Study On Vacuum/Steam Treatment Process Of Log And The Characteristics Of Treated Wood In Poplar Plantation

The speed of moisture conductivity in longitudinal is faster than in horizontal of wood. As a theoretical basis for this study, three Populus alba Linn. var. pyramdalis Bunge log, no heart hole and for80cm length with bark and double13cm for each end without bark, no heart hole and for45cm length with bark and double13cm for each end without bark, for72cm length with heart hole and for80cm length with bark and double13cm for each end without bark, had been treated by vacuum/steam. Then, the variation of temperature, moisture content in log had been tested, and gas permeability of treated wood had been researched. The aim of study is provide theoretical basis for impregnation and drying of log.The main conclusions are as follow:1. In the early of vacuum/steam treatment, the period far from steam and near from vacuum of log appearance a temperature drop. After the vacuum/steam treatment ended, that period appearance a temperature rise. Both the temperature rise and temperature drop at heartwood is lower than sapwood.2. In the heating stage of vacuum/steam treatment, wood moisture content in the period near steam rising rapidly and the supreme temperature is high, slower and lower to vacuum end. In the length range in log, conclude the range with heart hole in the log with heart hole, there is a huge variation for temperature raised. It is suggested that heat preservation is the effect factor for temperature variation at the period far from steam.3. At the stage of temperature arise with steam and vacuum, the moisture content of the period of near steam in log is increasing. At the stage of temperature falling with vacuum only, the moisture content have a little reduced. It is suggested that temperature is the force to move moisture in wood. The period near vacuum in log, as the temperature is low, moisture moved to this period, then, moisture content is rising. After the vacuum/steam treatment ended, the moisture content is increasing.4. Compared with the treated sample and control sample, the variation of permeability between heartwood and sapwood is a little large, the ratio of permeability for heartwood and sapwood almost is1:7. At the moisture content in the arrange of hygroscopicity,8%and25%,the ratio of permeability almost is1.5:1. The period of wood affected by vacuum or steam, the permeability have a rising, but the period near steam is more obviously. The log with heart hole, the period without heart hole and near vacuum, it’s permeability is more than vacuum end, that is under the effect of vacuum and steam.5. The equilibrium moisture content of absorption of heartwood in log is cutting down by steam/vacuum treatment, and increase the equilibrium moisture content of sapwood. The moisture barrier of sapwood is increasing by steam/vacuum treatment, the moisture barrier of heartwood is increasing at the period of near vacuum and steam.6. The sorption hysteresis of wood is reducing obviously by vacuum/steam treatment. The sorption hysteresis through high relative humidity is lower than sorption hysteresis through low relative humidity. At the difference position in log, the reducing of sorption hysteresis is most obviously for near steam, and then is near vacuum period. The sorption hysteresis is increasing by the increasing of relative humidity.