Porosity-Controlled Ethylcellulose Film Coating.I. Formation of Porous Ethylcellulose Film in the Casting Process and Factors Affecting Film-Density

Abstract

In an attempt to Develop a new simple porous film coating technique for oral controlled release dosage forms, the pore formation of ethylcellulose (EC) in the casting process was investigated. When an EC-ethanol-water ternary mixture was cast, the porous film was spontaneously formed via the processes of coacervation and gelation of the polymer. The visual and microscopic observations revealed that pore formation proceeDed on the basis of the phase separation mechanism, in which ethanol and water acted respectively as a solvent and a non-solvent for the polymer. Gelation, which is an important process for Determining the Density of the resultant film, occurred during evaporation when the Decreasing ethanol concentration reached the critical concentration of about 62%. This value was almost constant irrespective of polymer concentration and molecular weight. The Density of porous EC film was changed by formulation variables of the casting solution, such as ethanol or polymer concentration and organic solvent species. The permeation study of porous EC films was conducted using salicylic acid as the permeant. The permeability of salicylic acid was changed according to the film Density; that is, the permeability coefficient exponentially increased with a Decrease in film Density, suggesting that the drug permeability of the cast film can be modified by controlling film Density. © 1993, The Pharmaceutical Society of Japan. All rights reserved.