Effects of Melt-Spinning Speed on Structure Development of Polypropylene Fiber After Necking

The effects of melt-spinning speed (400–1200 m/min) on fiber structure development after necking were analyzed by wide-angle X-ray diffraction (WAXD) / small-angle X-ray scattering (SAXS) images taken with the time resolution of 0.19–0.34 ms during continuous drawing under the same drawing stress. Whereas an a*-axis oriented crystal and a low-oriented long-period structure was formed at lower speeds, a c-axis oriented crystal and highly oriented long-period structure were formed at higher speed. The long-period structure and low-oriented crystal survived for several hundred microseconds after necking, and after the breakdown of that structure, a highly c-axis oriented long-period structure and mesophase were reconstructed. A longer time was required for the structural change in the fibers spun at lower speed, likely because of stress bearing of the surviving a*-axis oriented crystals.