Preparation and structure of chitosan soluble in wide pH range

Two kinds of chitosans, namely N-acetylated and N-deacetylated chitosan were prepared by the modified processes. They can dissolve in both acid and alkali solution. 13C NMR was used to study the basic solution of chitosan, and XRD, FT-IR and SEM were used to study the structure of N-acetylated and N-deacetylated chitosan. The result from X-ray diffraction showed that a transformation of crystal structure occurred during the N-acetylation or N-deacetylation process with the decrease of crystallinity and expansion of crystal lattices. FT-IR spectra revealed that the intermolecular and intramolecular hydrogen bonds were destroyed by both treatments and a looser structure was observed by the SEM. The lower crystallinity, the decreased intermolecular interactions, the more disordered and looser structure were easy for the permeation of LiOH/urea aqueous solution and coordinated with the breakage of intermolecular and intramolecular hydrogen bond by LiOH at low temperature, the prepared chitosans dissolved in LiOH/urea/H2O mixture.