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.