Interfacial and mechanical properties of carbon fibers modified by electrochemical oxidation in (NH4HCO3)/(NH4)2C2O4·H2O aqueous compound solution

Polyacrylonitrile-based carbon fibers were electrochemical oxidized in (NH4HCO3)/(NH4)2C2O4·H2O aqueous compound solution to improve its tensile strength and interfacial bounding strength with resin matrix simultaneously. AFM, XPS, XRD and Raman spectra were employed to characterize morphology, chemical states, crystallites size and ordered degree of CFs surface. The results indicated that the optimal modified condition in this paper could increase the tensile strength of CFs by 17.1%, meantime improve the interlaminar shear strength (ILSS) by 14.5%. The improvement of interlaminar shear strength not only causes by increase of surface roughness, but also causes by interaction effects of oxygen-containing and nitrogen-containing functional groups on carbon fibers. Among oxygen-containing functional groups, -COOH functional group plays an important role in enhancing the ILSS. Furthermore, after electrochemical oxidation the crystallites size decreased by 23-27%; ordered degree on CFs surface has an increase with suitable etching which did not peel off the ordered region on CFs surface and create new cracks; both above increase the tensile strength of CFs.