40 SAMPLING
Figure 5: Microscopy images for the cutter blade samples at 10 x magnification (left) and 20 x magnification (right) This was evident by the settling of the
emulsion droplets had been formed. The samples produced with just the polysorbate showed the most uniform dispersion, whereas the sample with cetearyl olivate and sorbitan olivate had non uniform platelet artifacts. This is thought to be the mica which is of 10-60 µm in size.
The sample made with cetearyl olivate and
polysorbate 60 indicated some larger artifacts which is thought to be a portion of cetearyl alcohol, which potentially crash cooled on addition to the batch. The particle size by laser diffraction showed minimal differences between the samples, with broad peaks ranging from approximately 5-100 µm, this is thought to be due to the detection of the kaolin and mica, and not just the oil droplets. As the stated particle size is 25-35 µm for
the kaolin and 10-60 µm for the mica there may be some agglomerates present, which could be reduced by further homogenisation of the batch or by pre-milling of the solid materials. Therefore, it is suggested that if a specific size of the oil droplets is needed, a different technique should be deployed. The stability of the different formulations
was tested by acceleration through the use of a centrifugal force, followed by analysis using spectral transmission. Although the centrifuge managed to force separation, and visibly show differences between samples, the instability index, did not correlate to what was visibly apparent. The instability index is based on differences between the spectral transmission of a batch of samples, with a higher number indicating a higher degree of instability. Again, due to the large particle size
materials incorporated in the formulation, the transmission signal not only picked up the separation from the oil phase but also the kaolin and mica. Microscopy was then used to support the
sample analysis and showed that the sample with the higher inclusion level of cetearyl olivate and sorbitan olivate was the most stable and the sample with the lower level of polysorbate 60 was the least stable.
PERSONAL CARE June 2025
coloured mica. This is not surprising as the cetearyl olivate and sorbitan olivate form a liquid crystal at the oil and water (O/W) interface, whereas the polysorbate 60 does not. Again, further developments of spectral analysis would be suggested but the use of centrifugal force to accelerate instability is sufficient. Both rotational and oscillatory rheology
measurements were conducted to evaluate differences between samples. For the rotational rheology, viscosity measurements were recorded when samples were subject to shear rates from 0.1-100 reciprocal seconds. Viscosities of the samples with the lower melting point emulsifier (polysorbate 60) were lower than that of the samples made with higher melting point liquid crystal materials (cetearyl olivate and sorbitan olivate, and cetearyl alcohol with polysorbate 60), which is expected. All samples showed shear thinning
behaviour which is standard for a product that needs to be applied to the skin. The oscillatory rheology supports this and shows that all samples showed elastic behaviour below 10% strain amplitude but at 100% strain amplitude, most turn plastic. Again, the samples made with the
polysorbate 60 showed a lower tan delta value, meaning they are most elastic in behaviour, compared to the other samples. This part of the project has demonstrated
that automated platforms can be used to successfully make complex formulations with a wide variety of material types. Limitations have also been found in the dispensing of high melting point materials using the heated HV, with some improvements required for the efficiency of dispensing materials similar to that of kaolin. Developments can be made through engineering efforts from the robotic manufacturers or through minimal manual interventions.
Conclusion To conclude, this project proves that
automated techniques can produce similar results to those produced via classical benchtop techniques. Opening the use of robots in the research and development space will offer the production of large quantities of samples with potential efficiencies in processes. However, evaluations would have to be
made on whether the front-loading of the automated processes outweighs the potential time savings from the actual mixing of the batches. Preparations for a robot run include writing
the workflows and prepping materials, in the form of working out dispense parameters and decanting into robot-compatible vials. Suitability of batch sizes would also need to be considered as they are limited by the robotic specific formulation vessels or vials that fit into the engineered racks. Nevertheless, robot workflows
automatically record more precise and accurate parameters such as mixer speed, vial temperatures and run times. With 12 formulation vessels, it means that 12 emulsions could be made in one run, leaving the operator free to plan more experiments or process data. Although the analysis of these samples
was performed manually, developments in the industry will mean more techniques will become available and part of the workflow as standard in the future. This project has demonstrated the use of
automation for emulsion preparation, needing high shear mixing from rotor-stator mixers but robotic platforms can be used for a much broader cosmetic offering. Samples of smaller volumes and that
do not need high shear mixing are ideal candidates for robotic platforms, with shaker racks holding up to ninety-six 20 mL vials, a large throughput of samples can be performed. It is hoped that this study has
demonstrated the sound potential robotic platforms have in supporting formulators with their innovations, transforming the future of the personal care market at an accelerated rate.
PC
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