Wetting of carbon fibers by coal-tar pitch melts

The wettability of carbon fibers from different manufacturers with finish, rinsed of finish, and heat treated at 2000A degrees C by the model liquids water and octane was studied comprehensively. The polar and dispersion components of the carbon-fiber surface free energy were calculated. It was shown that finished fiber had a polar nature whereas removal of the finish could increase or decrease the surface polarity. This could be related to the fiber preparation method. The surface tension of pitch melts was measured and factored into its components. It was shown that the contribution of the polar component to the pitch surface tension was always at least 50% for the studied pitches. The surface tension correlated well with the pitch viscosity but was not related to the softening temperature. Edge wetting angles of the carbon fibers by pitch were calculated based on the experimental results. Fibers for which the contribution of the surface-energy polar component was greater demonstrated better wettability.