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. This study is part of a project that is aimed at improving wood service properties by combining thermal modification (TM) and impregnation with Cu-organic preservatives. The objective of the present study was to investigate peculiarities of interaction between liquids and 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 to reduced absorption capacity of TM wood compared with unmodified birch of similar density. Permeability, which characterises the ease with which liquid is transported through wood porous system, was evaluated by capillary absorption tests through the specimens’ tangential and radial surfaces. TM made birch wood less permeable through both surfaces as well as less anisotropic regarding transverse absorption rates. Moreover, TM caused also decrease in drying rates for wood impregnated with both water as well as biocide solution. Reduction in permeability influences impregnation process of boards and not full saturation was detected for TM boards when impregnation schedule providing complete saturation for unmodified boards was applied. On the other hand, less water was absorbed by TM boards exposed to rain on outdoor weathering racks