Influence of the carbon fiber surface microstructure on the surface chemistry generated by a thermo-chemical surface treatment

Carbon fibers made of textile and aerospace grade polyacrylonitrile precursor fibers were surface treated by a continuous gas phase thermochemical treatment. The surface chemistry generated by the surface treatment was characterized by X-ray photoelectron spectroscopy. The surface and the average entire microstructure of the fibers were characterized by Raman spectroscopy and X-ray diffraction, respectively. Depending on the grade of the precursor, the final surface concentration of oxygen was comprised between 14% and 24%, whereas the typical commercial electrochemical surface treatments led to concentrations of around 8% with the same fibers. The final concentration of oxygen was directly correlated to the size of the crystallites which was a function of the grade of the polyacrylonitrile precursor and to the corresponding surface microstructure. The thermochemical surface treatment enabled a better control of the nature of the oxygen-containing functionalities as well. Whatever the grade of the precursor, desired hydroxyl groups and carboxylic acid functionalities were preferably generated, which is observed to be difficult with electrochemical surface treatments.