A Quantitative Correlation of the Effect of Density Distributions in Roller-Compacted Ribbons on the Mechanical Properties of Tablets Using Ultrasonics and X-ray Tomography

Enabling the paradigm of quality by design requires the ability to quantitatively correlate material properties and process variables to measureable product performance attributes. In this study, we show how heterogeneities in compacted ribbon densities quantitatively correlate to tablet mechanical properties. These density variations, which have been purposely modulated by internal and external lubrications, are characterized longitudinally and transversally by nondestructive ultrasonic and X-ray micro-computed tomography measurements. Subsequently, different transversal regions of the compacted ribbon are milled under the same conditions, and granules with nominally the same particle size distribution are utilized to manufacture cylindrical tablets, whose mechanical properties are further analyzed by ultrasonic measurements. We consider three different ribbon conditions: no lubrication (case 1); lubricated powder (case 2); and lubricated tooling (hopper, side sealing plates, feed screws, and rolls) (case 3). This study quantitatively reveals that variation in local densities in ribbons (for case 1) and process conditions (i.e., internal case 2 and external lubrication case 3) during roller compaction significantly affect the mechanical properties of tablets even for granules with the same particle size distribution. For case 1, the mechanical properties of tablets depend on the spatial location where granules are produced. For cases 2 and 3, the ribbon density homogeneity was improved by the use of a lubricant. It is demonstrated that the mechanical performances of tablets are decreased due to applied lubricant and work-hardening phenomenon. Moreover, we extended our study to correlate the speed of sound to the tensile strength of the tablet. It is found that the speed of sound increases with the tensile strength for the tested tablets.