Changes in the mechanical properties of wood during a period of moisture conditioning

Abstract

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 (~)

Sorption of water–ethanol mixtures by poplar wood: swelling and viscoelastic behaviour

“…Wood-water interactions and its influence on dynamical mechanical properties are already well documented (Ebrahimzadeh and Bertilsson 1998). The final modifications of E′ and tanδ after impregnation with water are comparable to the results obtained by Ishimaru et al (2001b) and Obataya et al (1998). For ethanol, as no Evolution of viscoelastic properties of poplar veneers specimens immersed in pure water and pure ethanol at 40 °C.…”

Influence of variation in modulus of elasticity on creep of wood during changing process of moisture

“…Recently, it has been demonstrated that MOE also depends on the moisture-conditioning period, even if the wood has the same MC and is at the same temperature (Ishimaru et al 2001b). It was reported that woods stored under various relative humidities (RHs) reach equilibrium MC after approximately 3 weeks, but the MOE continued to increase gradually, even after 9 weeks.…”

Efecto del comportamiento termo-higromecánico a macroescala de madera bajo compresión perpendicular a la fibra en las propiedades nanomecánicas de su estructura celular

“…Con respecto a los ciclos ambientales, durante el segundo ciclo, tanto en invierno como en verano, la dureza en la pared celular de los tres tratamientos, aumentó en promedio un 12%. Ishimaru et al (2001) sugirieron que el incremento de las propiedades mecánicas en la madera tras haber pasado por varios cambios cíclicos de humedad, estaría asociado a una reorientación de las cadenas moleculares de las componentes de la madera, puesto que éstas intentan alcanzar una estabilidad en estos procesos.…”