Powder Flowability PDF

Powder flowability Introduction Flow properties: Flowability can be defined as the ease of flow of the whole powder mass. The flowability of a powder is of critical importance in the production of pharmaceutical dosage forms. It is important for uniform feedin...

Powder flowability Introduction Flow properties: Flowability can be defined as the ease of flow of the whole powder mass. The flowability of a powder is of critical importance in the production of pharmaceutical dosage forms. It is important for uniform feeding to have weight uniformity. Even powder flow is important to avoid entrapped air within the powder, which may cause capping or lamination in case of tableting. Numerous factors affect the flow properties of powders, e.g. particle shape, particles size, size distribution, roughness of surface of the particles, packing properties, etc. Powder flowability: It is the ability of the powder to flow in a desired manner in a specific piece of equipment. The interaction between particles (cohesion) or between particles and container (adhesion) influences the flow powder. Electrical surface charge which induced by frictional movement. Van der Waal's forces and surface tension at the surface of contact between particles induced by moisture, are mechanisms by which particles cohere together or adhere to the container. These effects depend upon both the chemical and physical form of the powder. Cohesion and adhesion increase as the size of the particle decreases. For larger particles, the gravitational force becomes much greater The attraction then becomes smaller, since the particles cannot easily approach each other. To improve the flowability, the fine particles are removed and the size range is decreased. The larger the particle size, the better the powder usually flows Powder flow properties: It is the specific bulk characteristics and properties of the powder that affect flow such as particle size, density (compressibility), cohesion and wall friction. So, during manufacturing of solid dosage forms like tablet and capsules powder formulation must possess an adequate flow in order to produce products with desired properties. Poor powder flow can be improved by: 1. By addition of excipient e.g 1. Glidents eg aerosol -Prevent cohesion (attractive forces between like surfaces) II. Lubricants eg magnesium stearate (well known )Prevent adhesion (attractive forces between unlike surface) tablet and die cavity. (Fig 1). *Both must not exceed the maximum concentration e.g. Mg stearate Mix con. is 1% So ,lf the mix. Con. dose not improve the flow then go to granulation 2. By granulation (size enlargement) It is a process whereby particles are agglomerated into larger semi-permanent aggregates with sizes ranging from about 0.1 to 2.0 mm. Fig1 - Single Punch Tablet Compression Mechine Several methods can applied to investigate powders flow properties powder such as flow meter, % compressibility (carr index) and angle of repose. Angle of repose When the powder is allowed to flow from an orifice (e. g. funnel) on a horizontal surface will form a heap (cone). Angle of repose is defined as the maximum angle formed between the sides of the heap and the horizontal axis. (Fig 2) The calculation formula is as follows; r (Radius) = D, + D,/ 4 Tan 0 = h/r Where h = height of the heap r = radius of base of heap © = angle of repose Factors affecting angle of repose The uneven and non-uniform surface of the particles will produce a larger angle of repose. Less particle size shows high angle of repose. Lubricants at low concentration lower the angle of repose and vice versa. Therefore, in order to maintain good powder flowability, it is necessary to maintain the optimal lubricant concentration to maintain angle of repose. Fines increases angle of repose. Orifice Narrow opening Side of heap h r Horizontal axis Fig-2 Fixed Funnel Method Experiment. 1 Evaluation of influence of particle size on the powder flowability by using angle of repose. fixed Funnel Method) Fig 2 &Table Particles size( m) h (cm) D1 (cm) D2 (cm) r (cm) Tan Sd Table. 1 Inflence of particles size Experiment. 2 Evaluation of the influence of lubricant and concentration on powder flowabillity by using angle of repose. (fixed Funnel Method) Fig.2S Table.2 Lubricant (%) Table.2 Inflnence of Lubricant%