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

本文研究了等规和无规聚丙烯腈（iso-PAN和at-PAN）的单轴拉伸。首先通过固态共挤出（第一阶段拉伸）将干燥的凝胶膜拉伸至挤出拉伸比为16，然后在100-200℃下进一步拉伸拉伸（第二阶段拉伸）。iso-PAN的最佳二段拉伸温度为130-140℃，明显低于at-PAN的最佳二段拉伸温度（160-180℃），反映了它们的结晶软化温度在100 vs. 150℃）。对于这些PAN，最大达到的总拉伸比是相当的。尽管iso-PAN的最大拉伸模量以及给定DR下的模量略高于at-PAN（28.5对23.0 GPa），但每种PAN的最大拉伸强度在0.90 GPa下是相当的。纤维的应力/应变曲线的形状显着不同的iso-PAN和at-PAN之间反映其不同的链构象：一个主要的3/1螺旋构象的iso-PAN和平面锯齿和螺旋序列的at-PAN。SAXS的at-PAN纤维制备的固态共挤出的初生PAN在控制条件下形成的已检查。虽然溶液纺丝PAN纤维及其拉伸产品通常没有显示出X射线长周期散射，但初生PAN及其制备的纤维显示出明显的SAXS最大值，这取决于挤出温度（T_<ext>）和拉伸比（EDR）。这些观察结果表明，PAN纤维的X射线长周期散射的存在或不存在取决于初始形态和拉伸变量。

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.