Magnetic resonance imaging investigation of the mixing-segregation processin a pharmaceutical blender

Magnetic Resonance Imaging (MRI) was used to study the mixing process of bi nary mixtures of free flowing sugar beads in a Turbula((R)) mixer. In order to make particles MRI-sensitive, some reference beads were doped with an o rganic oil. Doped and undoped particles were mixed and MRI was used to non- destructively image the particle bed for a given number of mixer rotations (N-R), bead diameter ratio (R = d(ref)/d(f)) and rotation speed (V). All th e results were quantified on the basis of image analysis to characterise th e degree of mixing. Studies showed that for binary mixtures of identical pa rticle size, the mixing was complete after 30 rotations, whereas for beads of different size (R = 2.8) a segregated steady state was obtained after ne arly 10 rotations. Experiments revealed that segregation appeared as soon a s X = 0.9. Moreover, the lower the rotation speed, the-more segregated the final state was. It appeared that for a filling level greater than 80%, dea d regions appeared in the centre of the powder bed. In conclusion, when the particles are non-cohesive, the Turbula((R)) blender perfectly mixes ident ical beads but segregation occurs for beads of different size after just a few rotations. (C) 2001 Elsevier Science B.V. All rights reserved.