A comparative study on the acetylation of wood by reaction with vinyl acetate and acetic anhydride

A comparative study on the acetylation of maritime pine wood by reaction with vinyl acetate (VA) and acetic anhydride (AA) has been undertaken. The reactivity of wood, cellulose and lignin with regards to VA or AA was examined using different techniques. The products dissolved in the reaction medium after acetylation of wood by the two different methods were analyzed by HPLC chromatography. Results suggested that the cellulose sites in wood were more attacked by VA than by AA in our experimental conditions. Besides, the unreacted cellulose sites of the AA-acetylated sample could be further esterified by vinyl propionate, which 13C NMR signals could be differentiated from the acetyl signals. The esterified materials obtained after modification of isolated cellulose and lignin were also characterized by FTIR, 13C CP-MAS NMR and 13P NMR spectroscopy and compared. Results indicated that VA could acetylate both biopolymers, but they also showed that AA reacted more readily with lignin than VA. Moreover, FTIR spectroscopy revealed that unexpected side reactions concurrently occurred in lignin when VA was used. It is hypothesized that some C-acetylation also took place between VA and a number of lignin aromatic rings during the treatment.