Effect of the particle size uniformity and flow-ability on the Content uniformity and Disintegration of the Tablets.

• The successful manufacturing of tablets demand good flow properties and a uniform particle size of the grains. Grains that show poor flow-ability usually result either as deviation in the content uniformity or weight variation in the tablets. A particle size uniformity ensures a homogenize mixing of all the materials. Because mixing of materials that vary in their particle size result in an uneven distribution, issues related to the content uniformity arise. The most common approach for achieving a uniform particle size is sieving. Sieving all the materials through a common sieve create an even sized particles.
  Similarly after granulation, it is essential to pass the grains through an appropriate sieve to produce uniform grains. This practice eliminate weight variation during compression.
  In addition to the uniformity in the particle size, the poor flow of the grains also result in the weight variation. In order to check the flow-ability, two methods are normally utilized. One of them is “Compressibility Index” while the other is “Angle of Repose”.
  Compressibility index is determined by using the difference of the bulk density and the tapped density. For this purpose, grains are filled in a graduated cylinder and the volume is determined before and after tapping the cylinder. Both the volumes are noted and the compressibility index is determined by using the following equation.
  
  
  Where,
  V bulk = Volume before tapping
  V tapped= Volume after tapping
  
  
  
  On the other hand, angle of repose is determined by forming a cone of the grains by allowing it to flow through the funnel.  The radius and the height of the cone is used to determine the tan θ.
  
  
  
  Particle size also impart an effect on the disintegration time of the tablets. Grains with small particle size produce tablets with less disintegration time and vice versa. But the flow-ability of the grains decrease with a drop in the particle size. Therefore, a fine adjustment of particle size is required to achieve good flow and the required disintegration time.
  Glidants, like stearic acid, are also used to improve the flow of the grains but there is a limitation to their use. Glidants and lubricants have a tendency to increase the disintegration time of the tablets. Normally quantity of the glidant that is not more than 1% of the tablet do not create a considerable change in the disintegration time of the tablet.