Detailed review of Freeman Technology FT4 Powder Rheometer

How did Evonik identify the potential of the FT4 and how was investment justified?

Silica is added to a very wide range of products to, for example, enhance dispersion, prevent caking, control fluid rheology, and as a defoamer. Multiple industries rely on silica to improve powder flowability. Evonik offers a range of precipitated and fumed silica products to deliver this diverse functionality, customising solutions to meet the specific requirements of individual applications. A rigorous understanding of the mechanisms associated with the beneficial performance of silica is therefore business critical. The company has long invested in equipment for powder flow testing.

“Around 35 years ago we developed some home-grown methods for assessing powder flow using funnels we made in-house,’ said Chris Proulx, Technical Director for AEROSIL® and SIPERNAT® silica products. 

“We’ve refined these funnels over the years, and we still offer them to our customers as a useful tool for a simple, flow through an orifice type assessment. We’ve also worked with tapped density methods, Carr’s Index measurements, angle of repose, shear cell, and compressibility among others but in truth, these methods work in just one-dimension. They simply can’t provide the information we need in an efficient way. For example, it will take about 20 minutes to measure the angle of repose for a pharma formulation.  In that time, we can do many measurements with the FT4.”

“When I first saw the FT4 at a show, well over a decade ago, I could see it had real potential to rationalise and prove how our products worked, notably in pharma where there was already clear evidence of successful application. It was also evident from the outset that engineers had a real affinity for the instrument, which was helpful in encouraging uptake and use of the data. Extending our understanding of powder behaviour is an ongoing task and it soon became obvious that the FT4 held the key to improvement.”

Further investigation of the instrument, including sample testing, confirmed this early assessment of potential, with investment initially justified to support a significant sale into the food industry. Evonik offers a wide range of potential products, with specific performance advantages depending on the specific use case.

“This device allowed us to demonstrate comprehensive understanding of industrial applications and demonstrable performance of our products to solve problems. The FT4 delivered key data and proved pivotal to securing business.”

How easy is it to learn how to use the FT4?

Today training on the FT4 cascades easily through Evonik with subsequent ‘generations’ of scientists rapidly brought up to speed by those that precede them. A two-to-three hours initial hands-on session is typical, and the instrument is commonly handed over to interns because it’s one of the easiest for inexperienced scientists to generate useful and reliable information with. However, what was it like for early users? And what is it like when you’re first getting started?

“Although the FT4 generates a lot of data, it proved to be a straightforward instrument to learn,’ said Chris Proulx, ‘and there is a lot of support available. The website is rich in useful, relevant content and the company is both responsive and knowledgeable, providing excellent support whenever needed. Measurements are quick relative to all those traditional methods because it is doing several tests at the same time. You can actually generate a lot of useful data in a relatively short amount of time.”

“The instrument guides you through all the tests you need” says Vikram Devarajan, Managing Director Structured Polymers, “with pictures and instructions for every step of the test. So, training requirements are minimal even when starting from scratch – it’s not a steep learning curve. Straight out of the box you get a comprehensive toolkit for powder testing.  The documentation that comes with it is very good.”

“The standard test protocols, level of automation and software make the FT4 genuinely user-friendly,” agrees Jonathan Gorka, Application Scientist. “Prepping and running samples is very easy, so you can quickly be producing significant amounts of information. There’s a balance to be struck in powder testing between the ability to customise methods and ease of use of the instrument. Some instruments offer greater flexibility to customise but the price is greater complexity and a much steeper learning curve. The FT4 has the balance just right. You can tailor testing to the extent you need to, but the basics are all in place to get you productive, rapidly.”

What information does the FT4 generate and how does it elucidate powder performance?

“The FT4 allows you to bridge the micro and the macro,’ says Saiid Mohammed, Sr Technical Marketing Manager. “What I mean by that is that it allows you to see the bulk effect of changes made at the particulate level. The silica we use often has a very fine particle size and impacts behaviour by attaching onto larger substrate particles. We can look at attachment, particle surface coverage and associated changes in morphology with techniques such as scanning electron microscopy, but we need to understand the practical benefits. What the resulting changes in particle interactions mean in terms of application relevant properties such as flowability. This is the information we get from the FT4.”

Scientists at Evonik use the full functionality of the FT4 which includes dynamic, shear, and bulk powder testing capabilities, and everyone is keen to emphasise the importance of applying different testing protocols to gain multi-dimensional insight into any given powder sample.

“It’s like completing a jigsaw,” continues Saiid Mohammed, “Each test provides you with a separate piece. Shear cells tell you one part of the story, then you add in say compressibility and permeability, and learn more. We almost always apply the baseline dynamic test protocol and aeration testing is often uniquely valuable too. It’s a thrill to see all the pieces of the puzzle laid out in front of you and to slot them together to develop the robust understanding needed to optimise a customer solution.”  

For applications such as 3D printing the dry flow behaviour of powders is particularly important and the ability to repeatably quantify flowability is a defining focus. On the other hand, shear cell testing has proven especially illuminating for detergent characterisation, where the requirement is to elucidate interactions in powder systems made sticky/tacky by the addition of liquid surfactants. “As the mixture becomes more saturated with surfactant, we can measure the effect on cohesion easily.  We can also measure the effect of shear on release of the surfactant.” Cohesion is also a useful parameter when it comes to assessing the amount of liquid a formulation can hold, for applications that call for absorbency.

However, the theme of multi-faceted powder testing is one the group repeatedly return to.  

“Having the FT4 is like having multiple testers in a single instrument and the language of powder rheology really resonates with me, because of my background in liquid rheology,” says Christina Sotelo, Scientist, Personal Care and Cosmetics.

