DISSOLVING STATES OF CELLULOSE AND CHITOSAN IN TRIFLUOROACETIC-ACID

Chemical structures of cellulose and chitosan dissolved in trifluoroacetic acid (TFA) and those of cellulose and chitosan films cast from their TFA solutions were studied by C-13-NMR and infrared (IR) spectroscopy. Cellulose is trifluoroacetylated selectively at the C6-hydroxyl groups in the TFA solution, and chitosan is dissolved in TFA by forming amine salts with TFA at the C2-amine groups. IR analyses of cellulose films cast from its TFA-acetic acid solutions showed that partly trifluoroacetylated cellulose in the solution state turns to partly acetylated cellulose in the solid state during evaporation of the solvents in air by the ester interchange. Chitosan films cast from its TFA-acetic acid solutions still have the amine salts with TFA. These acetyl groups in cellulose films and TFA in chitosan films are removable by soaking the films in 1N NaOH at room temperature for 1 day.