冻结红松和大青杨湿木材内部水分存在状态及含量测定

为对立木在冬季冻结时内部水分存在状态及含量进行研究,采用差示扫描量热仪(DSC204)分别对红松和大青杨湿木材试样进行降温(20℃到-60℃)和升温(-60℃到20℃)扫描测试,通过DSC曲线观察木材中水分冻结和融化所产生的放热峰和吸热峰位置,并采用积分法计算吸热峰面积,估计木材中水分存在状态及含量。结果表明:1)采用DSC能够对冻结木材中水分存在状态、含量进行比较清晰的判定,从DSC曲线可知,冻结湿木材中含有冻结自由水、冻结结合水和非冻结水3种类型水分;2)温度降低时,红松和大青杨中自由水冻结产生的放热峰位置约为-13℃和-18℃;温度升高时,冻结结合水和自由水融化所产生的吸热峰位置分别约为-0.4℃,6℃和0.8℃,9℃;3)温度-60℃时,红松边材晚材、边材早材、心材晚材和心材早材试样中冻结水占木材总含水量的80.3%,75.8%,75.2%和77.3%,而大青杨分别为69.4%,68.5%,63.3%和89.0%。

Determining the States of Water and Its Fraction in Frozen Populus ussuriensis and Pinus koraiensis Green Timbers

To determine the states of water and its fraction in frozen tree in winter,the heating and cooling curves of Populus ussuriensis and Pinus koraiensis green timber specimens were tested and analyzed respectively using differential scanning calorimetry(DSC 204).The positions of exothermic and endothermic peaks,which were shown on the DSC curves,caused by freezing and melting of water in wood were located,and the areas of endothermic peaks were measured by using an integration method,then the states of water and its fraction in frozen wood were evaluated.The results showed that:1) It was feasible to determine the states of water and its fraction in frozen wood using DSC.The DSC curves illustrate that there were three types water in green wood:frozen free water,frozen bound water and nonfrozen water.2) The positions of exothermic peak induced by freezing of free water in Pinus koraiensis and Populus ussuriensis specimens were about-13 ℃ and-18 ℃ as temperature decreased;the positions of endothermic peak induced by melting of bound water and free water were about-0.4 ℃,6 ℃ and 0.8 ℃,9 ℃ respectively as temperature increased.3) Considering latewood and earlywood of sapwood and heartwood,the ratios of frozen water contents to moisture content were 80.3%,75.8%,75.2% and 77.3% in Pinus koraiensis,69.4%,68.5%,63.3% and 89.0% in Populus ussuriensis when temperature was-60 ℃.