A Review of Chitin Solvents and Their Dissolution Mechanisms
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REVIEW
POLYMER SCIENCE
https://doi.org/10.1007/s10118-020-2459-x Chinese J. Polym. Sci.
A Review of Chitin Solvents and Their Dissolution Mechanisms Yi Zhonga, Jie Caia,b,c*, and Li-Na Zhanga,b a College of Chemistry & Molecule Sciences, Wuhan University, Wuhan 430072, China b Hubei Engineering Center of Natural Polymer-based Medical Materials, Wuhan University, Wuhan 430072, China c Research Institute of Shenzhen, Wuhan University, Shenzhen 518057, China
Abstract Chitin is an abundant natural nitrogen-containing biopolymer with great application potential in materials, environment, energy, and health. However, the structure characteristics and processing technologies have required intense research in related applications. In particular, there have been great efforts to developing solvents for chitin, and the results so far are quite encouraging. This review summarizes the main solvent systems used for chitin, namely the aqueous solvent systems (mineral acids, inorganic salt aqueous solutions, alkali aqueous solutions) and non-aqueous ones (LiCl-dimethylacetamide solvents, CaCl2·2H2O saturated methanol, ionic liquids, deep eutectic solvents, and protic organic solvents). The solvent properties, dissolution methods, and solution properties are discussed in detail. Special attention is paid to the dissolution mechanism in each system. This review can provide a reference for understanding the dissolution behavior of chitin and finding suitable solvents for it. Keywords Chitin; Solvents; Dissolution mechanism; Hydrogen bonding Citation: Zhong, Y.; Cai, J.; Zhang, L. N. A review of chitin solvents and their dissolution mechanisms. Chinese J. Polym. Sci. https://doi.org/10.1007/s10118-020-2459-x
INTRODUCTION Chitin, which is composed of β-(1-4)-linked 2-acetamido-2deoxy-D-glucose, is the most abundant biopolymer after cellulose (Fig. 1).[1] It can be found in crustaceans, mollusks, algae, fungi, and insects.[2,3] The annual production of crustaceans and mollusks around the world is about 7.86 million and 17.14 million tonnes, respectively, and most of it takes place in Asia (7.06 and 15.84 million tonnes).[4] The discovery of chitin dates from 1799, when Hatchett decalcified shells of crabs, lobsters, prawns, and crayfish with mineral acids.[5] In 1963, it was determined that crystalline chitin exists in three distinct forms, the α-, β-, and γ-form;[6] and the crystalline structures of α- and βchitin were refined in 1980.[7] Recently, more accurate crystalline structures (1 Å resolution) of α-chitin[8] and β-chitin[9] and their hydrogen bonding network structures were determined (Fig. 2).[8,10] From the perspective of sustainable chemistry and marine economy, the exploitation of chitin as a high-value material has attracted growing interest[1,11−15] due to its good biological function, biocompatibility, and biodegradability.[5,16] In the area of advanced materials, chitin is typically used to fabricate chitin nanocrystals, chitin nanofibers, chitin derivatives, and other chitin-based materials (such as c
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