Abstract: [Objective] The effects of high temperature heat treatment on the equilibrium moisture content and sorption isotherms characteristics of Pinus sylvestris var. mongolica,Cunninghamia lanceolata and Populus nigra were studied. The research result could be used in scientific evaluation of moisture adsorption characteristics of wood, and the relevant data could also be used as a reference in actual production.[Method] In this study water vapor was used as protective medium and three levels of heat treatment temperature were set, which was 180, 200 and 220℃, respectively. The sorption experiments were performed in the two-chamber setup, the relative humidity of air was controlled by eight kinds of salt solutions and the air temperature of sorption experiments were 25℃. The sorption isotherms of high temperature heat-treated wood was fitted by Hailwood-Horrobin equation, and the effects of high temperature heat treatment on the isothermal adsorption behavior, equilibrium moisture content, monolayer water and polylayer water were analyzed.[Result] The equilibrium moisture content of 180, 200, 220℃ treated samples were equivalent to 80%, 70% and 50% equilibrium moisture content of control samples, respectively. The Hailwood-Horrobin equation could be used to fit the isothermal adsorption curves of three species wood and their high temperature heat-treated wood, and their isothermal adsorption curves all belonged to typeⅡ, the fitting degree of isothermal adsorption curves were higher than 0.980 0 for all the conditions. The higher the treatment temperature was, the closer the isothermal adsorption curve is to the straight line. The parameter W which means the apparent molecular mass of the dry wood per sorption sites was significantly increased after heat treatment, meanwhile, the moisture content of monolayer and polylayer water in different relative humidity environment was significantly decreased after heat treatment. The monolayer water of samples reduced about 20%, 30% and 50% for 180, 200, 220℃ heat-treated wood comparing with those of control samples, respectively. The influence of high temperature heat treatment on polylayer water was similar. The maximum amount of monolayer water, polylayer water and the total amount of adsorbed water was significantly reduced compared with control samples after heat treatment, and the higher the treatment temperature, the greater degree of decline was found.[Conclusion] The equilibrium moisture content of wood could be significantly reduced by high temperature heat treatment, and the higher the treatment temperature, the greater the decreasing in the equilibrium moisture content was obtained. The Hailwood-Horrobin equation could be used to describe the isothermal adsorption curve of high temperature heat treatment wood, and the fitting degree is fairly high. The isothermal adsorption curve of wood could be significantly influenced by high temperature treatment. The amount of monolayer water, polylayer water and total adsorbed water could be significantly reduced by high temperature heat treatment, and the higher the treatment temperature, the more obvious of the influence was found. The maximum content of monolayer water, polylayer water was significantly reduced after heat treatment, which would affect the maximum amount of adsorbed water.

Key words: wood sorption isotherms characteristics, high temperature heat treatment, Hailwood-Horrobin model, monolayer water adsorption, polylayer water adsorption