TABLETING


R COMMON PROBLEMS IN


Hartmut vom Bey & Barbara Fretter discuss the infi nite PSD spiral driven by the amount of fi nes


OLLER COMPACTION


Fig. 1. The infi nite PSD spiral driven by the amount of fi nes


unfavourable progression can be observed that, in principle, is a self-perpetuating downward spiral from focusing on the amount of fi nes (Fig. 1). It’s an infi nite particle size distribution (PSD) spiral: at best, it can result in numerous unnecessary trials; at worst, it could be concluded that roller compaction is not possible for a specifi c product.


D


A shift to much more complex 46 www.scientistlive.com


uring the development stage of dry granulation products, several considerations and optimisations must be made. In this context, an


and costly granulation methods is the consequence, along with further delaying time-to-market. Interestingly, some decisions that lead to this spiral are based on correct assumptions, but an important eff ect is often ignored.


THE START OF THE SPIRAL T e entrance point into the spiral is often the choice of the granulator screen size. Based on wet granulation experience, too small screens (e.g., 0.8 mm or 1.0 mm) are chosen for normal sized tablets of 8 mm and larger. Due


to a lack of other acceptance criteria, the particle size distribution and particularly the amount of fi nes is often used to evaluate the granules. Here, two problems arise. Firstly, there is no unique defi nition of fi nes. Some companies defi ne everything below 355 µm as fi nes. In other regions, you can fi nd defi nitions such as anything below 500 µm. Occasionally, 90 µm, 100 µm, or even the d10 can be used to categorise fi nes. Secondly, the amount of fi nes is not always an accurate parameter for predicting granule quality and fl owability.


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