INVESTIGATION OF FILM CURING STAGES BY DIELECTRIC ANALYSIS AND PHYSICAL CHARACTERIZATION

A dielectric analysis (DEA) method was developed to monitor the curing of Eudragit RS30D plasticized with 20% acetyltributyl citrate and to investigate the effects of over curing on the barrier properties of th e film. Permittivity (epsilon') obtained from DEA is related to the de gree of mobility of permanent dipoles present in the sample. Changes i n the epsilon' values were observed in various film sample types cured at 60 degrees C. Four distinct regions of curing were identified from the epsilon' versus time curves; namely, under-cured, optimally-cured , over-cured, and super-cured. The epsilon' values were high in under- cured films, and decreased to a minimum when the films became optimall y-cured. Continued curing beyond the optimum stage caused an increase in the epsilon' values, corresponding to an over-cured stage, whereas in the super-cured region, the values decreased again. The changes in dielectric properties manifested the changes in the structure of the f ilm, which correlated with the dissolution rates of the active drug fr om the film-coated beads as well as with the changes on their surface morphology at the same stage of cure. A mechanism of film curing was p roposed based not only on the dielectric properties and dissolution da ta but also on the amount of plasticizer remaining in the film-coated beads, the changes in film thickness, and the surface electron microgr aphs of the cured film-coated beads.