中间相沥青分子在成纤过程中沿纤维轴向及径向的取向控制

Mesophase pitch-based carbon fiber owns properties of high modulus and high thermal conductivity, which makes it an indispensible material for national defense. The rigid and small flat molecule structure with strong Van der Waals' force makes the molecules orient along not only the fiber axis but also the transverse direction, and the later orientation would result in graphitic layers with weak interaction that decreases the carbon fiber strength. Moreover, the weak strength of pitch fiber makes it difficult to prepare carbon fiber, which influences the reliability of the research on structure and properties of the carbon fiber. This project would be carried on a set of reliable devices including a spinning machine with twin screw and undisturbed cross air blow, and an equipment for oxidation-carbonization allowing pitch fiber going above its glass transition temperature during the whole procedure. Based on theories of two dimensional orientation of discotic mesophase, polymer blending and carbon alloy formation, the project is aimed at investigating: (1) influence of the zone length and temperature near spinnerets on the orientation of mesophase along the fiber axis; (2) effects of polymer blending and capillary structure on the transverse structure of mesophase pitch fiber; (3) formation of the carbon alloy structure and its impact on the interaction of derived graphitic layers.

中间相沥青碳纤维具有高模量、高导热的优异特性，成为国防战略武器的关键材料。由于中间相沥青分子是刚性平面分子，熔融纺丝时沥青分子具有二维取向性，即除沿纤维轴向取向外，在径向方向也会进行有序排列，而后者会削弱所生成的类石墨层间作用力，从而降低碳纤维的拉伸强度。此外由于沥青分子小而分子间作用力大，因此纺丝粘度大且沥青纤维力学性能低，导致实验稳定性差而影响到碳纤维结构性能研究的可靠性。本项目拟采用具有无扰环吹风的双螺杆纺丝机和全封闭连续氧化碳化装置，解决纺丝及碳化工程问题。根据中间相沥青分子在纺丝过程中的二维取向规律，结合高分子共混和碳合金形成理论，进行以下研究：（1）通过控制孔口牵伸区温度及长度提高中间相沥青分子的轴向取向度；（2）通过高分子共混纺丝和改变喷丝孔导流区结构控制其径向取向；（3）通过共混高分子与中间相沥青共碳化形成合金结构增强类石墨层片间的作用力，从而达到提高碳纤维拉伸性能的目的。

本项目立项以添加低分子量聚丙烯腈与中间相沥青共混纺丝控制碳纤维横截面结构为目的，研究了喷丝板结构、近喷丝孔环吹风温度、共混聚丙烯腈分子量及添加量对沥青纤维及碳纤维结构和性能的影响。同时研究了集束油剂、加压氧化对中间相沥青纤维束粘连并丝行为的影响；研究了立管式反应器非等温聚合对中间相沥青族组成的影响。结果表明：.（1）在中间相沥青中添加低分子量聚丙烯腈进行共混纺丝可以使纺丝顺利进行，聚丙烯腈的加入对纤维的径向结构有一定的影响，但可以显著提高碳纤维的拉伸强度。.（2）中间相沥青纤维的氧化反应活性是决定其束丝粘连并丝的主要因素，对于氧化活性较高的沥青纤维可采用低浓度含硅油剂集束实现束丝生产，对于氧化反应活性低的沥青纤维可通过加压氧化来解决。.（3）沥青聚合中的自加速现象，即分子量越大反应速度越快，导致中间相沥青的分子量分布宽。通过采用立管式反应器分温区聚合，即上、中、下温度依次降低，有利于提升中间组分的含量。如在450℃下均匀聚合，苯不溶-吡啶可溶的含量为12%左右，采用上中下温度分别为480、430、300℃，苯不溶-吡啶可溶含量提升到25%左右。这对于提升中间相沥青的可纺性具有重要意义。