Abstract
Surface tension of solid wood surfaces affects the wettability and thus the adhesion of various adhesives and wood coatings. By measuring the contact angle of the wood, the surface tension can be calculated based on the Young-Dupré equation. Several publications have reported on contact angle measured with different test liquids, under different conditions. Results can only be compared if the test conditions are similar. While the roles of the drop volume, image shooting time etc., are widely recognized, the role of the wood surface moisture content (MC) is not evaluated in detail. In this study, the effect of wood moisture content on contact angle values, measured with distilled water and diiodomethane, on sanded birch (Betula pendula) surfaces was investigated, in order to find the relationship between them. With increasing MC from approximately 6% to 30%, increasing contact angle (decreasing surface tension) values were measured according to a logarithmic function. The function makes possible the calculation of contact angles that correspond to different MCs.
Highlights
The surface of machined wood products may need to be treated with wood preservatives, stains, coatings, adhesives or other materials to improve their properties
Linear regression analysis (LRA) showed that between 6.03% moisture content (MC) and 17.96% MC there are no significant differences in the surface roughness values, but the roughness values of 29.97% MC differ significantly from the previous ones
Based upon contact angle measurements taken on sanded birch (Betula pendula) surfaces, which had different MC, revealed that the variation of moisture content has a significant effect both on the contact angle and on the surface tension values
Summary
The surface of machined wood products may need to be treated with wood preservatives, stains, coatings, adhesives or other materials to improve their properties. Surface tension is not directly measurable, it is usually calculated from the Young Dupré equation, using the measured value of the contact angle (Zenkiewicz 2007). European Journal of Wood and Wood Products (2021) 79:907–913 surface tension of the solid In all these theories, distilled water (DW) is one of the most suitable liquids to be used as polar component, and diiodomethane (DIM) (among other test liquids) is a commonly used dispersive test liquid (Oberhofnerova and Panek 2016; Qin et al 2014; Mohammed Ziegler et al 2006; Jankowska et al 2018; Laskowska and Kozakeiwicz 2017). It is a value that depends on which liquid is selected for contact angle testing, and which surface energy theory is selected for data analysis. The calculated surface tension of a solid is primarily suitable for the evaluation of differences occurring during an ongoing process, rather than being the absolute value of the surface tension (Krüss GmbH 1999)
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