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

Abstract

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 ( 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 R h 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.