Chitosan-LiOH-urea aqueous solution--a novel water-based system for chitosan processing.

A solution of partially N-deacetylated chitosan in aqueous lithium hydroxide (LiOH)/urea was prepared successfully through a freeze-thawing process and the dissolution behavior was studied. The results indicated that chitosan can directly dissolve in LiOH/urea aqueous solution. LiOH mainly contributed to the breakage of intramolecular and intermolecular hydrogen bonds in chitosan. Urea, LiOH, and chitosan formed inclusion compound (IC) with urea as the IC host, and the LiOH-chitosan complex as the guest. Aqueous 4.8 wt% LiOH/8.0 wt% urea was verified to be the optimal solvent for chitosan. The results of rheology and viscosity characterizations revealed that chitosan/4.8 wt% LiOH/8.0 wt% urea aqueous solution was pseudoplastic fluid, and was more stable than the solution of chitosan in acetic acid at ambient temperature.