(721d) Mixing Conditions for Oil-in-Water Emulsions Manufacture As Factors for Scaling-up and Product Design.

Cosmetics demand had shifted towards the use of organic and natural products.¹ Because of this, different tools have been proposed to simplify and accelerate the cosmetics design, including in-silico design, molecule modelling, and other approaches. In all cases, the production process and its scaling-up are factors that must be considered, especially when working with structured products (e.g., emulsions). This task can be time-consuming, resource-intensive and complex.

Several variables must be considered to ensure that product properties will be the desired ones. In the case of emulsions, equipment geometry, stirring rates, process temperatures, mixing times and heating and cooling rates, play a major impact in the final characteristics of the product. During scale-up, the influence of these variables is reinforced due to the reduction in geometrical relations such as available mixing power and volume-to-transfer-area. These variables must be adjusted during scale-up, and that is usually made by trial-and-error strategies making this process highly inefficient. Different scale-up strategies have been developed for emulsions production using dimensionless numbers in the ND^α.^2,3 This approach guarantees that the drop size is conserved in all scales, although we have confirmed that it is not enough to maintain all product characteristics.

In this sense, this work studied the influence of emulsification temperature, addition time, stirring rates, and cooling rate in the final characteristics of a real cosmetic emulsion (i.e., skin moisturizer) during scale-up. Experiments were accomplished at three different processing scales (i.e., 100mL, 1L and 10L) and based on the obtained results, it was found that a dimensionless number in the form of ND^α was conserved with α=0.5. As part of the product design approach, we analyzed the influence of each variable in the final quality of the product, and proposed some factors that must be considered during the product design process.

References

(1) L’Oréal. Cosmetics market - L’Oréal Finance: Annual Report 2018 https://www.loreal-finance.com/en/annual-report-2018/cosmetics-market-2-1/ (accessed Aug 9, 2019).

(2) May-Masnou, A.; Ribó-Besolí, J.; Porras, M.; Maestro, A.; González, C.; Gutiérrez, J. M. Scale-up Model Obtained from the Rheological Analysis of Highly Concentrated Emulsions Prepared at Three Scales. Chem. Eng. Sci. 2014, 111, 410–420. https://doi.org/10.1016/j.ces.2014.03.004.

(3) May-masnou, A.; Maestro, A.; González, C. Scale Invariants in the Preparation of Reverse High Internal Phase Ratio Emulsions. 2013, 101, 721–730.