Use of surface energy distributions by inverse gas chromatography to understand mechanofusion processing and functionality of lactose coated with magnesium stearate.

The purpose was to employ a new finite dilution approach to determine total surface energy distributions of mechanofused powders by inverse gas chromatography (IGC) to contribute to the understanding of their improved flow properties and to help optimise the magnesium stearate (MgSt) coating. Pharmatose 450M was mechanofused with between 0.1 and 8% (w/w) of MgSt. The non-polar, polar and total surface energies and work of cohesion at infinite dilution and the energy distributions at finite dilution were constructed using IGC. Brunauer-Emmet-Teller (BET) surface area and particle morphology were determined by IGC and scanning electron microscope, respectively. Surface energies determined at finite dilution appeared more consistent with the observed flow behaviour of mechanofused powders than comparative surface energy determination at infinite dilution. Polar and total surface energy distributions together with BET surface area measurements were the lowest when lactose was mechanofused with 1-2% MgSt (w/w). In conclusion, the surface energy distribution profiles measured at finite dilution were argued to be more informative and useful in reporting the surface energy changes during mechanofusion, optimising MgSt concentration in the mechanofusion process, and the flow behaviour of mechanofused powders.