Addition of chelated trivalent cations to solutions of the polymer sodium carboxymethylcellulose (CMC)

This study was comprised of two related projects: a viscosity variability study and a trivalent cation study. For the first study, the dependence of viscosity of solutions of the polymer sodium carboxymethylcellulose (CMC) on temperature was quantitatively determined so that the viscosity measurements from four sets of viscosity versus age of solution data could be normalized. The four sets of age of solution data were obtained for two solutions containing Al cation and for two solutions containing Mg cation. The temperature normalization procedure proved viable. Factoring out the variability due to temperature led to a decrease in overall variability of the viscosity data of the three solutions for which temperature fluctuation had been problematic. The trivalent cation study involved addition of Al3+ or Cr3+ cation to solutions of CMC. The overall objective was to produce high viscosity CMC solutions by promoting crosslinking through the trivalent cations to anionic sites along the polymer chains. Addition of A1C13 solution to the CMC solution was ineffective: at low ionic strengths, polymer precipitated out of solution. To prevent precipitation it was necessary to deliver the trivalent cation more slowly. This was accomplished by adding trivalent cation either in combination with a chelating agent or already in the form of a metal complex. The chelating agents citric acid, malic acid, and EDTA, in combination with Al3+ cation, were ineffective in yielding CMC solutions of high viscosity. Oxalic acid in combination with both Al3+ and Cr3+ cation as well as basic aluminum acetate and chromium (III) acetate hydroxide did produce high viscosity CMC solutions. In terms of ligands, acetate was even more effective than oxalate. In terms of cations, Cr3+ was even more effective than Al3+