Effect of moisture sorption state on transverse dimensional changes in wood

The purpose of the study was to understand the transverse dimensional changes and corresponding anisotropicity in wood during different states of moisture sorption. Oven dried samples of Erythrina variegata, Lannea coromandelica, Gmelina arborea and Albizia chinensis were adsorbed and subsequently desorbed at constant temperature (35degreesC). Tangential and radial dimensional changes (swelling) were analysed with respect to relative humidity and moisture content during both the states of sorption. Dimensions in tangential direction were found to change at a relatively greater rate than in radial direction at high humidities. It was observed that transverse dimensions were more during desorption compared to adsorption at a given equilibrium moisture content. This confirms presence a second order effect of moisture sorption on dimensional movement. This effect was found to be more prominent in tangential direction compared to radial direction resulting in higher coefficient of anisotropy (alpha(T)/alpha(R) ratio) during desorption. The magnitude of this phenomenon was found to vary from species to species.