A modeling approach for understanding effects of powder flow properties on tablet weight variability

In this paper we focus on the effect of cohesion and compression speed on the outcome of the compression process for both monodisperse and polydisperse granular systems. A three dimensional discrete element model (DEM) which incorporates static and dynamic friction is used in this study to simulate die filling, and the compaction and decompaction of cohesive granular system in a confined cylindrical die similar to those used in a commercial tablet press driving the pre-compressive stage. The magnitude of the cohesive force is represented in terms of a parameter K = Fcohes/mg, where K is called the bond number and is the measure of cohesiveness. Force displacement curves are used to characterize the compression and deformation properties of the materials and are obtained by measuring the force on the upper punch and the corresponding displacements in the die. Results show that a considerable more energy is needed to compress the cohesive material as compared to free flowing materials. It is found that the time required to fill the die strongly depends on the cohesion of the material. The energy for the tableting process is directly proportional to the upper punch speed.