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Abstract: The structural development of poly(ethylene 2,6-naphthalene dicarboxylate) (PEN) fibers was analyzed by in situ X-ray diffraction and fiber temperature measurements. The PEN fiber was drawn continuously under three drawing stresses, where the neck-drawing point was fixed accurately by CO2 laser irradiation heating. The developed crystal structures of the drawn fibers depended on the drawing stresses, that is, only the α-crystal was obtained under a drawing stress of 148 MPa, an α-rich mixed crystal was obtained for 54 MPa, and a β-rich mixed crystal was obtained under 23 MPa stress. Fiber containing over 70% β-crystal was obtained in the third case. Orientation-induced crystallization rates (K) and crystallization induction times (t 0) were estimated for the three drawing stresses: K = 2210 s−1 and t 0 = 0.5 ms for 148 MPa, K = 940 s−1 and t 0 = 1.0 ms for 54 MPa, and K = 655 s−1 and t 0 = 4.0 ms for 23 MPa. In addition, the drawing stress acted as a definitive influence not only on the resulting crystal form but also on the chain conformation of the mesophase structure. The d-spacing of the (001′) diffraction increased with drawing stress, and the longer (001′) spacing generated the α-crystal while the comparatively shorter (001′) spacing yielded the β-crystal. The d-spacings of 1.27 and 1.23 nm for the drawing stresses of 148 and 23 MPa, respectively, were somewhat shorter than the c-axis lengths of the α- and β-crystals of 1.32 and 1.27 nm, respectively. [Copyright &y& Elsevier]

Abstract: The structure development in the continuous laser-heated drawing process of poly(ethylene 2,6-naphthalene dicarboxylate) (PEN) fiber was analyzed by in-situ X-ray diffraction measurement. Because of the rapid and uniform laser heating, and the resultant steady-state nature of the necking-drawing, the structure development after the on-set of necking could be measured in the time resolution of several hundred microseconds. We found for the first time the temporal appearance of meridional (001′) diffraction at several milliseconds after the on-set of necking indicating that the mesophase structure similar to the one reported for poly(ethylene terephthalate) was also formed in the initial stage of fiber structure development of PEN. The d-spacing of the (001′) diffraction 1.230±0.003nm was shorter than the c-axis lengths of both α and β crystals. [Copyright &y& Elsevier]