Abstract
In this study, we evaluated the distribution of weight percent gain (WPG) in the longitudinal direction of a sugi (Cryptomeria japonica D. Don) heartwood sample with a size of 100 mm (longitudinal direction) × 20 mm (radial direction) × 20 mm (tangential direction), which was acetylated using supercritical carbon dioxide (CO2). Two connected batch containers were used for the acetylation treatment. One of them contained a mixture of supercritical CO2 and acetic anhydride, which was injected into the second batch container containing a vertically fixed oven-dried wood specimen and small amount of acetic anhydride. The acetylation was performed at 120 C˚ and 10–12 MPa for 8 h using various amounts of acetic anhydride. The experiments revealed that the mixture of acetic anhydride with supercritical CO2 contributed to the acetylation on the upper side of the specimen, penetrating mainly through the upper cross section. Instead, acetic anhydride contained in the batch container with the specimen, contributed to the acetylation on the lower side of the specimen by penetrating from the bottom cross section. It was thus assumed that gaseous acetic anhydride in the batch container was pushed into the specimen by the injected supercritical CO2. Therefore, it was demonstrated that the specimen can be uniformly acetylated by adding the appropriate amount of acetic anhydride in both batch containers.
