Plasma treatment of pitch-based ultra high modulus carbon fibers

Pitch-based ultra high modulus carbon fibers were oxygen or argon plasma treated to compare the anodized fibers. As a result, the plasma treated samples obtained much higher adhesive strength to an epoxy resin than did the anodized samples. In order to characterize the surface, the coulostatic method (an electrochemical method) was applied and laser Raman spectroscopy was employed. The specific surface area and active surface area was determined by BET surface area measurement. As a result of the plasma treatment, the double layer capacity of the surface, which was related to the apparent surface area, dramatically increased. The surface crystalline size became smaller, and the active surface area increased. We therefore proposed the following model for plasma treatment mechanism which was quite different from anodic oxidation. The surface layer was peeled and the aromatic bonds in the basal plane were broken, so the number of active sites on the surface greatly increased, thus enabling strong adhesion to epoxy resin.