MOISTURE SORPTION AND TENSILE-STRENGTH OF SOME TABLETED DIRECT COMPRESSION EXCIPIENTS

Moisture sorption and desorption isotherms, at 25-degrees-C, have been measured for some direct compression (DC) excipients and analysed according to the Young and Nelson equations and the GAB equation, which distinguish different physical forms of moisture. The mechanical characteristics, such as tensile strength and derived tableting indices (brittle fracture propensity and tensile strength isotropy) of compacts produced from the same DC excipients, have been determined after storage at various environmental relative humidities. The tensile strength reaches a maximum value and then begins to decrease when the moisture content is about double that corresponding to a tightly bound monomolecular layer. The changes in the mechanical characteristics have been explained by the combined effect of moisture on the interparticle and intermolecular forces.