Ribbon density and milling parameters that determine fines fraction in a dry granulation

A challenge in the dry granulation (DG) process is the generation of an excessive amount of fines during milling, which can cause problems in die filling due to poor flowability and content uniformity of tablets. Using a design of experiments (DOE) approach, we show that the amount of fines generated during milling decreases with either increasing ribbon density or screen size, while impeller speed has negligible effect. Moreover, under identical milling conditions, the percent fines can be accurately predicted from ribbon density. Thus, controlling ribbon density and screen size is important for optimizing the amount of fines produced during DG process. Because density has a central role in the outcome, it is a critical ribbon property that needs to be controlled to improve robustness of the DG process.