科研之友
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摘要
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 (SA)(S) was used to characterize the variation in length of the microvoids (L), the chord length of cross section 4 the orientation angle (Beg), 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.
