Thermodynamic analysis of energy dissipation by pharmaceutical tablets during stress unloading.

A thermodynamic analysis of the energy transformations occurring within pharmaceutical tablets during the unloading phase of compaction was performed on Avicel, calcium phosphate, acetaminophen, and calcium oxalate. This analysis was based on viscoelastic stress data collected using an instrumented rotary press and was conducted for the purpose of determining the extent and nature of energy release, beyond that of force displacement, during this phase of compaction. The four materials investigated were selected to reflect a range of compaction properties, and the viscous vs force-displacement energy distributions were seen to be consistent with their brittle vs plastic character. Magnesium stearate, added in various concentrations up to 4% w/w, was found to act both as an internal lubricant for particle-particle slipping and as a moderator of interparticulate bonding.