WATER SORPTION BEHAVIOR AND SOME OTHER PROPERTIES OF CHITOSAN POLY(GLUTAMIC ACID) COMPLEX FILMS

Clear polyionic complex films of chitosan with poly(glutamic acid) (PGA) were prepared by casting from 60% aqueous formic acid solution and physical properties of the polyionic fiims were examined. The degree of swelling in water was minimal when the molar ratio of the repeating units of chitosan/PGA was between 3/7 and 2/8. The larger the molar ratio of chitosan, the larger the degree of swelling in acidic solution, whereas the swelling property in basic solution was almost independent of the chemical composition. IR-spectra showed a new absorption band at 1630 cm-1 for the complex films of 5/5 and 3/7 ratios, which was assigned to cross-linking bond formation. Further, the pattern of the spectra varied significantly for the complex films from 3/7 to 1/9 ratios. C-13 NMR spectra showed novel peaks at 20 approximately 60 and 180 ppm for the complex films of 2/8 and 1/9 ratios, respectively. DSC studies showed that the amount of free water absorbed in the film increased, and that of bound water decreased, with an increase in the chitosan content.