液态丙烯腈低聚物修复聚丙烯腈基碳纤维微孔缺陷

提出一种全新的缺陷修复的方法,即将聚丙烯腈基(PAN)碳纤维T300在液态丙烯腈低聚物(LAN)中浸渍后,再进行预氧化和碳化热处理,可以将T300的拉伸强度提高25%.应用二维小角X射线散射(SAXS)法可以计算出LAN修复缺陷前后T300微孔缺陷的长度(L)、横截面尺寸(lp)、取向角(Beq)、相对体积(Vrel)的变化,结果表明碳纤维的拉伸性能越好,微孔的长度、取向角、相对体积含量越小.T300拉伸性能的提高是由于缺陷修复的结果.应用BET比表面积法、扫描电子显微镜(SEM)表征LAN修复缺陷前后T300的比表面积以及表面形貌的变化,结果表明,T300在LAN中浸渍并经过预氧化和碳化热处理,比表面积变小,表面缺陷明显减少.进一步验证LAN对碳纤维中的微孔缺陷具有修复作用.应用X射线光电子能谱(XPS)法表征LAN修复前后T300表面化学成分的变化,结果表明,LAN修复后含氧官能团(C―OH,C=O,HO―C=O)显著增加,有利于增强碳纤维与树脂基体之间的相互作用,从而提高碳纤维的力学性能.

Modification of Microvoid Defects in Polyacrylonitrile-Based Carbon Fibers by a Liquid Oligomer of Acrylonitrile

The strength of industrial carbon fibers (CFs) is far lower than their theoretical strength because of defects in the microstructure of carbon fibers and these are the main restrictions in improving their performance. The most effective way to improve the strength of CFs is to reduce the amount of these defects. We thus report a novel method using a liquid oligomer of acrylonitrile (LAN) to modify the defects. Briefly, Polyacrylonitrile (PAN)-based CFs T300 were infused into LAN, and subsequently oxidized in air and carbonized in nitrogen. Their tensile strength increased by 25%. Two-dimensional small angle X-ray scattering (SAXS) was used to characterize the variation in length of the microvoids (L), the chord length of cross section l_p, the orientation angle (B_eq), and the relative volume (V_rel). The results show that the length, orientation, angle and relative volume of the microvoids were much lower and the tensile property improved. The improvement in the tensile property comes from the modification of defects in CFs T300 by LAN. The BET method and scanning electron microscopy (SEM) were used to characterize the specific surface area and the morphology of T300 before and after LAN treatment. The results show that after the treatment of LAN the specific surface area decreased and the amount of surface defects also decreased.We further prove that the liquid oligomer of acrylonitrile can modify the defects in CFs. X-ray photoelectron spectroscopy (XPS) was used to study the chemical composition of LAN-treated CF surfaces. The results show that the relative content of oxygen-containing functional groups on the surface of the CFs (C―OH, C＝O, HO―C＝O) increased significantly. The increase in oxygen-containing groups enhanced the surface polarity of the CFs, improving the interaction between the treated CFs and the epoxy resin, which acts as a carbon fiber substrate. Therefore, the mechanical properties of the CFs improved.