Study of ethyl cellulose-benzoic acid interactions in matrices for controlled drug release by DSC

The physical state of benzoic acid (BA) and its interaction with ethyl cell ulose (EC) were examined in ethyl cellulose-benzoic acid matrices by Differ ential Scanning Calorimetry (DSC). The glass transition temperature (T-g) o f EC of various matrices having BA in solid solution form (upto 27.7%) was reduced. The BA in matrices containing more than 38.9% drug exhibited disti nct melting endotherms due to crystalline form. The peak temperatures of th ese endotherms were lowered and they broadened as the concentration was low ered. The solubility of BA increased at its melting point as compared to am bient temperature. The melting enthalpy of BA, when plotted as a function o f its concentration yielded a straight line with intercept of 330 mg g(-1) of matrix. This is the solubility of BA in EC at its melting temperature. F ourier Transform Infra Red Spectroscopy (FTIR) investigations confirmed tha t hydrogen bonding occurred between EC and BA through hydroxyl groups.