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Pellets of different shapes were produced by modifying the processing parameters of a standardized pellet formulation. The target size of these pellets was 1-1.4 mm. Initially the shape of the pellets was assessed by visual observation. In total, eight batches of pellets were produced of which four were considered to be round, whereas the other four deviated from the spherical shape by various degrees. The different pellet fractions were then characterized for their size, shape, surface, and density properties employing a series of established techniques in order to identify the most appropriate method of characterization and the interrelationships between these properties. The results showed that attempting a task of preparing pellets of graded differences in shape from the same powder blend can result in changes of other important pellet properties such as surface roughness, surface area, and pellet dimensions. Some of these changes could be anticipated by considering the process variables involved, whereas others changed in a manner for which there is no immediate explanation.

The aim of this paper was to study the surface roughness of pellets after the application of a film coat. In total eight batches of pellets were examined of which four were considered to be round, whereas the other four deviated from the spherical shape by various degrees. The determination of the specific surface area of the coated pellets suggested that, although the film appeared to have filled the pores, the final film structure still mirrored the original surface structure of the pellets. However, profilometry was able to evaluate these gross results in more detail. From the latter measurements it appeared as though the pellet shape was another major influence factor on the final surface texture of the film coating. Pellets with a more elongated and irregular shape such as dumbbells provided more possibilities for interparticulate contact during the coating process, whereby film forming material was ripped off the pellet surfaces making these appear more rough due to surface defects. The use of alcoholic binder solutions during the pellet production might have resulted in surfaces with slightly changed surface free energy, which allowed a better spreading and adhesion of the polymer film and resulted in less textured film surfaces.

There are numerous reasons for which film coatings are applied to pellet formulations; for example, controlled release, taste masking, and improved stability. The aim of this paper was to study the influence of pellet shape on the deposition of film coatings in a fluid-bed process by monitoring the pellet shape as a function of the film thickness formed. Eight pellet batches were used, of which four were spherical visually, and the other batches can be described as ovoids, dumbbells, long dumbbells, and cylinders. The average coat thickness of the pellets assessed by cross-section measurements did not appear to be influenced by the initial shape of the pellets. The fluid-bed process, however, had an impact especially for those pellets that had an aspect ratio greater than 1.5. The change in the pellet shape during film coating could only be monitored effectively employing a three-dimensional shape factor. Significant changes in shape occurred at the beginning of the coating process up to approximately the first 15 min, after which the shape remained constant.