On the Kissinger equation and the estimate of activation energies for non-isothermal cold crystallization of PET

The activation energy for nonisothermal cold crystallization of polyethylene terephthalate (PET) and its blends with 1% polystyrene (PS) and 1% styrene-acrylonitrile copolymer (SAN) were measured based on differential scanning calorimetry (DSC). The Kissinger method was used to compute the activation energies in all cases, obtaining mean values of 120, 100, and 85 kJ/mole for neat PET, PET/1%PS and PET/1%SAN. A modified Kissinger procedure is proposed to estimate activation energies in polymer systems in which the relative crystallinity - measured at constant heating rates - can be correlated by the Ozawa model with a temperature-independent exponent. Values of the activation energy of 115 and 160 kJ/mole were obtained for cold crystallization of PET in the PET/1%PS and PET/1% SAN blends using the modified Kissinger procedure.