Characterizing compaction-induced thermodynamic changes in a common pharmaceutical excipient

Work, heat, and internal energy change values were measured during compression of a common pharmaceutical tablet excipient, anhydrous lactose, using a compression calorimeter. Heat of solution measurements were used independently to measure the energy change caused by compaction. Both the compression calorimeter and the heat of solution measurements showed an increase in anhydrous lactose's energy state as a result of the net compression and decompression process. Excellent agreement between the energy change measured by compression calorimetry (0.94 J/g) and the energy change measured by solution calorimetry (0.91 J/g) strongly supports the data and results generated by the compression calorimeter. Furthermore, specific volume and specific surface area measurements were used to investigate the nature of the measured energy increase. The results indicate that the vast majority of the stored energy is most likely associated with residual strain within the compacted particles.