Light Scattering and Viscosity Investigation of Dilute Aqueous Solutions of Carboxymethyl Starch

Three samples of corn starch and three samples of potato starch were transformed to carboxymethyl starch (CMS) using a two-step etherification with sodium monochloroacetate in ethanol as the reaction medium. The degree of substitution (DS) of the synthesized samples was between 0.40 and 1.10. The structure parameters - solution properties relationships of the CMS samples were investigated by static light scattering and dilute solution viscometry in water and sodium-chloride aqueous solutions of different concentrations at 25 degrees C. The values of the mass average molar mass, M-W, radius of gyration, R-g, and second virial coefficient, A(2), were determined for all samples together with the limiting viscosity number. The results indicated that the M-w - R-g correlation was independent of the origin of the starch, as well as the exponent a(eta) and constant K-w from the Kuhn-Mark-Houwink equation. Values of the exponent nu for CMS in all sodium-chloride aqueous solutions were between 0.450 and 0.472, while for the CMS samples in aqueous solution the value of nu was 0.580. The values of the exponent a(eta) were around 0.3, which is typical for branched macromolecules.