| Powder behaviour can be complex and challenging to understand. Tim Freeman of Freeman Technology explains vial filling and the powder parameters of relevance for this industrially important unit operation
Many pharmaceutical products are handled in the form of powders at some point during manufacture. This makes effective powder processing an important goal; however, powders can be difficult to characterise reproducibly in ways that relate to processability. Consequently, there is a lack of published information about powders, so that manufacturers are overly reliant on experience rather than true knowledge or understanding. Tools that can provide relevant information and insight are extremely valuable for process design and operation.
This article discusses the unique properties of powders with reference to their processing behaviour, and illustrates how materials can be characterised in ways that relate to their performance in specific processes. It also describes how the data are used to optimise formulations in relation to processability.
UNDERSTANDING POWDER BEHAVIOUR
The properties of powders, unlike those of a gas or liquid, are not simply a function of composition, temperature and pressure. A wide range of primary variables (such as particle size and shape, hardness and porosity) and secondary or system variables (including moisture and air content) influence behaviour. This complexity explains why the flow properties of powders:
- Have not been extensively determined and are not widely presented in published databases
- Cannot be determined directly from basic physical properties of the powder such as particle size, shape and texture – the complexity of the challenge puts them beyond our current capabilities
- Vary according to processing history. Moisture loss or uptake, changes in air content, segregation and attrition can all occur easily in an uncontrolled way during processing, so influencing behaviour. These are complicating factors in relation to sensitive and reproducible powder characterisation
The optimal approach for powder assessment is firstly to use testing methodologies that provide reproducible data, and secondly to evaluate flow performance in ways that relate to powder behaviour in real industrial processes. This means quantifying the effects of consolidation, vibration, segregation, moisture uptake, fines, aeration, flow rate, air entrainment and a number of other factors. Such characterisation using complementary methodologies has wide application in the formulation, processing and QC sectors of most powder processing industries. |
