Cellulose is the most abundant biorenewable material, with a long and well-established technological base. 1 Derivitized products have many important applications in the fiber, paper, membrane, polymer, and paints industries.Cellulose consists of polydisperse linear glucose polymer chains ( Figure 1) which form hydrogen-bonded supramolecular structures; 2 cellulose is insoluble in water and most common organic liquids. The growing willingness to develop new cellulosic materials results from the fact that cellulose is a renewable resource, although many of the technologies currently used in cellulose processing are decidedly nongreen. 3 For example, viscose rayon is prepared from cellulose xanthate (production over 3,000,000 tons per year) utilizing carbon disulfide as both reagent and solvent. Most recently, processes using more environmentally acceptable nonderivitizing solvents (N-methylmorpholine-N-oxide (NMNO) and phosphoric acid) have been commercialized. Solvents are needed for dissolution that enable homogeneous phase reactions without prior derivitization. 4 Graenacher 5 first suggested in 1934 that molten N-ethylpyridinium chloride, in the presence of nitrogen-containing bases, could be used to dissolve cellulose; however, this seems to have been treated as a novelty of little practical value since the molten salt system was, at the time, somewhat esoteric and has a relatively high melting point (118°C). We were interested in examining whether other solvents that would now be described as ionic liquids (ILs) 6 would dissolve cellulose and, especially, whether the availability of a wide and varied range of ILs, coupled with the current understanding of their solvent properties, 7 would allow flexibility and control in the processing methodology, with increased solution efficiency and reduction or elimination of undesirable solvents.Ionic liquids, containing 1-butyl-3-methylimidazolium cations ([C 4 mim] + ) were screened with a range of anions, from small, hydrogen-bond acceptors (Cl -) to large, noncoordinating anions ([PF 6 ] -) also including Br -, SCN -, and [BF 4 ] -. In addition, variations in cation alkyl-substituent from butyl through octyl were investigated for the chloride salts. Dissolution experiments were carried out using cellulose-dissolving pulps (from cellulose acetate, lyocell, and rayon production lines), fibrous cellulose (Aldrich), and Whatman cellulose filter papers. The cellulose samples were added to the ionic liquids without pretreatment, in glass vials, and heated without agitation on a heating plate or in a domestic microwave oven. Table 1 summarizes the results obtained using high MW dissolving pulp (DP ≈ 1000). Stirring cellulose in the ILs under ambient conditions did not lead to dissolution, although the cellulose fibers were wetted by the ILs. However, on heating to 100-110°C , cellulose slowly dissolved in the Cl --, Br --, and SCN --containing ILs to yield increasingly viscous solutions.Dissolution rates could be significantly improved by heating in a microwave oven. ...

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The potential for performing cellulase-catalyzed reactions on cellulose dissolved in 1-butyl-3-methylimidazolium chloride ([bmim]Cl) has been investigated. We have carried out a systematic study on the irreversible solvent and ionic strength-induced inactivation and unfolding of cellulase from Trichoderma reesei (E.C. #3.2.1.4). Experiments, varying both cellulase and IL solvent concentrations, have indicated that [bmim]Cl, and several other ILs, as well as dimethylacetamide-LiCl (a well-known solvent system for cellulose), inactivate cellulase under these conditions. Despite cellulase inactivity, results obtained from this study led to valuable insights into the requirements necessary for enzyme activity in IL systems. Enzyme stability was determined during urea, NaCl, and [bmim]Cl-induced denaturation observed through fluorescence spectroscopy. Protein stability of a PEG-supported cellulase in [bmim]Cl solution was investigated and increased stability/activity of the PEG-supported cellulase in both the [bmim]Cl and citrate buffer solutions were detected.

A new method for introducing enzymes into cellulosic matrixes which can be formed into membranes, films, or beads has been developed using a cellulose-in-ionic-liquid dissolution and regeneration process. Initial results on the formation of thin cellulose films incorporating dispersed laccase indicate that active enzyme-encapsulated films can be prepared using this methodology and that precoating the enzyme with a second, hydrophobic ionic liquid prior to dispersion in the cellulose/ionic liquid solution can provide an increase in enzyme activity relative to that of untreated films, presumably by providing a stabilizing microenvironment for the enzyme.

The extraction of both UO2(2+) and trivalent lanthanide and actinide ions (Am3+, Nd3+, Eu3+) by dialkylphosphoric or dialkylphosphinic acids from aqueous solutions into the ionic liquid, 1-decyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide has been studied and compared to extractions into dodecane. Radiotracer partitioning measurements show comparable patterns of distribution ratios for both the ionic liquid/aqueous and dodecane/aqueous systems, and the limiting slopes at low acidity indicate the partitioning of neutral complexes in both solvent systems. The metal ion coordination environment, elucidated from EXAFS and UV-visible spectroscopy measurements, is equivalent in the ionic liquid and dodecane solutions with coordination of the uranyl cation by two hydrogen-bonded extractant dimers, and of the trivalent cations by three extractant dimers. This is the first definitive report of a system where both the biphasic extraction equilibria and metal coordination environment are the same in an ionic liquid and a molecular organic solvent.