New solvents for cellulose: Hydrazine/thiocyanate salt system

The hydrazine/thiocyanate system was found to be an excellent solvent for cellulose. The solubility and solution properties were investigated. Even at room temperature, the combinations of hydrazine and lithium, sodium, and potassium thiocyanate had high dissolution power for cellulose, up to an 18% (w/w) maximum, unrelated to the polymorph, whereas a combination with ammonium thiocyanate exhibited a solubility difference among celluloses I, II, and III. The effect of the temperature cycling of the system for the rapid dissolution of cellulose was investigated thermodynamically. In these systems, a high concentration of salts was necessary to effect the cellulose dissolution; this suggested that an undissociated salt-solvent complex played an important role in the cellulose dissolution as implied by electroconductivity measurements of the hydrazine/salt system. Gel and liquid-crystal formation was observed in all systems above 4 and 6% (w/w) cellulose concentrations, respectively. The values of both critical concentrations were quite similar to those observed in the ammonia/ammonium thiocyanate system studied earlier in our laboratories. The gelation temperature was between approximately 10 and 50 degreesC, depending on the salt and cellulose concentration. The dependence of the cellulose solubility on the degree of polymerization was also examined. It is suggested that these solvent systems have great potential for the fiber and film formation of cellulose. (C) 2002 John Wiley Sons, Inc.