The Influence of Film Coating on the Surface Roughness and Specific Surface Area of Pellets

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.