MANUFACTURE Flow rate and mixing time: Flow rate
determines how efficiently the product circulates through the mixing system. Consistent flow ensures uniform emulsification and prevents localized instabilities. Mixing time must also be optimized to avoid over- processing, which can degrade sensitive natural ingredients.
Temperature Temperature plays a crucial role during emulsification, particularly for lipid-based ingredients that require melting. Maintaining the ideal temperature range prevents premature crystallization and ensures proper phase combination.
Technologies of emulsification Several technologies are used for emulsification, depending on the application and industry, i.e. cosmetics, food, chemicals etc. ■ Mechanical agitators. The most common method involves a vessel with an agitator that mixes the phases. ■ High-pressure homogenizers. These devices apply high pressure to the liquids, mixing them while breaking one liquid into smaller droplets dispersed in the other. ■ Static mixers. These use micro-channels and internal structures to reduce the droplet size of one liquid and mix it into the other. They are often used in specialized applications like foams. ■ Ultrasound technology. Commonly seen in bioprocessing, ultrasound helps create small droplets through high-frequency vibrations. ■ Membrane emulsification. A newer technology where liquids pass through a membrane to create droplets, ensuring precise control over size distribution. One technology belonging to the
mechanical agitator type that stands out, particularly in the cosmetic industry, is the rotor-stator. Rotor-stator systems are widely used in the cosmetic industry for their ability to generate high shear forces and produce fine, stable emulsions.
Focus on rotor-stator emulsification Rotor-stator systems are widely used in
45
Suspension Rupture (dmax)
Coalescence (dmin) STABILITY
Mixing speed (N) Figure 3: Influence of mixing speed and droplet size on emulsion stability. Source: VMI
industries such as cosmetics and food for their ability to generate high shear forces, producing fine and stable emulsions. These systems consist of two key
components: the rotor, a mobile, rotating part that generates movement and shear forces, and the stator, a fixed, non-moving outer part that works with the rotor to create turbulence and shear. The rotor rotates within the stator, creating a flow of the product between the two components. The product is sucked through openings at
the top and bottom of the stator, then forced into the narrow gap between the rotor and stator, where high shear forces break down droplets. The product exits through openings on the sides of the stator, ensuring thorough emulsification through radial flow as it repeatedly enters and exits the system.
Rotor-stator geometry The design of the rotor-stator—including
Suction from above
Stator
Shearing zone
Rotor-stator Geometry
Shearing/flow rate Mixing time
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Radial discharge
Rotor
Suction from below
Figure 4: Rotor-stator characteristics and design. Source: VMI Air gap
the geometry and gap size—directly impacts the efficiency of emulsification. Smaller gaps generate higher shear forces, enabling finer droplet sizes. This is particularly beneficial for clean-label products, where natural emulsifiers require enhanced mechanical action to achieve stability.
Advantages of rotor-stator systems Rotor-stator systems offer several advantages, including the ability to produce fine droplet sizes as small as 0.5 microns, which results in highly stable emulsions. They also ensure consistency, which is essential for applications in clean-label cosmetics and food products. Their versatility of geometry allows them
to handle various viscosities and ingredient combinations, making them suitable for a wide range of formulations. In clean-label products, where natural
emulsifiers like lecithin or proteins are used, rotor-stator systems provide a distinct advantage. The high shear rate compensates for the reduced emulsification capacity of natural ingredients, ensuring a stable, uniform product that meets consumer expectations for both performance and ingredient transparency.
Case study: Clean label formulation strategies with different types of rotor-stator Rotor-stator systems are integral to clean- label emulsification, offering precision and adaptability for natural formulations. A thorough understanding of their mechanics and comparison with other technologies helps optimizing emulsions for both low- and high- viscosity applications. Key insights into rotor- stator processes, highlighting geometry, shear rate, operational parameters, and their impact on emulsion quality are listed below.
The role of geometry and shear rate June 2025 PERSONAL CARE
Droplets size (d)
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