Comparison of Pressure and Atmospheric Steaming Processes and Their Effects on Selected Properties of Beech Wood (Fagus sylvatica L.)

The aim of the study was to investigate the effect of hydrothermal treatment (different steaming process) conditions, specifically temperature, pressure, and steaming time on selected physical properties of beech wood (Fagus sylvatica L.), such as moisture content, density, colour, and longitudinal contraction. The research was conducted using two steaming modes: pressure steaming process (108 °C, 181 kPa, 7 h) and atmospheric steaming process (80 °C, 101 kPa, 15 h). The results showed that pressure steaming caused a more significant decrease in moisture content (by 16.9%) compared to atmospheric steaming (by 8.0%) and a smaller variation in values, which is favourable for subsequent drying. The differences in density after steaming were not statistically significant. On the contrary, longitudinal shortening was significantly greater with pressure steaming, which may indicate the release of tension reaction wood. The colour change was similar in both modes; lightness (L*) decreased and the wood acquired a redder hue without a significant effect of steaming conditions on the overall colour differentiation (ΔE). The results confirm that steaming temperature and pressure have a significant effect on the moisture change and longitudinal contraction of beech wood, while density and colour change remain relatively stable. The length of the steaming process has a major effect on the colour change of the wood.