Novel green solvents for cellulose: synthesis, properties and applications of gemini ionic liquids in cellulose chemistry

Abstract

Green chemistry is directing the development of the next generation of processes and products. Biodegradable polymers based on renewable biomass are promising feedstock to replace synthetic polymers; of these cellulose and its derivatives are prime candidates. The presence of strong inter- and intra-molecular hydrogen bonds within cellulose structure prevents its dissolution in common organic solvents. Cellulose dissolves physically (i.e., without formation of covalent bonds), however, in several solvents, e.g., ionic liquids, ILs. The latter have generated much interest because of their polarity, chemical and thermal stability, and structural versatility. Limitations to the use of ILs in cellulose chemistry include their high cost and the high viscosity of the solutions obtained. Recently, gemni-type (i.e., dicationic) ionic liquids, GILs, in which two monocations are covalently linked with a "spacer" have been introduced. These offer an additional structural flexibility because the structure of the cations, and the length of the spacer group that links the two cations can be changed. To our knowledge, there is no information on the efficiency of GILs as solvents for the dissolution, regeneration, and derivatization of cellulose. The present project aims at determining the dependence of cellulose dissolution and acylation in GILs on their molecular structure, either pure or, where required, their mixtures with dipolar aprotic solvents, DAS. The use of mixtures of ILs with DAS is expected to decrease the viscosity of the biopolymer solution. Microcrystalline- and fibrous cellulose samples (cotton and sisal) will be employed, the latter both native and mercerized. Selected GILs and/or mixtures GIL/molecular solvents will be employed as solvents for the acylation of cellulose. The results will be compared with other cellulose solvent systems. (AU)