Nc. Guma et al., INVESTIGATION OF FILM CURING STAGES BY DIELECTRIC ANALYSIS AND PHYSICAL CHARACTERIZATION, Journal of pharmaceutical sciences, 86(3), 1997, pp. 329-334
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.