Cellulose modification using ionic liquids
The aim of this project was to investigate ways of chemically modifying cellulose using ionic liquids. Cellulose is a readily available, naturally occurring, polymeric carbohydrate which is ideal for chemical modification owing to the high density of its functional groups. However, it is insoluble in all common organic solvents. Therefore, interest has recently turned to the use of a novel class of solvents, ionic liquids, which have been found to dissolve cellulose. Initially, studies were undertaken into the acylation of simple carbohydrates using a Lewis acidic choline based ionic liquid, (ZnCl 2)2ChCl. It was found that the yields obtained were comparable to those achieved when traditional solvents and catalysts have been used. It was also found that when only one equivalent of acylating agent was used, all of the carbohydrate hydroxyl groups were acylated. This was thought to be unique to this ionic liquid system. The acetylation of cellulose was also studied in (ZnCl2)2ChCl. Here, it was discovered that the ionic liquid alters the morphology of cellulose by wetting or dissolution thus enabling a range of acetylated products to be produced. Research into the cationic modification of cellulose in an ionic liquid based on chlorcholine chloride (ClChCl) and urea was also undertaken. In this case, it was found that the ionic liquid could act as both the reagent and solvent. It was shown using this system, that all the available (surface) hydroxyl groups on cellulose were modified and that the material produced was significantly more hydrophilic than unmodified cellulose. Finally, preliminary investigations were untaken into other potential surface modifications of cellulose in ionic liquids.