Solubility and dissolved cellulose in aqueous calcium- and sodium-thiocyanate solution

Attempt was made to investigate the solubility and the dissolved state of various celluloses in aqueous (aq) calcium-and sodium-thiocyanate solution. Almost all celluloses used in this study were soluble in 55 wt% aq calcium thiocyanate (Ca(SCN)(2)) soln. at about 100 degrees C, while 60 wt% aq sodium thiocyanate (NaSCN) soln. dissolves only limited cellulose mainly regenerated from cellulose solution. The solubility of cellulose in 60 wt% aq NaSCN was independent of the crystal form, crystallinity and the degree of polymerization of cellulose and this was explained only in terms of the degree of breakdown of intramolecular hydrogen bonds in the cellulose solid. Using 2-dimensional NMR six carbon peaks in C-13 NMR spectra of cellulose in two solvents were successfully assigned. The comparison of chemical shifts of cellulose in 55 wt% aq Ca(SCN), solution and 10% sodium hydroxide (NaOH) solution strongly suggested that calcium atoms as electron accepters coordinate with oxygen atoms in glucose ring and primary alcohol at C(6) position, in the same manner of cellulose dipped in 55 wt% aq Ca(SCN)(2) solution at room temperature. In the C-13 NMR spectrum of cellulose-60% aq NaSCN solution system, C(3), C(2), and C(6) peaks were observed at lower magnetic field side, implying that sodium atoms interact with hydroxide groups at C(2), C(3), and C(6) positions of glucopyranose in cellulose molecules.