Study of the thermooxidative degradation kinetics of poly(tetrafluoroethene) using iso-conversional calculation procedure

The thermooxidative degradation kinetics of poly(tetrafluoroethene) (PTFE) in air flow has been studied at different heating rates (6, 10, 12 and 15 K min(-1)) by non-isothermal differential thermal analysis (DTA). Six calculation procedures based on single TG curves and iso-conversional method, as well as 27 mechanism functions were used. The comparison of the results obtained with these calculation procedures showed that they strongly depend on the selection of proper mechanism function for the process. Therefore, it is very important to determine the most probable mechanism function. In this respect the iso-conversional calculation procedure turned out to be more appropriate. In the present work, the values of apparent activation energy E, pre-exponential factor A in Arrhenius equation, as well as the changes of entropy Delta S-not equal, enthalpy Delta H-not equal and free Gibbs energy Delta G(not equal) for the formation of the activated complex from the reagent are calculated. All calculations were performed using programs compiled by ourselves.