A novel method of acetylation of wood using supercritical carbon dioxide

Sugi heartwood was acetylated with acetic anhydride in supercritical carbon dioxide (CO(2)) (120 degrees C or 130 degrees C, 1.0-12 MPa). As a result, the weight percent gain increased with increasing acetylation time up to 16%-20% at 1 h and 24%-28% at 24 h. The antiswelling efficiency of the acetylated specimens reached 75%-80% at 3-4 h of acetylation. It is supposed that the acetylation in supercritical CO(2) has a high bulking effect compared with liquid-phase and vapor-phase acetylation with uncatalyzed acetic anhydride. The results showed that the acetylation progressed rapidly because supercritical CO(2) and acetic anhydride formed a single phase at more than 90 degrees C, and the acetic anhydride reached the reaction sites in the wood quickly.