The effect of carbon-fiber surface properties on the electron-beam curing of epoxy-resin composites

The objective of this work is to analyze the mechanism of interaction between AS4 carbon fiber and a phenolic epoxy matrix in composites cured by electron beam and to improve the interlaminar shear strength (ILSS) of the composites by modifying the carbon fiber. Some promising results have been achieved by electrochemical treatment of the carbon fibers and subsequent coating with an electron-beam-compatible coupling agent. The ILSS of an electron-beam-cured composite was improved from 72.1 to 81.1 MPa. The morphologies of untreated and treated carbon fibers were characterized by the scanning electron microscope (SEM), the atomic force microscope (AFM) and X-ray photoelectron spectroscopy (XPS) respectively. Surface analysis showed that after treatment in electrolytes, the surface of the carbon fibers chemisorbed both oxygen-containing groups and nitrogen-containing groups, and the surface roughness was increased. It is observed that the properties of the carbon fiber surface play an important role in the adhesion between carbon fibers and the matrix resin in electron beam cured composites. The carbon fiber surface properties varied according to the type of electrolyte used in the anodic oxidation. Acidic electrolytes such as sulfate acid are recommended as effective electrolytes for electrochemical treatment to improve interfacial adhesion in the EB curing process, since no improvement in fiber/matrix interfacial adhesion is found in alkaline electrolytes. The EB curable coupling agent can screen the basic groups on the carbon fibers from hindering the cationic polymerization, consequently improve ILSS of EB cured composites.