Study On Permeability And Its Improvement About Two Kinds Of Fast-growing Plantation Species

Permeability reflects difficulty level of fluid passing through wood. Wood permeability is one of the most physical properties. Increasing permeability can also raise drying rate and impregnation effects during wood modification. Poplar and Eucalyptus that are the main fast-growing plantation species will become dominating raw material increasingly. Compare with natural forest, fast growing plantation's usage are limited with loose material,lower strength,easy decay,difficult drying. So, improving fast growing plantation's comprehensive properties,increasing the value of usage are the most important issues we face. But wood drying and functional improvement was restricted by wood permeability, such as dying,fire retardant,preservation,strengthen treatment and so on.Gas permeability of Poplar and Eucalyptus camaldulensis are studied systematicly in this paper, and the result shows that: during same moisture content, permeability differences are not obvious among different radial position of Poplar, and increase differently with moisture content decreasing, longitudinal permeability is much bigger than that of transverse, radial permeability is a little bigger than that of tangential, and built mathematical equation of permeability and MC change. During same moisture content, transverse permeability differences of Eucalyptus camaldulensis are not regular or obvious from heartwood to sapwood; the similarity of longitudinal permeability was also found in heartwood, but increases from sapwood to bark. Transverse permeability is very low, and there are little differences between radial and tangential permeability.Conclusions are made by pre-treatment to Poplar and Eucalyptus camaldulensis: gas permeability after streaming and boiling pre-treatment increase with time extension during same temperature, in the same period of time, gas permeability of high temperature is better than that of low temperature. During same temperature of explosion pre-treatment, Permeability of high pressure is better than that of low pressure, permeability of high temperature is better than that of low temperature during the same pressure. The effects of increasing permeability: streaming pre-treatment is first, boiling pre-treatment is second, explosion pre-treatment is not so apparent for Poplar by paired comparison t-test (a=0.05);Explosion pre-treatment of Eucalyptus camaldulensis is high remarkable, streaming and boiling pre-treatment are the next, the differences of improvement effect are little between streaming and boiling pre-treatment. These pre-treatments could be referenced in production. The result of conventional kiln drying experiment shows that: when samples'moisture content is higher than 30%, two kinds of wood species'drying rate are increased differently,free water flowing in wood is permeability which is forced by the capillary pressure, water flow intensity is increased at the same time, wood permeability is increased by pre-treatment; When moisture content is below 30%, all the effects are not obvious. Conventional kiln drying experiment proves that pre-treatment can improve wood permeability.