Abstrael Some properties of wood (hinoki: Charnaecyparis obtusa) moisture-conditioned by an adsorption process from a dry state and by two desorption processes (from a water-saturated state and from a state with a moisture content slightly below the fiber saturation point) were investigated. The moisture contents of wood conditioned by the adsorption process and by the desorption process continued to approach to one another for the moisture-conditioning period of over 50 weeks. Accordingly, sorption hysteresis should be regarded as a transitional phenomenon that occurs during the process of approaching the true equilibrium, which requires a long time. The wood conditioned by the desorption process beginning from a water-saturated state showed slightly smaller dimensions than those conditioned by the adsorption process with the same moisture content; however, the wood conditioned by the desorption process from a moisture content below the fiber saturation point showed slightly larger dimensions than those conditioned by the adsorption process. The wood conditioned by the adsorption process from a dry state showed a higher modulus of elasticity and modulus of rupture than did the wood conditioned from a water-saturated state with the same moisture content. The mechanical properties of the wood also varied based on the states at which the desorption process was started. This is a notable characteristic of the relation between the drying condition and the mechanical properties of wood.

Changes in the modulus of elasticity (MOE), modulus of rupture (MOR), and stress relaxation in the radial direction of wood (hinoki: Chamaecyparis obtusa) moisture-conditioned by the adsorption process from a dry state and by the desorption process from a moisture content slightly below the fiber saturation point were investigated. The MOE and MOR of wood conditioned by the adsorption process showed significant increases during the later stages of conditioning when the moisture content scarcely changed. However, with the desorption process they did not increase as much during later stages of conditioning, though they increased during early stages of conditioning when the moisture content greatly decreased. The stress relaxation of wood decreased with an increase in the conditioning period with both the adsorption and desorption processes. These results suggest that wood in an unstable state, caused by the existing state of moisture differed from that in a true equilibrium state shows lower elasticity and strength and higher fluidity than wood in a true equilibrium state. Furthermore, the present study demonstrates that the unstable states of wood induced during the course of drying, desorption, and possibly adsorption of moisture are slowly modified as wood approaches a true equilibrium state.Key words Moisture-conditioned wood 9 Modulus of elasticity -Modulus of rupture -Stress relaxation uids showed higher elasticity and strength as the wood approached the swelling equilibrium, and it showed lower fluidity than wood swollen in water to the same degree. However, if the wood was far from the swelling equilibrium, it showed lower elasticity and strength and a higher fluidity than wood swollen in water to the same degree)These results are interpreted to suggest that the mechanical properties of wood in an unstable state during the process of approaching a true equilibrium state differ from those of wood in an equilibrium state; in other words, such wood shows lower elasticity and strength and higher fluidity than that in a true swelling equilibrium. Furthermore, it was previously found that the moisture content of wood conditioned by adsorption and desorption changed continuously during a moisture-conditioning period of over 50 weeks) In light of this result, the sorption hysteresis of wood is thought to be a phenomenon that occurs during a transitional process as wood approaches the true sorption equilibrium.There seem to be no systematic studies in which the mechanical properties of wood were investigated in terms of an unstable state of wood. Hence, this study aimed to clarify some of the mechanical properties of wood in unstable states approaching the sorption equilibrium. It was achieved by examining the elastic, strength, and viscoelastic properties of wood during the moisture-conditioning process of adsorption and desorption of moisture. Y. Ishimaru (~)

No abstract