High Temperature Drying Process of Beech Wood (Fagus sylvatica L.) with Different Zones of Sapwood and Red False Heartwood

Structure of wood can affect intensity of color change in remarkable ways. This article was focused on the analysis of the color changes red false heartwood and mature wood by different methods such as ΔE* (Total color difference), h* (Hue angle), C*_ab (Color saturation) and S_ab (Saturation). The aim of this study was to evaluate the color properties of red false heartwood and mature wood by using different chromacity coordinates. Our observations suggested that the density in the absolute dry state was equal between the red false heartwood and mature wood. The biggest difference was in the area of the free water domain, thus from an initial MC value to the fiber saturation point (FSP). The shorter drying time of the red false heartwood samples was caused by their lower initial MC. Due to the different MC, the temperature created a different color intensity of the compared samples. Mature wood samples achieved more saturated color in the drying process than did the samples of red false heartwood.

The cost of raw materials has a major role in the wood industry. From this point of view, it is necessary to pay attention to the correct log-sawing pattern, which will optimize the sawing process and increase the quantity and quality of the material as well. For measurements, we used beech wood (Fagus sylvatica L.). Beech wood (Fagus sylvatica L.) is the most common wood species in the Slovak Republic; the total amount in forests is 34.8%. Beech wood has a high frequency of defects, such as red false heartwood, reaction wood (i.e., tension wood), dote, cracks, and so on. This research aimed to analyze the effect of the log-sawing patterns of through-and-through sawing, cant sawing, and quarter sawing on the resulting quantitative–qualitative yields of beech timber. The results showed that the highest quantitative yield was observed with the cant sawing pattern, at 84%, which was, on average, 17.3% higher compared to other types of cutting. It was found that quarter sawing resulted in a higher qualitative yield compared to through-and-through sawing or cant sawing (V₅ = 62.69% and V₆ = 47.86%).

The results of experimental research on the colour changes of beech wood at different depths of the tested layer are presented. Beech wood (Fagus sylvatica L.) dried in a conventional kiln was tested. Half of the wood samples were steamed prior to the drying process. Colour changes were measured at various depths after the face milling process was used to remove the material to expose to the deeper surface. The colour changes were measured based on the three-axis CIELAB system, recommended by CIE (Comission Internationale de l'Eclairage) and according to ISO 11664-2 and ISO 11664-4 standards. As a result of the analysis, four parameters were determined: the colour changes ( $\mathrm{\Delta }E$), the colour chroma (C_ab), the hue angle (h) and the colour saturation (S_ab). The performed experimental research revealed that the surface of steamed wood is more susceptible to colour change. A significant colour change in both steamed and dried wood occurs only up to a depth of about 2 mm.

The technology of high temperature drying has a great influence on dimensional and selected physical changes in tension wood. Article is focused on the measurement properties such as moisture content, color changes and longitudinal warping. The quality of beech wood is determined based on structure and properties of wood, frequency of defects in wood material. The tension wood is considered as an important wood defect causing negative alterations in solid wood quality and limits industrial application of wood. The different values of longitudinal warping which were measured after drying were higher in tension wood than in normal wood. Impact of radial and tangential angle of growth rings is non-significant factor.

Beech wood has a high frequency of defects such as red heartwood, reaction wood (tension wood). For the experimental measurements four logs without visible defects like red heartwood, which can noticeably affects the measurements' results were qualified. The drying medium temperature in the first phase of the process before the moisture content of the specimens fell below the FSP was maintained at 45 °C. Then, the temperature was gradually increased to the maximum value 65 °C. The results showed that different initial wood moisture content does not affect to final value of tension and normal wood. The colorimetric parameter L* was much higher for tension wood. After steaming, there were greater differences in the colorimetric parameters, respectively, a* and b*. After drying the difference of all colorimetric parameters between tension and normal wood was significantly less. The color changes were only noticed in the surface layers of specimens. Differences were small, and thus, the impact of the tension wood on the color changes was not confirmed. However, since the lightness of tension wood plays a key role for its visual detection, it may be adequate to only measure the lightness parameter (L*).