Shape and surface smoothness of pellets made in a rotary processor

The shape and surface smoothness of pellets made in a rotary processor by the wet granulation technique has been studied. Optical microscopy combined with image analysis was used to determine three shape parameters (circularity, roundness and elongation) and the fractal dimension, which is a characteristic for the surface smoothness of the pellets. This study reveals that pellets made in a rotary processor by the wet granulation technique are more variable in terms of their sphericity than in terms of their elongation. In order to obtain very spherical pellets, spheronization should go on for a long time with sufficient intensity. Furthermore, the spheronization enhancing properties of microcrystalline cellulose-thanks to its plastic properties when wetted-are confirmed. The fractal dimensions of the surface are close to 2, indicating that the pellets are characterized by a rather smooth surface. Nevertheless, small but significant differences in surface smoothness can be detected using this fractal approach. From the experiments performed in this study, it can be concluded that using the wet granulation technique in the rotary processor under the appropriate conditions, it is possible to produce excellent pellets in terms of sphericity and surface smoothness. (C) 1997 Elsevier Science B.V.