无规聚丙烯腈纤维热处理过程相转变行为的同步辐射研究

Phase Transition Behavior of the at-Poly( acrylonitrile) during Heat Treatment Based on the in situ Synchrotron Measurements

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 region in at-PAN fiher during heat treatment was investigated based on the temperature-dependence measurements of in situ synchrotron wide-angle X-ray diffraction （WAXD）, DSC and FTIR. According to the results of WAXD, the position of diffraction arc for （110） planes was shifted to low q value with the increasing of temperature. However, there was an obviously mutation at 110 ℃ during this shifting. At this temperature, the linear expansion rate of crystalline region increased from 4. 15 ×10-4 nm/K （al） to 1.13 ×10-3nm/K （a2）,and the DSC curve also emerged an exothermal peak around 110 ℃ , which results from the phase transition of crystalline region. From the FTIR measurements,the relative intensity of 1230 cm ^-1 and 1250 cm^-1 bands, which stands for the 3/1 helix and planar zigzag conformation respectively, was also changed during heat treatment. Through the relationship between C = I1250/I1230 and heat treatment temperature,there was also a dramatical change at 110 ℃ ,where C was decreased obviously. It implies that the molecular chains in at-PAN fiber were more likely to take the planar zigzag conformation below 110 ℃ and transferred to 3/1 helix conformation above 110 ℃. So it can be concluded that the phase transition of the at-PAN fiber at 110 ℃ was originated from the transformation of planar zigzag to 3/1 helix in chain conformation.