Application of intrinsic viscosity and interaction constant as a formulation tool for film coating. I. Studies on ethyl cellulose 10 cps in organic solvents

Abstract

The dilute solution properties intrinsic viscosity, [η], and interaction constant, k', of ethyl cellulose 10 cps in organic solvent systems have been studied in order to select an appropriate solvent system for a coating process. The results indicate that, when considering a rigid polymer such as ethyl cellulose, both [η] and k' have to be taken into consideration when deciding the solvent system of preference since [7;] or k' alone may show an incomplete picture of the solvent system's ability to solve the polymer. A solvent system consisting of méthylène chloride and ethanol in the ratio of 60/40% (w/w) was found to effectively solve the model polymer ethyl cellulose 10 cps. Addition of up to 10% of water, a non-solvent for ethyl cellulose, was found to be advantageous for this solvent system. However, if high water concentrations are present in the film coating system, uncontrolled situations may occur in a coating process during the evaporation of the solvents due to the precipitation of the ethyl cellulose.