Compression Modulus and Apparent Density of Polymeric Excipients during Compression—Impact on Tabletability

The present study focuses on the compaction behavior of polymeric excipients during compression in comparison to nonpolymeric excipients and its consequences on commonly used Heckel analysis. Compression analysis at compaction pressures (CPs) from 50 to 500 MPa was performed using a compaction simulator. This study demonstrates that the particle density, measured via helium pycnometer (ρ(par)), of polymeric excipients (Kollidon(®)VA64, Soluplus(®), AQOAT(®)AS-MMP, Starch1500(®), Avicel(®)PH101) was already exceeded at low CPs (<200 MPa), whereas the ρ(par) was either never reached for brittle fillers such as DI-CAFOS(®)A60 and tricalcium citrate or exceeded at CPs above 350 MPa (FlowLac(®)100, Pearlitol(®)100SD). We hypothesized that the threshold for exceeding ρ(par) is linked with predominantly elastic deformation. This was confirmed by the start of linear increase in elastic recovery in-die (ER(in-die)) with exceeding particle density, and in addition, by the applicability in calculating the elastic modulus via the equation of the linear increase in ER(in-die). Last, the evaluation of “density under pressure” as an alternative to the ρ(par) for Heckel analysis showed comparable conclusions for compression behavior based on the calculated yield pressures. However, the applicability of Heckel analysis for polymeric excipients was questioned in principle. In conclusion, the knowledge of the threshold provides guidance for the selection of suitable excipients in the formulation development to mitigate the risk of tablet defects related to stored elastic energy, such as capping and lamination.