Mie Yoshimura

Structure Formation of Blend and Sheath/Core Conjugated Fibers in High-Speed Spinning of PET, Including a Small Amount of PMMA

The blend of poly(ethylene terephthalate) (PET) and a small amount of polymer that has higher T g than PET, such as polymethylmethacrylate (PMMA)—and is dispersed finely as immiscible particles in PET—exhibits lower molecular orientation than pure PET under high-speed fiber spinning. To obtain insight into the mechanism of the lower molecular orientation of the blend fiber, the sheath/core structure of PET (sheath)/PMMA (core) conjugated fiber (the same PET/PMMA weight ratio as in the blend fiber), was produced as a model. The thinning profile of the fiber diameter along the spinning line and the birefringence distribution of the cross-section were examined and compared among pure PET fiber, the conjugated fiber, and the blend fiber. The conjugated fiber had the lowest molecular orientation of PET in the sheath part, and its thinning process was accelerated similar to the blend fiber. As a result of the distribution of molecular orientation across the diameter of the conjugated fiber, it is considered that PMMA, having the high T g , tends to solidify at a higher temperature (upstream) than PET in the thinning process, making the flow of PET accelerate as if it was pushed by PMMA. This causes the maximum dv/dx just before the solidification point to be smaller; therefore, the lower spinning stress, resulting in smaller birefringence of PET, can be considerable. This acceleration was generated at the interface of PET and PMMA, and spread toward the fiber surface as both polymers were thinning in elongational flow (in melt). On the other hand, close to the interface, molecules of PET were stretched by PMMA, resulting in an increase of birefringence. Such discussion is also considered to apply to the blend fiber. However, because the blend fiber had a significantly larger interface area compared with the conjugated fiber, it is considered that the increase of birefringence of PET by the interface drag force cannot be neglected. The larger particles of PMMA dispersed in PET results in the lower birefringence of PET that is supported by the elongation effect (i.e., the interface drag force).

Analysis of the Effect of Incorporation of a Small Amount of PMMA on Fiber Structure Formation of PET

The presence of a small amount of finely dispersed polymer, which has higher Tg than the matrix poly(ethylene terephthalate) (PET) and is immiscible with PET, such as polymethylmethacrylate (PMMA), suppresses orientated crystallization of PET under high-speed fiber spinning. To examine the mechanism of the reduced degree of oriented crystallization in the fibers, experimental data were compared with the results from computational calculations in terms of diameter or strain rate profile along the spin line. The computational simulation for the diameter and the strain rate profiles, assuming an increase of solidification temperature and an increase of elongational viscosity under higher strain rate, was qualitatively in good agreement with the experimental results. On the other hand, the measured birefringence of PET/PMMA fiber was substantially lower than the calculated one, which requires further improvement considering the skin‐core structure and stress distribution in both PET and PMMA as a future research item.

Hue Change in Interference-Colored Fibers with an Alternating Multilayer Structure

The change in hue of interference-colored fibers, which are consisting of alternating multilayer structure of poly(ethylene terephthalate) (PET) and polyamide 6 (Ny-6) covered with PET clad, was investigated in comparison with that of ordinary dyed PET fibers. The results indicated that, when an incident light was applied to the dyed PET fibers either parallel to or vertical to the fiber axis, although the chromaticness index (a*, b*) plotted on a*- b* coordinates changed in distance from the origin as the receiving angle β was increased from -30° to 70°, no change was observed in its track direction. On the other hand, the track of the chromaticness index for the interference-colored fibers changed substantially between incident lights parallel to and vertical to the fiber axis. In the former case, the chromaticness index plots were virtually all near the origin even though β was varied and tended to move substantially away from the origin in the range of specular reflection angles between 44° and 46°. In the latter case, however, the track of the chromaticness index moved counterclockwise in an arc shape from the second quadrant to the third and fourth quadrants with increasing β, clearly indicating a substantial change in hue. The interference-colored fibers were regarded as an alternating multilayer structure, and their reflection spectra were simulated taking into account the refractive index anisotropy (birefringence) of PET and Ny-6. The chromaticness index was found from the data thus obtained and plotted as coordinates in the same way as described above. As a result, the index was evaluated on the basis of an analysis of the simulation results and its track was plotted on the a*- b* coordinates. It was observed that the tendency of the chromaticness index track relative to the change in β was nearly the same as that seen when an incident light was vertical to the fiber axis. It is thought that the change in hue of the interference-colored fibers due to β is mainly attributable to the variation in the length of the optical path in their alternating multilayer structure.