Recrystallization studies on isotropic cold-crystallized PET: Influence of heating rate

Abstract

The nanostructural changes associated to the multiple melting behaviour of isotropic cold-crystallized poly(ethylene terephthalate) (PET) have been investigated by means of simultaneous wide-and small-angle X-ray scattering, using a synchrotron radiation source. Variations in the degree of crystallinity, coherent lateral crystal size and long period values, as a function of temperature, for two different heating rates are reported for cold-crystallized samples in the 100e190 C range. The Interface Distribution Function analysis is also employed to provide the crystalline and amorphous layer thickness values at various temperatures of interest. Results suggest that samples crystallized at both low (T a ¼ 100e120 C) and high (T a ¼ 160e190 C) temperatures are subjected to a nearly continuous nanostructural reorganization process upon heating, starting immediately above T g (z80 C) and giving rise to complete melting at z260 C. For all the T a investigated, a meltinge recrystallization mechanism seems to take place once T a is exceeded, concurrently to the low-temperature endotherm observed in the DSC scans. For low-T a and slow heating rates (2 C/min), a conspicuous recrystallization process is predominant within T a þ 30 C T 200 C. In contrast, for high-T a , an increasingly strong melting process is observed. For both, high-and low-T a , an extensive structural reorganization takes place above 200 C, involving the appearance of new lamellar stacks simultaneously to the final melting process. The two mechanisms should contribute to the high-temperature endotherm in the DSC scan. Finally, the use of a high heating rate is found to hinder the material's overall recrystallization process during the heating run and suggests that the high-temperature endotherm is ascribed to the melting of lamellae generated or thickened during the heating run.

Relaxation behavior of flax-reinforced ethylene–propylene–diene rubber

“…Extensive thermal analysis studies performed previously on poly(ethylene terephthalate) stated that high heating rates and low frequencies favor melting over crystallization. 24,28 The characteristics of the tan peak subsequent to the glass transition are consistent with its assignment to melting. At the same time, it is very possible that the end side of the relaxation peak, which is shifted to higher temperature with increasing frequency, covers up the melting peak, which is anyway diminished at higher frequencies.…”

SAXS study on the crystallization of PET under physical confinement in PET/PC multilayered films

“…This indicates that not all the volume of the PET layer is filled with stacks of crystals but, on the contrary, stacks of crystals are separated by large amorphous regions. The presence of stacks of crystals separated by large amorphous regions is a common feature for a semistiff polymer such a non-confined PET [33,34]. It has been further shown that the volume of the interstack regions rises with increasing confinement in the PET/PC films.…”

Coupling effects of spinodal decomposition and crystallization on mechanical properties of polyolefin blends

“…Lamellar thickness l c could be generally determined from the z position at the peak in the interface distance distribution function which was identical with the second derivative of the 1-dimensional electron density correlation function, K 00 (z) [19,20]. K(z) could be calculated in a straightforward manner as Eq.…”