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The wood-water interactions of modified beech wood (Fagus sylvatica L.) were studied. Specimens were thermally modified at 180 (TM1), 200 (TM2) and 220 °C (TM3), acetylated (Acet), and melamine formaldehyde (MF) resin (Mel) modified. Afterwards, the water vapour characteristics, i.e. water vapour sorption isotherms, equilibrium moisture content (EMC), dimensional stability of specimens conditioned at 30, 65 and 90% RH and liquid water characteristics, i.e. water absorption, maximum moisture content (MC), leachability and swelling kinetics, were determined and the results compared with reference (Ref) specimens. From the results, it is evident that the scale of wood-water interactions was highly dependent on the thermal modification temperature and type of chemical modification. The water vapour isotherms of thermally modified wood decreased, whereas more severe treatment exhibited more distinct reduction. The EMC values of the Mel and TM1 specimens decreased only at high RH, whereas the most significant decrease, within the whole range of observation, was found in the Acet group. The maximum MC reduction was achieved by acetylation. As a consequence of swelling reduction, dimensional stability expressed as anti-swelling efficiency (ASE) was considerably improved. A relatively high initial linear-phase swelling rate was found for the Ref specimens, whereas modified wood exhibited comparatively slow and gradual swelling.

The aim of this paper was to analyze selected properties of beech wood (Fagus sylvatica L.) treated by one-sided surface charring. Specimens were one-side charred with a hot plate using several time-temperature combinations (from 200 to 400 °C). Characteristics such as colour, discoloration, surface roughness, fire resistance, total carbohydrate content at several wood layers and decay resistance were evaluated. Surface charring was applied to the radial and tangential surfaces. Colour measurements showed that the surface of the wood turned grey due to charring. In addition to colour measurements, other experiments showed significant differences between radial and tangential specimens due to their different structures. The higher the temperature used in treating them, the lower the roughness values for radial specimens, while the trend for tangential specimens was the opposite. A smoother surface is more fire resistant, so radial specimens are generally better in this regard. Tangential specimens are more susceptible during preparation to forming cracks that impair flame resistance because a continuous protective densified layer is not formed. The determination of total carbohydrates revealed significant changes at various wood depths after surface charring. These changes were more predictable in radial specimens due to the annual ring orientation, because each layer consisted of a similar earlywood/latewood ratio. Finally, when decay resistance was assessed, weight loss was found to be lower in all specimens than in the references. The results suggest that charring at a particular combination of temperature and time improved the investigated properties of the surface-modified beech.

Surface carbonization, or charring, of wooden cladding boards is a promising, low impact process that can substitute inorganic coatings. The char surface is inert and hydrophobic and possibly a long-lasting solution for exterior uses. To determine the performance of surface-charred wood, several sorption experiments were established. Sapwood of two hardwoods (aspen, birch) and two softwoods (pine, spruce) were used as the experimental material, modified by contact charring and gas flame charring, including surfaces coated with oil for further protection. The results showed that flame charring modification is equal to a double layer of acrylic paint on primer in terms of permeability on all wood species, with higher moisture exclusion efficiency at high relative humidity. Contact charring modification presented much improved properties in comparison to both flame charring and acrylic paint in all implemented sorption experiments, but the dimensional stability was poor with strong cupping in wetting. However, hardwoods and especially birch exhibited less dimensional distortion than the other investigated species, and oiling further reduced the cupping. The contact charring modification produced more repeatable results with less impact from substrate and all wood species benefitted, whereas the flame charring modification is more dependent on inherent properties of the wood species, and does not seem to suit aspen as well as birch, and pine as well as spruce, although oiling affected the observed results.

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