THERMAL-ANALYSIS OF GELS AND MATRIX TABLETS CONTAINING CELLULOSE ETHERS

This paper reviews the use of thermal analysis in probing the performance of hydrophilic matrices. Thermomechanical analysis, in isothermal mode, can monitor the rate of gel formation around matrix tablets following their exposure to water; in expansion mode the technique can follow the swelling of matrices exposed to water. DSC can follow the moisture uptake by matrices containing hydrophilic polymers, such as cellulose ethers. In new data, DSC and DTA have been used to assess the water content of gels containing hydroxypropyl-methylcellulose (HPMC). The techniques showed that gel syneresis occurred on storage, liberating free water, and that the inclusion of a model drug (propranolol hydrochloride) redistributed the water contained within the gel. Following storage for 24 h, DSC showed that each polymer repeating unit of HPMC was associated with 6.5 moles of water.