Investigation of an 11mm diameter twin screw granulator: screw element performance and in-line monitoring via image analysis

As twin screw granulation (TSG) provides one with many screw element options, characterization of each screw element is crucial in optimizing the screw configuration in order to obtain desired granule attributes. In this study, the performance of two different screw elements - distributive feed screws and kneading elements - was studied in an 11mm TSG at different liquid-to-solid (L/S) ratios. The kneading element configuration was found to break large granules more efficiently, leading to narrower granule size distributions. While pharmaceutical industry shifts towards continuous manufacturing, inline monitoring and process control are gaining importance. Granules from an 11mm TSG were analysed using the EyeconTM, a real-time high speed direct imaging system, which has been used to capture accurate particle size distribution and particle count. The size parameters and particle count were then assessed in terms of their ability to be a suitable control measure using the Shewhart control charts. d10 and particle count were found to be good indicators of the change in L/S ratio. However, d50 and d90 did not reflect the change, due to their inherent variability even when the process is at steady state.