Effect of Liquid Isothermal Bath in High-Speed Melt Spinning of Poly(ethylene 2,6-naphthalene dicarboxylate).

Abstract

The high-speed melt spinning process of poly (ethylene 2,6-naphthalene dicarboxylate) (PEN) was modified using a liquid isothermal bath (LIB) which was kept at a liquid temperature of 150 or 170°C. The structure and mechanical properties of the as-spun fibers thus produced in the take-up velocity range of 0.5 to 7.0 km/min were characterized. The fiber structure development in the low take-up velocity region was promoted by the use of the LIB and the promotion becomes more prominent by raising the liquid temperature. In case of the fibers produced with the LIB temperature of 170 °C, initial Young's modulus of about 25 GPa and tenacity of about 800 MPa, which are equivalent to the properties for the fibers prepared in the standard high-speed spinning process of 7 to 9 km/min, were obtained at 3 to 4 km/min. On the other hand, plots of the structural and mechanical parameters against the birefringence for the LIB fibers showed a similar relation in comparison with the fibers prepared in a standard high-speed spinning process indicating that the general mechanism of fiber structure development is similar in both the spinning processes. The LIB fibers obtained in the high-speed region were found to have a large amount of β modification crystals as in the case of the common high-speed spun fibers. The amount of β form crystals in the LIB fibers increased with an increase in the take-up velocity. From these results, it was concluded that the β form crystal can be formed even at a much lower temperature than the critical temperature for the formation of β form crystals in an isotropic state, and that the formation of β form crystals can be promoted by applying a higher tensile stress in the spin-line.