Rheological studies of high-concentration cellulose sulfate-acetate solutions

Abstract

661.728.014:532.78 With the method of homogeneous synthesis, various salt forms of cellulose sulfate-acetate containing Li + , Na + , K + , Ca 2+ , Mg 2+ , Zn 2+ , and Co 2+ as compensating cations have been obtained. The flow curves, the concentration and temperature dependences of the shear viscosity of aqueous solutions of cellulose sulfateacetate have a form characteristic of liquid-crystal systems. For solutions of all salts except for potassium salt, spontaneous formation of the anisotropic phase in the form of individual spherulites, spherulite bands, structures of the fingerprint type, and other more complex formations has been registered. A new hydrodynamic criterion that permits predicting the realization of lyotropic mesomorphism in solutions of cellulose derivatives is proposed.At the Scientific-Research Institute of Physicochemical Problems of the Belarusian State University, for the first time a polymer electrolyte containing in each anhydroglucose link an acetate and a sulfate group and, as compensating counterions, one-and two-charge cations Li + , Na + , K + , Ca 2+ , Mg 2+ , Zn 2+ , and Co 2+ has been synthesized and isolated from solution of cellulose sulfate-acetate (CSA) in the salt form.Synthesized salts of cellulose sulfate-acetate are characterized by a high solubility in water (up to 70 mass %). High-concentration aqueous solutions of salt forms of CSA, except for potassium salt, exhibit stable birefringence. In the stationary state and in flowing they opalesce, changing their color from yellow-red to violet, which is one of the outward signs of the cholesteric mesophase formation [1][2][3].To register and predict the liquid crystalline (LC) ordering of cellulose sulfate-acetate salts, we have made rheological, polarization-microscopic, and hydrodynamic studies of their aqueous solutions in a wide range of concentrations.Experimental. Cellulose sulfate-acetate in the salt form was obtained by the method of homogeneous synthesis [4]. The degree of substitution (DS) for sulfate and acetate groups was, respectively, 0.9-1.0 and 0.8-1.0, and the polymer molecular mass was 46,000.Solutions of CSA salts were prepared by dissolving polymer samples previously dried to a constant mass at a temperature of 60 2 o C in water, water-salt and water-alcohol media at a different ratio of components. The dissolution process was considered to be completed under the condition of the absence of undissolved polymer fragments from the optical microscope field of view. Concentrated viscous solutions of CSA were deaerated for 48 h. The concentration of prepared solutions was refined by the gravimetric method [5]. To register the isotropic-anisotropic phase transition, a drop of the prepared solution was placed on a microscope slide and pressed by a cover glass. Then the thin solution layer obtained was observed in polarized light with an "Amplival" optical microscope equipped with two polaroids. The observed structural changes were recorded on a film by means of a photographic attachment. Rheological studies of ...

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