Mechanism of surface lubrication: influence of duration of lubricant-excipient mixing on processing characteristics of powders and properties of compressed tablets.

A mathematical expression for tablet hardness was related to lubricant mixing by considering increases in the surface coverage with prolonged mixing time. The duration of lubricant mixing significantly changed the apparent bulk volume of the mix, ejection force during tableting, hardness, and disintegration and dissolution properties of tablets. These findings may provide some rationale for the changes in processing characteristics and properties of finished drug products often encountered in the scale-up of solid dosage formulations. Several lubrication mechanisms are discussed in connection with the duration of mixing effects and scanning microscopy studies.