Holz Roh Werkst (2004) 62:50–55 DOI 10.1007/s00107-003-0437-y ORIGINALARBEITEN · ORIGINALS S. S. Chauhan · P. Aggarwal Effect of moisture sorption state on transverse dimensional changes in wood Published online: 17 December 2003  Springer-Verlag 2003 Abstract 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 (35C). 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 coeffi- cient of anisotropy (a T /a R ratio) during desorption. The magnitude of this phenomenon was found to vary from species to species. Einfluß der Feuchteaufnahme auf die transversale Dimensionsänderung in Holz Zusammenfassung Ziel der Arbeit war es, die transver- sale Dimensionsänderung und die entsprechenden aniso- tropen Verhältnisse in Holz während unterschiedlicher Grade der Feuchteaufnahme zu untersuchen. Ofenge- trocknete Proben von Erythrina variegata, Lannea coro- mandelica, Gmelina arborea und Albizia chinensis wurden bei konstanter Temperatur (35C) einer Sorption und anschließender Desorption unterworfen. Tangentiale und radiale Dimensionsänderungen wurden analysiert im Hinblick auf die relative Feuchte und den Wassergehalt in beiden Zuständen. Bei hohen Feuchten änderten sich die tangentialen Dimensionen schneller als in radialer Richtung. Bei einer gegebenen Gleichgewichtsfeuchte war die transversale Dimensionsänderung stärker wäh- rend der Desorption als während der Sorption. Dies bestätigt einen Effekt zweiter Ordnung für den Einfluss der Feuchteaufnahme auf die Dimensionsänderung. Die- ser Effekt war in tangentialer Richtung vorherrschender im Vergleich zur radialen Richtung, woraus sich ein höherer Grad an Anisotropie (a T /a R; -Verhältnis) während der Desorption ergibt. Die Größe dieses Effekts variiert je nach Holzart. 1 Introduction Wood being a hygroscopic material adsorbs or desorbs moisture with changes in relative humidity and temper- ature of surroundings to attain equilibrium moisture content. This moisture movement leads to dimensional changes in wood namely, swelling during adsorption and shrinkage during desorption. The swelling and shrinkage of wood are the result of moisture interaction within and between cell walls which internally deform wood tissue (Naderi and Hernandez 1997). These dimensional chang- es are anisotropic due to inherent directional orientation of cells. Normal wood is most dimensionally stable in the parallel to grain direction and least so in the tangential direction (Skaar 1988). The anisotropy in dimensional movements results in warping, cracking and angular deformation in wood when put to use. Since environmental conditions never remain stable and ambient relative humidity and temperature changes continuously, repeated adsorption and desorption of moisture takes place and moisture content of wood seldomly reaches to equilibrium level with surrounding. It has been observed by several researchers that wood behaves differently during adsorption and desorption and some of its physical and mechanical properties are influenced by the state of sorption (Goulet and Hernan- S. S. Chauhan ( ) ) School of Forestry, University of Canterbury, Private Bag 4800, Christchurch, New Zealand e-mail: shaktisc@rediffmail.com P. Aggarwal Institute of Wood Science and Technology, Malleswaram, 18th Cross, Bangalore, India