Predicting the Angle of Internal Friction from Simple Dynamic Consolidation Using Lactose Grades as Model
Abstract
Purpose Powder flow and packing behavior are among other factors determined by particle friction, which is traditionally measured in shear cells as the angle of internal friction (AIF). Considering that an AIF at a normal stress should be comparable to friction during tapping consolidation, this work aims at whether dynamic consolidation under gravity can be used to estimate an AIF.
Methods Powder consolidation by controlled tapping was studied for seven commercially available types of lactose. A porosity factor was determined, and values were compared with the AIF obtained from Jenike shear cell measurements.
Results Plotting porosity factor vs. number of applied taps provided an estimated angle of internal friction (AIF(E)) that was obtained from the slope of a linear relationship. A significant linear correlation (r = 0.825; p = 0.0223) was evidenced between AIF(E) and those AIF(J) estimated from linearized yield locus measurements of using the Jenike shear cell.
Conclusions The good linear correlation between the angle of internal friction estimated from dynamic powder consolidation and the internal friction obtained by a shear cell is of high practical relevance. The latter shear cell behavior is only occasionally studied in the pharmaceutical industry, whereas dynamic powder tapping is a standard analysis.