Relationship of dissolution rate to viscosity of polymeric solutions.

The influence of viscosity on the dissolution rate of benzoic acid in aqueous solutions of methylcellulose, hydroxypropyl cellulose, and guar gum was investigated. The viscosities were measured by capillary and rotational viscometers and were calculated from experimental diffusion coefficients by means of the Stokes-Einstein equation. The relationship of the dissolution rate to viscosity may be represented by a single curve. An equation is presented relating the dissolution rate of benzoic acid to solubility, diffusion coefficient, and viscosity for these nonionic viscosity-enhancing agents. To demonstrate that additional factors affect the dissolution rate, similar data were determined using solutions of xanthan gum, which is anionic. The electrical effect modified mass transport so the quantitative relationship of dissolution rate and viscosity was not the same as in the nonionic carbohydrate solution.