Understanding die compaction of hollow spheres using the multi-particle finite element method (MPFEM)

Powder compaction is a complex manufacturing process, even though the procedural description is simple. While different methods are used in the literature, it is still challenging to understand the governing principles. It is especially challenging for empirical studies to investigate particle-level interactions. Thus, computational analyses are required for particle-level understanding. A wide range of computational methods has been developed, such as the discrete element method (DEM) and the multi-particle finite element method (MPFEM), to characterize powder compaction at the particle level. However, a limited number of studies in the literature have analyzed powder compaction using the 3D multi-particle finite element method. Historically, these studies focus only on solid particles. The compaction behavior of hollow spheres, common to pharmaceutical spray drying, was investigated both computationally and experimentally. In the computational analysis, two different particle sizes with different shell-thicknesses were examined using the 3D multi-particle finite element method. In the experimental study, polymer hydroxypropyl methylcellulose acetate succinate (HPMCAS) particles spray-dried at two different outlet temperatures (45 °C and 80 °C) were used. The results showed that particle diameter/shell-thickness (d/w) plays an essential role in powder compaction behavior. Regardless of the particle size, reducing shell-thickness reduced the required global axial stress to reach equivalent levels of relative density. However, with a constant ratio of d/w, changes to particle size (d) did not significantly influence the global compaction behavior. Similar results were observed in experimental studies. Simulation results showed that thinner-shell particles yield early in the compaction stage. Additionally, both experimentally and computationally, a spherical hollow particle buckling effect was observed. In summary, this study provides new information on how powder compaction behavior was influenced by particle size and particle shell-thickness.