Preparation and Carbonization of Ultra-Oriented Poly(acrylonitrile) Fibers: Effect of Stereoregularity

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Uniaxial drawing of isotaotic and atactivc poly(acrylonitrile)(iso-PAN and at-PAN) were studied. Dried gel films were initially drawn by solid-state coextrusion (first-stage draw) to an extrusion draw ratio of 16, followed by a further tensile draw at 100-200℃(second-stage draw). The temperature for optimum second-stage draw of iso-PAN, 130-140℃, was significantly lower than that (160-180℃) of at-PAN, reflecting their crystal softening temperatures 〓00vs. 150℃). The maximum achieved total draw ratios were comparable for these PANs. Although, the maximum tensile modulus, as well as modulus at a given DR, was slightly higher for iso-PAN than for at-PAN (28.5 vs. 23.0 GPa), the maximum tensile strength was comparable for each PAN, at 0.90 GPa. The shapes of stress/strain curves for fibers were significantly different between iso- and at-PAN reflecting their different chain conformations: a predominantly 3/1 helical con formation for iso-PAN and planar zigzag and helical sequences for at-PAN.SAXS of at-PAN fibers prepared by solid-state coextrusion of a nascent PAN formed under controlled conditions has been examined. Although solution-spun PAN fibers and their drawn products generally show no X-ray long-period scattering, the nascent PAN and the fibers prepared from it exhibited a clear SAXS maximum, depending on the extrusion temperature(T_<ext>) and draw ratio (EDR). These observations reveal that the absence or presence of an X-ray long-period scattering for PAN fibers depends on the initial morphology and the drawing variables.