FILM FORMATION WITH COATING SYSTEMS OF AQUEOUS SUSPENSIONS AND LATEX DISPERSIONS OF ETHYLCELLULOSE

We examined the film formation of an aqueous suspension system using m icronized ethylcellulose (EC) in comparison with an EC latex system. T he minimum film-forming temperatures (MFT) of the two systems and the glass transition temperature (T(g)) of EC were measured with a micro m elting point apparatus and a differential scanning calorimeter, respec tively. Replicas of the free films prepared from the two systems were examined under a transmission electron microscope. The release of theo phylline from granules coated with the two systems was compared to inv estigate the effect of curing, in which the coated granules were heate d for an hour at 80-degrees-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 late x system was lower than T(g). A replica of the free film from the susp ension system showed no shapes of the EC particles used; in contrast, that from the latex system showed the shape of individual latex sphere s 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 coale scence of latex particles was more complete after curing than before. These results demonstrate that the mechanisms of film formation of the se two systems are different, and that this difference results in diff erent properties of films prepared by the two systems.