Study on Properties of Waterlogged Woods Treated by Supercritical Drying in a Long-Term Conservation

Ambient humidity is one the most important factor which affects the degradation of waterlogged woodsin a long-term conservation. Change of the humidity affects不只是on物理性能such asexpansion and/or contraction of woods but also on chemical change of wood fiber such asdecomposition and degradation. In the present study，we investigated the effects of humidity on the waterlogged wood from the view点传输phenomena.Frist, we measured equilibrium moisture contents in the woods，并发现他们提供相关的humidity for the humidity少于80%.下一个，wood weight curves of the weight were measured for step change of the humidity from 30% to 80%. .Comparing the sponse curves for woods with different size，we found diffusion of moisture in the wood is the rate controling step. Then，diffusion coefficients were estimated based on the diffusion model. As a result，我们发现了following correlation between the diffusion coefficient， d_aand apparent density of wood, rho_b: d_arho_b g/(cm day)where，d_a and rho_b are in cm^2/day and g/cm^3，Comparing the similar correlation we obtained previously for natural drying，the diffusion coefficients obtained in the present study about 3.5 times as large as the onesfor natural drying, because no extreme contraction of wood occured for the supercritical drying，woods contracted extremely in the falling-rate period for the natural drying. Further，我们measured the diffusion coefficient for a wood impregnated with polyethylene glycol . thediffusion coefficient for wood impregnated with PEG was about one tenth the one estimated from the关于correlation. Consequently，我们发现(d_a for supercritical drying wood)>(d_a for natural drying wood)>（d_a for wood）impregnated with PEG . This fact implies that the reponse of wood weight against the change ofhumidity is the fastest among three of them above

Ambient humidity is one the most important factor which affects the degradation of waterlogged woods in a long-term conservation. Change of the humidity affects not only on physical properties such as expansion and/or contraction of woods but also on chemical change of wood fiber such as decomposition and degradation. In the present study, we investigated the effects of humidity on the waterlogged wood from the view point transport phenomena.Frist, we measured equilibrium moisture contents in the woods, and found that they are propportional to the relative humidity for the humidity less than 80%. Next, reponse curves of the wood weight were measured for step change of the humidity from 30% to 80%. Comparing the response curves for woods with different size, we found diffusion of moisture in the wood is the rate controling step. Then, diffusion coefficients were estimated based on the diffusion model. As a result, we found the following correlation between the diffusion coefficient, D_A, and apparent density of wood, rho_B :D_Arho_B g/(cm・day)where, D_A and rho_B are in cm^2/day and g/cm^3, respectively. Comparing the similar correlation we obtained previously for natural drying, the diffusion coefficients obtained in the present study were about 3.5 times as large as the ones for natural drying, because no extreme contraction of wood occured for the supercritical drying, : woods contracted extremely in the falling-rate period for the natural drying. Further, we measured the diffusion coefficient for a wood impregnated with polyethylene glycol (PEG). The diffusion coefficient for wood impregnated with PEG was about one tenth the one estimated from the above correlation. Consequently, we found that (D_A for supercritical drying wood)>(D_A for natural drying wood)>(D_A for wood impregnated with PEG). This fact implies that the reponse of wood weight against the change of humidity is the fastest among three of them above.