Predictive formulation of high-solid-content complex dispersions

High-solid-content dispersions of solid particles of size about 1-50 microns in a liquid phase (HSCDs) occur ubiquitously in industrial applications, from cement and ceramic pastes to catalyst washcoats, paints, foods and drilling fluids. The reliable and efficient processing and manufacture of these diverse products presents 'grand challenges' to formulation technology because at high solids volume fraction process flow and product behaviour become increasingly unstable and unpredictable. But achieving high volume fraction is often desirable in many applications: in generic process flow, to maintain throughput and cut energy/materials costs; in ceramics manufacture, higher volume fraction green bodies sinter to mechanically stronger products; increasing volume fraction of a slurry for spray drying reduces drying time; higher volume fraction drilling fluids reduce problems of fluid and gas influx and collapse in bore holes. Conversely, unstable flow at large viscosity is sometimes actually desirable, as long as it is predictable, e.g., in breaking aggregates to disperse catalytic converter washcoats or pigments in a mixer.

In all these applications and many others the ability to control and predict rheology for a given formulation--to 'dial up' required behaviour--would transform formulation science and practice with HSCDs. However, experience repeatedly shows that as volume fraction increases, the flow and stress become increasingly unstable, and characterization, measurement, control and prediction increasingly challenging and unreliable. Conventional rheological characterization of HSCDs is often poorly reproducible and also fails to predict correct flow behaviour in the complex, non-rheometric geometries encountered in applications. Notoriously, small changes beyond the manufacturer's control, e.g. due to unforeseen variations in processing conditions or a change in supplier, can have catastrophic effects (e.g. a normally flowable formulation can suddenly fracture rather than flow). On top of this, industrial applications span many length scales, from < 100-particle-diameter extrusion mouldings and printed films to kilometre-deep bore holes so that predicting and characterizing HSCD flow faces the simultaneous requirements of scale up and scale down. Faced with these ubiquitous challenges, and because the basic science of flow at high volume fraction is not understood and predictive engineering tools are not established, formulators often resort to accumulated experience and informal procedures such as 'finger rheology' (rubbing samples between fingers!) to guide their work. Thus, existing formulations are often sub-optimal, and problems arising from these formulations are solved mostly by trial and error, while the risk associated with formulation innovation severely limits development of new products and processes.

Our vision, inspired by recent major scientific advances by members of the project team, is to transform practice in the formulation of HSCDs through a tight collaboration of researchers and major multi-sector industry partners. Our new scientific understanding will provide new methodology of characterization, measurement, prediction and control, leading to reliable process and manufacture of HSCD-based products. The project will enable manufacturers to formulate their products according to rational design principles, using parameters deduced from well-characterised reproducible flow measurements. This approach will yield step changes in control and predictability over multiple length scales and multiple application sectors.

The proposed research could benefit manufacturers, industrial and end users of HSCDs and the general public through improved product quality and energy efficiency, and wealth creation as described in the following.

HSCDs are important as intermediate or final products in chemical, pharmaceutical, personal care, food and oil & gas industries. All of these sectors are crucial to the UK and global economy, e.g., the chemical and pharmaceutical sectors alone are worth £113B in the UK and represent 12% of total manufacturing; drilling fluid and cement have approximately £4B market (2012-13) in the UK supporting oil and gas production. Needless to say, these sectors are also global and the UK has the potential to lead innovations by solving key research questions.

Processing HSCDs represents one of the main items of the energy budget in many cases. In lieu of design principles based on fundamental understanding, uncontrolled processing and product failures are common. The establishment of design principles based on sound fundamental understanding will therefore reduce energy and raw materials consumption, increase manufacturing throughput, and speed up the innovation cycle.

Formulation of such products becomes increasingly crucial to high value manufacturing as industries move towards high-margin customer-specific products, new products, or new processes. The predictive formulation capability we will generate should enable partner companies to optimise products, operate processes at lower costs, giving them a competitive edge in innovating new products, e.g. high-solids paints or washcoats with superior drying properties, or new 3D printing processes using designer pastes.

Many of the products and sectors above have an exceptional impact on everyday life, ranging from pharmaceuticals and foods to personal care products, cosmetics and decorative products. Hence, the impact of the work will extend beyond the scale of simply efficiency or cost improvements for manufacturers, towards production of better products that can improve health and wellbeing. Through the project we will seek to engage with wider audiences, improving education about and appreciation of the importance of high-solid-content dispersions and processing and their significance in everyday life.

Impact activities will include scientific workshops, sandpit 'grand challenge' events, SME-focussed Industry Clubs, public and social media engagement, and key skills training for project staff. Impact will be further promoted by the highly integrated group of industry partners, ranging from specific global companies (Johnson Matthey, Schlumberger, DuPont, Chemours, AkzoNobel) to key innovation and impact promotion centres such as the National Formulation Centre and the Centre for Process Innovation.