Water-vapour sorption of welded bond-line of European beech and Scots pine

Abstract

Abstract The wood–water interactions of welded bond-lines of European beech (Fagus sylvatica L.) and Scots pine (Pinus sylvestris L.) were in this paper studied for the first time with dynamic vapour sorption equipment. The aim of this study was to characterize the water sorption in the welded bond-line and to define to which extent it deviates from water sorption of the unwelded wood. The objective was to provide deepened knowledge about water sorption of the welded bond-line, which could be used to improve the moisture resistance of welded wood in the future. The welded wood generally had lower equilibrium moisture contents than the unwelded wood. The welded bond-lines of beech and pine showed greater hysteresis than the unwelded wood from 0 to 55 % relative humidity. All specimens showed faster adsorption than desorption. However, the welded wood showed slower adsorption but faster desorption than unwelded wood. The time to complete half of the fractional change in moisture content (E(t) = 0.5) increased as the moisture content increased. The adsorption diffusion coefficients of beech and welded beech were higher than those of pine and welded pine up to 50 % and 40 % RH, respectively. In desorption, pine had a higher diffusion coefficient than beech in the whole range of 85–0 % RH. Analogously, welded pine had a higher diffusion coefficient than welded beech in the range of 85–5 % RH. In contrast to the desorption, the welded wood always had lower adsorption diffusion coefficients than the corresponding unwelded wood. The diffusion coefficients showed irregular patterns in some ranges of the RH. Therefore, it was hard to make a clear conclusion about the water-sorption behaviour of the specimens based on the defined diffusion coefficients.