CHANGE IN CRYSTAL DENSITY OF ACETYLSALICYCLIC ACID DURING COMPACTION

The compression properties of acetylsalicylic acid are investigated by the use of a compaction simulator. The results confirm that acetylsal icylic acid undergoes pronounced plastic deformation characterized by a mean yield pressure of 35 MPa. The porosity of the compact becomes c lose to zero at pressures below 100 MPa, and apparently negative at hi gher pressures, because the true density of the crystals increases. In the decompression phase, the crystal recovers rapidly to the original density which gives rise to a weak compact. The changing crystal dens ity has implications for the Heckel analysis of the volume reduction d ata. Estimates of the mean yield pressure vary between 34 and 135 MPa depending on the applied pressure range.