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Characterization of powder properties using a powder rheometer
* 1 , 2 , 2 , 1
1  Department of Pharmacy, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, DK-2100 Copenhagen, Denmark
2  Product Development and Life Cycle, H. Lundbeck A/S, Ottiliavej 9, DK-2500 Valby, Denmark

Abstract: Powder properties are critical material attributes that affect pharmaceutical powder processing and therefore the quality of the final product. During processing, powders are subjected to several physical environments requiring different behavioral properties [1-2]. Thus, characterization of powder properties using only one traditional single index methods, e.g. Carr\'s Index or flow through a funnel, is insufficient for screening of excipients and prediction of in-process performance of powders [2]. Instead a multiple approach should be applied in which powders are tested by several methods each evaluating different powder properties relevant to manufacturing. Recently, Dumarey et al. have shown how an FT4 Powder Rheometer can be a valuable tool to increase the understanding of how raw material attributes affect a roll compaction process and thus the final tablet quality [4]. The FT4 Powder Rheometer is designed to characterize powders under various conditions in ways that resemble large-scale production environments [3]. The rheometer provides a comprehensive series of methods that allow powder behavior to be characterized across a whole range of process conditions. The methods include rheological, shear, compression and permeability tests which can be performed using small bulk samples, i.e. 1, 10 or 25 ml depending on the test in question. The basis for all these methods is a bench-top rheometer with a built-in balance and a PC, a set of test vessels besides an aeration control unit used for aeration tests. In this study, eight generally used excipients, i.e. microcrystalline cellulose, lactose and mannitol from various suppliers, were tested by seven different methods provided by the FT4 Powder Rheometer. In most of the tests, several of the excipients showed a different behavior (n=3, p=0.05). Still, the most differentiating parameters were obtained by a rheological stability test and a shear cell test indicating that these two methods might detect highly important powder properties. Hence, the powder rheometer is a promising tool for assessing and understanding critical raw material attributes. Powder rheology could therefore be an important step towards implementation of Quality-by-Design into pharmaceutical powder processing. [1] Howard SA. Flow Properties of Solids. In: Swarbrick J, Boylan JC, editors. Encyclopedia of Pharmaceutical Technology. 2nd ed. New York, NY: Marcel Dekker; 2002. p. 1264-85. [2] Prescott JK, Barnum RA. On Powder Flowability. Pharmaceutical Technology 2000 Oct:60-85. [3] Freeman R. Measuring the properties of consolidated, conditioned and aerated powders - A comparative study using a powder rheometer and a rotational shear cell. Powder Technol. 2007;174:25-33. [4] Dumarey M, Wikström H, Fransson M, Sparén A, Tajarobi P, Josefson M, Trygg J. Combining experimental design and orthogonal projections to latent structures to study the influence of microcrystalline cellulose properties on roll compaction. Int J Pharm. 2011;416:110-119.
Keywords: Powder, rheologi, raw materials, powder properties