SAMPLING
39
Mixing Capability
Robot
Formulation Vessel 1: Homogeniser
and development campaign. A coloured face mask formulation was chosen as this is produced using a range of materials, including high melting point waxes and powders with different particle sizes. A total of six different formulations were
made to represent a classic comparison study. This involved using a blend of different emulsifying agents per batch. The emulsifiers chosen were cetearyl olivate and sorbitan olivate, cetearyl alcohol and polysorbate 60. The full formulations contained water, kaolin, fractionated coconut oil, glycerine, preservative, mica, xanthan gum and lavender essential oil. Common analytical techniques in the form of microscopy, particle size distribution by laser diffraction, rheology and accelerated stability by centrifugal force, were used to assess the differences between batches. To accommodate the wide range of
materials and mixing needs the following parts of the robotic platform were tested: the heated high viscosity liquids dispenser, for the high melting point emulsifiers; the heated vial racks, which accommodate 20 mL glass vials, for the premix of polysorbate 60 and the oil phase of the sample. As part of the platform’s dispensing
Formulation Vessel 2: Cutter Blade
Figure 3: Flow diagram breakdown of the projects and the mixers used
capability, materials are dispensed gravimetrically with a mass loss system using the system’s gravimetric dispense units, also known as GDUs. For this project, the tools used were the GDU-V for the dispense of low-viscosity liquids; gravimetric dispense unit-P (GDU-P) for the kaolin and the solid dispense unit (SDU-P) for the xanthan gum and coloured mica. Dispense parameters for each material
were established independently before the run, to allow for a more efficient campaign. This establishes parameters such as chunk size, speed and levels of slow and fast dispense steps and precision of dispense. The formulation vessels with the rotor-stator mixer (as before) were used as the main mixing vessel. As this part of the project was to assess the capabilities and limitations of the automated platform comparisons to benchtop equipment were not made, as material preparation and incorporation at the bench top is well established. To facilitate the dispersion of the xanthan
gum in the water phase the glycerine was added to the water phase first, using the GDU-V. The mica was then dispensed before the scraper arms and agitator (rotor-stator mixer) were initiated. The formulation was
then mixed until dispersed. The shear was then turned off, but the scraper arms left on, before the kaolin was added, to reduce the chance of forming a dust cloud. It was mixed until fully incorporated. The heating was started and the vessel’s temperature increased to 60°C before the addition of the different emulsifier blends. Coconut oil followed and the whole batch was subject to shear until the emulsions looked uniform. The formulation vessels were then cooled to below 40°C before the addition of the lavender essential oil and preservative. The batches were then mixed for two minutes, to allow for incorporation of these materials. Although the dispensing part of the
campaign was largely successful there were some areas for improvement. The addition of the higher melting point materials proved difficult using the heated-HV, so a manual addition of these materials was chosen, after being heated up in an oven. Although the kaolin dispense parameters were optimised for the most accurate weight dispense, in practise the dispense was slow and would therefore have to be improved upon in the future. After the mixing regimes were complete, the
samples were removed from the formulation vessels and taken for analysis. Microscopy images indicated that uniform
ULTRA TURRAX
Benchtop Silverson
Figure 4: Microscopy images for the homogeniser head samples at 10 x magnification (left) and 20 x magnification (right)
www.personalcaremagazine.com June 2025 PERSONAL CARE
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