Effects of treatment on the surface composition and energy of carbon fibers

Abstract The surface composition and energy of carbon fiber has been carefully analyzed and quantified. Untreated, AU, surface‐treated, AS, and heat‐treated AHT fibers were all studied. AS fiber was surface‐treated by an electrolytic oxidation process. AHT fiber was heat‐treated at elevated high temperatures under vacuum. X‐ray photoelectron spectroscopy (XPS or ESCA) was used to investigate the surface elemental concentration of carbon fibers. The corresponding surface free energies of these fibers were calculated from the contact angles measured by a dynamic contact angle analyzer. Results showed a strong correlation between the surface treatment and heat‐treatment history and the surface chemistry of carbon fibers. After oxidation treatment, the surface free energy was increased by adding functional group elements (oxygen and nitrogen). However, these added elements could be removed by high temperature treatment under vacuum. The diffusion of O, N, and Na was discussed. The correlation between oxygen and nitrogen concentration and carbon fiber surface free energy has been plotted. These fibers would be used to quantify the relationship between carbon fiber surface free energy and the interfacial shear strength of the fiber‐polymer interface.