Dissolution of natural polymers in ionic liquids: A review

Abstract

Natural polymers are produced by living organisms, e.g. plants, animals, microorganisms. Natural polymer materials have gained increasing attention due to their high strength and stiffness combined with carbon neutral, biocompatibility, biodegradability, renewability and sustainability. However, due to the strong inter- and intra-molecular hydrogen bonds, many natural polymers are extremely difficult to be dissolved in water or traditional organic solvents. The processing difficulties tremendously limit the applications of natural polymers in many fields. Recently, using ionic liquids (ILs) as novel solvents to dissolve natural polymers has attracted increasing attention. ILs has been shown to be highly effective at dissolving some natural polymers to technically useful concentrations. In this article, the structure and basic properties of ILs are introduced; the recent progress is reviewed in the dissolution of several important natural polymers using ionic liquids, including cellulose, chitin and chitosan, wool keratin fibers, silk fibroin and collagen fibers. The dissolution mechanisms of natural polymers using ILs as solvents are analyzed. The structure and properties of native and regenerated natural polymers are discussed in details.