SUPERSTRUCTURE IN ULTRAHIGH SPEED SPUN FIBERS OF POLY(ETHYLENE-TEREPHTHALATE)

Ultrahigh speed spinning of poly (ethylene terephthalate) (PET) was carried out at various take-up velocities from 5 to 10 km/min. The superstructure of as-spun fibers was characterized by small-angle X-ray scattering (SAXS), wide-angle X-ray diffraction (WAXD), viscoelastic properties, and scanning electron microscopy (SEM). Above 6 km/min the peaks or shoulders that are due to the interference between microfibrils appear on the equatorial SAXS intensity curves. The interfibrillar spacing estimated from the peak position increases with increasing take-up velocity. Comparison of the spacing with the lateral crystal sizes estimated from the broadness of the crystal (hk0) WAXD peaks indicates that the microfibril diameter becomes thick with increasing take-up velocity. Although the orientation and density in amorphous region for high-speed spun fibers are very low on the average, it can be seen that a few highly extended tie molecules exist in that region, and the number of these molecules increases with increasing take-up velocity. The modes and mechanisms of fibrillation induced by a rubbing test are discussed relating to these results.