Thermal degradation of poly(ethylene terephthalate): A kinetic analysis of thermogravimetric data

The thermal decomposition of poly(ethylene terephthalate) has been studied using a conventional dynamic thermogravimetric technique in a flowing air atmosphere at several heating rates between 0.1°C and 100°C/min. The dynamic thermogravimetric analysis curve and its derivative have been analyzed using a variety of analytical methods reported in the literature to obtain information on the kinetic parameters. The degradation was found to be a complex process composed of at least three overlapping stages for which kinetic values can be calculated. The best approaches to solving the kinetics of the decomposition were found to be the multiple heating rate techniques of Friedman and Ozawa. The Friedman technique gave apparent activation energies (kJ/mol) for the three main decomposition stages of 122.2 ± 12.9, 201.0 ± 8.5, and 141.9 ± 12.7, with a value of 85.5 ± 10.2 for the prestage at low conversion. The Ozawa method, meanwhile, gave values of 101.6 ± 2.6, 182.6 ± 7.4, 142.5 ± 3.8, and 158.4 ± 26.1 for the prestage.