Dielectric and surface properties of wood modified with NaCl aqueous solutions and treated with FE-DBD atmospheric plasma

Abstract

The hygroscopic and electrical properties of the wood surface of Norway spruce (Picea abies (L.) Karst.) and common beech (Fagus sylvatica L.) were altered by the application of differently concentrated NaCl aqueous solutions. The presence of Na+ and Cl– ions increased the equilibrium moisture content in both woods in environments with a relative humidity of 75% to a nearly saturated state. The electrical resistance of the wood decreased, while the electrical capacitance of the wood increased with increasing amounts of NaCl introduced. Inverse trends were observed for both properties in wood modified with the two most concentrated solutions (18 and 36% molality). Microscopic analysis of the outer layers of the wood samples using scanning electron microscopy and energy-dispersive X-ray spectroscopy showed that the amount of NaCl decreased linearly up to about 1 mm from the modified surface. The presence of Na+ and Cl– ions in wood increased the intensity and improved the homogeneity of the plasma discharge generated during treatment of samples in air at atmospheric pressure. Both modification of wood with NaCl and subsequent treatment with plasma increased the surface roughness of the substrates. Finally, it was shown that the wettability of wood with a waterborne coating was improved after plasma treatment, regardless of the presence of NaCl on the surface. These findings have a good potential not only for the study of surface treatment processes of wood with plasma discharges, but also for other technical applications of lignocellulosic materials.