Atmospheric Plasma Treatment of Carbon Fibers for Enhancement of Their Adhesion Properties

Plasma processing of carbon fibers is aimed to provide better contact and adhesion between individual plies without decrease of the carbon fiber (CF) mechanical resistance. This work deals with surface modification of CFs by atmospheric pressure dielectric barrier discharge (DBD) in air. Scanning electron microscopy (SEM) of a single untreated fiber showed many thin tracks aligned along the fiber. This feature can be explained by the fiber manufacturing process. SEM of the treated samples revealed many small particles distributed over entire surface of the fiber. These particles are product of the fibers surface etching during the DBD treatment that removes the epoxy layer covering as-received samples. The alteration of CF surface morphology was also confirmed by the Atomic force microscopy (AFM), which indicated that the CF roughness increased as a result of the plasma treatment. Analysis of the surface chemical composition provided by X-ray photoelectron spectroscopy (XPS) showed that oxygen and nitrogen atoms are incorporated onto the surface. The polar oxygen radicals formed on the surface lead to increasing of the CF surface energy. Both, the increase of surface roughness and the surface oxidation contribute for enhancement of CF adhesion properties.