Über das Sorptionsverhalten wärmebehandelter Hölzer

Summary

The heating of solid wood to higher temperatures is the simplest and cheapest means for stabilizing its dimensions. Caused by the partial thermal degradation of the chemical components of the wood occurring in heat stabilization, also other physical properties are considerably changed. For the investigation of the effect of thermal treatment on the sorption of the wood, oven-dry samples of beech-wood, vakwood, and pine sapwood were heated in presence of air at temperatures of 70°–200°C for different periods (6, 24, and 48 hours). Subsequently, for these samples the adsorption and desorption isotherms were taken up at 20°C in a vacuum-sorption apparatus, and there from the avarage sorption of the woods was determined. When heated at 70°C the sorption capacity of the three woods was not changed. The thermal treatments at 100°, 130°, and 150°C resulted in a decrease in the sorption capacity, being the greater the higher the temperature and the longer the time of heating were. The heating-treatments of 6 and 24 hours at 180°C yielded, in an equal sense, even greater decreases in the sorption capacity, though after 48 hours of heating the decrease was less than after 24 hours. During the interval of 24 to 48 hours at 180°C, consequently chemical processes must have taken place in the woods now resulting in a rise of the sorption capacity. This should have been caused by the sampleting of the lignin. The determined changes in the sorption of the heat-treated woods are explained by the sorption behaviour of the chemical wood components cellulose, wood polyoses, and lignin and their proportions in the chemical composition of the wood as well as their different thermal stability.