Investigating density distributions for tablets of different geometry during the compaction of pharmaceuticals

The axial and radial powder movements during the compaction process were investigated using flat- and curved-face punches for the case of single-ended axial strain applications. The density distributions in microcrystalline cellulose tablets were determined experimentally using a colored layer technique and digital image analysis. Nondestructive topography measurements were taken to assess the variation in surface roughness of the tablets and relate this to the forming pressure and density distribution. Results showed that the tablets produced were highly non-homogeneous with high density regions in the "top corners" (adjacent to the moving punch surface) and "middle bottom half" for the flat-face tablets. For instance, at 92.7 MPa, density values were recorded at greater than 1.2 g/cc in the high density regions and greater than 0.6 g/cc in low density regions with regards to experimental results. High density regions were noted in the corners where the powder was in contact with the die wall for the curved-face tablets; both axial and radial powder movement was seen to be taking place. Surface topography and surface form results also showed that the geometric location of the corresponding surfaces of the tablets were relocated after the compaction process due to elastic recoil and stress relief.