Highly Hydrophobic Wood Surfaces Prepared by Treatment With Atmospheric Pressure Dielectric Barrier Discharges

Atmospheric dielectric barrier discharge (DBD) treatments of wood were done to attain water repellency on wood surfaces. A specially designed frequency controlled parallel-plate DBD reactor was utilized to produce the discharges. Ethylene, methane, chlorotrifluoroethylene and hexafluoropropylene were used as DBD reagents. Contact angle, water absorption, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) measurements on the modified surfaces were performed. For methane and ethylene, XPS data showed an increased surface atomic concentration of carbon from 72.7% on untreated samples up to 80.7 and 96%, respectively, whereas nearly 50% fluorine concentration was observed with fluorinated reagents. The C-1s spectrum of hexafluoropropylene-DBD-treated wood sample showed that the CF3 group was introduced in a relative amount of 19%. AFM images showed distinct features for each of the DBD treatments, such as a deposit of a thin uniform film in the case of ethylene-DBD treatment, whereas the hexafluoropropylene-DBD treatment resulted in the nucleation of plasma-derived entities at the fiber surface and the subsequent growth of a film. Under optimized conditions the water contact angle was in the range of 139 degrees- 145 degrees. The combination of depositing a low surface energy polymer on an already rough surface gave the surface-treated wood a highly hydrophobic character.