European beech wood modification using gas- and liquid-phase acetylation

Wood treatments involving chemical reactions are increasingly common in the construction industry, with acetylation being one of the most widely applied methods. In this study, European beech wood (Fagus sylvatica L.) was modified using acetylation in both traditional liquid phase (LP) and gas phase (GP) under varying temperatures (100 to 130 °C) and reaction times (1 to 4 h). The two methods were compared based on weight percentage gain (WPG), bulking coefficient (BC), water-related properties, and chemical changes confirmed by Fourier transform attenuated total reflectance infrared (FTIR-ATR) spectroscopy. The results showed that LP acetylation achieved the highest WPG (19.6%), while GP acetylation provided comparable results under higher temperatures and extended reaction times. Both methods significantly reduced equilibrium moisture content, water absorption, and volumetric swelling, thereby enhancing dimensional stability compared to reference (REF) samples. FTIR analysis confirmed substitution of hydroxyl groups by acetyl groups in both phases. Despite slightly lower WPG values in some regimes, GP acetylation provided similar improvements in water-related properties with reduced consumption of acetic anhydride (AAH). This indicates its strong potential for industrial applications, although further research is necessary to optimize the process for large-scale European beech wood components.