Production of Cellulose Fibers Using Ionic Liquids

Abstract

Room temperature ionic liquids are considered green solvents and typically have low vapor pressure and good dissolution power and are easily recyclable [10Mak]. Ionic liquids used to dissolve cellulose should have low melting points, should not decompose cellulose, and should be stable and easily recoverable and relatively inexpensive. Considerable research has been done on dissolving cellulose using ionic liquids. Some of the ionic liquids that have been used to dissolve cellulose with concentrations of 10 % or above are listed in Table 19.1 [10Mak]. Dissolution of cellulose by ionic liquids is mainly related to the combined properties of the cations and anions and the basicity of the hydrogen bonds. Smaller cations were found to be more efficient in dissolving cellulose, and cations containing hydroxyl end groups had lower solubility [05Zha]. This is because the hydroxyl groups in the cations react with acetate of chloride anions and compete with cellulose to form hydrogen bonds. Ionic liquids with high hydrogen bond basicity were also found to have better solubility for cellulose. Ionic liquids are considered to be non-derivatizing solvents for cellulose, and therefore changes to the structure of cellulose are not expected. However, depolymerization of cellulose has been observed at high temperature when ionic liquids such as 1-allyl-3-methylimidazolium chloride [AMIM][Cl] were used [05Zha], whereas [BMIM][Cl] did not depolymerize cellulose.