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

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, C-13 NMR, X-ray diffraction and gel-permeation chromatographic (GPC) techniques were used to characterize their molecular structures. The moisture-absorption (R-a) and -retention (R-h) abilities of CM-chitosan are closely related to the DD and DS values. Under conditions of high relative humidity, the maximum R-a, and R-h were obtained at DD values of about 50%, and when the DD value deviated from 50%, R-a and R-h decreased. Under dry conditions, when the DD value was 50%, the Rh was the lowest. With the DS value increasing, R-a, and R-h increased. However, further increase of the DS value above 1.0 reduced the increasing tendency of R-a and R-h, and even some decreases in R-a and R-h were observed. Intermolecular hydrogen bonds play a very important role in moisture-absorption and retention ability of CM-chitosan. (C) 2002 Elsevier Science Ltd. All rights reserved.