Surface esterification of cellulose by vapor-phase treatment with trifluoroacetic anhydride

Vapor-phase esterification of cellulose was achieved by exposing filter paper and tunicate cellulose film to mixed vapor of trifluoroacetic anhydride (TFAA) and acetic acid (AcOH) or TFAA and acetic anhydride (Ac2O) at room temperature. Both treatments gave high hydrophobicity to the specimens. The hydrophobicity of TFAA/AcOH-treated sample was resistant to water immersion, but that of TFAA/Ac2O-treated sample was lost due to hydrolysis. In spite of high hydrophobicity, the bulk degree of substitution for acetyl groups was as low as 0.07, indicating localization of acetyl groups on the fibril surfaces. Detection of ester groups by X-Ray photoelectron spectroscopy corroborated this feature. Infrared spectroscopy of tunicate cellulose revealed that the esterification occurred preferentially to the weakly hydrogen-bonded hydroxyl groups. This vapor-phase process is potentially useful in modifying cellulosic materials without immersing in solvents or liquid reagents.