Surface Fractal dimensionality and hygroscopicity for heated wood

The relationship between hygroscopicity and the microsurface of heated wood was examined using the fractal surface dimensionality. The hygroscopicity of heated wood decreased with the increase in heating temperature to 250 degreesC, and then decreased again above 350 degreesC after increasing up to 350 degreesC. This change corresponded to chemical changes in the wood, especially a reduction in hydroxyl groups, up to 250 degreesC, and to the temperature dependence of the fractal dimensionality calculated from nitrogen gas adsorption above 250 degreesC. The fractal dimensionality increased gradually from 100 to 250 degreesC, followed by a rapid increase above 250 degreesC with a peak at 350 degreesC, and leveled off above 400 degreesC. From the results, it is concluded that hygroscopicity of heated wood changes at 250 degreesC and that it is dependent upon the chemical properties of wood below 250 degreesC and upon the surface complexity above 250 degreesC.