高强度微波辐射对落叶松木材渗透性的影响

Effects of Intensive Microwave Irradiation on the Permeability of Larch Wood

采用高强度微波辐射落叶松木材,将微波处理的木材试件与未处理试件在相同的条件下进行加压注水试验,测定吸水增重率(WAR),用于评价木材的渗透性。研究了试材初含水率、处理材心层温度、微波辐射功率、微波辐射时间等处理工艺条件与落叶松木材渗透性的关系。结果表明:适当控制上述处理条件,高强度微波辐射处理可以改善落叶松木材的渗透性。落叶松木材适宜的初含水率范围是25%～60%;适宜的微波辐射功率与落叶松木材的初含水率有关,本文条件下辐射功率可选择9～24kW;适宜的辐射时间取决于木材的初含水率和选择的辐射功率,当落叶松木材的含水率为30%左右,9.23kW微波功率下辐射55s或20～24kW微波功率下辐射25s时,经微波处理木材的吸水增重率是未处理材的200%以上,木材的渗透性得到显著改善。对微波处理改善落叶松木材渗透性的机理进行讨论,认为微波能够迅速使木材内部的水汽化,在木材内部产生较大的蒸汽压,冲破木材细胞壁薄弱组织,形成细微裂隙,疏通水汽传导的途径。随着微波功率的升高有利于微细裂隙的形成,所需辐射时间缩短,但是过高的辐射功率或过长的辐射时间易造成木材开裂。

To improve the permeability of larch wood, high intensive microwave irradiation was applied to wood. The microwave treated and untreated larch wood was water-impregnated by pressure at the same conditions, and then the water absorption ratio （WAR） of the microwave-treated wood samples and the untreated （control） was calculated to evaluate the permeability of the wood. The relationship was discussed between the permeability of larch wood and the conditions of microwave treating process such as the initial moisture content （MC） of wood, the inner temperature of treated wood, microwave power and the time of microwave treatment. The results showed that by controlling the microwave treating conditions properly, the permeability of larch wood can be improved. The proper range of the initial MC of wood was from 25% to 60% for intensive microwave treatment in the conditions of this paper. The proper microwave power is related to the initial MC of the wood, and it was 9 - 24 kW in this paper. While the proper time of microwave treatment is determined by the initial MC and the microwave treating time applied to the wood. When the initial MC of larch wood was about 30% , being irradiated for 55 s by the microwave power of 9.23 kW, or being irradiated for 25 s by the microwave power of 20 - 24 kW, the WAR of the microwave-treated larch wood was more than 200% of the untreated, indicating the permeability of larch wood was improved remarkably. The mechanism of permeability improvement of larch wood by intensive microwave irradiation was discussed. As intensive microwave was applied to larch wood, the water inside the wood cell boiled rapidly, forming vapor. When the vapor pressure increased high enough, it broke down the weaker part of the wood cell and formed tiny invisible cracks in the cell wall, forming new channels for water and vapor going through the cells, and the permeability of larch wood was thus improved. Increasing microwave power accelerated the formation of the tiny cracks in the cell wall and shortened the treatment time, but excessive microwave intensity or too lc.ng treatment time might result in surface checking and inner checking of wood.