| Popis: |
The rate of solvent evaporation, during the formation of ethylcellulose microcapsules employing polyisobutylene with theophylline ion-exchange resin as the core material, was found to affect the type of coat formed. The predominantly mononucleated microcapsules showed rapid release rates when formed by very fast and very slow solvent evaporation rates while coats formed at intermediate rates had slow release rates. The rate of solvent evaporation affected the shape, surface morphology, porosity and the purity of the ethylcellulose coat. At a very slow solvent evaporation rate tails were formed and the coats were porous. Shorter evaporation times eliminated tails, led to smooth but wrinkled coats and plasticization with light liquid paraffin. Coat porosity was minimized with intermediate evaporation rates. The coat structure and morphology was found to explain the release rates and suggest possible mechanisms for the coat formation. |
