Closing the costly knowledge gap in predicting fluid stability

In the world of formulated fluid products, there is a costly knowledge gap in being able to predict a fluid’s stability. This has been the focus of a highly successful collaboration between Procter & Gamble (P&G) (the world’s largest consumer products manufacturer) and UNSW’s School of Chemical Engineering Complex Fluids Group. 

“Yield stress” probably isn’t top of your mind when you reach for your shampoo, shaving gel or mascara, but this property is absolutely critical for the integrity of these types of products.

Our specific research aim was to incorporate existing and new theories into a quick and simple predictive test that could identify whether stability would hold or not

A/Prof Patrick Spicer

The majority of formulated fluid products (including cosmetics, foods and pharmaceutical preparations), remain physically stable during their shelf-life as a result of yield stress, which makes it solid-like at rest, but fluid-like when sufficiently disturbed.

As a result, robustly manufacturing and controlling yield stress fluids is a central goal of formulated product design; but according to P&G the biggest technical delay in moving a product from concept to market is the experimental time required to test the long-term stability of product suspensions. Because the failure of yield stress suspensions cannot be predicted, it typically requires from two to 12 months to test each new formulation’s stability.

Considering the costs associated with this testing period, not to mention the competitive advantage that may be lost during this time, Associate Professor Patrick Spicer says it is highly surprising that there is no theoretical or empirical model that can predict whether a given formulation’s bulk physical properties will stabilise a known load of suspended particles, or for how long. “This kind of capability would vastly accelerate new product development,” says Spicer who is a co-founder of UNSW’s Complex Fluids Group.

This issue was why he was particularly interested in teaming up with P&G to develop new ways to characterise these fluids. “This project is about linking the processing history of a fluid to its microstructural length scale distribution, its yield stress, and its stability,” continues Spicer, who previously formed P&G’s Microfluidics and Structured Fluids research group before joining UNSW in 2012. 

“Our specific research aim was to incorporate existing and new theories into a quick and simple predictive test that could identify whether stability would hold or not. The idea was to reduce dependence on some of these long-term empirical tests.” The project examined the creation of networks of cellulose fibres in consumer products as these can keep products stable for much longer shelf lives.  The image shows a dispersion of these tiny fibres, with bubbles trapped in their network, and a zoomed-in photo of the fibre network from a microscope.

With the four-year project now coming to a close, Spicer says they have made great progress, but he stresses that much of the credit must go to his PhD student, Jie Song, who has been in charge of the experimental studies.

“Jie made such ready progress at the beginning of the project that we were soon able to think more broadly about what we could do with the insights gained. She has developed an innovative small-scale testing unit which has shown such fascinating results that P&G have invited her to their headquarters in the United States for several months, at their expense, to continue the work. I think this recognises both her capability and just how important the project has been to them.”

Spicer says the most satisfying part of working on this type of project is being linked to the newest developments in industry while still being able to ask really interesting, fundamental questions. “These two systems feed back into one another nicely and I love sitting in the middle of that,” continues Spicer who says the research has generated many more ideas for projects with P&G in the future.

“Development and testing of a new means to evaluate fluid rheology and be more predictive about our product and material stability is a great outcome. We’re also delighted to be able to bring the PhD student on the project, Jie Song, to our Research Centre in the US for a six-month project with our group. Projects like this are an excellent way to expose talented technologists to applied problems. They also enable us to learn from, and sometimes recruit, top talent.” Marco Caggioni, Senior Engineer at Procter & Gamble

 

Partnership in Summary

Partner: Procter & Gamble

Type of partnership: Contract research  

Funding: $80,000 over four years (funded by P&G plus in-kind support)

Purpose: Close an important knowledge gap by linking the processing history of a fluid to its microstructural length scale distribution, its yield stress and its stability.
Outcomes: An innovative small-scale rheometer that can test

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