Film Formation with Coating Systems of Aqueous Suspensions and Latex Dispersions of Ethylcellulose

Abstract

We examined the film formation of an aqueous suspension system using micronized ethylcellulose (EC) in comparison with an EC latex system. The minimum film-forming temperatures (MFT) of the two systems and the glass transition temperature (T_g) of EC were measured with a micro melting point apparatus and a differential scanning calorimeter, respectively. Replicas of the free films prepared from the two systems were examined under a transmission electron microscope. The release of theophylline from granules coated with the two systems was compared to investigate the effect of curing, in which the coated granules were heated for an hour at 80°C. MFT and T_g decreased as the amount of triethyl citrate used as a plasticizer increased in both systems. MFT of the suspension system was higher than T_g, while that of the latex system was lower than T_g. A replica of the free film from the suspension system showed no shapes of the EC particles used; in contrast, that from the latex system showed the shape of individual latex spheres in coalescence. Curing had no effect on the release behavior of the suspension-coated granules, whereas it remarkably delayed release from the latex-coated granules. The replica method revealed that the coalescence of latex particles was more complete after curing than before. These results demonstrate that the mechanisms of film formation of these two systems are different, and that this difference results in different properties of films prepared by the two systems.