Why Measure the Flow Properties of Powders?

It has been estimated that over 50% of the materials used in all industrial applications were at some stage in a powder form. These powders need to be transported, injected, propelled and be able to pass through various process stages before they achieve their final form. This final form may be a tablet, a suspension or indeed a powder formulation. The need to be able to measure, control or test for reproducible powder flow has been well established in many industrial applications. Powder flow characteristics are important for:

• Reduction in cost of raw process materials: reject bad batches before processing
• Maintenance of the optimum formulation for the process concerned
• Reduction in process costs
• Maintaining the quality and consistency of the final product
• Maintaining process efficiency and costs by optimization of product storage, packing, handling and transportation
• Maintaining powder quality from different suppliers or from the same supplier over a long time period
• Development of new processes where powders are required to be formulated into end products
• Checking moisture effects: use of powders in open systems in different climates
• Investigating and maintaining the quality of dry mixes

In processes, which rely on powder and / or powder, mix integrity, the need to have the correct powder flow characteristics is paramount. These powder mixes have to be formulated, mixed and certainly transported. Transportation, even over small distances an easily lead to classification of sorts such that “fines” may drop out and alter the particle size distribution and hence the flow characteristics.

For example, we can look at formulated mixtures, which are fed into tableting machines: these powders need to flow in exactly the same way from batch to batch. Generally, the active ingredients are materials that have no natural flow properties. They are sticky (cohesive) and prone to agglomeration. Additionally, the requirement of active material in ever decreasing dosages means that the active must be able to be dispersed in a non-active medium (normally made up of wellestablished and mainly natural products) in a reproducible way in the mixers prior to the introduction of the formulation into the tablet press.

The fact that the non-active materials such as MCC (Micro Crystalline Cellulose), starch and lactose are natural products means that these materials are prone to variations in particle size, agglomeration, surface area, and so on, depending on the product source. Then we have to consider the effect of the introduction of materials such as silica (e.g., Aerosil 300), which aid the flow of these normally quite stubborn powders. The need to control each of the components as well as the final mix now becomes clear. Control of this type can save a lot of time, wasted money and resources if checks are made at the right time on these component powders.