SYNOPSISThe process of melt-spinning poly(ethy1ene terephthalate) (PET) filament a t high speeds was modified through the inclusion of a liquid isothermal bath (LIB) in the spinline. A wide range of positions, temperatures, and depths associated with the operation of the LIB were utilized in this study. The structural characteristics and mechanical properties of the as-spun fibers were characterized by birefringence, wide-angle X-ray diffraction (WAXD), infrared spectroscopy, and tensile testing. Experimental results showed that the structure and mechanical properties of the as-spun fibers were significantly influenced by the LIB operating conditions. The as-spun fibers prepared under optimum LIB conditions exhibit high birefringence and excellent mechanical properties. Results suggest the development of a critical value of threadline stress that is determined primarily by LIB depth and takeup velocity. Below this critical value, raising of LIB temperature, LIB depth, and take-up velocity resulted in increases of the apparent crystallite size, sample crystallinity, and both the crystalline and amorphous orientation. As would be expected, the mechanical properties of the fiber samples were improved in a corresponding manner. Above this critical stress value, molecular chains in the amorphous phase are stretched tautly, but the crystal growth process is restricted, resulting in a decrease in crystallite size and crystallinity, as well as a continued increase in mechanical properties. The fiber properties were also found to be very responsive to the relative location of the LIB. A unique structure, believed never before obtained in a one-step high-speed P E T melt-spinning process, has been achieved that combines high amorphous orientation, low crystallinity, and high tenacity. 0 1995 John Wiley & Sons, Inc.
ABSTRACT:The ability to produce as-spun poly(ethylene terephthalate) (PET) filaments that possess previously unsurpassed levels of as-spun orientation and tensile properties was achieved through the implementation of a device described as a liquid isothermal bath (LIB). Although much has been published regarding the general effect of the LIB on various properties and structural features, the results of the present study further contribute to the continued development of this unique technology by investigating the positional dependence of the device, as well as the effect of a subsequent annealing process. Characterization methods employed in the present study included birefringence, percent crystallinity, tensile properties, loss tangent temperature dependence, DSC melting behavior, and wide-angle and small-angle X-ray scattering. Strong inferences drawn from the loss tangent temperature dependence indicate that all of the as-spun and annealed LIB filaments possess a more rigid amorphous phase than that present in either the as-spun or annealed no LIB filament and that the extent of rigidness appears to become more profound as the bath is operated at a position more distant from the spinneret. DSC melting endotherms of the as-spun LIB filaments consist of dual overlapping peaks, one component of which is believed to represent the presence of a novel extended chain type of crystalline structure. Application of a simple two phase model allowed for the quantitative evaluation of an amorphous orientation factor, which was found to range, depending on the bath position, from 1.7 to 3.9 times higher in the as-spun LIB filaments than that present in the asspun no LIB filament. The annealing process was found to play an important role in facilitating the transformation from an as-spun highly oriented and predominantly amorphous structure to a well-defined semicrystalline fibrillar structure.
SYNOPSISA high molecular weight polyethylene terephthalate was spun into fibers in the speed range from 3,000-7,000 mpm. The effect of modifying threadline dynamics through a combination of enhanced and/or retarding air quenches on the resulting spinning performance, fiber structure, and mechanical properties was examined. Particular combinations of these threadline temperature profile modifications were shown to result in significant improvements in spinning performance and as-spun fiber structure. Extensive characterization of select fiber samples revealed higher orientation and crystallinity, larger crystal dimensions, and greater mechanical properties. These results also demonstrated the ability to provide continued improvement in fiber properties at very high take-up speeds where typically a decline is observed. It is concluded that the threadline temperature profile can be altered in such a way as to significantly enhance the resulting spinning performance and fiber structure over a wide range of take-up speeds.
ABSTRACT:The effect of initial take-up speed on the properties and structure of both as-spun and drawn/heat-set poly(ethylene terephthalate) filaments was characterized through measurements of birefringence, percent crystallinity, tensile properties, high temperature shrinkage, loss tangent temperature dependence, DSC melting behavior, and wide-angle (WAXS) and small-angle X-ray scattering (SAXS). While a steady trend toward improved as-spun filament orientation and tensile properties occurred with increasing initial take-up speed, the reduced drawability of these more structured precursor filaments resulted in corresponding drawn/heat-set filaments that were of relatively lower overall orientation and tensile strength. The observed trends in tenacity, initial modulus, and high temperature shrinkage of the drawn/heat-set filaments appeared to be well correlated with the extent and distribution of amorphous phase rigidity as perceived through inferences made from the loss tangent temperature dependence. The WAXS patterns of the drawn/heat-set samples indicated that these filaments all possess a well-developed and highly oriented crystalline structure. Application of a simple two phase model allowed the determination of an amorphous orientation factor, which for the drawn/heat-set filaments was generally found to decrease as the draw ratio imposed in order to achieve comparable levels of elongation to break decreased. The SAXS patterns of the drawn/heat-set filaments indicated that comparable long period spacings exist in all cases and that a transition from a four-point pattern to a two-point bar-shaped pattern occurred when the precursor filament possessed some significant amount of as-spun crystallinity.
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