The influence of post-treatments on acetyl content for removal of chemicals after acetylation

When solid wood is acetylated, improved dimensional stability and fungal resistance are obtained. The acetylation procedure used consists of an initial vacuum/pressure impregnation with acetic anhydride after which excess anhydride is drained off, and the impregnated wood is reacted at 120-130 degreesC. After completed reaction a vacuum can be applied while still heating the wood in order to remove unreacted acetic anhydride and by-product acetic acid. In this work, microwave energy was used as the source of heat for the acetylation of solid wood. Different methods have been studied for the removal of residual chemicals after completed acetylation reaction. Results presented show that the way of removal strongly influenced the final acetyl content obtained and emphasize the importance of an effective recovery of residual chemicals to prevent unnecessary waste of chemicals. When water-leaching before oven-drying at 90 degreesC was used as a post-treatment, a much lower acetyl content was obtained in comparison with that found for samples oven-dried at 90 degreesC after acetylation. This is explained by an additional acetylation taking place in samples just oven-dried and by a deacetylation in the case of the water leached samples due to hydrolysis of ester bonds under acidic aqueous conditions.