Untersuchungen zum Feuchteverhalten und zur Porosität von thermisch modifiziertem Holz

Investigation on moisture behaviour and porosity of thermally modified timber.

The influence of thermal modification (nitrogen atmosphere, 170 to 180 °C) on the moisture behaviour of samples of spruce, beech and ash conditioned under standard climatic conditions (20 °C, 65 % relative humidity) was investigated. The sorption rate, water vapour resistance factor and water absorption coefficient were tested according to DIN EN ISO 15148: 2003-03 and DIN EN ISO 12572:2001-09. Further, the pore volume was determined using mercury porosimetry. As a consequence of the thermal treatment, the raw density of beech and ash was reduced (up to +20 %) and the total pore volume increased (+3.2 and +23.4 % respectively). The thermally modified spruce, in contrast, partially showed increased raw density values (+9 %) and thus a reduction of the pore portion (-10 %). Generally, treatment results in a decrease of the sorption rate (up to -62 %) and the water absorption coefficient (up to -76 %) as well as an increase of the water vapour resistance factor (up to +574 %). It can be derived from the determined results that the sorption and diffusion behaviour is not dependent on the increase (spruce) or the decrease (beech and ash) of the density and changes in pore volume portion involved, respectively. Primarily it is influenced by the hydrophobising of the thermal treatment.