Feasibility of relationships between tablet physical quality parameters and mechanical properties of dry powder formulation

Compaction is a key unit operation in many particulate industries. Accordingly, this study addresses a research question of considerable importance concerning compact (or tablet) formation, i.e., the feasibility of using mechanical properties of powder formulations in low to medium pressure regime (<10 MPa) as predictors of tablet (i.e., compact) quality parameters. For the feasibility study, mechanical properties, i.e., elastic and elastoplastic, of dry powder formulations at three binder contents were determined using a flexible boundary cubical triaxial tester in low to medium pressure regime. For the same formulations, tablets formed at two pressing pressures (70 and 90 MPa) were tested for four physical quality parameters, i.e., diametral strength, axial penetration strength, indentation hardness, and friability. Some of the key findings were: bulk modulus increased with pressure and binder; shear modulus increased with confining pressure; tablet hardness increased with binder content upto a point and thereafter decreased or remained constant. All the powders' properties related with tablet qualities, i.e., had R²>0.80; i.e., demonstrating the feasibility of using powder properties as initial predictors of tablet quality for formulations tested. In particular, the spring-back index, compression index, and bulk modulus were found to be most correlated with tablets' diametral strength, axial penetration strength, indentation hardness, and friability. An elastic energy based hypothesis was proposed to provide a fundamental basis for mechanical properties of powder formulations vs. tablet quality relationships. The positive outcome of this feasibility study suggests that the approach could be used for other similar powder formulations.