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使用在线同步辐射广角X射线衍射(WAXD)和原位变温傅里叶红外(FTIR)研究了无规聚丙烯腈(at-PAN)纤维热处理过程中晶区的相转变行为.研究发现,WAXD图像中由(110)晶面衍射形成的衍射弧在加热过程中其q值随温度的变化速率不完全一致,在110℃存在突变点,此温度下晶区的热膨胀率从4.15×10-4nm/K(α1)突变为1.13×10-3nm/K(α2),同时DSC曲线在110℃附近出现放热峰,说明发生了晶胞结构转变.通过升温FTIR测试发现1230 cm-1和1250 cm-1处吸收峰的相对强度随热处理过程也发生变化,两峰峰强分别对应纤维中31螺旋构象与平面锯齿构象的相对含量,通过C=I1250/I1230与热处理温度的关系发现C值在110℃突然急剧减小,说明at-PAN纤维晶区分子链在110℃附近发生了平面锯齿构象向31螺旋构象的剧烈转变,而正是由于这种转变导致晶区层间距的变化使得WAXD图像中衍射弧的位置随温度变化速率不一致,即相转变行为是由分子链构象的变化引起的.
The phase transition behavior of crystalline regions during the heat treatment of atactic polyacrylonitrile (at-PAN) fibers was investigated by using synchrotron radiation wide angle X-ray diffraction (WAXD) and in situ temperature-changing Fourier transform infrared spectroscopy (FTIR) .It was found that WAXD images In the heating process, the rate of change of q value of the diffraction arc formed by the diffraction of the (110) crystal plane is not exactly the same at the temperature of 110 ° C, and the thermal expansion coefficient of the crystal region at this temperature ranges from 4.15 × 10-4 nm / K (α1) was changed to 1.13 × 10-3nm / K (α2), and the exothermic peak appeared near the DSC curve at 110 ℃, indicating that the transition of unit cell structure took place.FTIRR of 1230 cm-1 and 1250 cm- The relative intensities of the absorption peaks at 1 and 2 also change with the heat treatment. The peak intensities of the two peaks correspond to the relative contents of the 31 helix conformation and the plane sawtooth conformation in the fiber respectively. The C value is found to be 110 ° C by the relationship between C = I1250 / I1230 and heat treatment temperature Suddenly abruptly decreased, indicating that at-PAN fiber crystal chain molecular chain at about 11O0C the plane sawtooth conformation to the 31-helical conformation of the dramatic change, and it is precisely because of this change led to crystal layer spacing changes in the WAXD image diffraction The location of the arc varies with the rate of temperature, Phase transition behavior is caused by changes in the molecular chain conformation caused.