Dissolution of Zein Using Protic Ionic Liquids: N-(2-Hydroxyethyl) Ammonium Formate and N-(2-Hydroxyethyl) Ammonium Acetate

Certain protic ionic liquids (PILs) were found to dissolve zein, which is one of the industrially important natural protein polymers. We prepared two PILsN-(2-hydroxyethyl) ammonium formate (HEAF) and N-(2-hydroxyethyl) ammonium acetate (HEAA)and their ability to dissolve zein was investigated. Up to 70% zein solution may be prepared, but it was difficult to process, because of high viscosity. Zein solutions with 5%−20% concentration were easily prepared by heating at 95 °C or higher with aid of microwave treatment, even in the presence of small amounts of water. A two-step microwave-only heating process can also be useful in preparing solutions with up to 20% zein. No significant disparity was found between HEAF and HEAA, in terms of dissolving zein. Both HEAF and HEAA could be economically viable and environmentally benign solvents, not only over conventional organic solvent systems, but also over other imidazolinium-type ionic liquids, such as 1-butyl-3-methylimidazolinium, which had been suggested as a solvent for zein.