Abstract
Polycrystalline particles with a roughly spherical shape (spherulites) have been identified in the industrial production of an aromatic amine derivative, where powder handling is one of the downstream processes following crystallization. This comparative study focuses on how uniaxial flow functions as measures of flowability of dry material of L-glutamic acid and an aromatic amine are affected by the crystal morphology and size, as analyzed by the chord length distribution measurements (FBRM) and scanning electron microscopy (SEM). L-glutamic acid was chosen as a model substance since it can be crystallized as spherulites as well as needle-shaped and polyhedral particles. Failure strength values were measured as a function of consolidation stress using the uniaxial tester. The failure strength values of L-glutamic acid were found to be lower for polyhedral particles than for needle-shaped particles with approximately the same mean chord length. Needle-shaped particles were found to have lower values for failure strength than L-glutamic acid spherulites with smaller chord lengths. It has been shown that spherulites are more unstable with respect to particle breakage than the other morphologies. Although the chord length distributions of the L-glutamic acid spherulites were shifted towards smaller values than those of the aromatic amine spherulites, the failure strength of the aromatic amine particles is more than four times as large. This can be explained by more extensive particle breakage during filtration, sample storage, and consolidation of the aromatic amine.