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

摘要

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, ~(13)C 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 the 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 values 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.