_Applied_  
_sciences_  
_Article_  
**Effect of One-Sided Surface Charring of Beech Wood on Density Profile and Surface Wettability**  
**[PERSON] 1, [PERSON] 2, [PERSON] 3, [PERSON] 1, [PERSON] 2, [PERSON] 1, [PERSON] 3 and [PERSON] 1,* 4  
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service life and, at the same time, reduce their disadvantages, such as natural variability, dimensional instability, and biological degradability [3; 4]. The resistance of natural wood species to biological degradation is closely associated with a higher moisture content in timber structures (above 20%), and the chemical composition of wood, e.g., presence of extractives, etc. Water uptake and water release into the environment may cause surface cracking of wooden structures as a result of the internal stresses caused by swelling and shrinkage. The damaged surface and high moisture content of wood can favor the risk of biological degradation [5]. Hygroscopicity of wood, which is one of the main characteristics increasing the risk of rot decay, can be temporarily or permanently eliminated using modification methods, such as chemical, thermal, and mechanical treatments [6; 7; 8]. The thermal modification of wood at elevated temperatures (160-260 \({}^{\circ}\)C), as one of the most commonly used commercial methods, decreases the equilibrium moisture content (EMC) and improves its dimensional stability and biological durability [9]. An alternative to traditional thermal modification is to modify only the exposed surfaces, saving time and costs, and preserving the material properties of the interior of the wood [10; 11; 12; 13]. Recent scientific work shows that wood can be one-sided surface charred using a hot plate under controlled conditions--i.e., temperature and time--leaving the structural properties of the wood relatively unchanged [11; 12; 13]. It is well known that wood undergoes a number of overlapping chemical reactions as a result of thermal degradation when high temperatures are applied. At lower temperatures (180-250 \({}^{\circ}\)C), wood undergoes important chemical transformations that result in the decomposition of non-crystalline carbohydrates [14; 15; 16; 17; 18; 19], while lignin and cellulose degradation occurs somewhat above 280 \({}^{\circ}\)C [20; 21]. Heating to 300 \({}^{\circ}\)C results in the depolymerization of cellulose, the production of volatile compounds, the formation of oxidation products (carbonyl and carboxyl compounds), and finally charring, causing extensive mass loss [22]. Most of the hemicelluloses have decomposed at 300 \({}^{\circ}\)C and the most rapid rates of decomposition of cellulose and lignin take place at approx. 360 \({}^{\circ}\)C, while the remaining lignin continues to decompose above 400 \({}^{\circ}\)C [12; 23]. Even though there has recently been interest in this topic, one-sided surface charring using a contact heating system at a temperature range of 200-400 \({}^{\circ}\)C has not yet been tested.  
Beech is the most widespread broadleaf species in forests of the Czech Republic and there is strong demand to find new and alternative ways to commercially use this traditional timber, especially for outdoor conditions. It is hypothesized that by applying an appropriate combination of charring parameters, i.e., time and temperature, the optimum treatment intensity can be determined, decreasing the surface wettability properties of beech wood when compared with untreated material.