WELLEN, R. M. R.; http://lattes.cnpq.br/5406259642631461; WELLEN, Renate Maria Ramos.
Résumé:
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.