Nonisothermal cold crystallization of poly(ethylene terephthalate)

The thermal transitions and the nonisothermal cold crystallization kinetics of poly(ethylene terephthalate) (PET) at constant heating rates were investigated using differential scanning calorimetry. It was found that the glass transition and crystallization temperature increased with the heating rates, while the melting temperature showed a little variation for the heating rates used. Crystallization and melting latent heats were remarkably constant, independent of the heating rate. Kinetics parameters were determined using Ozawa model. Two different kinetic regimes were identified, corresponding to primary and secondary crystallization, at low and high fractional crystallization, respectively, both following Ozawa’s model. Kinetics parameters were determined for the primary and secondary regimes; the pre-exponential constant (KT) and Ozawa’s exponent (m) decreased with increasing crystallization temperature. The combined kinetic parameter $Z = K_{\rm{T}}^{{\rm{1/}}m} $ increased exponentially with temperature; activation energies were estimated using Arrhenius plots for the two PET crystallization regimes.