In this work, we studied the effects of electrochemical oxidation treatments of carbon fibers (CFs) on interfacial adhesion between CF and epoxy resin with various current densities. The surface morphologies and properties of the CFs before and after electrochemical-oxidation-treatment were characterized using field emission scanning electron microscopy, atomic force microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and single-fiber contact angle. The mechanical interfacial shear strength of the CFs/ epoxy matrix composites was investigated by using a micro-bond method. From the results, electrochemical oxidation treatment introduced oxygen functional groups and increased roughness on the fiber surface. The mechanical interfacial adhesion strength also showed higher values than that of an untreated CF-reinforced composite.

In this work, oxyfluorination treatments on carbon fiber surfaces were carried out to improve the interfacial adhesion between carbon fibers and polarized-polypropylene (P-PP). The surface properties of oxyfluorinated carbon fibers were characterized using a single fiber contact angle, and X-ray photoelectron spectroscopy. The mechanical properties of the composites were calculated in terms of work of adhesion between fibers and matrices and also measured by a critical stress intensity factor (K(IC)). The K(IC) of oxyfluorinated carbon fibers-reinforced composites showed higher values than those of as-received carbon fibers-reinforced composites. The results showed that the adhesion strength between the carbon fibers and P-PP had significantly increased after the oxyfluorination treatments. As the theoretical and practical comparisons, OF-CF-60s showed the best mechanical interfacial performance due to the good surface free energy. This indicates that oxyfluorination produced highly polar functional groups on the fiber surface, resulting in strong adhesion between carbon fibers and P-PP in this composite system.

We studied the effects of anodic oxidation treatments of carbon fibers on interfacial adhesion of the carbon fibers-reinforced epoxy matrix composites with various current densities. The surface of treated carbon fibers was characterized by atomic force microscope (AFM), field emission-scanning electron microscope (FE-SEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). The interlaminar shear strength (ILSS) of the composites was determined by a short beam shear test. This result showed that both the roughness and oxygen group of the carbon fibers surface increased in proportion to the current density. After anodic-oxidation-treated, the ILSS also increased as a function of the current density. In addition, the proportional relationship between ILSS and phenolic hydroxyl group was confirmed. The ILSS of the CF-2.0 sample increased by 4% compared to that of the CF-AS sample, because the anodic oxidation treatment increased the oxygen group and roughness on the carbon fibers surface, which leading to the improvement of the interfacial adhesion of the carbon fibers-reinforced epoxy matrix composites. Among these, the phenolic hydroxyl group which has the proportional relationship with ILSS is found to be the most important factor for improving the interfacial adhesion of the carbon fibers-reinforced epoxy matrix composites.