A generalized model for swelling-controlled release systems

A generalized model has been developed for simultaneous transport of an active agent and an organic penetrant in a planar glassy polymer matrix. The active agent diffuses out of the matrix undergoing macromolecular chain relaxation and volume expansion due to absorption of the organic penetrant from the environment into the matrix. The swelling behavior of the polymer is characterized by a stress-induced drift velocity term "v" corresponding to the so-called case-II velocity. The change of volume due to the relaxation phenomenon is assumed instantaneous. The model incorporates convective transport of the two species induced by volume expansion and by stress gradient. The proposed phenomenological model reduces to a number of special cases depending on polymer-penetrant system behavior.