Thermally modified birch wood interaction with liquids

Large research work is currently being performed concerning different elaborated new wood protection methods. However, combining industrially well-approbated processes is also considered potentially quite promising and such approach is being actively studied. The objective of the present study was to investigate peculiarities of interaction between liquids and thermally modified (TM) birch wood (Betula spp.). This knowledge is essential for proper TM wood post-treatments involving its impregnation as well as for evaluation of potential wood moisture dynamics in outdoor applications. Changes caused by TM (150–170 °C) in a closed system under elevated pressure in wood wettability, permeability, liquid absorption capacity, and drying characteristics were evaluated. The results concerning absorption capacity, which is mainly related to wood anatomical features and is density-dependent, indicated reduced absorption capacity of TM wood compared with unmodified birch of similar density. Permeability, which characterises the ease with which liquid is transported through a wood porous system, was evaluated by capillary absorption tests through the samples’ tangential and radial surfaces. TM made birch wood less permeable through both surfaces as well as less anisotropic regarding transverse absorption rates. Moreover, TM also caused a decrease in drying rates for birch wood impregnated with water. Reduction in permeability influences the impregnation process of boards and no full saturation was detected for TM boards when applying an impregnation schedule providing complete saturation for unmodified boards. On the other hand, less water was absorbed by TM boards exposed to rain on outdoor weathering racks.