Precise deposition of complex particles for structured functional products

In the pharmaceutical industry, coatings have a very important place in manufacturing and product development. Solid dosage forms like tablets, pellets, granules etc. are typically coated in order to control the drug release within the body, and also to protect against external factors like moisture or attrition. This is often achieved through dry coating with fine powders, since this provides reduced environmental concerns (no volatile organic solvents emitted) and lower energy consumption (no subsequent drying or evaporation operations required). However, the dry coating process is wasteful in terms of coating powder used and energy input, since when the coating uniformity does not meet the requirement, the entire batch is disposed of. To mitigate this, an excess of coating powder is often used, with excessive energy input to ensure all solids are sufficiently coated. We aim to address these problems by determining for a given combination of substrates and powder coatings: (i) How is coating of a single powder layer influenced by particle properties? (ii) How should a mixer operate to provide uniform coating across the entire batch? (iii) What is the minimum energy input to ensure uniform product coating?

In this research we will determine how coating is achieved on the fundamental, particle level, by controlling and manipulating the distribution of particle physical (size, shape) and surface (roughness, interface energy) properties and characterising the resulting coating quality. Coating powders are typically extremely fine and cohesive, and hence are prone to agglomerating to form large clusters. Industrial powder coating requires these coating powder agglomerates to be consistently broken down to single particles and precisely delivered to the host. We will establish how the process can be tailored to enhance the ability of the system to achieve this for any powder. By determining the underlying principles of powder coating, and the influences of material properties and process parameters, we will create a regime map for dry powder coating, which will enable industry to tune coating operations to minimise powder and energy use.

The proposed research will achieve impacts in terms of knowledge, economy and people. In terms of knowledge, we will determine how coating is achieved on the fundamental, particle level, in order to optimise mixer design and operation; creating a regime map for dry powder coating. The developed framework will establish the fundamental science behind powder structuring in response to mechanical application. This knowledge will in itself be transformative, by allowing precise control of a single powder layer to be achieved. This also has far-reaching implications for industrial processes, such as dry powder spray-coating (e.g. of automotive and aviation vehicles), and additive manufacturing. Knowledge of the optimal combination of material properties to deliver dense, even coatings, will enable new coating materials, application methods and operational conditions to be developed.

In terms of economy, the improved understanding of coating mechanisms and optimisation of mixing processes developed in this research will lead to increased efficiency in pharmaceutical dry coating processes, through improved powder utilisation, reduction in waste batches and reduction in energy use. This will provide significant savings in resources (material and energy) and processing time. In the short term this will provide the greatest benefit to the UK pharmaceutical industry, a flagship of the UK manufacturing sector. The natural extension of this research to powder spray-coating and additive manufacturing will provide economical advantage to the UK automotive and aviation industries.

In terms of people, this research will train researchers to become highly skilled experts on powder structuring, mixing and surface interactions of powders. There is a distinct lack of this knowledge within the pharmaceutical sector, and so the trained researchers will be of great value to the UK workforce. The training of these researchers will be enhanced by (i) exposure to the UK and international research community through active conference attendance and participation (ii) in-coming and out-going visits between university and industry (iii) co-supervision of PhD and Masters Student research projects with the PI/Co-I in areas related to the project (iv) access to a wide range of training courses at the University of Surrey/Imperial College to boost their skills and develop their career, including public engagement training.