“In the personal care sector, we use rheology to bring science and statistics to subjective assessments of product quality and desirability and I’ve been able to do that successfully with the FT4. By comprehensively testing ingredients such as corn starch, mica, and talc I’ve identified properties that quantify ‘silkiness’. We can also directly investigate the effect of moisture absorption, another critical parameter for body powders. With those measurements we have been able to add our ingredients to a basic formula to improve the silkiness of a formula which is perceivable in panel studies.” 

“I often find that permeability and compressibility are really differentiating when it comes to detecting the impact of silica on the polymeric powders I test,” said Jonathan Gorka. “Permeability is notably sensitive to the presence of fines which can have a major impact on powder performance.  Plastic powders can become a solid block when under pressure.  Our additives can modify the packing of the particles.  On the other hand, dynamic flowability parameters are good at distinguishing the effects of electrostatic build up, which can be problematic for low conductivity powders.   With the FT4 we can see these problems in the powder and solve them with our products.”

“It really is valuable to apply a variety of tests efficiently to see value-added selling points for our products.   For example, we can measure the effect of pressure and shear on a powder with liquid absorbed and see a measure of how much of our product is needed in the formula, how durable the mixture is, and how will it flow when filling packages.”

What have been the top line benefits of having an FT4?

For Evonik working with the FT4 has delivered benefits in three main areas. First is greater efficiency and savings in time and money. Second is the ability to solve technical problems and come up with robust, rationalised solutions that answer directly to customer requirements. Finally, the increase in credibility notably with customers who see us as an expert in this field but also with other parts of the business.

“When we’re developing new polymeric powders for 3D printing, we might screen as many as 500 formulations,” said Vikram Devarajan. “With the FT4 we can make a 100g of each and rapidly narrow down our options from test data. We can tell whether a formulation is overlubricated and eliminate bad candidates without a print trial. This can easily save around two months of printer time – a major gain with respect to faster progress and waste reduction.”  

“A project we carried out for a pharmaceutical manufacturer provides a nice example of the depth of understanding you can reach with the FT4,” said Chris Proulx. “We were approached to improve a formulation for patients that was failing in the packaging process.  Many pharma formulations make it through all the drug development stages only to fail in drug delivery.   The powder became too sticky to flow easily into the package the more it was mixed and conveyed.   The active ingredients were leaking from the granular formulation due to friction on the granules.  We determined with the FT4 how much shear would cause a rise in cohesion and which and how much flow additive to use to reduce friction in the formula which reduced stress on the granules and solved the cohesion problem during packaging.”

“The FT4 is iconic,” says Saiid Mohammed. “When you tell customers you use it, they are predisposed to working with you because it is indicative of the level of expertise and service you offer. You’re effectively selling an advanced ability to diagnose and solve powder processing problems, that positions you as a strong partner. When I present FT4 data I’m never challenged on its quality and I have a high degree of confidence in it, I know the science is sound. These are extremely important gains for our business.”

This latter point regarding data integrity is echoed by the others in the group. Learning to interpret it, for example, experience with the terminology, understanding the capabilities of the machine, experience with particle metrics and in-process performance, can take time but is worth the effort as the insights above demonstrate.

What advice would you offer to anyone looking to optimise their approach to powder testing and/or considering the FT4?

There’s some practical advice for FT4 users…

“Be sure to rigorously follow the test procedures each time,” says Dr Abhi Bhat Sr Scientist, Structure Polymers. “They are well-defined and it’s important to stick to them. Steps like the conditioning cycle mean that you can expect very high repeatability from the FT4 and minimal operator-to-operator variability, but you need to follow a few simple instructions to safeguard optimal performance.”

“We’re actually beginning to transfer the FT4 into production, for product QC,” adds Vikram Devarajan. “Repeatability and ease of use are important factors in this environment, but we are confident that the FT4 will perform well on both counts.”

All agreed with a striking degree of consensus when it comes to more general advice for powder testing which is don’t try to make sense of powder behaviour with just a single piece of data.

“Once you have the capability to measure multiple parameters in a relatively short timeframe you can discover which properties are most relevant to your application,” says Christina Sotelo. “It’s a bit like forensic science and you need to gather your evidence. You develop a checklist to work through – permeability, aeration data, shear etc. The core dynamic test is universally relevant though – we all apply the repeated measurement of Basic Flowability Energy/Variable Flow Rate test protocol.” 

“I’d certainly like to go back and advise myself to stop spending so long trying to make sense of just one piece of information,” says Saiid Mohammed. “It’s so much more efficient to run a range of tests, put all the information in front of you and then piece together the story. The more time I spend with the instrument, the more I learn but that’s certainly a lesson that could have saved some hours in the beginning!”

“It takes time to understand what the FT4 is telling you, to interpret the data within the context of your powder and application,” says Chris Proulx. “Powder behaviour is complex but being able to generate reliable, multidimensional data is a critical first step to solving formulation and processing problems. We now have a large database of FT4 data to draw on. These data never age so we can use them to elucidate new problems, to predict how novel formulations will behave. We continue to learn but it becomes easier and easier to understand and control the behaviour we see with our additives.”

In conclusion

Talking to the scientists from Evonik it’s clear that the FT4 is a trusted, well-used and valued instrument that has earned its place in the lab. There’s no skirting the issue that it’s taken time to learn to fully use the data – though not the instrument, an important distinction – but the pay-off has clearly been worthwhile. No instrument can eliminate the complexity of powders. Rather, by providing precise, relevant, and reliable data the right instrument can help those working with powders to exploit that complexity to devise robust and rewarding industrial solutions. Experience at Evonik demonstrates what is possible.