The acetylation of cellulose was carried out under atmosphere pressure using HSO4 as catalyst according to our previous study. In a typical reaction, 3.24 g [0.02 mol of anhydroglucose units (AGU)] of loosened cotton cellulose, 20.4 g (0.2 mol) of acetic anhydride, and 0.2 molar equivalents of ILs with respect toper mole of AGU were mixed and heated at 100◦C for 3 h. The reacted mixture was poured into 100 mL of ethanol and stirred for30 min. The solid consisting of CA and unreacted cellulose was filtered and washed with ethanol three times and then dried in avacuum oven at 60◦C for 24 h. In order to extract water-soluble CA, the sample was then refluxed for 24 h by the Soxhlet extraction method using deionized water as the solvent. The filtrate was then filled into a diameter petridish (80 mm) and allowed to evaporate over 72 h at ambient temperature to produce water-soluble CA film.