TABLETING
FIG. 2. Influence of the specific roll force on the particle size distribution, example Avicel 101
Small differences between both units can be observed in the extent of the strongest particle fraction between 1000 µm and 1400 µm, which lead to a slight shift of the particle size distribution towards coarser particles for the Small Scale Mill. Te extent of this small deviation seems to be material specific. Tey are caused by the other process parameters of the Macro-Pactor, which cannot be transferred to the manually operated Small Scale Mill. During scale-up these process parameters will be optimised, hence the small differences in particle size distribution can be neglected during development. From the results it can be concluded that both solutions show almost identical particle size distribution and that therefore, the Small-Scale Mill is an ideal tool for milling small amounts of material to representative granulates.
Te number of fines is usually reduced at higher roll forces during roller compaction.[2]
However, the extent of
the influence of the roll force depends on the used pharmaceutical formulation and cannot be generalised.
FEATURES OF THE MILL In some situations, e.g. during development, when the API (active pharmaceutical ingredient) is rare or very expensive, it is desirable to be able to mill small amounts. Prior studies showed that small lab or household mills are not suitable for achieving the same PSD as roller compactors for production.[1]
Terefore, a Small Scale
Mill (manually operated) was developed by Gerteis that reproduces the grinding principles of the Pactor line. Te various wire mesh screens and rasping screen are changeable, which allows the user to mount different mesh sizes, depending on the requirements. Te material – tablets or roller compactor ribbon pieces – is forced through the screen by milling bars, which are manually operated. Te material is processed into the milling chamber and final granules are collected in a drawer. A few grams of material up to 50g can be milled in one pass, which is often enough for first tableting experiments. Te overall design of the manual mill is constructed for an easy use: mounting and cleaning of all parts is simple and fast. Te material used in construction complies with all pharmaceutical requirements.
TWO SOLUTIONS For comparing the performance of the Small Scale Mill, four different excipients were tested.[1]
COMPARISON OF THE Te same material
concerning densification and strength was milled with the manual mill and the Macro-Pactor (production scale roller compactor). Te results in Fig. 3 show good
correlations between the granulates obtained by the Small Scale Mill and Macro-Pactor for all four substances. All granulates follow the typical PSD of dry granulates, which is rather broad. A certain amount of fines (particles below 100 µm) is present, but below 10 -20%.
References 1. Potschadl, J., PhD Theses, Scale-down des Walzenkompaktierprozesses Entwicklung eines Trockengranulats im Kleinstmaßstab University of Bonn (2013)
2. Wiesweg, S., PhD Theses, Einflussfaktoren des Walzenkompaktierprozesses auf die Partikelgrößenverteilung von Granulaten, University of Bonn (2009)
Hartmut vom Bey is with Gerteis & Barbara Fretter is with Solids Development Consult.
www.gerteis.com
FIG. 3. PSD of different substances milled with the manual mill and the Macro-Pactor with pocketed granulator [1]
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