Application of Microwave Heating for Acetylation of Beech (Fagus sylvatica L.) and Poplar (Populus hybrids) Wood

Microwave and conventional acetylation of wood was carried out to determine its efficacy on the material properties. Beech (Fagus sylvatica L.) and poplar (Populus hybrids) samples with dimensions 14 mm × 14 mm × 14 mm were impregnated using acetic anhydride, and chemical reactions were initiated by microwave and conventional heating. The microwave acetylation process was carried out using laboratory equipment at a frequency of 2.45 GHz in several testing modes to reduce time of the reaction. The uptake of substance, equilibrium moisture content, wood swelling, and dimensional stability were determined in order to evaluate the efficacy and degree of acetylation. Both microwave and conventional heating positively affected the selected material properties. The results showed that no significant differences were found between microwave and conventional heating; therefore, microwave heating can be used as a valid replacement in the acetylation process. Microwave power of 2 kW and 0.1 m∙min conveyor speed were the optimum conditions for microwave acetylation. These process parameters resulted in 39.4% ASE T and 35.2% ASE R for beech and 38.0% ASE T and 16.3% ASE R for poplar samples. This work provides insight into the details of wood acetylation using microwave heating.