This paper deals with the impact of heat treatment on the elastic and strength properties of two diffuse porous hardwoods, namely Fagus sylvatica and Betula pendula. Two degrees of the heat treatment were used at temperatures of 165 °C and 210 °C. The dynamic and static elasticity modulus, bending strength, impact toughness, hardness, and density were tested. It is already known that an increase in treatment temperature decreases the mechanical properties and, on the other hand, leads to a better shape and dimensional stability. Higher temperatures of the heat treatment correlated with lower elastic and strength properties. In the case of higher temperature treatments, the decline of tested properties was noticeable as a result of serious changes in the chemical composition of wood. It was confirmed that at higher temperature stages of treatment, there was a more pronounced decrease in beech properties compared to those of the birch, which was the most evident in their bending strength and hardness. Our research confirmed that there is no reason to consider birch wood to be of a lesser quality, although it is regarded by foresters as an inferior tree species. After the heat treatment, the wood properties are almost the same as in the case of beech wood.

This work deals with the quality of birch (Betula pendula) wood from different sites and the impact of heat treatment on it. Two degrees of heat treatment were used, 170 °C and 190 °C. The resulting property values were compared with reference to untreated wood samples. These values were wood density, compressive strength, modulus of elasticity (MOE), bending strength (MOR), impact bending strength (toughness), hardness, swelling, limit of hygroscopicity, moisture content and color change. It was supposed that an increase in heat-treatment temperature could reduce strength properties and, adversely, lead to better shape and dimensional stability, which was confirmed by experiments. It was also shown that the properties of the wood before treatment affected their condition after heat treatment, and that the characteristic values and variability of birch properties from 4 sites, 8 stems totally, were reflected in the properties of the heat-treated wood. Values of static MOR were the exception, where the quality of the input wood was less significant at a higher temperature, and this was even more significant in impact bending strength, where it manifested at a lower temperature degree. Impact bending strength also proved to be significantly negatively affected by heat treatment, about 48% at 170 °C, and up to 67% at 190 °C. On the contrary, the most positive results were the MOE and hardness increases at 170 °C by about 30% and about 21%, respectively, with a decrease in swelling at 190 °C by about 31%. On the basis of color change and other ascertained properties, there is a possibility that, after suitable heat treatment, birch could replace other woods (e.g., beech) for certain specific purposes, particularly in the furniture industry.

The growing demand for sustainable composites has increased interest in natural fiber reinforcements as alternatives to synthetic materials. This study evaluates the bending properties of sandwich structures with flax fibers and 3D-printed lightweight foaming PLA cores compared to conventional designs using glass fibers and traditional cores. Three-point bending tests (EN 310) and density profile analysis showed that, despite its lower density, the 3D-printed foaming PLA core achieved a modulus of elasticity of 2269.19 MPa and a bending strength of 31.46 MPa, demonstrating its potential for lightweight applications. However, natural fibers influenced resin absorption, affecting core saturation compared to glass fibers. The use of bio-based epoxy and foaming PLA contributes to a lower environmental footprint, while 3D printing enables precise material optimization. These findings confirm that 3D-printed cores offer a competitive and sustainable alternative, with future research focusing on further optimization of internal structure to enhance mechanical performance.

This work is a follow-up contribution to the characteristics of Betula pendula (silver birch) wood from different habitats and the impact of the subsequent heat treatment. Specifically, it focuses on the surface properties of birch wood in the form of veneers, namely color, hardness, roughness and wetting, and in particular on the marketing evaluation of the attractiveness of colored birch wood and, thus, its possible use in practice in the Czech Republic. Three heat treatment steps at 170, 190 and 200 °C were used. The resulting values of the properties of the treated birch veneers were compared with the untreated reference veneers and also with beech veneers. These properties were the wood density, the colorimetric parameters, the roughness parameters, the wetting parameters, the hardness and density, and none of the parameters studied showed negative changes due to the temperature adjustment. Overall, both in terms of properties and in terms of marketing appraisal, there is the potential for birch to replace, for example, beech, especially in the furniture industry, by application in the form of heat-treated veneers after suitable heat treatment. The conclusions of the marketing analysis resulting from the questionnaire survey conducted on a sample of respondents show the significant preference for the heat-treated birch wood compared to reference birch samples without heat treatment.

This paper deals with the effect of heat treatment on the selected physical properties of birch wood. Five stages of heat treatment were used, ranging from 160 °C to 200 °C, in 10 °C increments, having a peak treatment duration of 3 h for each level. Primarily, changes in thermal characteristics, namely conductivity, diffusivity, effusivity, volume heat capacity, changes in colour and gloss parameters, mass loss due to modification and different moisture content in wood under given equilibrium climatic conditions, were monitored. The ISOMET 2114 analyser was used to measure the thermal characteristics. The measurement principle of this analyser is based on the analysis of the thermal response of the analysed material to pulses of heat flow. Measurements of colour, gloss, density and moisture content were carried out according to harmonised EN standards. The aim was to experimentally verify the more or less generally known more positive perception of heat-treated wood, both by touch and sight, i.e., the warmer perception of darker brown shades of wood. In terms of thermal characteristics, the most interesting result is that they gradually decrease with increasing treatment temperature. For example, at the highest treatment temperature of 200 °C, there is a decrease in thermal conductivity by 20.2%, a decrease in volume heat capacity by 15.0%, and a decrease in effusivity by 17.7%. The decrease in thermal conductivity is nearly constant at all treatment levels, specifically at this treatment temperature, by 6.0%. The fact mentioned above is positive in terms of the tactile perception of such treated wood, which can have a positive effect, for example, in furniture with surface application of heat-treated veneers, which are perceived positively by the majority of the human population visually or as a cladding material in saunas. In this context, it has been found that the thermal modification at the above-mentioned treatment temperature of 200 °C results in a decrease in brightness by 44.0%, a decrease in total colour difference by 38.4%, and a decrease in gloss (at an angle of 60°) by 18.2%. The decrease in gloss is only one essential negative aspect that can be addressed by subsequent surface treatment. During the heat treatment, there is also a loss of mass in volume, e.g., at a treatment temperature of 200 °C and subsequent conditioning to an equilibrium moisture content in a conditioning chamber with an air temperature of 20 ± 2 °C and relative humidity of 65 % ± 5%, there was a decrease by 7.9%. In conclusion, the experiments clearly confirmed the hypothesis of a positive perception of heat-treated wood in terms of haptics and aesthetics.

This article investigates the effects of pressure vacuum impregnation using inorganic, organic, and natural flame retardants on enhancing the fire resistance and chemical composition of structural beech wood (Fagus sylvatica). The study examines fire resistance characteristics such as the limiting oxidation number and heat of combustion, which indicate the effectiveness of the flame retardants used. Chemical changes in the beech wood were characterized through various analyses, including changes in chemical composition, FTIR spectra, DSC thermograms, and SEM images. The relationships between combustion characteristics and chemical changes were assessed using multiple methods. The results demonstrate that using 5% potassium acetate achieved a lower heat of combustion compared to 15% sodium phosphate, and it was significantly lower than the heat of combustion observed with 5% arabinogalactan or the reference sample of beech wood. However, neither potassium acetate nor diammonium phosphate significantly affected the macromolecular structures of the wood when compared to the reference sample. Low concentrations of flame retardants reduce environmental release and environmental impact while increasing fire resistance, which could be used for structural solutions made of hardwoods.