(19e) The Modified Drucker-Prager/Cap Properties of Pharmaceutical Powder Blends: The Influence of MgSt and Acetaminophen Concentrations

In granulation processes involving applications of mechanical force, the mechanical properties of the powder being processed often dictate the key characteristics of the end-product.  For that reason, the modified Drucker-Prager/Cap properties of common pharmaceutical blends were measured in this study.  In particular, the influence of magnesium stearate (MgSt) and acetaminophen (APAP) concentrations on the DPC parameters was studied.  It was found that adding up to 2% w/w MgSt to a pure excipient system (microcrystalline cellulose Avicel PH200) resulted in a considerable decrease in the powder’s internal friction angle and cohesion, but had a corresponding increase in the hydrostatic yield stress and elastic parameters (Young’s modulus and Poisson’s ratio).  The influence of MgSt appeared to asymptote, however, as adding the MgSt concentration past 2% w/w did little more to the above-mentioned parameters. Adding APAP to an Avicel system generally resulted in an increase in both cohesion and internal friction angle. The APAP’s influence on the elastic parameters, however, was complex; increasing the APAP concentration up to 50% w/w resulted in a decrease in both the Young’s modulus and Poisson’s ratio, but increasing it past 50% w/w resulted in an increase in both parameters.  Hypotheses for the observed trends will also be presented.