hydroxyl radicals in thepolymeric matrix, thereby producing mono- and di-hydroxyl substituted species. This was also observed inthe thermo-mechanical degradation process.