Fiber Structure Formation in High-speed Melt Spinning of Sheath-Core Type Bicomponent Fibers.

High-speed melt spinning of sheath-core type bicomponent fibers was performed and the change of fiber structure with increasing take-up velocity was investigated. Four kinds of polymers, poly (ethylene terephthalate) (PET), polypropylene (PP), high-density polyethylene (PE) and polystyrene (PS), were selected and three sets of core/sheath combinations, PET/PP, PET/PE and PET/PS, were studied. The structure of each component in high-speed spun bicomponent fibers was analyzed through the birefringence, wide-angle X-ray scattering pattern and DSC thermogram measurements. The development of the molecular orientation and the starting of the orientationinduced crystallization of PET in PET/PP and PET/PE bicomponent fibers occurred at lower take-up velocities as compared to those in the single component spinning. On the other hand, PP in PET/PP fiber showed low orientation pseudo-hexagonal structure at all the take-up velocities investigated and the birefringence of PE in PET/PE fibers obtained at 6km/min was almost negligible, meaning fiber structure formation of PP and PE components was suppressed. On the contrary, in the PET/PS combination, structure formation of PET was suppressed and there was no indication of orientation-induced crystallization even at 7km/min. Oppositely, the molecular orientation of PS component was enhanced. The mechanism of the mutual interaction of two components on structure formation in the high-speed spinning of bicomponent fibers was speculated based on the characteristics of the constituent polymers, and it was concluded that the structure formation of a component having higher temperature-dependent elongational viscosity and higher solidification temperature is expected to be enhanced.