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.

One-sided surface charred European beech wood (Fagus sylvatica L.) was studied. Radial and tangential specimens of dimensions of 50 × 25 × 350 mm were one-sided surface charred at 200, 250, 300, 350, and 400 °C for various times using a contact heating system. Specimens of dimensions of 50 × 25 × 50 mm3 were prepared for treatment intensity analysis and its effect on surface wettability. Density profiles of the radial and tangential charred specimens were determined using X-ray densitography with a resolution of 0.05 mm. The wettability of the one-sided surface charred wood specimens was analyzed via contact angle, measured using the sessile drop method and determined over 10 to 150 s. The oven-dried specimens were partially submerged in water and water uptake was recorded after 2, 4, 6, 8, 10, 48, and 72 h according to EN-927-5. The surface density of the radial specimen groups charred at 200 °C for 6 min and 250 °C for 4 min decreased by about 4.5 to 8.2%. With increasingly severe charring, the surface density decreased by about 15.5 to 33.5%. A mild charring process produced a surface charred layer of approx. 2 mm, while higher temperatures and longer times affected the density up to 4–6 mm beneath the surface. Differences were found between the water uptake of the radial and tangential charred beech specimens. The most significant decrease of 56% in water uptake was recorded for the radial group prepared at 200 °C for 20 min after floating in water for 72 h. Water uptake in the radial groups modified at 250 °C for 4 and 6 min after 72 h decreased by 38% and 36%, respectively. The tangential groups did not show any statistically significant decrease. The average water uptake of the groups charred at 200 °C for 20 min, 350 °C for 2 min and 400 °C for 1 min was greater than that of the reference; the variability of the measured data was significantly greater due to the highly anisotropic character of the tangential specimens. Micro cracks were also visible on the surface. Concluding from the results of this study, one-sided surface charred beech wood exhibits increased potential in terms of wood–water related properties when a temperature range of 200–400 °C is applied.

This article focuses on hygrothermal problems in massive wooden sandwich structures. Wood in sandwich structures is already artificially dried before processing, and therefore does not further shrink, as it does in the case of log cabins. Analysed sandwich structure is composed from three layers, and is formed of wooden beam in interior side, thermal insulation and wooden beam in the exterior side. The composition of analysed structure is considered in different thickness with respect to the required heat transfer coefficient. Massive wooden beam on the exterior side causes troubles which exhibits in the reducing capacity of diffusion of water vapor. It is therefore possible that water vapor condenses on the interface of wood and the thermal insulation under certain boundary conditions. Therefore, it is appropriate to place massive wooden beam closest to the interior side. This solution would improve the balance of the diffusion permeability to water vapor permeating from the interior side to the exterior side.

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