Dissolution and regeneration behavior of chitosan in 3-methyl-1-(ethylacetyl)imidazolium chloride

3-methyl-1-(ethylacetyl)imidazolium chloride (EtMIM]Cl), was synthesized for chitosan dissolution, and the dissolution and regeneration behaviors of chitosan in EtMIM]Cl were thoroughly investigated. The solubility of chitosan in EtMIM]Cl was measured at temperatures ranging from 40 °C to 110 °C, based on which the thermodynamic parameters of chitosan in EtMIM]Cl were calculated. The polarizability and hydrogen bond accepting ability was determined by solvatochromic UV/vis spectroscopy. The regenerated chitosan from EtMIM]Cl by adding methanol was characterized by thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Density functional theory (DFT) computations were performed to study the interactions between EtMIM]Cl and chitobiose. Five kinds of hydrogen bonds, C-H/O, O-H/O, O-H/Cl, C-H/Cl, N-H/Cl were found, suggesting strong interactions between EtMIM]Cl and chitobiose. In particular, the oxygen atom and the active methylene group of carboxylic ester in EtMIM]⁺, formed strong hydrogen bonding with chitobiose. The molecular simulation results indicated that both the Cl^? anions and EtMIM]⁺ cation played important roles in the chitosan dissolution process, by the disruption of native hydrogen bonds of chitosan.