Rheological properties and diffusion dissolution behaviour of hydrophilic polymers.

In a mathematical model that has been recently proposed to predict drug release from polyvinyl alcohol matrices, polymer dissolution is described as a chain disentanglement process and characterized by a threshold polymer concentration. In present work viscosity measurements were employed for defining the characteristic entanglement concentration of polymer solutions. The viscosity of aqueous polymer solutions of differing concentrations was measured over a wide range of shear rate using a rotational viscometer. The flow curves were fitted according to an asymptotic model and from the best fit equation the relevant viscosity parameters were obtained. The relationships between polymer concentration and viscosity parameters were also examined. The critical concentration at which an abrupt change of viscosity properties occurred was identified and related to the molecular chain disentanglement conditions.