PPT_539_Physical Properties of powders (2nd Lecture) 2024.pdf

Pharmaceutical Technology III PPT 539 Pharmaceutical Quality Control Dr. Rawan Bafail Dr. Marey Almaghrabi Dr. Amani Abdelaziz 1446 /...

Pharmaceutical Technology III PPT 539 Pharmaceutical Quality Control Dr. Rawan Bafail Dr. Marey Almaghrabi Dr. Amani Abdelaziz 1446 / 2024 Physical Properties of Powder 2 Physical Properties of Powder Powder Density 01 Powder flow properties 02 03 Particle size 04 Loss on drying 3  Powder Flow The four commonly reported methods for testing powder flow are: Flow rate through Angle of repose an orifice Compressibility Index or Shear cell Hausner ratio 4  Powder Flow Numerous variations of each of these basic methods are available. Given the number of test methods and variations, standardizing the test methodology, where possible, would be advantageous. 5  Angle of Repose Angle of repose is a characteristic related to inter- particulate friction or resistance to movement between particles. Definition The angle of repose is the constant, three-dimensional angle (relative to the horizontal base) assumed by a cone-like pile of material formed by any of several different methods. Angle of repose test results are reported to be very dependent upon the method used. 6  Angle of Repose Experimental difficulties arise as a result of: 1 Segregation of material. 2 Consolidation or aeration of the powder as the cone is formed. Despite its difficulties, the method continues to be used in the pharmaceutical industry. 7  Angle of Repose Methods for determining the static angle of repose can be classified based on the following two important experimental variables: The height of the “funnel” through which the powder 1 passes May be fixed relative to the base, or the height may be varied as the pile forms. 8  Angle of Repose Methods for determining the static angle of repose can be classified based on the following two important experimental variables: 2 The base upon which the pile forms May be of fixed diameter or the diameter of the powder cone may be allowed to vary as the pile forms. 9  Variations in Angle of Repose Methods Drained Angle of Repose Determined by allowing an excess quantity of material positioned above a fixed diameter base to “drain” from the container. Formation of a cone of powder on the fixed diameter base allows determination of the drained angle of repose. 10  Variations in Angle of Repose Methods Dynamic Angle of Repose Determined by filling a cylinder (with a clear, flat cover on one end) and rotating it at a specified speed. The dynamic angle of repose is the angle (relative to the horizontal) formed by the flowing powder. 11  Angle of Repose Fixed height cone Fixed base cone angle of repose angle of repose Rotating cylinder dynamic angle of repose 12  Angle of Repose a b a a b Ledge Drained angle of repose Crater Drained angle of repose b Platform Drained angle of repose 13 13  Angle of Repose Scale of Flowability Although there is some variation in the qualitative description of powder flow using the angle of repose è much of the pharmaceutical literature appears to be consistent. There are examples in the literature of formulations with an angle of repose in the range of 40 to 50 that were manufactured satisfactorily. When the angle of repose exceeds 50, the flow is rarely acceptable for manufacturing purposes. 14  Angle of Repose Scale of Flowability Flow Property Angle of Repose (degrees) Excellent 25–30 Good 31–35 Fair—aid not needed 36–40 Passable—may hang up 41–45 Poor—must agitate, vibrate 46–55 Very poor 56–65 Very, very poor >66 15  Angle of Repose Experimental Consideration Angle of repose is not an intrinsic property of the powder; i.e., it is very much dependent upon the method used to form the cone of powder. The peak of the cone of powder can be distorted by he impact of powder from above. 01 By carefully building the powder cone, the distortion caused by impact can be minimized. 16  Angle of Repose Experimental Consideration The nature of the base upon which the powder cone is formed influences the angle of repose. 02 It is recommended that the powder cone be formed on a “common base” which can be achieved by forming the cone of powder on a layer of powder. 17  Angle of Repose Experimental Consideration The nature of the base upon which the powder cone is formed influences the angle of repose. 03 This can be done by using a base of fixed diameter with a protruding outer edge to retain a layer of powder upon which the cone is formed. 18  Powder Flow The four commonly reported methods for testing powder flow are: Flow rate through Angle of repose an orifice Compressibility Index or Shear cell Hausner ratio 19  Compressibility Index and Hausner Ratio In recent years the compressibility index and the closely related Hausner ratio have become the simple, fast, and popular methods of predicting powder flow characteristics. The compressibility index and the Hausner ratio are determined by è measuring both the bulk volume and the tapped volume of a powder. 