| Larch wood resource is abundant in China. In furniture and decoration industry larch wood has great application potential because of its beautiful visual characteristics, the high hardness and strength. But larch wood has poor permeability and inside stress, so it is hard to dry and easy to crack or deform, in addition larch wood is rich in resin and thus it is difficult to treat with preservative solution. Therefore larch wood is used mainly in the form of log in the industry such as architecture, pulp and mine. It is not used widely. The main reason for poor permeability of larch wood is that the pit membrane and the pit border of heartwood besides the cell surface is covered with one layer non-cellulosed membrane. Moreover, when the sapwood transforms into heartwood, the torus deviate from the original place and it will block pit aperture and the pathway of vapor, and that the cell cavity contains much cell resin and gum which blocks the flow of water or vapor in wood resulting in the poor permeability.In order to improve its permeability, larch wood timber was treated by high-intensity microwave (MW), a physical method of modification. High steam pressure inside the wood with proper moisture content was generated by MW radiation in a short time, which can destroy the pit membrane or ray parenchyma forming new channels for water and vapor, the micro-cracking. By adjusting the power of MW, the quantity, the size and distribution of the micro-cracking can be controlled. In this way the radial and axial section permeability of larch wood can be improved. The research results showed that, Firstly, the permeability was increased after radiating the larch wood specimen high-intensity MW, and the extent of this effect depended on the original moisture content of the specimen, the power and the time duration of microwave radiation. Secondly, the microstructure of larch wood was changed to some extent, the observed changes by scanning electronic microscope were the pit membrane cracking and the cross crack on radial section of the specimen. Thirdly, when treating condition is proper the bending strength and modulus of elasticity of larch wood specimen was nearly unchanged and the toughness of larch wood specimen was increased to some extent. Finally, only minor changes on the hygroscopicity and dimension stability of larch wood was observed, and no significant change on chemical composition of larch wood was determined by FTIR. |
