Shear cells characterization

Because the compressibility index can be thought of as a measure of the likelihood of arch formation and the ease with which arches will fail [44], and because it can be rapidly completed, it appears to be a useful measure of flow. Obviously, exceptions will occur, and caution should be exercised in its interpretation. As we will dicuss, the compressibility index values reported in Tables 2 and 3 and Fig. 4 are quite consistent with shear cell characterization. 

Fig. 9 Graphical representation of several parameters that can be obtained using shear cell characterization. (Adapted from Ref. 48 with permission of the publisher.)...

A powder s strength increases significantly with increasing previous compaction. The relationship between the unconfined yield stress/, or a powder s strength, and compaction pressure is described by the powder s flow function FE The flow function is the paramount characterization of powder strength and flow properties, and it is calculated from the yield loci determined from shear cell measurements. [Jenike, Storage and Flow of Solids, Univ. of Utah, Eng. Exp. Station Bulletin, no. 123, November (1964). See also Sec. 21 on storage bins, silos, and hoppers.]... 

Amidon and Houghton [48] completed a comparative study of several common methods of characterizing powder flow. Table 2 contains experimental results for a number of commonly used pharmaceutical excipients. Compressibility index, angle of repose, flow rate through an orifice, and shear cell data are presented. 

As with the Jenike cell, this process is time-consuming. Amidon and Houghton, " however, used a single yield locus with this cell for comparative purposes. Hiestand et al., ° in comparing this apparatus to the Jenike cell, claimed that this simple shear cell can be used to provide characterization of the unconfined yield strengths of powders. The results from the two devices are not identical. However, as much as the Hiestand device requires less powder and the consolidation step is more automated and consistent, it provides an inexpensive alternative to the Jenike-type cell to characterize pharmaceutical powders. Amidon and Houghton used the cell to examine the effect of moisture on the powder flow properties of microcrystalline cellulose. ... 

Interesting attempts to characterize the flow and extrusion characteristics of ceramic compounds, pastes and damp bulk solids have been made by Felder [12] and Raschka [13], using a torsional shear cell and an annular shear Instrument specially developed for this purpose. 

A powder is characterized running an experiment in a Jenike s shear cell. The results are given in Table 2.4. Determine the failure properties that can be derived from the yield locus of the powder. 

Rheological characterization of pharmaceutical powders using tap testing, shear cell and mercury porosimeter. Int. J. Pharm., 189, 91-103. 

Ennis BJ, Mehos G, Wu S, Patel P. Characterizing the impact of flow aids on flowability of pharmaceutical excipients by automated shear cell. AAPS Annual Meeting. 

Other shear cells have been used to characterize the flowability of blends. Carr and Walker describe an annular shear cell that measures the resistance to the angular movement of the shoe that is placed on top of the powder (53). The advantage to this type of design is that unlimited travel of the shoe provides the opportunity to measure successive initial consolidation loads without reloading the powder (53) Hiestand (52) and later on, Amidon and Houghton (54), describe a plate-type shear cell that is similar to the Jenike shear cell, with the exception that the powder bed is unconstrained at the edge of the bed. 

Those stmctural variables most important to the tensile properties are polymer composition, density, and cell shape. Variation with use temperature has also been characterized (157). Flexural strength and modulus of rigid foams both increase with increasing density in the same manner as the compressive and tensile properties. More specific data on particular foams are available from manufacturers Hterature and in References 22,59,60,131 and 156. Shear strength and modulus of rigid foams depend on the polymer composition and state, density, and cell shape. The shear properties increase with increasing density and with decreasing temperature (157). 

The rheological behavior of storage XGs was characterized by steady and dynamic shear rheometry [104,266]. Tamarind seed XG [266] showed a marked dependence of zero-shear viscosity on concentration in the semi-dilute region, which was similar to that of other stiff neutral polysaccharides, and ascribed to hyper-entanglements. In a later paper [292], the flow properties of XGs from different plant species, namely, suspension-cultured tobacco cells, apple pomace, and tamarind seed, were compared. The three XGs differed in composition and structural features (as mentioned in the former section) and... 

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