Breaking of polymer filament during melt spinning was studied for several polymer materials. Tension on the filament was measured as a function of the take-up velocity, and the breaking stress (the stress at which the filament was broken) was determined. The breaking stress was independent of the spinning conditions such as initial take-up velocity, acceleration of take-up velocity, spinline length, and dimensions of the spinneret. It was also independent of the extrusion temperature, molecular weight and molecular weight distribution of the materials. These findings showed that the breaking stress was an intrinsic characteristic of each polymer and the polymers with higher cohesive energy density tended to have larger breaking stresses.

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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.

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Structure of poly (ethylene terephthalate) (PET) fibers produced at various spinning speeds was studied by the X-ray and thermal analyses. With the increase of spinning speed, the crystallite size of (010) and (100), and the long period increased, and simultaneously amorphous orientation function decreased. By the cord treatment, the crystallite size of (010) and (100) increased, however, the long period decreased with the increase of the speed. For both PET fibers and cords, the effect of tension applied to the samples during heating on the melting temperature became smaller with the increase of spinning speed. From these results, the dimensional stability of PET fibers and cords was related with the orientation of amorphous segments and interlinks between fibrils.

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The dry-wet spinning mechanism of regenerated cellulose fibers was examined by using N-methylmorpholine N-oxide (MMNO), which is known as a good organic solvent of cellulose. The special interest was paid on the effects of an air-gap length and a draft ratio of spinning process on mechanical properties and micro-structure of regenerated cellulose fibers, so as to control the mechanical properties of the fibers. In this study, cellulose MMNO solution with high concentration and high viscosity could be made due to the good solubility of MMNO. The regenerated cellulose fibers spun from MMNO solution gave the cellulose II crystalline unit cell. The mechanical properties of the regenerated fibers were widely changed by changing the air-gap length and the draft ratio, and the high-tenacity fibers were obtained by spinning conditions of 10-50mm of air-gaps and greater than 6 of draft ratios. The maximum modulus and tenacity in this series of the fibers were 214g/d and 5.8g/d, respectively.

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The solution spun fibers were obtained from Nylon 6/lithium chloride/formic acid mixtures. The structure and tensile behavior of as-spun fibers were studied as a function of salt content in the as-spun fibers. Spinning solutions were prepared by dissolving the polymer and LiCl in 98 wt% formic acid at room temperature. Concentrations of polymer and LiCl in the spinning solutions were 25 wt% and 0-10 wt%, respectively. The solutions were extruded through a conical die with a diameter of 0.2mm and a length of 5 mm at room temperature. Temperature dependence of wide angle X-ray diffraction patterns of as-spun fibers revealed that the apparent melting temperature (Tm) decreased from 200 to 135°C with increasing salt content from 0 to 10 wt%. The glass transition temperature of as-spun fibers increased with increasing salt content. At a given deformation ratio and draw temperature, the stress on draw of as-spun fibers decreased with increasing salt content. However, the improvement of deformability of as-spun fibers by the decrease in the stress was less. The draw efficiency evaluated from the tensile modulus of drawn fibers decreased with increasing salt content. The deformability of as-spun fibers was improved by the drawing above Tm of as-spun fibers. The crystal form in the drawn fibers was dependent on the draw temperature (Td). For Td<Tm, the α-form was predominant. On the other hand, mixtures of α and γ forms were observed in the fibers drawn above the Tm. Most of the LiCl in the drawn fibers could be removed by a methanol extraction.

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Nylon 6-clay hybrid (NCH) was a nano-composite consisting of Nylon 6 and uniformly dispersed silicate monolayers of montmorillonite. Three samples with different clay contents were prepared. Extruded and drawn samples were obtained from the three samples. The structure and also the thermal and mechanical properties of these samples were investigated. We obtained the following results. The clay had high heat capacity and this ability slowed down the cooling rate of the NCH composites. The direction of the fiber axis of γ-type crystallite formed in extruded sample was perpendicular to the extruded direction. The temperature at which the samples deformed largely under a constant load increased with increasing clay content. The clay in NCH prevented the migration of water in NCH. Although the elastic modulus of undrawn NCH increased with increasing clay content, the modulus of drawn NCH did not increase markedly.

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