Surface structural evolvement in electrochemical oxidation and sizing and its effect on carbon fiber/epoxy composites properties

An evolvement of surface physicochemical structure in the process of electrochemical oxidation and sizing treatment was monitored by scanning electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. An effect of this evolvement on the properties of carbon fiber/epoxy composites was also researched. The results showed that the root mean square roughness increased from 4.6 nm for untreated fibers to 9.1 nm for surface-treated fibers, and the root mean square value of sized fibers decreased to 8.5 nm. The relative contents of oxygen and nitrogen atomic on carbon fiber surface increased obviously after electrochemical oxidation. Oxygen atomic concentration took a further improvement after sizing treatment and only hydroxyl functional group was found on its surface. The interfacial strength between carbon fiber and the resin matrix improved after surface electrochemical oxidation and sizing, and the mechanical interlock was considered to be the governing factor in fiber/resin adhesion of carbon fiber/epoxy composites.