Thermal Degradation of Poly(ethylene terephthalate) at the Processing Temperature

Several isothermal degradation experiments on poly(ethylene terephthalate) (PET) were conducted in the temperature range of 270-370 C, in order to simulate the reactions that take place during the processing of PET under inert atmosphere (N2). The structural characterisation of the reaction products was performed by MALDI mass spectrometry and by NMR analysis. The results indicate the formation of cyclic oligomers that decompose at higher temperature. Vinyl ester terminated oligomers could not be detected by MALDI and also by 1H and 13C NMR, whereas the formation of anhydride containing oligomers is well apparent. Formation of acetaldehyde in PET samples processed at various temperatures was detected by 1H NMR. We have also included in the present study a set of experiments where 0.5%w p-TsOH.H2O was added to PET. Our results show that the addition of small amounts of p-TsOH.H2O to PET, heated at 270 and 285 C, induces a strong hydrolytic reaction with consequent increase of carboxyl terminated polyester chains.