Single droplets to particles - size, shape, shell thickness and porosity analyses using X-ray computed tomography

The drying kinetics of single droplets of crystallizing and skin-forming species were investigated via acoustic levitation to provide a well-controlled environment mimicking spray drying operations. Particles manufactured by drying aqueous solution droplets containing varying ratios of D-mannitol and polyvinylpyrrolidone (PVP) were analysed using a range of techniques to elucidate their morphology and microstructure. Size, porosity and surface roughness of the manufactured particles increased with D-mannitol concentration in water, while the sphericity decreased, a consequence of the unique morphologies. The change in particle shell thickness was found to be minimal. Considering varying proportions of PVP led to a variety of fascinating structures, contrasting to those manufactured from pure D-mannitol. Temperature effects were further considered, and the results were matched by that from a lab and pilot scale spray dryer. Analysis of the solid form further demonstrates the opportunity to prepare different polymorphic forms of D-mannitol.