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Influence of spinning velocities on the mechanical and structural properties of polyethylene terephthalate (PET)/nylon 6 blend fibers have been reported. Fibers of PET/nylon 6 containing a small percentage of nylon (5% by weight) have been melt-spun at 3 different spinning velocities (2,900; 3,200; 3,600 m/min). The fibers have been characterized by thermal, morphological, structrual, and mechanical analysis. Various techniques such as SEM, DSC, X-ray diffraction, hot water shrinkage (HWS), viscosity, and birefringence have been used. SEM analysis revealed that in the blend, nylon 6 is well-dispersed as spheres in the PET matrix. The blend shows a marked decrease in the melt-flow index, which in turn leads to a beneficial effect on the rheological properties of the PET without negatively influencing its mechanical characteristics. This finding results in a saving on energetical requirements of the processing, as both temperature and pressure of spinning can be decreased. © 1995 John Wiley & Sons, Inc.

The nucleating activity of antimony catalyst remnants on the melt crystallization of poly(ethylene terephthalate) (PET) is proved through comparisons, for samples with Sb concentrations in the range 180-1850 ppm, of the crystallization behaviors before and after a complete extraction of the catalyst remnants. These comparisons are performed by analysis of the crystallization peaks of differential scanning calorimetry (DSC), by the study of the isothermal crystallization kinetics from X-ray diffraction experiments, and by optical microscopy observations of the size of the spherulites. The dependence of the crystallization temperature (Tc, as evaluated by the position of the DSC peak) on the Sb concentration, reported in the literature, is shown to be largely overestimated. In particular, it is found that the Tc of commercial samples are essentially unaffected by the presence of the standard concentrations of Sb catalyst remnants. © 1993 John Wiley & Sons, Inc.

Some properties and structural aspects of fibers obtained by spinning, in a wide range of take-up speed (2,800–4,400 m/min), of commercial samples of PET, produced by dimethyl terephthalate (DMT) and the terephthalic acid (TPA) processes, are compared. For a same take-up speed, the considered fibers from TPA are spun at lower pack pressures and always show higher tenacity and lower ductility than fibers from DMT. X-ray diffraction, density, and birefringence measurements indicate that, for the fibers from the DMT process, an earlier crystallization occurs which prevents the progress of the orientation of the amorphous phase. The lower molecular orientation in the amorphous phase of the fibers from DMT, in turn, accounts for their lower tenacity. The earlier crystallization of the fibers from DMT would be related to their slightly higher melting temperatures and melt viscosities, which could be due to the lower amount of constitutional defects (diethylene glycol content) in the considered PET samples from DMT compared with those from TPA. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 889–896, 1997

The conformation and the packing of poly(ethylene terephthalate) (PET) chains in the mesomorphic form have been investigated by accurate X-ray diffraction measurements, conformational energy analysis, and calculations of Fourier transforms of models. The X-ray diffraction pattern presented here is richer than those previously reported. In particular, besides the known meridional peaks at zeta = 1/c and 3/c, corresponding to a periodicity of 10.3 angstrom, a stronger meridional peak at zeta = 5/c has been shown. The reported Fourier transform calculations of isolated-chain models indicate that the experimental diffraction pattern of the mesomorphic form of PET can be qualitatively accounted for by extended linear chains obtained by random sequences of monomeric units in different minimum energy conformations. These random sequences of monomeric units generate chains in which any long-range correlation between the planes of the phenylene rings, along the chain, is absent.