Relationships between the molecular structure and moisture-absorption and moisture-retention abilities of carboxymethyl chitosan: II. Effect of degree of deacetylation and carboxymethylation Original Research Article

Carboxymethyl chitosans (CM-chitosan) of various degrees of deacetylation (DD 28–95%) and substitution (DS 0.15–1.21) were successfully prepared from N-acetylchitosans in NaOH of varying concentrations. Infrared spectroscopy (IR), elemental analysis, potentiometric titration, 13C NMR, X-ray diffraction and gel-permeation chromatographic (GPC) techniques were used to characterize their molecular structures. The moisture-absorption (Ra) and -retention (Rh) abilities of CM-chitosan are closely related to the DD and DS values. Under conditions of high relative humidity, the maximum Ra and Rh were obtained at DD values of about 50%, and when the DD value deviated from 50%, Ra and Rh decreased. Under dry conditions, when the DD value was 50%, the Rh was the lowest. With the DS value increasing, Ra and Rh increased. However, further increase of the DS value above 1.0 reduced the increasing tendency of Ra and Rh, and even some decreases in Ra and Rh were observed. Intermolecular hydrogen bonds play a very important role in moisture-absorption and retention ability of CM-chitosan.