38 SAMPLING
the rotor-stator head still had a layer of oil on the top of the batch. After ten minutes, the dispersions looked similar with both showing some unincorporated material. Microscopy images showed that both mixing methods had produced similar-sized droplets, all of which looked to be below 100 µm. Although both types of mixing heads
produced similar results, it was decided that only the rotor-stator head would be taken forward and used in contrast against the benchtop equipment, as they were most comparable. An investigation of both robotic and benchtop cutter blades would be something of interest for a future project.
Robotic versus benchtop emulsion preparation The next phase of the project involved producing emulsions on the robotic and benchtop equipment at three different speeds with particle size assessments being made after five, ten and 15 minutes. For the benchtop mixer, this was 2000 rpm, 4000 rpm, and 8000 rpm; for the formulation vessel 1500 rpm, 3000 rpm, and 6000 rpm. For the overhead robotic rotor-stator mixer, 12000 rpm, 16000 rpm, and 20000 rpm. Again, for this section of the project, a basic emulsion used for the previous test was prepared, with a base formulation of water, xanthan gum, and glycerine being prepared on the benchtop equipment. The xanthan gum was premixed into the glycerine before being added to the water and sheared at 2000 rpm for five minutes. For the processing to be comparable to the classic benchtop recipe, the mixing regime had to be translated into a robotic workflow. This consisted of many more steps as one task for a human operator such as ‘mix for five minutes’ has to be broken down into several steps, for example, ‘switch agitation on, wait five minutes, switch agitation off’. An example of the robotic workflow for the initial agitation is as follows: agitation on, scraping on, wait five minutes, agitation off, scraping off, wait for five minutes. Samples would be analysed then this process would be repeated for a further two times five-minute mixing regimes. As this part of the project was just to establish the difference in mixing techniques, materials were manually added to the formulation vessels (once the agitation had stopped and it was safe to do so). Particle size distributions of the
formulations were assessed using laser diffraction. For the Formulation vessel and overhead robotic mixer, the results showed that mixing time had minimal impact on the particle size with the mean particle size remaining between 2-4 µm at each testing point. The data for the benchtop equipment was inconclusive so a further investigation into the effects of time using this method would have to be conducted. To compare the effects of mixing speeds,
the particle size analysis was compared after 15 minutes of mixing. As to be expected, as the mixing speeds increased the particle sizes decreased. The benchtop mixer and
PERSONAL CARE June 2025
Wall Shear Stress: Magnitude (Pa) 3000.0
2400.0 1800.0 1200.0 600.00 0.00000
Figure 1: CFD model of stress areas of rotor stator mixing head on robot platform
Wall Shear Stress: Magnitude (Pa) 3000.0
2400.0 1800.0 1200.0 600.00 0.00000
Figure 2: CFD model of stress areas of cutter blade mixing head on robot platform
formulation vessel showed comparable data at each mixing speed and at their highest speed settings, the benchtop and formulation vessel showed comparable results to the overhead robotic mixer. The overhead robotic mixer was largely independent of mixing speeds and showed a mean particle size of 2-4 µm at each speed. This is expected as the slowest speed setting for the overhead robotic mixer is double that of the formulation vessel. Microscopy images supported these findings. In summary, this work has demonstrated
that comparable formulations can successfully be produced using robotic platforms and classic benchtop equipment. This offers confidence in the results from the automated
platform and offers efficiencies by way of not having to make a comparative batch for every robotic run, as well as offering a starting point for a high throughput campaign in terms of translating mixing speeds from a benchtop process into a robotic workflow. Indications are also provided that if very high shear is needed the overhead robotic mixer should be considered.
Exemplar workflow design The second package of work for this project was to test the capability of the robotic platform as a whole, by producing more complex formulations with subtle differences, to represent a typical research
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