Dissolution and regeneration behavior of chitosan in CO2 aqueous solution

Chitosan was easily dissolved in CO2 gas aqueous solution by the way of forming chitosan gel. The dissolving process of chitosan gel in CO2 aqueous solution was observed and recorded by a polarizing optical microscopy, and the factors which influence the solubility of chitosan gel were discussed. Chitosan particles in CO2 aqueous solution gradually became smaller, decreased and disappeared as the dissolving time increased. The appearance of chitosan gel suspensions changed from milky and opaque solution before bubbling in CO2 to transparent and viscous solution after completely dissolving in CO2 aqueous solution. The maximum solubility of chitosan gel in CO2 aqueous solution was 2.8 wt% with the dissolving temperature of 5°C and the dissolving pressure of 0.4 Mpa. The regenerated chitosan from CO2 aqueous solution by heating the system were characterized by Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). The results indicated that no derivatization reactions occurred during the preparation process of chitosan gel, the dissolution and regeneration process of chitosan gel in CO2 aqueous solution. During the preparation of chitosan gel, partial chitosan molecules were hydrolyzed and degraded. However, the dissolution and regeneration processes of chitosan gel in CO2 aqueous solution didn't disrupt the main chains of chitosan macromolecules and only destroy the hydrogen bonds among chitosan molecules.