Surface Morphology of Granules Coated with Different Materials from Fluidized Bed Spray Granulation

Fluidized bed spray granulation is a versatile process that can be used for production of a broad variety of particulate products, for example in the pharmaceutical, food, and chemical industry. Along with the possibility to produce such tailor-made granular materials comes the challenge to adjust the process in such a way that required product properties are met when working with different materials. During granulation, the structure formed from primary particles and injected coating material is determined by the interaction of the three phases involved in the process and various micro mechanisms occurring due to these interactions. Depending on the materials used in the process, different phenomena are decisive for the formation and final structure of the coating layer.

In this work, granulation experiments were carried out in a lab-scale fluidized bed with Cellets®500 as core particles. As coating material, sodium benzoate and calcium carbonate were used and injected in form of an aqueous solution and suspension, respectively. For both materials, experiments were performed at varied process parameters to investigate how these changed conditions influence the coating layer formation. In order to analyze the surface morphologies, the surface roughness of the granules was measured using confocal laser-scanning microscopy. Additionally, the coating layer around the Cellet®500 core was characterized regarding its thickness using SEM images of cut particles as well as particle size distribution measurements. In case of sodium benzoate as coating material, layer structure seemed to be predominantly dependent on the crystallization of the salt on the particle surface. In contrast, in the suspension-based coating other micro mechanisms like droplet spreading have a more pronounced impact on surface morphology.