GLASSY-RUBBERY TRANSITION KINETICS FOR HPMC IN WATER

Purpose: Hydroxypropyl methylcellulose (HPMC) is a polymer widely used in tablet formulation. It belongs to the class of polymers which undergoes glassy-rubbery transition and swelling in contact with a liquid solvent. Its behaviour can be described by one-dimensional mathematical models describing mass transport with moving boundaries. A classical kinetics for swelling, used for many polymer-solvent systems, is the Astarita-Sarti law (AS). In this study, we investigated AS best fitting parameters for the HPMC+water system. Methods: A classical partial differential equation (PDE) model for swelling, which includes AS, was numerically solved by finite elements method in Comsol Multiphysics 3.5a. Values of AS kinetic parameters were best fitted on experimental HPMC+ water swelling and erosion fronts from literature. Once the kinetic parameters were obtained, fronts from the resulting fully predictive model were compared with further experimental data. Results: Astarita-Sarti law with best-fitted parameters describes with satisfactory agreement all the investigated experimental sets of data, in radial and axial set up. Conclusion: Kinetic parameters for a fully predictive model for HPMC swelling in aqueous medium are obtained and validated on several experimental data from different techniques