2.3. Characterization2.3.1. Degree of substitutionThe degree of substitution (DS) was determined according to themethod proposed by Kim, Nishiyama, and Kuga (2002). The acety-lated and non-acetylated CNFs (100 mg, solid content of 2%) wereplaced in conical flasks. Consequently, 40 mL of 75% ethanol wasadded and the flasks were kept at 50◦C for 30 min. Finally, 40 mLof NaOH (0.5 N) solution was added to the mixture and heated to50◦C for 15 min. The mixture was kept at room temperature for48 h under constant stirring. The excess of NaOH was titrated withHCl (0.5 N) until a pH of 7 was obtained.