Stretching Deformation Mechanism of Polyacrylonitrile-based Carbon Fiber Structure at High Temperatures

Abstract

In a high-temperature environment, polyacrylonitrile-based carbon fiber (PAN-CF) can be deformed by stretching, where the stretching deformation ability of PAN-CF is enhanced with the increase of the temperature. Further, the hightemperature stretching deformation of PAN-CF directly affects the control of the carbon crystalline orientation. Based on the techniques of high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, X-ray diffraction and in situ tension testing, the variation regularity and the intrinsic mechanism of high-temperature stretching deformation ability of PAN-CF obtained at different preparation temperatures were systematically studied in a high-temperature environment. The results indicated that the essence of PAN-CF high-temperature deformation was the relative motion of the carbon crystallite. Further, the main structural parameters that affected the high-temperature stretching deformation ability of PAN-CF were the degree of cross-linking between the carbon crystallites, the orientation angle(OA) of the carbon crystallite and the nitrogen content. When the testing temperature was lower than the preparation temperature, only physical structure changes were observed in the PAN-CF. For the PAN-CF tested undergoing physical structure changes, as the degree of cross-linking between the crystallites and the orientation angle decreased, the slipping of crystallites became easier. In the same environment, as the stretching tension decreased, the stretching deformation ability improved. When PAN-CF was tested under temperatures higher than the preparation temperature, the microcrystalline cross-linking in the PAN-CF was prone to fracture and slipping, and the high-temperature stretching deformation ability was enhanced. Also, for PAN-CF of lower preparation temperatures in PAN-CF containing no nitrogen (i.e., <0.15 wt%), the cross-linkages increased and the structures were more unstable, inducing an increase in the fracture of weak bonds and a reduction of the stretching tension. For nitrogen-containing PAN-CF, the removal of nitrogen led to severe shrinkage in the graphite layer and interlayer, and the fiber tension was thus increased, causing the high-temperature stretching deformation ability of the PAN-CF with less nitrogen content to be improved.