Effects of mesylate-/tartrate-based ionic liquids-water mixtures on the phase transition behaviors and stability of corn starch: A comparative study

Abstract

As one of the most important biopolymers, starch has been applied to replace petroleum-derived polymers for “green” materials. Discovery of novel solvents and understanding of the solvent effects are critical challenges for the destruction of strong hydrogen bonds of starch molecules for manufacturing bio-based materials. Herein, two ionic liquids (ILs), 1-ethyl-3-methyl-imidazolium mesylate ([Emim][MS]) and 1-ethyl-3-methyl-imidazolium tartrate ([Emim][Tar]), were explored as novel solvents for starch. Their effects on phase transition behaviors, microstructure, hydrogen-bond interaction, crystalline structure, micromorphology and thermal stability of corn starch were compared systematically. With the IL/H2O ratio increasing, the starch/IL/H2O mixtures underwent endothermic, exothermic/endothermic and exothermic processes, sequentially. However, the starch properties were very different in two ILs-water systems, which were closely related to the solvent composition and IL structure. These differences were further explained by the interactions among starch, water and the two ILs on the basis of the quantum chemical calculations. It was found that [Emim][MS] had a stronger interaction with water than starch, whereas [Emim][Tar] preferred to bind with starch. This study not only provided experimental supports for understanding the starch behaviors in novel “green” solvents, but also laid the theoretical foundation for starch modification and industrial applications of starch-based materials in more appropriate solvents.