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Control of Fiber Structure Using a Liquid Isothermal Bath in High-Speed Melt Spinning of Poly (vinylidene fluoride)
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Murata, Akira / Ito, Hiroshi / Kikutani, Takeshi / Okui, Norimasa
A liquid isothermal bath (LIB) was introduced into the high-speed melt spinning process of poly (vinylidene fluoride) (PVDF) to modify the temperature and stress profiles in the spinning line. The LIB was placed at 100 or 150 cm below the spinneret and the liquid temperature was controlled to 40, 70, 100 and 130. The structure of as-spun fibers was characterized by the wide-angle X-ray diffraction, birefringence and Lorentz density measurements. The high-speed spun fibers obtained at the take-up velocities of above 1.5 km/min using the LIB showed the mixture of Ώ and ΐ modification crystals, whereas the fibers obtained without the LIB (standard fibers) showed only the Ώ modification crystals. This result indicates that the ΐ modification crystals can be formed directly from the melt in the modified melt spinning process. The weight fraction of ΐ modification crystals showed a minimum with an increase in the liquid temperature suggesting that the mechanism of the formation of ΐ modification crystals in the low and high temperature regions are different. The birefringence and Lorentz density of the as-spun fibers increased with an increase in the take-up velocity and the fibers obtained at high speeds with high liquid temperatures showed higher birefringence and Lorentz density than the standard fibers obtained at the same take-up velocities. The weight fraction of ΐ modification crystals and birefringence were higher for the fibers produced using the LIB with increased liquid depth. The mechanism of fiber structure formation in the spinning process modified with the LIB was discussed based on the enhanced elongational stress and controlled filament temperature, which originated from the high friction force and high heat transfer coefficient at the interface between the liquid and the running filament.
Key words: High-speed melt spinning@/@Liquid isothermal bath@/@Poly(vinylidene fluoride) / Fiber structure