Rapid and Continuous Atmospheric Plasma Surface Modification of PAN-Based Carbon Fibers

In this work, a continuous and rapid atmospheric plasma setup was developed for rapidly modifying the surface of PAN-based carbon fibers (CFs). The interlaminar shear strength (ILSS) of CFs increased from 64.9 to 80.0 MPa with 60 s plasma treatment. Further mechanical and surface structural characterizations revealed that the effect of plasma was different, depending on the treatment time. When the treatment time was lower than 15 s, the effect of plasma was mainly on physically etching the surface of CFs, and the ILSS of CFs increased rapidly. Further extending the plasma treatment time did not increase surface roughness but promoted the addition of oxygen-containing functional groups on the surface of CFs, corresponding to a slower growth rate of ILSS. The atmospheric plasma was generated via a dielectric barrier discharge (DBD) method, and its energy intensity was significantly lower than that of plasma generated under low pressure. Accordingly, a mechanism was proposed for the plasma treatment of CFs: atmospheric plasma was not strong enough to simultaneously etch all the carbon atoms on the surface of CFs; therefore, carbon atoms on the graphitic plane were selectively etched, followed by the attaching of oxygen-containing functional groups on the exposed carbon sites caused by etching.