Cinética de cristalização a frio do poli (tereftalato de etileno).

Abstract

The exothermic peak that is frequently observed during the heating scan of a differential scanning calorimetry (DSC) experiment of poly (ethylene terephthalate) (PET) is due to a cold crystallization process, originating from the rearrangement of the amorphous regions into a crystalline phase. In this work the isothermal and non-isothermal cold crystallization kinetics of PET was investigated by using DSC, X-ray diffraction and tensile experiments. The isothermal rate of crystallization was determined as a function of temperature and the AVRAMI analysis was conducted, indicating that in low temperatures the cold crystallization process occurs in two regime behavior, while for high temperatures just one stage was observed. The constant of isothermal crystallization rate K increased and the half time of crystallization (ti/2) decreased with the increase in the crystallization temperature. AVRAMI exponent n presented values close of 2, and this corresponds to a disc-like morphology formed by heterogeneous nucleation. The cold crystallization increased the crystallinity and therefore the tensile properties of the samples. Non-isothermal cold crystallization kinetics of PET was studied using the OZAWA model by applying different heating rates. The cold crystallization temperature of PET increased progressively with the heating speed, suggesting a reduction in general speed of crystallization with the increase of the scanning rate. OZAWA exponent m showed a reduction with increase of crystallization temperature, following the same tendency of the isothermal crystallization. The constant of speed K' had a significant reduction with the increase of temperature, in opposite trend as observed by isothermal conditions.