Analysis of enthalpy relaxation in amorphous poly(ethylene terephthalate)

Endothermic peaks below or superposed to Tg have been observed by Differential Scanning Calorimetry in samples of amorphous poly(ethy1ene terephthalate) (PET) which were submitted to a wide range of annealing conditions. These endothermic peaks allow the obtention of the excess of enthalpy (6) and subsequently the effective relaxation times T(eff) On applying an empirical equation of T∼∼, with separate contribution of temperature and structure (6), kinetic parameters have been found in a range close to Tg, resulting for PET an apparent activation energy of 860.5 kJ/mol (between 60 and 68OC). This parameter has been also calculated from de dependence of Tg with the heating rate in a DSC scan and the values found are between 314 and 419 kJ/moL