Type I and type II carbon fibers were covered with a thin plasma polymer film and etched by an oxygen or an argon plasma to reinforce the interfacial adhesion with poly(phenylene sulfide). Plasma etching of the fibers increased the interfacial shear strength up to 2.5 times which is much better than plasma polyacrylonitrile deposited fibers. Electron spectroscopy for chemical analysis surface analyses show different mechanisms of adhesion enhancement. Film deposited fibers which possess more abundant oxygen functionalities and aromatics show improved adhesion. On the other hand, increased adhesion with etched fibers occurs as a result of a larger area of unoxidized carbon structure. Surface nitrogen atoms also play a role in the interfacial adhesion.
