CONSOLIDATION MECHANISMS OF PHARMACEUTICAL SOLIDS - A MULTI-COMPRESSION CYCLE APPROACH

Purpose. The consolidation behavior of various pharmaceutical solids w ere characterized using compression-cycle profiles. Compression-cycle profiles for both uncompacted powder and formed tablets were obtained. These profiles were used to qualitatively and quantitatively characte rize the consolidation mechanism of pharmaceutical solids. Methods. An Instron Universal Testing apparatus and a specially instrumented die coupled with a computerized data acquisition system were utilized to m easure the upper-punch pressure and the corresponding die-wall pressur e during the compression cycle. Results. Compression cycle profiles we re obtained for a variety of pharmaceutical materials. Based on these profiles, parameters such as hysteresis areas, loading slopes, and unl oading slopes were calculated for the materials studied.Conclusions. M aterials that consolidate by plastic deformation have similar compress ion cycle profiles for the first and subsequent compression cycles ind icating that the plastic deformation process occurs to the same extent on the first as well as subsequent compression cycles. For brittle ma terials, the brittle fracture process occurs during the first compress ion cycle. During subsequent cycles the tabletted material does not un dergo further yield or failure and primarily undergoes elastic deforma tion. Low molecular-weight polyethylene glycol is an excellent model m aterial for plastically deforming materials, whereas sucrose or sodium citrate are excellent examples of materials that consolidate by britt le fracture.