ABSTRACT:Dissolution of cellulose into aqueous (aq) calcium thiocyanate solution was investigated with emphasis on solvent structure and interactions with cellulose. The aq calcium thiocyanate (Ca(SCNh) solution with concentration (CcaT) more than 48.5 wt% could dissolve any celluloses. Solvation measurement revealed that in wt%, the solvent system is formulated by Ca(NCS)2 • xH20 (x 4) + yH 2 0 (y 6), which exhibits mainly non-dissociated thiocyanate with high specific viscosity, as proved by electric conductivity, specific viscosity and IR or 13 C NMR measurements on solvent as a function of concentration of calcium thiocyanate. In this regard, the most stable 4 hydrate calcium thiocyanate is concluded from energy calculation as trans-trans configuration of Ca(-N = C = S) · 4H20. DSC and IR analyses suggested that dissolution of cellulose takes place by first attack of Ca(NCS)2 • xH2 0 (x 4) towards ring oxygen in cellulose. Ca(NCSh · xH2 0 (x 4) becomes 4-hydrates-like structure (sixcoordinate complex of Ca) and cellulose forms a 5-membered ring by coordinating two oxygen atoms (0(5) and 0(6)) in the glucopyranose unit, and then cellulose dissolves on heating. In this process, some ligand exchange might occur if the hydration number is more than 2. This coordination of cellulose is quite characteristic, compared with other solvents, such as cuprammonium hydroxide, which coordinate with 0(2) and 0(3) hydroxyl groups.
: We attempted to develop a high wet strength cellulose fiber using cellulose/aqueous calcium thiocyanate solution (aq.Ca(SCN)2) gel, as a precursor. The aq.Ca(SCN)2 showed a high dissolving power against several cellulose resources. The cellulose/aq.Ca (SCN) 2 gel generated using various organic and inorganic gelling agents were examined in terms of tenacity, elongation, and the morphology. From the results, it was found that rigid and homogeneous cellulose gels with low crystallinity were formed in a short time when ketones, such as acetone and methyl ethyl ketone, and alcohols, such as methanol and ethanol, were used as a gelling agent since aq.Ca (SCN) 2 is extracted from the cellulose solution. The wet spinning of the cellulose/ aq.Ca (SCN) 2 system was carried out using acetone or ethanol as a gelling agent. In both cases, we successfully obtained cellulose filaments with much higher tensile strength in conditioned and wet states than that of commercially available viscose and cuprammonium rayons for cloth uses.
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