Abstract:

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 long treatment time might result in surface checking and inner checking of wood.

Key words: larch wood, intensive microwave irradiation, permeability