Auto-agglomeration of dry ibuprofen powder under mechanical vibration: Effect of particle morphology and surface properties

This study investigates the effect of ibuprofen particle morphology and surface properties on its tendency to auto-agglomerate. Four diverse particle morphologies were produced by recrystallisation of ibuprofen from solvents with different polarities. The aspect ratio and the polar component of the recrystallised particles decreased as follows: methanol > ethanol > acetonitrile > hexane. The auto-agglomeration process was induced by mechanical vibration and the agglomerate strength was assessed by the Dispersion and Agglomerate Strength indices. Relatively strong agglomerates were detected only in the case of ibuprofen recrystallised from ethanol and acetonitrile, whereas weaker and no agglomerates were formed during mechanical vibration of ibuprofen recrystallised from methanol and hexane, respectively. It was found that tendency of ibuprofen powder to auto-agglomerate was associated with lower tribo-electric charges during mechanical vibration, hypothetically linked to the competitive advantage of electrostatic attraction of high surface polarity particles to the walls of the vibration box which can hinder particle-particle interactions. Crystal surface polarity could be altered by the crystallisation protocol and/or by particle breakage (exposing more crystal facets of high polarity) during mechanical vibration.