20  Compressibility Index and Hausner Ratio The compressibility index has been proposed as an indirect measure of: Cohesiveness of Bulk Density Surface area material 1 3 5 2 4 Size and shape Moisture content 21  Compressibility Index and Hausner Ratio Basic method of determination Although there are some variations in the method of determining the compressibility index and Hausner ratio, the basic procedure is to measure The unsettled apparent volume, V0 The final tapped volume, Vf Vf : After tapping the material until no further volume changes occur 22  Compressibility Index and Hausner Ratio Basic method of determination The compressibility index and the Hausner ratio are calculated as follows: V 0 - Vf Compressibility Index =100 x V0 V0 Hausner Ratio = Vf 23  Compressibility Index and Hausner Ratio Basic method of determination Alternatively, the compressibility index and Hausner ratio may be calculated using measured values for bulk density (ρ bulk) and tapped density (ρ tapped) as follows: ptapped - pbulk Compressibility Index =100x ptapped ptapped Hausner Ratio = pbulk 24  Compressibility Index and Hausner Ratio Basic method of determination Compressibility Flow Character Hausner Ratio Index (%) 10 Excellent 1.00–1.11 11–15 Good 1.12–1.18 16–20 Fair 1.19–1.25 21–25 Passable 1.26–1.34 26–31 Poor 1.35–1.45 32–37 Very poor 1.46–1.59 >38 Very, very poor >1.60 25  Compressibility Index and Hausner Ratio Experimental Consideration 1 Compressibility index and Hausner ratio are not intrinsic properties of the powder; i.e., they depend on the methodology used. Important considerations include: 1. The diameter of the cylinder used. 2. The number of times the powder is tapped to achieve the tapped density. 3. The mass of material used in the test. 4. Rotation of the sample during tapping. 01 26  Compressibility Index and Hausner Ratio Experimental Consideration 2 Recommended procedure: 1. Use a 250 mL volumetric cylinder with a test sample weight of 100 g. 2. Smaller weights and volumes may be used, but variations in the method should be described with the results. 3. An average of three determinations is recommended. 01 27  Powder Flow The four commonly reported methods for testing powder flow are: Flow rate through Angle of repose an orifice Compressibility Index or Shear cell Hausner ratio 28  Flow-Through an Orifice The flow rate of a material depends upon many factors, some of which are particle-related and some related to the process. Monitoring the rate of flow of material through an orifice has been proposed as a better measure of powder flowability. Its particular significance is due to the utility of monitoring flow continuously because pulsating flow patterns have been observed even for free-flowing materials. 29  Flow-Through an Orifice Changes in flow rate as the container empties can also be observed. Empirical equations relating flow rate to the diameter of the opening, particle size, and particle density have been determined. However, determining the flow rate through an orifice is useful only with free-flowing materials. 30  Flow-Through an Orifice The flow rate through an orifice is generally measured as the mass per time flowing from any of types of containers (cylinders, funnels, hoppers). 31  Powder Flow The four commonly reported methods for testing powder flow are: Flow rate through Angle of repose an orifice Compressibility Index or Shear cell Hausner ratio 32  Shear Cell To put powder flow studies and hopper design on a more fundamental basis, a variety of powder shear testers and methods that permit more thorough and precisely defined assessment of powder flow properties have been developed. 33  Shear Cell Basic method of determination The methods have been successfully used to determine critical hopper and bin parameters. 34  Shear Cell Cylindrical shear cell Basic method of determination ü The cylindrical shear cell is split horizontally, forming a shear plane between the lower stationary base and the upper moveable portion of the shear cell ring. ü After powder bed consolidation in the shear cell, the force necessary to shear the powder bed by moving the upper ring is determined. 35 Shear Cell Cylindrical shear cell Basic method of determination 36  Shear Cell Annular shear cell Basic method of determination ü Annular shear cell designs offer some advantages over the cylindrical shear cell design, including the need for less material. ü A disadvantage, however, is that because of its design, the powder bed is not sheared as uniformly; i.e., material on the outside of the annulus is sheared more than material in the inner region. 37 Shear Cell Annular shear cell Basic method of determination 38  Shear Cell Plate-Type shear cell Basic method of determination ü Consists of a thin sandwich of powder between a lower stationary rough surface and an upper rough surface that is moveable. 39  Shear Cell Advantage A significant advantage of shear cell methodology in general is a greater degree of experimental control. Disadvantage The methodology is rather time-consuming and requires significant amounts of material and a well-trained operator. 40  Shear Cell The many existing shear cell configurations and test methods provide a wealth of data and can be used very effectively to characterize powder flow. They are also helpful in the design of equipment such as hoppers and bins. It is recommended that the results of powder flow characterization using shear cell methodology include a complete description of equipment and methodology used. 41 Shear Cell 42 Shear Cell 43 Shear Cell 44