(165e) Influence of Mixing Rate and Temperature during the up-Scaling of Emulsified Cosmetic Products

Global cosmetics market has been steadily growing during last years, and the most recent forecasts indicate that this tendency will remain. A major driver of this market boost is the high rate at which the new and innovative products are requested by the more sophisticated consumers. Then, in some cases, the minimization of the time required to introduce a product into the market is more important than an optimized product performance. In spite of the current availability and continuous development of tools for product conception and design, together with the availability of high throughput prototyping and manufacturing techniques, a major limiting factor remains in the up-scaling process. Specifically, in the development of structured products in the cosmetics industry (e. g. emulsions), up-scaling to industrial production is a time-consuming, resources-intensive, and complex process; reason why it frequently must incorporate trial and error techniques.

During the manufacture of cosmetic emulsions, several variables need to be considered to ensure obtaining the desired properties of the product and long term stability. Variables such as emulsification temperature, mixing times, stirring rates, equipment geometry, ingredients addition procedures, heating or cooling rates; all these play a major impact in the final characteristics of the emulsified products. During the up-scaling process, these variables need to be tuned and adjusted along the way, mainly through trial and error methods. This makes the process highly inefficient.

Alternatively, different systematic up-scaling techniques have been developed for cosmetics production. Specifically, for water-in-oil emulsions, the use of process invariants such as some dimensionless numbers of the form ND^α, have been incorporated as key parameters during the up-scale process. While N and D relate geometries and flow regimes used in the emulsification process,α is an adjusted parameter that largely depends on the nature (properties, compositions, specific synergies) of the mixture. Even when up-scaling with different equipment geometries, stirring rates, of operating policies, the same final product is expected to be obtained by maintaining constant such process invariants among scales.

Nevertheless, most emulsified cosmetics are oil-in-water emulsions, and the up scaling process of this type of products via process invariants has been seldom studied. In this regard, this work studied the influence of some process variables (emulsification temperature, mixer type and speed, and cooling rates) in the production of an oil-in-water cosmetic emulsion. The impact on the major characteristics of the product (drop size distribution and rheological behavior) were assessed to define the corresponding process invariants during up-scaling. Experiments were carried out at different scales (from 100mL to 1 L) using rotor-stator mixer operating under high stirring rates (3000 to 10000rpm), an anchor mixer in rates among 50rpm and 200rpm, and emulsification temperatures between 70°C and 90°C. The ingredients of the cosmetic product corresponded to the base emulsion of a body cream. As a result of the study, process invariants for oil-in-water emulsions preparation were identified, and they were successfully validated in the up-scaling of the process to a larger batch (10 L).