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High molecular weight poly(ethylene-2,6-naphthalate)(PEN) has been melt spun at various take-up velocities from 0.9 to 10 km/min to prepare fiber samples. The effect of take-up velocity on the structure and properties of as-spun fibers has been characterized through measurements of birefringence, density, wide-angle X-ray diffraction, infrared analysis, DSC melting behavior, tensile properties and high-temperature shrinkage. With increasing take-up speed, a steady trend toward higher as-spun fiber orientation and crystallinity was observed, accompanied by improved physical properties. The WAXD patterns of the as-spun fibers prepared at a velocity range higher than 1.5 km/min indicate that these samples all possess a developed molecular orientation and crystalline structure. At a relatively low take-up velocity that range from 1.5 to 4 km/min, a high level of molecular orientation in both crystalline and amorphous region has been found. This may be attributed to the high spinning stress generated by the high-molecular weight polymer used. In the high take-up speed region of 5–10 km/min, the molecular orientation becomes saturated. The highest tenacity and initial modulus of the as-spun PEN fibers obtained in this region reached ca 8 and 200 g/d, respectively. |
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