Structure and properties of poly(ethylene terephthalate) fibers

The structure and properties of commercial poly(ethylene terephthalate) (PET) fibers, melt-spun at various spinning speeds is investigated by means of X-ray diffraction, differential scanning calorimetry, mechanical testing and other methods. All the fibers studied contained 0.5 wt.% TiO{dollar}sb2{dollar}. It is found that the amorphous material in fibers melt-spun at intermediate speeds (2.5-4.5 km/min) is essentially inhomogeneous and forms domains with low and high molecular orientations. The investigations demonstrated a three-stage crystallization process in these fibers, when the macroscopic shrinkage is prevented. The results are interpreted by assuming large scale interconnectivity among the oriented domains, in the form of a fine network.; To investigate the stress-strain behavior of the PET fibers at temperatures above the glass transition, a new method which minimizes the effect of the crystallinity development on the fibers response is introduced. The method is characterized by rapid heating ({dollar}sim{dollar}10{dollar}sp4{dollar} deg/s) and short measuring timespans (100-200 ms). On the basis of the high temperature investigations, a deformational mechanism which can qualitatively explain a large number of experimental observations, is proposed. Included are suggestions explaining specifics of the melt-spinning of PET at various spinning speeds and the possible influence of the additives.