Effect of stirring on film formation from a Eudragit RS aqueous dispersion

The permeable polymer film-formation behavior of a Eudragit RS dispersion was investigated in response to stirring at various rates and for various times in an Ultra Turrax instrument. No additives were used. The minimum film-forming temperature of the liquid, the thermal behavior of the film and the compositions of the dispersion and the foam arising were investigated. It was found that, at a given mixing time, shape-retaining foam formation could be detected at over 17,500 rpm. The polymer was enriched in the foam, while its quantity was decreased in the liquid. The minimum film-forming temperature of the liquid phase did not vary significantly, with the exception of the rate of 24,000 rpm, when a uniform film was not formed because of the bubbles. The glass-transition temperatures of the films formed did not exhibit any differences. Film formation was not influenced by the stirring time at a given rate. It was found that the efficiency of homogenization should not be increased by using a high stirring rate, as a uniform, smooth film did not develop, such a film being indispensable to ensure appropriate drug release. Copyright © 2006 John Wiley & Sons, Ltd.