Working with Powders

Powders are Versatile

Powders are utilised extensively across a broad range of industries and yet many of the flow properties of powders remain poorly understood. As final products, they are diverse in nature and may exist in the form of a loose powder in a sachet, a fluidised toner in a laser printer, or a powder that has been compressed into a tablet. The process operations employed during the manufacturing cycle are numerous, and can be very different in nature. It is perhaps no surprise then, when we consider the number of variables in a formulation, the diversity of unit operations employed during manufacturing, and the variety of applications, that working with powders is challenging.

Whether you are interested in formulation, process development, scale-up, commercial manufacturing, tech transfer, or quality assurance, there are many ways in which powder flow properties will be important. Powders have been utilised extensively because they possess a range of characteristics, which if well understood can be exploited to produce unique and highly valuable products.

Consider a dishwasher tablet that is processed as a powder, but then formed into an easy to handle compact of exact quantity, or a dry powder inhaler that provides a pain-free way of delivering a pharmaceutical drug directly to the target site within the patient’s lung. Powders have such versatility that they have long been employed ubiquitously across many industries.

The Challenge

As a consequence of a diverse range of properties, powders have proven to be highly functional materials, however they are notoriously difficult to handle. Powder behaviour is complex and cannot simply be categorised as universally “good” or “bad”. Powders can change their behaviour with a slight increase in ambient moisture, or if vibrated for a fraction of a second. Some have a tendency to stick to processing equipment, become electrostatically charged, change their characteristics if mixed at a different speed, or for an increased duration. These are complex materials, and if well understood their properties can be used to our advantage. However, if poorly characterised, a powder’s attributes can easily cause production problems and quality issues with the product.

The kinds of challenges confronted by industry vary enormously, but typical questions include: -

1. Can I use this new grade of raw material in my existing formulation without introducing production or quality issues?
2. What is the optimum water content required to ensure ideal final product attributes?
3. Can blend uniformity be achieved using a slower mixing speed, perhaps for a longer mixing time?
4. Will this powder flow out of my hopper in a consistent way?
5. How can we enhance this formulation so that we can run the process faster and make more product, without compromising quality?
6. Why is this batch giving us problems, when it should be performing as well as the last batch?
7. Is this powder so cohesive we won’t be able to eliminate the agglomerates during mixing?
8. Will this grade of raw material agglomerate and densify when passed through the screw feeder?
9. Why are the tablets laminating after compression?

There are literally hundreds of questions routinely asked across formulation, development, production and quality departments, and solving these normally requires an understanding of the characteristics of the powder. Whilst the solution is not always easy to attain, having access to important properties of the material being processed is the starting point to understanding the problems and engineering a solution.

Characterisation Leads To...

Utilising powder testing instrumentation from Freeman Technology, it is now possible to complete a detailed analysis of your powder’s behavioural properties, leading to the prediction and understanding of: -

• Flow and behaviour in: -
  • Hoppers (will the powder discharge with uniform flow rate, or will it bridge, block or result in pulsatile flow?)
  • Feeders (is flow rate uniform; does feeding result in agglomeration / densification of the powder; will the powder flood through the feeder?)
  • Filling systems (can the filling system be run at acceptable speed, whilst still achieving target fill weight; does powder fill the die uniformly?)
  • Conveyors (what air velocity is required for a given mass transfer; dilute phase vs. dense phase; will particles breakdown through attrition?)

• Mixing / blending performance
• The effect of feeding / conveying (agglomeration, attrition)
• Consolidation / caking potential
• The influence of changes in relative humidity / moisture content on powder behaviour

• Take a look at our App Note on Controlling the Impact of Humidity Using the FT4 Powder Rheometer 

• The influence of process variable changes (e.g. amount of water added during wet granulation, blender speed during mixing, turret speed whilst running a rotary tablet press, carousel speed when bag filling)
• The effect of formulation decisions on in-process performance, and the attributes and quality of final product
• Final product quality / attributes from upstream measurements of powder properties
• Optimum process settings for incoming raw materials / intermediates
• Quality of raw materials (in more detail than traditionally possible (beyond just particle size / density))
• Suitability of new product on an existing line, or existing product processed on different equipment
• What range of material properties can be handled in a specific process, and how process settings can be adapted to accommodate a broader range or material properties

Powder characterisation is more than just understanding the flowability of powder in a hopper! Powders have many behavioural characteristics, and all must be understood for optimal product development and efficient manufacturing.

Advantages of Comprehensive Powder Characterisation

Comprehensive powder characterisation does require significant capital investment and the resources to run measurements and trials. However, the many benefits and cost savings are substantial, and when implemented correctly, comprehensive powder characterisation can lead to:

• Improved product quality
• Faster time to market
• Reduced wastage
• Better equipment utilisation
• More efficient manufacturing - fewer stoppages, less batch to batch variation
• Better control of raw material quality and increased confidence when changing raw material suppliers
• Demonstrated interest to your customers and regulators that you are motivated to provide the best product

Advanced powder characterisation is already a key strategy for many powder processing companies, and it continues to be widely embraced by the broader community as the benefits to formulation, processing, QA/QC and technical services become increasingly understood.