Surface modification of PAN based carbon fiber (CF) paper was carried out by cold plasma treatment of oxygen or CF₄ to obtain high compatibility between CF and the matrix in CF paper/ cement composites (CFRC). CFRC plates (6mm in thickness) were prepared by lamination of 11 sheets of CF paper preimpregnated with portland cement paste (water/cement 0.4), followed by curing then in water (14 days). These CFRC's contain 2.7vol% of CF and their bulk density is 1.39g/cm³.
The flexural strength and Young's modulus of plates depend on the plasma treatment conditions and lamination methods. CFRC plates with O₂ plasma and/or CF₄ plasma-treated CF have in general higher flexural strength and Young's modulus than those with the untreated CF. Especially, the CFRC prepared by the lamination of 6 sheets of O₂ plasma-treated CF on tensile side and 5 sheets of CF₄ plasma-treated CF on compression side, showed high flexural strength (50MPa) and Young's modulus (6.9GPa), which are 1.6 times and 1.8 times as high as those of the CFRC with the untreated CF, respectively.

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The stability of fluorine-intercalated graphite fibers were improved by the surface coating of the fibers with graphite fluoride film. The preparation process of the GIC was composed of two steps. In the first step, the pitch-based graphite fibers were pre-treated with elemental fluorine at the temperature range of 300-410°C, so that the surface of the fibers were coated with graphite fluoride which has an excellent water-repellency. Then, in the second step, thus surface-coated fibers were intercalated by F₂ below 100°C.
The graphite fluoride-coated GICs showed higher stability than the non-coated one from the viewpoints of the change in weight decrease and electrical conductivity as a function of exposure time to air. Furthermore, X-ray diffractions showed no decomposition of the former GICs in air. Where as, the latter decomposed within a few days.

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An epoxy resin membrane in which carbon fibers are vertically arranged in array format was electrochemically oxidized to remove carbon fibers and to create microholes of diameter of the carbon fiber (4-7μm). Carbon fiber tips remained at one end of the holes. The microhole membrane possesses an acidic function at the surface of carbon fibers and hence is a charged membrane. The flow flux of water depended on the acidity of an aqueous solution and it increased when the solution was made an acidic.
Etching rate of PAN-based carbon fibers was much faster than that of mesophase carbon fibers.

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