Investigation on endurance of hydrophilic property of Carbon Fibers treated by air dielectric barrier discharge

Summary form only given. Recently, thermo plastics such as Polypropylene (PP) or polyimide are going to be used as matrix resin of Carbon Fiber (CF) composite materials because they have an advantage to be rewelded at above 130°C. However, mechanical strength of CF/PP composite materials is low because adhesion strength between CF surface and PP surface is low. Therefore, many researchers have investigated plasma surface modification to enhance the interfacial adhesion strength of CF surface¹. On the other hand, from the industrial point of view, we need to investigate how long the effect of plasma surface modification lasts. In this study, we investigated the improvement of the hydrophilic property of CFs by air Dielectric Barrier Discharge (DBD), and also measured the endurance of its effect. Room air (temperature: 20~20.3 °C, relative humidity: 39.1~42.5%) was used as source gas of the DBD. The barrier material is alumina (ε=9.1, Type: A473, Kyocera corporation). Gas flow rate was fixed to 5 L/min. Gap length was fixed to 1.5 mm. Spread CFs (Thickness: 0.1 mm, T700SC-12000, Toray Industries, Inc.) were used in this experiment and they were inserted in the center of the discharge gap. Discharge power was fixed to 50 W. Light emission from air DBD with CFs was observed by a multi channel spectrometer. Hydrophilic property was estimated by the water absorbing property test (Byreck method). DBD treatment time was changed from 10 s to 60 s. In order to clarify the endurance of the DBD effect, hydrophilic property of CFs was measured after 1 day to 3 days from DBD treatment. The results showed that (1) hydrophilic property of CFs increased with the increase of DBD treatment time and the rate of increase was 158% at 60 s DBD treatment in comparison with untreated CFs, (2) since O and OH radical were detected in air DBD with CFs, oxygen containing polar functional groups such as -OH and -COOH seemed to be incorporated on the CF surface- and (3) the hydrophilic property of CF treated by DBD slightly decreased with time and the rate of decrease was 9% at 3 days after the DBD treatment in comparison with untreated CFs.