Plasticizer-induced changes in the mechanical rate of response of film coatings: an approach to quantitating plasticizer effectiveness

Abstract

The plasticization of Eudragit S100, a polymeric-based enteric coating with polyethylene glycol 200 and dibutyl phthalate was investigated by analyzing changes in the time scale of mechanical response. Since all polymeric film coating solutions pass through the rubber-to-glass transition as solvent evaporates, this study focuses on the plasticization-induced changes in the rate of mechanical response in this region. Solvent cast films were mechanically analyzed using a low strain elongational creep compliance procedure and intrinsic mechanical response was analyzed via the application of a phenomenological approach of retardation spectrum analysis. Results indicate that at constant temperature, the addition of plasticizer changes the time scale of response by shifting the spectra negatively within the experimental time window. Using a free volume analysis a plasticizing effectiveness term, β, was calculated for the plasticizers in this study with β dbp = 0.144 and β peg = 0.108 . The higher value of β indicates a greater propensity to in the rubber-to-glass transition. The application of this technique may yield more relevant mechanical information for film coating systems without relying solely on glass transition temperature changes.