Flow properties of powders

Kazumi D, Kazutoshi K, Kazutaka K, Kotaro I, Hisakazu S, Akinobu O. Effect of particle shape on the compaction and flow properties of powders. Chem Pharma Bull 1989 37(11) 3070—3073. 

P. Marjanovic, Assessing the flow properties of powdered materials, IMechE Seminar on Hoppers and Silos, London, UK, 1994. 

P. Marjanovic, M.G. Jones, Assessment of a new technique for measuring flow properties of powdered materials stored in hoppers, IMechE J. Process. Mech. Eng. 210 (1996) 1-8. 

Ed. McNaughton and the Staff of Chemical Engineering. New York McGraw-Hill. Kamath, S., Puri, V. M., Manbeck, H. B. and Hogg, R. (1993). Flow Properties of Powders Using Four Testers Measurement, Comparison and Assessment. Powder Tech., 76,277. 

It is essential to characterize formulation flow properties—and the factors which impact on it (Table 7.8)—at the beginning of the formulation design and optimization stages. Several different methods are available for determining the flow properties of powder mixtures that can serve as tools for prototype formulation screening 55... 

M.D. Ashton, D.C.-H. Cheng, R. Farley and F.H.H. Valentin, Some investigations into the strength and flow properties of powders, Rheol. Acta, 4 (1965) 206—218. 

Tablet glidant Agent used in tablet and capsule formulations to improve flow properties of powder mixture Colloidal silica, corn starch, talc...

There are several different methods available for determining the flow properties of powders. Shear cell methods 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 being the Jenike shear cell [21]. 

Flow properties of powders are important parameters in mixing and segregation phenomena, essentially during storage. 

The excipients used are fillers, but the most important are lubricants, such as magnesium stearate, PEG 6000, calcium stearate, glycerol palmito stearate, and calcium behenate, which increase the flowability but at the same time modify the hydrophobic characteristics of powders. Their choice depends on compatibility with active ingredient and the flow properties of powders. The characteristics of the excipient have been described previously. 

Characterization of powders is essential to quality control of raw materials, active or excipient, in order to maintain product uniformity. Flow-property studies of powder materials facilitate the scientific design of formulations and processing equipment, such as the design of mass-flow hoppers. This article reviews the flow properties of powder materials. The factors affecting the flow properties of solids are briefly discussed first, followed by measurement of flow properties. 

Some work has shown a direct correlation between shape factor and the flow properties of powders. The flowability of fine powders, as measured by a shear-cell as well as by Carr s method, was found to increase with increasing sphericity, where the sphericity is indicated by a shape index approaching one, as measured by an image analyzer. Huber and co-workers derived an equuation in which flow rate was correlated to the volume specific surface as measured by laser diffractometry. Reasonable predictions were made for individual powders as well as binary and ternary mixtures. 

Peleg, M. Mannheim, C.H. Effect of conditioners on the flow properties of powdered sucrose. Powder Technol. 1972, 7, 45-50. 

Van Ooteghem, M. De Winter, B. Ludwig, A. Influence of the mixing conditions on the flow properties of powders to be filled into hard gelatin capsules. Acta Pharm. Jugosl. 1998, 38, 287-295. 

Bulk powder characteristics are important in understanding the handling properties of an excipient or a granulated product. A classification system to evaluate the flow properties of powders has been introduced by Carr.P A flowable powder is defined as free-flowing and tends to flow steadily and consistently, whereas a floodable powder exhibits an unstable, discontinuous, and gushing type of flow. A number of studies have investigated the bulk powder properties of starch " and granulations made with starch. The starch materials were found to exhibit poor to borderline flow properties. 

Lactose anhydrous has been used experimentally in hydrophilic matrix tablet formulations and evaluated for dry powder inhalation applications. Partial hydration of anhydrous lactose increases the specific surface area and reduces the flow properties of powders but has no effect on compactibility. A specification for lactose is included in the Food Chemicals Codex (FCC) see Factose, Monohydrate. The EINECS number for lactose anhydrous is 200-559-2. 

Neumann BS. The flow properties of powders. In Advances in Pharmaceutical Science Bean HS, Beckett AH, Carless JE, eds. Academic Press London, 1967 Vol. 2, 181-221. 

The electrostatic charges on the surface of a powder can affect the flow properties of powders. An electric detector can determine the electric field generated by the electrostatic charges on the surface of the powder. This acts as a voltmeter and allows the direct determination of both polarity and absolute value of the electrostatic field. As an example, the electrostaticity of the experimental compound ITF 296, when sieved at 200 pim, showed an electrostatic field of -60 V due to the charge on the powder surface (Dobetti et al. 1995). As a consequence, the powder formed stacked aggregates, which led to the unsieved powder being less wettable and difficult to handle. Ftihrer (1996) has reviewed interparticulate attraction mechanisms. 

It might be expected that inclusion of small particles in a powder could decrease porosity if they fit into voids between larger particles. In practice, the opposite effect is usually observed. The explanation for this follows from consideration of the main factors that determine closeness of packing and flow properties of powders the size, shape, and surface properties of the particles. It is often found that the effects of surface properties outweigh the others because they govern the friction and adhesion between particles. As the size of particles decreases, the ratio of surface to volume increases, thus magnifying frichonal resistance. Other factors that may contribute to increased friction or stickiness are the presence of liquid films and electrical charge effects. 

Sutton, Fi. M. 1976. Flow properties of powders and the role of surface character. In Characterization of Powder Surfaces, Parfitt, G. D. and Sing, K. S. W. (eds.). New York, NY Academic Press. 

Ashton, M.D., Cheng, D.C-H., Farley, R. Valentin, F.H.H. (1965) Some investigation into the strength and flow properties of powders. RheoL Acta, 4(3) 206-218. 

Reproducibility, and results independent on the operator, are requirements necessary for most applications, but these requirements are difficult to satisfy in measuring the flow properties of powders. In this respect the uniaxial tester developed by POSTEC [4] is one of the most reproducible methods available. Previous experience [5] indicated, however, that the procedure for filling the die was very important for the result, and one of the main reasons for the amount of scatter and operator dependency still remaining for the uniaxial tester. It was therefore decided to investigate different filling procedures in order to further improve the reproducibility of the results obtained by the tester. 

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