Chitosan membranes from acetic acid and imidazolium ionic liquids: Effect of imidazolium structure on membrane properties

Abstract

Mixed solvent systems of an acetic acid aqueous solution with different imidazolium ionic liquids were developed for successful chitosan dissolution at room temperature, then chitosan membranes were prepared using casting method. 1-butyl-3-methyl-imidazolium acetate ([Bmim]Ac), 1-ethyl-3-methyl-imidazolium chloride ([Emim]Cl), and 1-methyl-3-(3-sulfopropyl) imidazolium zwitterion (mPSO3) were used for chitosan dissolution. Chitosan membranes were characterized by Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance characterization (1HNMR), thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), water contact angle, swelling degree, and tensile strength. The effect of imidazolium ionic liquid addition upon the physicochemical properties of chitosan membrane was clarified. The results indicated that chitosan could not dissolve in common imidazolium-based ionic liquid aqueous solutions, while the imidazolium ionic liquid addition positively participated in chitosan dissolution of acetic acid aqueous solutions. The results also showed that imidazolium ionic liquids reduced the crystallinity of chitosan membranes, while improved the thermal stability and strength tensile of membranes. Moreover, imidazolium ionic liquids showed different effects on crystallinity reduction, contact angles, and swelling degree. It is possible of tuning the physicochemical properties of chitosan membranes by adding different imidazolium ionic liquids during aqueous acetic acid dissolution. The information obtained will shed light on the optimization of novel solvent systems for fast and rapid chitosan dissolution.