Powder flow properties

The bulk density of a powder is calculated by dividing its mass by the volume occupied by the powder (Abdullah Geldart, 1999). Tapped bulk density, or simply tapped density, is the maximum packing density of a powder achieved under the influence of well-defined, externally applied forces (Oliveira et al., 2010). Because the volume includes the spaces between particles as well as the envelope volumes of the particles themselves, the bulk and tapped density of a powder are highly dependent on how the particles are packed. This fact is related to the morphology of its particles and such parameters are able to predict the powder flow properties and its compressibility. 

Powder flow is most frequently thought of as relevant to formulation development, and there are numerous references attempting to correlate any one of a number of measures of powder flow to the manufacturing properties of a formulation [34—40]. In particular, the importance of physical properties in affecting powder flow has been well documented. Research into the effect of the mechanical properties on powder flow has, however, been very limited. It is, of course, important to be able to determine and quantitate the powder flow properties of formulations. It is of equal importance, however, to determine the powder flow characteristics of bulk drug early in the development process (preformulation phase). Often, the preformulation or formulation scientist is constrained by time, materials, and manpower. Yet certainly the preformulation studies carried out should be meaningful. Well-defined experimental methods and procedures should be used the information generated should be reproducible and permit useful predictions to be made. 

In an effort to put powder flow studies and hopper design on a more fundamental basis, Jenike [45] developed a powder shear tester and methodology that permits an assessment of powder flow properties as a function of consolidation load and time as well as powder-hopper material interactions. The methodology has been used extensively in the study of pharmaceutical materials [39,58-61]. From the yield loci obtained using this method, several parameters can be determined that influence powder flow, and discussions of these points are well documented in the literature [49,62,63]. 

Table 4 Powder Flow Properties of Several Excipients...

The mechanical properties of materials, though not often studied in detail, can have a profound effect on solids processing. Clearly, tableting properties are influenced by the elastic and plastic deformation properties as well as the viscoelastic properties of a material. As we have pointed out, the powder flow properties are also affected, as well as the tendency of materials to set up on storage. Because of the importance of mechanical properties, it is important to be able to... 

Zhou, Q., Armstrong, B., Larson, I., Stewart, P. J., Morton, D. A. V. Improving powder flow properties of a cohesive lactose monohydrate powder by intensive mechanical dry coating. J. Pharm. Sci., 99, 2010, 969-981. 

Glidant Aids powder flow properties during manufacture Colloidal silica, starch... 

P. Marjanovic, E. McGee, Determination of powder flow properties using different shear cells, Proceedings of the RelPowFlo 3, Pors-grunn, Norway, August 1999, pp. 151-158. 

TABLE 7.10 Classification of Powder Flow Properties Using the Schulze Ring Shear Tester... 

Chitin was evaluated as a direct-compression vehicle using powder flow properties and the physicomechanical properties of the manufactured tablets, and it was proven that this natural polymer has suitable characteristics for being used for this end. 

Improve the flow properties. Powders, especially some food powders, show a poor flow behavior. Often these powders are sticky, hygroscopic and may contain fats, all of which have a negative effect on the powder flow properties. By agglomeration of the powders, the flow properties usually improve substantially. 

D.A. Craig and R.T. Hossfeld, Measuring powder flow properties, Chem. Eng., 41-46 (September 2002). 

To improve powder flow properties for dosage filling and compression processes... 

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. ... 

Bhattachar SN, Hedden DB, Olsofsky AM, et al. Evaluation of the vibratory feeder method for assessment of powder flow properties. Int J Pharm 2004 269 385-392. 

Powder Flow Patterns and Scaling of Mixing Powder flow properties have a significant impact on high-shear mixing, particularly... 

Dry powder generation is hindered by aggregation of the particles [20]. This property may be attributed to surface charge characteristics of the powder and van der Waals forces. A factor that exacerbates this problem is the hygroscopic nature of many pharmaceutical powders [43,45,47]. Hygroscopicity is known to change the powder flow properties [187]. Attempts have been made to modify the surface characteristics of dry powders to reduce both aggregation... 

Crystal morphology or habit is important, since it can influence many properties of the compound. For example, powder flow properties, compaction and stability have all been found to be dependent on crystal morphology. It has been shown that tolbutamide B (platelike)... 

A number of other studies can be performed on a candidate drug to determine other important solid-state properties, for example, particle size, powder flow and compression and polymorphism. Therefore, when a sample undergoes initial preformulation testing the following parameters should be noted particle size, true, bulk and tapped density, surface area, compression properties and, powder flow properties. Some of these factors will be discussed in this chapter others, however, are dealt with in more detail in Chapter 11 on Solid Oral Dosage Forms. 

Developed to aid silo and hopper design, shear cells provide an assessment of powder flow properties as a function of consolidation load and time. There are a number of types of shear cells available, the most common type being the Jenike shear cell (Figure 11.3). 

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