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

超临界干燥长期保存浸水木材性能研究

基本信息

批准号：
07831010
负责人：
KAWAGOE Mikio
金额：
$ 1.66万
依托单位：
NARA NATIONAL COLLEGE OF TECHNOLOGY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1995
资助国家：
日本
起止时间：
1995 至 1996
项目状态：
已结题

项目摘要

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.

环境湿度是影响水涝林长期保存后退化的重要因素之一。湿度的变化不仅影响木材的膨胀和/或收缩等物理性质，而且影响木材纤维的分解和降解等化学变化。本研究从湿传递现象的角度探讨了湿度对湿害木材的影响，首先测定了湿害木材的平衡含水率，发现当湿度小于80%时，平衡含水率与相对湿度成正比。其次，测量了木材重量对湿度从30%到80%阶跃变化的响应曲线。比较不同尺寸木材的响应曲线，发现木材中的水分扩散是速率控制步骤。然后，扩散系数估计的基础上的扩散模型。结果表明，扩散系数D_A与木材表观密度rho_B之间存在如下关系：D_Arho_B g/（cm·day）其中D_A和rho_B分别以cm ^2/day和g/cm ^3为单位。与自然干燥的相似关系式相比，本研究得到的扩散系数约为自然干燥的3.5倍，这是因为木材在超临界干燥时没有发生极端收缩：木材在自然干燥的降速期发生极端收缩。此外，我们测量了用聚乙二醇（PEG）浸渍的木材的扩散系数。用PEG浸渍的木材的扩散系数约为根据上述相关性估计的扩散系数的十分之一。结果表明，超临界干燥木材的D_A>自然干燥木材的D_A> PEG浸渍木材的D_A。这一事实表明，木材重量对湿度变化的反应是上述三种中最快的。