46 MANUFACTURE R/S B - Time 10 mn


6 5 4 3 2 1


0 0 500 1000 Shear rate (s-1


1500 )


For this part, we will be comparing several rotor-stators show in the table below and doing two emulsions: ■ Emulsion 1 (E#1): low viscosity, no thickener ■ Emulsion 2 (E#2): high viscosity, with a thickener The geometry of the rotor-stator,


particularly the air gap between the rotor and stator, plays a pivotal role in determining the shear rate—a critical factor for emulsion quality. High shear rates are essential for creating fine, stable emulsions in low- viscosity systems, especially when synthetic thickeners are excluded. In viscous emulsions, however, higher flow rates are more important, underscoring the complementary role of shear and flow rate. The key observations were (1): high shear


rates (A & B) enable the creation of fine droplet sizes, crucial for low-viscosity formulations; and (2): for high-viscosity emulsions, beside shear rate, the flow rate (C) ensures even mixing and consistent texture.


Effects of speed and mixing time Speed and mixing time are key operational factors influencing emulsion quality: Speed: Increasing the rotor-stator speed


reduces droplet size and narrows droplet distribution, enhancing homogeneity. For example, high speeds achieved droplet sizes


100 80 60 40 20 0 0 5 10 15 20 Mixing time (mn) Figure 7: Evolution of the diameter of the fat droplets under different mixing conditions. Source: VMI PERSONAL CARE June 2025 25 30 35 40 2000 Figure 5: Viscosity variation as a function of shear rate with R/S B Source: VMI Forth ■ Back ■ Power■ 104 R/S C - Time 15 mn Forth ■ Back ■ Power■


103


100


10 1 10 Shear rate (s-1 ) Figure 6: Viscosity variation as a function of shear rate with R/S C Source: VMI


TABLE 1: SHEARING AND FLOW RATE CHARACTERISTICS DEPENDING ON ROTOR-STATOR DESIGN Rotor-stator


Shearing


R/S A R/S B R/S C


Rotor-stator range, compliant with VMI laboratory homogenizers


TABLE 2: IMPACT OF ROTOR-STATOR DESIGN AND MIXING SPEED ON APPARENT VISCOSITY Rotor-stator R/S A


Shearing 1500


R/S B R/S C R/S C


1500 1500 2000


as small as 5 microns. However, beyond a certain threshold (e.g., after ten minutes), further increases yield diminishing returns. Mixing time: Optimal emulsification


typically occurs within the first ten minutes of operation, during which droplet size and distribution improve significantly. Beyond this point, changes plateau, offering minimal additional benefit. Microscopic inspections confirmed the


impact of operational settings thus. Firstly, at higher speeds, emulsions were more uniform, displaying fewer large droplets and greater overall homogeneity. Secondly, at lower


R/S C-S1 ■ R/S C-S2 ■


Flow rate 2.8


3.5 141


185


E1 E2


+++ ++ +


Flow rate


- +


+++ 100 1000


Newtonian behaviour Shear - thinning behaviour


speeds, in contrast, resulted in heterogeneous emulsions with uneven droplet sizes, compromising stability and performance. By optimizing rotor-stator geometry, shear


rate, speed, and mixing time, manufacturers can achieve fine, stable emulsions suited for clean-label formulations. These systems excel at compensating for the reduced functionality of natural emulsifiers, making them invaluable in achieving the desired performance in modern cosmetic and food products.


Conclusion The clean-label cosmetics trends represent a transformative opportunity for the beauty industry to align with growing consumer expectations for transparency, sustainability, and performance. This shift reflects a deeper change in values, challenging manufacturers to innovate and adapt. Although achieving stable, high-performing


clean-label emulsions remains a complex challenge, it is one the industry can meet through careful process control. While ingredients play a significant role in regular cosmetics formulations, the process itself is equally crucial. Optimizing parameters such as shear


rate, flow rate, and temperature is essential to achieving stable and effective emulsions, especially in clean-label formulations. As the industry continues to innovate, attention to both formulation and process will be key to creating beauty products that meet performance and sustainability goals.


PC www.personalcaremagazine.com


Viscosity (mPa.s) Modal diameter (µm)


Viscosity (mPa.s)


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