44 MANUFACTURE
Colour/aspect: The visual appearance of the emulsion is closely related to droplet size. A microemulsion, with smaller droplets (0.1 to 0.01µm), will appear more transparent, while a coarse emulsion, with larger droplets (10 to 102µm), will take on a milky white appearance. This affects the aesthetic appeal and perceived quality of the product. Application on the skin: The selection of
fatty substances and the emulsion type (W/O or O/W) directly affects how the product interacts with the skin. These factors determine the absorption rate and penetration depth of the product, allowing for formulations that either provide quick absorption or create a richer, more protective layer on the skin. This customization ensures that products can cater to different skin needs, from fast-absorbing lotions to balms that offer long-lasting hydration.
Challenges in clean-label emulsification In regular emulsification processes, the use of conventional emulsifiers helps maintain emulsion stability. Thickeners help prevent phase displacement, such as creaming or sedimentation, while surfactants enhance repulsion between droplets, ensuring uniform dispersion. In clean-label formulations, manufacturers aim to eliminate synthetic ingredients, including emulsifiers, to create a ‘clean’ ingredient list. However, natural emulsifiers—such as
lecithin, proteins, and certain plant-derived compounds—often provide less stability than their synthetic counterparts which can lead to instable emulsions. This may include temporary changes that can be restored by stirring or more destructive phenomena, such as phase separation. There are several emulsion destabilization mechanisms: Creaming/sedimentation: when a phase
stagnates at the surface of the emulsion or at the bottom of the container used. This will depend on the density of the phases and the type of emulsion (O/W or W/O). These phenomena do not lead to the destruction of the emulsion, and it can be restored by mixing again. To prevent this, the viscosity of the continuous phase must be increased. Flocculation: the droplets will aggregate
together and form clusters. This phenomenon can be avoided by improving the repulsion phenomenon between the droplets, either by increasing the viscosity of the dispersing phase or by adding emulsifiers. Coalescence: This phenomenon is close
to flocculation, the difference being that the droplets obtained will come closer together and merge again, which leads to a phase break. The two phases separate, and the emulsion is broken. To avoid coalescence, other phenomena must be prevented, which requires better dispersion, an appropriate emulsifier, and proper viscosity. Since we can no longer rely on synthetic
emulsifiers in clean-label formulations, the key to preventing phenomena like phase separation, flocculation, and coalescence lies
PERSONAL CARE June 2025
Figure 1: Types of emulsion. The figure depicts two of the three types of emulsion: A Oil-in-Water (O/W) and B Water-in-Oil (W/O)
Phase inversion
Kinetically stable nano emulsion
inversion Phase
Creaming
Sedimentation
Flocculation Figure 2: Mechanisms of emulsion destabilization. Source: VMI
in selecting the right mixing parameters and technologies to optimize the emulsification process.
Key parameters in the emulsification process The stability of the emulsion is essentially related to the size of the droplets of the dispersed phase, their surface tension and their distribution in the dispersing phase. Optimizing the emulsification process is essential for overcoming the challenges of clean-label formulations. Several parameters play a pivotal role in achieving stable and high-quality emulsions:
Mixing tool The choice of mixing technology and the
geometry of the mixing tools and bowl are critical to achieving a stable emulsion. High- shear mixers, rotor-stator systems, and other technologies generate the shear forces necessary to break down droplets and ensure even distribution. The design of the mixing tool and the bowl shape directly influences the flow dynamics, ensuring that the product is consistently mixed and that fine droplets are formed.
Mixing parameters Shearing rate and speed: Shear rate refers to the force applied to break down droplets during emulsification. High shear rates are necessary to create fine droplets and enhance emulsion stability. However, excessive shear can lead to droplet coalescence, highlighting the need for precise control of mixing speed.
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Coalescence
Ostwald ripening
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