![]() The production capacity of a tablet press is directly determined by the rotation frequency of the die table and limited by powder flow into the dies. Because of powder flow limitations in this step, a slow-speed process that works well may not work at all when rates are increased. Weight variations in the final dosage form can occur when the flowability of the final formulation limits the separation of small quantities of powder from the larger mass of powder. In pharmaceutical processing, insufficient flow can lead to product quality failures, due to large weight or dosage variations. It determines for example whether bins can be used or hand scooping is required, to what extend product is scraped at the beginning or end of a run, and the allowable production rate of products. Flow is also relevant for manufacturing efficiency for batch processes. ![]() In a continuous manufacturing line for example, consistent and continuous flow through the system is a critical requirement for finished product quality. Often understanding powder behavior is crucial to properly design the process and equipment. Powders are used in many industries and in a broad range of processes and applications. This study also revealed that obtained insights on rheological behavior can be used to optimize agitator settings in a tableting machine. The presence of fines between larger particles turned out to reduce the rheological index, which the authors explain by improved particle separation at more dynamic flow fields. Particle size distribution was identified as a main contributing factor to the rheological behavior of powders. A new parameter for rheological behavior was introduced, which is a measure for the change in dynamic cohesive index upon changes in flow field. In the current study, the rheological behavior was investigated for a wide range of excipients with a wide range of material properties. One of the challenges in mimicking the die filling process is the impact of rheological powder behavior as a result of differences in flow field in the feeding frame. Many flow characterization techniques are present, but so far only a few have shown to mimic the die filling process successfully. With the emergence of quality by design in the pharmaceutical industry, it becomes imperative to gain a deeper mechanistic understanding of factors impacting the flow of a formulation into tableting dies.
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