Comparative Evaluation of Treatment Conditions on Physical and Mechanical Properties of Acetylated Beech (Fagus orientalis Lipsky) Wood

Esterified wood was produced from beech (Fagus orientalis Lipsky) using acetic anhydride via a soaking-impregnation process with varying impregnation (Im) and reaction (Re) durations. Oven-dried beech wood samples were immersed in acetic anhydride for either 60 or 180 minutes.The samples were then wrapped in foil and placed in an oven at 103 ± 2 °C for 60 or 120 minutes to facilitate the acetylation reaction. The weight percent gain (WPG) was determined to assess the extent of the chemical modification. Flexural strength (FS), flexural modulus (FM), impact strength (IS), and compression strength (CS), along with water absorption (WA), thickness swelling (TS), and anti-swelling and anti-shrinkage efficiencies were evaluated. The WPG increased with increasing reaction, reaching 9.1% for Im60-Re60 and 13.6% for Im180-Re120 treatments. Acetylation significantly reduced water absorption and dimensional changes compared with untreated wood. Higher WPG levels resulted in reductions in FS and IS, whereas FM and CS were not significantly affected. Among the tested conditions, the Im60-Re60 treatment provided the most balanced performance, achieving improved dimensional stability with minimal reduction in mechanical properties. These results demonstrate that controlled acetylation can enhance the moisture resistance and dimensional stability of beech wood while maintaining acceptable mechanical performance.