Strengthening of Carbon Fiber Paper/Cement Composites by Cold Plasma

The surface modification of PAN based carbon fiber (CF) was carried out with O2 or CF4 plasma generated by radio frequency (13.56 MHz) to obtain high compatibility between CF and matrix in CF paper/cement composites (CFRC). The wettability to water on CF surface was remarkably modified to hydrophilic by O2 plasma, and to hydrophobic by CF4 plasma. The CF paper after plasma treatment was used for the preparation of CFRC. CFRC plates (6 mm in thickness) were prepared by the lamination of 12 sheets of CF paper preimpregnated with portland cement paste (water/cement 0.4), and were cured in water. These CFRC's showed 1.5-1.8 g/cm3 in bulk density and 3.5 vol% in CF contents. The flexural strength of the CFRC plate prepared from O2 plasma-treated CF, was about 2.0 times higher (60 MPa) than that of CFRC without plasma treatment on CF. The CFRC plates prepared from CF paper pretreated in CF4 plasma, exibited 1.6 times higher (48 MPa) in flexural strength and 1.6 times larger in deflection com-pared with the CFRC from plasma-untreated CF. The fluoride ion transuded from CF4 plasma-treated CF surface, was interacted as the coupling agent between CF and portland cementhydrate. Therefore the cold plasma treatment on CF is regarded as strengthening of CFRC.