The influence of spheroniser plate surface protuberance geometry on pellets produced from spheronisation of paste extrudates was investigated using a model paste material (45 wt% microcrystalline cellulose/water). Four cross-hatched pattern plates of different dimensions and/or shape of the surface protuberances were studied in terms of their effect on pellet water content, spheronisation yield, pellet size and shape distributions, and surface morphology. In addition, the effect of the relative size of extrudates to protuberances was investigated by comparing pellets generated from 1 and 2 mm diameter extrudates. In this study, all the plates have the same groove line arrangement but differ in surface protuberance dimensions and/or shape, and so the focus differs from that of Michie et al. (2012) who investigated plates of different groove line arrangement. For all pellets the water content decreased with spheronisation time, more so for samples made from 2 mm extrudates. A systematic effect of protuberance geometry on the product yield (a measure of losses due to fines) was evident for both extrudate sizes, with yields decreasing in the order (large studs), (pyramidal), (saw-toothed), and (small studs). Analysis of two-dimensional images of dried pellets indicated that the 2 mm diameter extrudates generated pellets with narrower size distributions and better shape quality parameters (aspect ratio and circularity). This was confirmed via SEM images showing the surface morphology. The results indicate that the size of extrudates relative to the plate features is important and should be investigated further.
