New solvents for cellulose. II. Ethylenediamine/thiocyanate salt system

The ethylenediamine/thiocyanate salt system was found to be a new solvent for cellulose. The solubility, dissolution behavior, solution properties, and cellulose recovered from the solutions were investigated. The dissolution took place at room temperature, and the maximum solubility achieved was 16 % (w/w) for cellulose of DP210 in the ethylenediamine/sodium thiocyanate 54/46 (w/w). The dependence of cellulose solubility on DP is also described. Tracing the dissolution behavior of the cellulose by CP/MAS C-13 NMR measurements revealed the polymorphic conversion of cellulose I to III to amorphous structure during the dissolution process. The cellulose dissolved was stable for 30 days storage at room temperature. Microscopic observations and steady-shear viscosity measurements of the solutions indicated mesophase formation of cellulose in the ethylenediamine/ sodium thiocyanate system. This anisotrpoic phase appeared from ca. 10 % (w/w) cellulose with DP210 and greatly depended on the cellulose concentrations. Coagulation studies disclosed that cellulose 11 and amorphous cellulose were recovered from the cellulose/ethylenediamine/thiocyanate salt solutions when water and alcohol were used as a coagulant, respectively. It was suggested that this solvent system has high potential for cellulosic fiber and film formations.