Measuring Thermal Crystallinity in PET
The mechanical properties of poly (ethylene terephthalate) (PET) depend on the degree of crystallinity. PET crystallizes from both thermal and strain-induced process paths. Strain-induced crystallization occurs under uniaxial or biaxial stretching, the latter is common in stretch blow molding. Thermal crystallization takes place when cooling from the melt or under sustained elevated temperature which are both common during injection and blow molding. The current work focuses on comparing methods used to quantify the percent thermal crystallinity in injection molded water bottle preforms. An injection molded preform with a gradient of induced thermal crystallinity was examined using Differential Scanning Calorimetry (DSC), Micro X-ray Diffraction (μXRD), and Raman Spectroscopy. Correlating these three techniques for percent thermal crystallinity, helps with the development of nondestructive crystallinity measurement methods to aid with process optimization and part quality.
Infrared spectra of high polymers: Part IX. Polyethylene terephthalate
Abstract Infrared spectra of polyethylene terephthalate and three of its deuterated analogs have been obtained in the region of 70 to 3600 cm−1, polarized spectra having been obtained down to 330 cm−1. On the basis of analysis of the predicted spectrum, and with the aid of data from benzene and substituted benzenes, a complete assignment of the spectrum has been made. This assignment suggests a modification of the proposed chain structure of this polymer. It also leads to the conclusion that the changes in the spectrum which occur upon crystallization of the polymer are not associated with different isomeric forms of the OCH2CH2O portion of the chain, but rather with changes in the symmetry and resonance characteristics of the substituted benzenoid ring frame-work.
Crystallization in oriented poly(ethylene terephthalate) fibers. I. Fundamental aspects
The nature of crystallization- and mobility-induced changes during annealing of melt-spun poly(ethylene terephthalate) precursor fibers of a range of orientations has been examined. The kinetics of crystallization and the accompanying orientational changes have been studied under conditions of constant, low tensile stress, with the accompanying dimensional changes and under a constraint against shrinkage in length, with the stress developed being monitored. The effects of precursor orientation and externally imposed constraints on the course of the fundamental crystallization and orientational relaxation processes are revealed. Oriented crystallization has been shown to have a significant effect on the stress developed and on the dimensions of oriented precursor fibers, with a strong tendency to spontaneously extend as a consequence of the reorientation of crystallizing segments predominantly along the preferred fiber direction. The sequence in which crystallization and major orientational relaxation, if any, occur is found to have a profound effect on the structure and thus the deformability of oriented fibers after annealing above the glass transition temperature.