Kinetics and mechanism of sol-gel transformation on polyelectrolytes of divalent metal-alginate gel complexes with formation of capillary ionotropic polymembranes

The kinetics of gelation between Zn(II), Cd(II) and Pb(II) metal ion electrolytes and sodium alginate polysaccharide sol have been studied complexometrically at temperatures between 35 and 65°C. Using a large excess of alginate sol concentration, the pseudo first-order plots of exchange between Na+ counter ions of the macromolecular chains of alginate sol and the metal ions give sigmoidal curves with two distinct regions. The initial part was relatively fast and curved significantly at early times, followed by a slow decrease in the rates at longer times. The rate constants of gelation were found to show second-order overall kinetics and first-order in the concentration of both reac-tants. The kinetic parameters have been evaluated and a consistent gelation mechanism is suggested.