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The wood of five European species: black poplar (Populus nigra L.), European beech (Fagus sylvatica L.), European ash (Fraxinus excelsior L.), European oak (Quercus robur L.), and Scots pine (Pinus sylvestris L.) was subjected to thermal modification in nitrogen atmosphere at 190 °C during 6 h. Native and modified wood was varnished and oiled in industrial conditions. Thermally modified (TM) wood was characterized by a greater absorption of varnish and oil when applying the first layer to the surface, which finally resulted in higher application values compared to native wood. In particular, after varnishing, there was a significant increase in gloss and radical change of colour. Regardless of the wood species, finishing process (varnishing, oiling), the ΔE values were close to or higher than 6, which proves high colour changes. Modified poplar, ash, and oak after varnishing had a different colour (ΔE higher than 12). The surface colour changes as a result of UV photoaging was individual, depending on the wood species and the method of finishing. In the case of the thickness of varnish coatings, the wood structure was important, i.e., on ring-porous hardwood and softwood they were thicker. In the case of wood species with a lower density, i.e., black poplar and pine, the thermal modification in nitrogen atmosphere process did not reduce the resistance of the varnish coat, and in the case of species with a higher density (oak, ash, beech) it decreased by one level. Thermal modification reduced the Brinell hardness of wood with wide rays (oak and beech) by 11%. The applied process of surface finishing by double varnishing or oiling did not significantly change the hardness of tested wood. [ABSTRACT FROM AUTHOR]

The study examined the influence of ultraviolet radiation on the colour of thermo-mechanically modified beech (Fagus sylvatica) and oak (Quercus robur). The wood colour parameters were measured using the mathematical CIE L*a*b* and L*C*h colour space models. The higher the temperature of thermo-mechanical treatment, the least susceptible beech and oak wood was to a change in L*, a* and b* under the influence of light irradiation. The greatest changes in the colour of non-densified and densified beech and oak wood occurred after 20 h of light irradiation. The higher the temperature of thermo-mechanical treatment, the smaller were the total changes in the colour of beech and oak wood under the influence of ultraviolet radiation. The total changes in the colour of beech densified at temperatures of 100°C and 150°C that took place under the influence of ultraviolet radiation were twice as high as in the case of densified oak wood. The colour of oak wood modified at a temperature of 200°C did not change significantly in 300 h of light irradiation. [ABSTRACT FROM AUTHOR]

Beech (Fagus sylvatica L.), oak (Quercus robur L.) and pine (Pinus sylvestris L.) wood were volume-densified by means of thermo-mechanical modification. At first stage the wood was heated in a hydraulic press at temperature 100°C for 720 s, and then one-step densified in order to obtain the target thickness. The wood was cooled in a hydraulic press with unheated plates. Density profiles parallel and perpendicular to the grain were examined. The analysis of the density profiles was carried out on the basis of the following parameters: mean density, minimum to mean density ratio, maximum density, and the distance between the maximum density area and the wood surface. Wood hardness was determined according to the Brinell method. Volume-densified pine wood was characterized by considerably lower susceptibility to densification than beech or oak wood. Densified beech wood had the highest mean density 921 ±7 kg/m³, and the highest maximum density 968 ±12 kg/m³. The Brinell hardness of densified beech, oak and pine wood was twice as high as before the densification. The greatest hardness after the densification 78.60 ±10.56 N/mm² was observed in beech wood. [ABSTRACT FROM AUTHOR]