Abstract
Chitin cannot be dissolved in conventional solvents due to the strong inter- and intrasheet network of hydrogen bonds and the large number of crystalline regions. Some ionic liquids (ILs) have been suggested in the literature as possible solvents for chitin. Seven of them, all having an ethyl group as substituent in the cationic ring, have been tested in this work: [Emim][Cl], [Emim][Br], [Emim][I], [Emim][OAc], [Emim][Lact], [Epyr][I], and [EMS][BFSI]. Chitin was insoluble in [EMS][BFSI] while for all other ILs solubility was limited due to high viscosity of solutions and equilibria have not been reached. Changes in physical structure, particle size distribution, and crystallinity of recovered chitin depended on ionic liquid used. Increase in porosity was observed for chitin treated with [Emim][Cl], [Emim][I], [Emim][Br], and [Emim][Lact]; changes in particle size distribution were observed for [Emim][AcOH] and [EMS][BFSI]; increase in crystallinity was noticed for chitin treated with [Epyr][I] while decrease in crystallinity for [Emim][I] was noticed. All tested ionic liquids were reused four times and changes in FTIR spectra could be observed for each IL.
Highlights
Chitin, a poly N-acetylglucosamine, is a nontoxic, natural biopolymer that has not found wide industrial application due to its chemical resistance
Increase in porosity was observed for chitin treated with [Emim][Cl], [Emim][I], [Emim][Br], and [Emim][Lact]; changes in particle size distribution were observed for [Emim][AcOH] and [EMS][BFSI]; increase in crystallinity was noticed for chitin treated with [Epyr][I] while decrease in crystallinity for [Emim][I] was noticed
Seven ionic liquids were tested as solvents for chitin, with the assumption that most of them would be able to modify particle size, structure, or crystallinity of the chitin particles
Summary
A poly N-acetylglucosamine, is a nontoxic, natural biopolymer that has not found wide industrial application due to its chemical resistance. This property can be regarded as advantageous when we search for a new carrier for enzymes. It is chemically, mechanically, and thermally stable but its particles are flat, often rectangular, and nonporous. Ionic liquids (ILs) have been investigated as new solvents for chitin. Ionic liquids are not as “green” as they were previously thought, they can be regenerated and reused several times, which would decrease their environmental impact significantly
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