A new method for the control of size of pellets in the melt pelletization process with a high shear mixer.

Abstract

The control of the melt pelletization process in an 8-l high shear mixer using specific energy consumption of the impeller motor was studied. Lactose was used as the bulk material with polyethylene glycol 3000 as a meltable binder. The effects of binder concentration, mean particle size of bulk material and post-melt impeller speed on the relationship of specific energy consumption and pellet growth were examined. Specific energy consumption was found to be a suitable tool for monitoring the melt pelletization process, and specific energy consumption correlated well with pellet growth. The mean size of the pellets formed becomes correspondingly larger with increasing specific energy consumption. Concerning the impeller speed, specific energy consumption is more useful as a tool for end-point control of the process than post-melt mixing time. Similar size pellets can be obtained with comparable specific energy consumption, independent of the impeller speed. The control of pellet size requires a correlation between pellet growth and specific energy consumption that is established for the formulation and process conditions used. For this purpose, mathematical modelling of the pellet growth process is presented. The predictions of pellet growth by the mathematical model are in agreement with the experimental findings.