• Simple repeatable index of flowability of powders
• Flowability testing before set-up of tableting or capsule filling equipment
• The establishment of a reliable flowability index for purchasing and quality assurance specifications
• Avoiding high coefficient of variation in product uniformity

• particle size and shape
• unit surface
• actual and bulk density
• electrostatic charge
• "fines"
• porosity
• settling

Flocculi are groups of low-cohesion fines; they cannot be isolated in a laboratory because they disintegrate easily in sieves. In production equipment powder containing flocculi tends to adapt to the container (the hopper), a behavior similar to that of a liquid gelatinizing in its container.

Flocculation occurs when the large surface area - and therefore large contact area - of fines favors cohesion forces. These are the same cohesion forces that greatly increase during compression to produce hard tablets; in powder bulk, however, these forces are too weak to force out the air created by the well-known embolic property of capillaries. Distances between granules therefore remain at 100 Å = 0.01 μm. Lactose, starches, and calcium carbonate provide classic examples of flocculation.

Humidity favors the occurrence of flocculation by increasing the contact surface among powder particles, by reducing electrostatic repulsion force since the dielectric constant of water is 80, and by favoring the leakage of electrostatic charge. On the other hand, a light electrostatic charge - obtained, for example, through sifting or by the addition of Cabosil - might contribute to the elimination of flocculi.
Footnote: FLODEX is a Trademark of Hanson Research Corporation

Contents taken from FLODEX Technical Bulletin, Pharmaceutical Technology Feb. 1980.

Principle Behind The Method
The basis for this method is the powder's ability to fall freely through a hole in a plate. The diameter of the smallest hole through which the powder passes three times out of three is taken as the flowability index. This method has proved easily reproducible. Each trial is considered valid when the powder that falls involves the entire height of the powder (not to be less than 60mm).

Description of The Equipment
Very simply, the Dow-Lepetit device for testing intrinsic powder flowability, consists of a cylinder with a series of replaceable disks—of different diameters—in the bottom. The hole is closed by a mobile shutter. The actual components of the system are as follows:

1. A stainless steel cylinder with an approximate capacity of 200 ml.
2. A series of stainless steel disks. Each disk has a precise hole in the center in graduated sizes differing 1-2 mm in diameter and is easily attached to form a bottom for the cylinder.
3. A shutter that covers the hole and that may be quickly removed without vibration to allow the powder to flow through the selected hole.
4. An adjustable funnel for loading the sample cylinder with a free fall of the test powder.
5. A suitable container to collect the powder that flows through the unit.

The Procedure
The ring is secured to the bearing to allow the bottom of the funnel to be near but not touching
the powder surface. A powder load of 50 g is then poured through the funnel into the middle of the cylinder. When loading is completed, 30 seconds must be allowed for possible formation of individual flocculi or mass flocculation of the whole load.

Now the lever device is operated to open the hole in the disk quickly and without vibration. A very flowable powder will slowly flow through the small-diameter holes, leaving a cavity shaped like an upside-down, truncated cone. A powder that flocculates in bulk, on the other hand, will fall abruptly, forming a cylindrical cavity. If the experiment is negative - i.e., if the powder falls as just described - the powder must be tested again with a disk having a larger hole.