热处理木材的水分吸着热力学特性

为了弄清楚热处理木材细胞壁中的水分吸着环境，即由半纤维素和木素组成的无定形区构造的变化，本研究通过对未处理及１５０，１８０，２３０℃处理云杉材在温度为２０℃和５０℃时的水分吸着等温线的测定，得到了吸着水的微分吸着热ＱＬ、微分吸着自由能ΔＧ及微分吸着熵ＴΔＳ与水分吸着量Ｗ、热处理温度之间的关系．结果表明：①与未处理木材相比，热处理木材的水分吸着机构发生变化，即第一层吸着和第二层吸着不具有时间上的重叠性；②随着热处理温度的升高，水分吸着量减少，这是由于吸湿性的半纤维素发生变化而致；③在相对湿度为６０％时，微分吸着热ＱＬ和微分吸着熵ＴΔＳ随着热处理温度的升高而减少，这一现象意味着水分子与木材分子之间形成的氢键结合数量上的减少．

Thermodynamic Characteristics of Water Absorption of Heat treated Wood

The purpose of this study is to make clear the environment of water absorption in the cell wall of heat treated wood,that is, the structural change of Matrix made up of hemicelluse and lignin.In this study,water absorption isotherms for untreated Dragon spruce (Picea asperata Mast.)and heat treated Dragon spruce(150,180 and 230℃) at 20 and 50℃ are determined.By these isotherms,the relationship between differential heat of absorption Q L,free energy change ΔWTBX]G,entropy change TΔS and moisture content W,heat treated temperature can be worked out.The conclusions are as follows:①Compared with untreated wood,the water absorption mechanism of heat treated wood changes.The absorption of first layer has been finished before the absorption of second layer when wood is heat treated.②With the increase of heat treated temperature,moisture content decreases.The reason is that hygroscopic hemicellulose changes to furfural polymer.③Differential heat of absorption Q L and entropy change TΔS decreases with the increasing of heat treated temperature at 60%RH.It means the decrease of the number of hydrogen bonding between water molecules and wood molecules.