Armos fiber (F-12 aramid fiber in paper) was provided with broad application foreground
as reinforcement material for advanced composites in aviation and spaceflight field, due to its
outstanding properties, such as high modulus, high strength, high temperature resistance, erosion
resistance and so on. However, the exertion of property was still limited by slippery surface, low
surface energy and weak interfacial adhesion performance. In this study, the effects of oxygen plasma
treatment time on polar functional groups introduced onto the fiber surface, surface free energy and
surface topographic images were discussed by X-ray photoelectron spectroscopy (XPS) analysis,
dynamic contact angle analysis system (DCA) and atomic force microscopy (AFM), respectively. It
was found that the content of oxygen element and polar functional groups on fiber surface were all
increased obviously after oxygen plasma treatment. The content of oxygen element on surface for
untreated F-12 aramid fiber was 11.13%, while it increased to 15.20% after oxygen plasma treatment
for 10 min; The content of polar functional groups on surface for untreated F-12 aramid fiber was
28.14%, while it increased to 38.11% after oxygen plasma treatment for 10 min. The polar
component (γp) of fiber surface energy increased sharply from 6.82 mN/m to 36.68 mN/m after 10
min plasma treatment, the total surface free energy was increased from 46.26 mN/m to 64.66
mN/m.The results indicated that oxygen plasma treatment had introduced a large amount of reactive
functional groups onto the fiber surface, and these groups can form together as covalent bonding to
improve the surface wettability and increase the surface energy of fibers. At the same time, oxygen
plasma treatment was able to generate a mass of bulges and grooves on F-12 aramid fiber surface,
which had an active effect on increasing the chemical bond and mechanical function between fiber
and resin and enhancing the interfacial adhesion performance of composite. The fiber surface grooves
had been increased with the time prolonging before 10 min while decreased after 10 min, the results
maybe relate to partial organic on fiber surface melting. It had an adverse effect on the interfacial
adhesion properties of composite. Therefore, the optimum plasma treatment time was between 5 min
and 10 min.