Plasma treatment of pitch-based ultra high modulus carbon fibers

Pitch-based ultra high modulus carbon fibers were oxygen or argon plasma tr eated to compare the anodized fibers. As a result, the plasma treated sampl es obtained much higher adhesive strength to an epoxy resin than did the an odized samples. In order to characterize the surface, the coulostatic metho d (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 d ouble layer capacity of the surface, which was related to the apparent surf ace area, dramatically increased. The surface crystalline size became small er, and the active surface area increased. We therefore proposed the follow ing model for plasma treatment mechanism which was quite different from ano dic oxidation. The surface layer was peeled and the aromatic bonds in the b asal plane were broken, so the number of active sites on the surface greatl y increased, thus enabling strong adhesion to epoxy resin. (C) 1999 Elsevie r Science Ltd. All rights reserved.