Abstract
The dissolution rates of sulfanilamide in the solutions of two kinds of carboxymethylcellulose sodium (CMC-Na) in the presence or absence of NaCl were measured by the fixed disk method. At the same time, viscosities of these solutions were determined at various rates of shear with a cone and plate viscometer. In the case of simple CMC-Na solutions, it was found that the dissolution rate of sulfanilamide depends almost only upon the viscosity of the solution, irrespective of the degree of polymerization of CMC-Na. Also, it is supposed that the decrease in the dissolution rate occurs by different mechanisms according to whether the solution belongs to the Newtonian or to the non-Newtonian fluid. On the other hand, additional influences due to the actions by NaCl become more or less evident in the mixed solutions of CMC-Na and NaCl. One of them is the salting-out effect and has a tendency to decrease the dissolution rate, while the second acts to increase the rate through viscosity decrease of the solutions by shrinking CMC-Na molecules.
