Studies of post drawing relaxation phenomena in poly(ethylene terephthalate) by infrared spectroscopy

Abstract

In this paper, we study the relaxation behavior of initially amorphous poly(ethylene terephthalate) (PET) films drawn, at 80°C using a draw rate of 2 cm/min, to a draw ratio (A) from 1 to 5 and then quenched to room temperature. These films were then heated at different temperatures from 68 to 80°C for different times and their orientation determined. The orientation measurements were performed by transmission infrared spectroscopy and the bands used for the determination of orientation were those at 1340 and 970 cm-' for the trans conformers, normalized using the 1410 cm-' benzene ring vibration. The crystallinity was determined by thermal analysis. It is shown that when PET is drawn to A values up to 2-2.5 (before stress-induced crystallization), the orientation relaxes rapidly a t temperatures close to the glass transition temperature of PET. For A values of 3 or higher, the orientational relaxation of the amorphous regions is hindered. This effect is ascribed to the development of strain-induced crystallites, which are believed to act as pseudo-crosslinks.

Strain-Induced Crystallization during Relaxation Following Biaxial Stretching of PET Films: A Real-Time Mechano-Optical Study

“…Using this approach, several authors 15,16,23 have suggested that PET behaves as a rubber-like network when deformed at low to moderate draw ratios (λ ≤ 2.5), where PET will follow the Gaussian network model which predicts an increasing slope in the orientation function plotted as a function of λ, as given by Treloar: 21…”

Characterization of molecular orientation in injection–stretch–blow‐molded poly(ethylene terephthalate) bottles by means of external reflection infrared spectroscopy

“…Furthermore, the estimated draw ratio of 3.8 is higher than the critical value of around 2.2-2.5 required to generate shear-induced crystallization and inhibit molecular relaxation during the cooling phase. 8,15 Thus, the points generally tend toward the transverse apex, with f cT lying between 0.3 and 0.5, whereas the values of f cM and f cN are negative. As was observed for the type I bottles, for some points the value of f cN is not the lowest of the three, and this suggests a certain preference of the chains for the thickness direction.…”

“…One way of alleviating this problem is to increase the crystallinity of the polymer during processing. 8 It is clear that if plastics are to compete successfully with glass, all the aforementioned properties must be optimized, and this means that it is important to characterize the morphology and to understand how it varies as a function of the processing conditions. Information can be obtained by means of various techniques, including birefringence, X-ray diffraction, heat-shrinkage measurements, differential scanning calorimetry, and infrared (IR) and Raman spectroscopy.…”

Broad poly(ethylene terephthalate) nanofiber sheet prepared by CO 2 laser supersonic continuous multi-drawing

“…These two bands have been assigned to the CH 2 rocking of glycol [19e22]. The trans conformation can be present in both crystalline and amorphous phases [23], but the gauche conformation is found only in the amorphous phase [24]. The increase in the amount of the trans conformation can be attributed to a morphological change from a folded chain to an extended chain.…”