Physico-chemical characterization of the ionic permeability of an enteric coating polymer

Cellulose acetate phthalate (CAP) is widely used as an enteric coating polymer. In this work, radiotracer and impedance measurements were performed in order to study the evolution in time of CAP films immersed in different solutions including artificial gastric juice. The membrane permeabilities demonstrate a strong dependence on the pH value, suggesting our film to behave like a cation-exchange membrane. A two-step transport mechanism is proposed to explain the variation of the experimental data with time. The effects of different plasticizers and solvents were also investigated, our observations showing the importance of using a hydrophobic plasticizer to improve the gastroresistance of the polymer.