Chemical industry has experienced major changes over past decades as a consequence of a more competitive and globalized market[1]. This has yielded an improvement in the efficiency of the operational processes in chemical facilities[2] and the development of research for designing products with higher added value[3], for instance, cosmetic emulsions. In this regard, understanding the relationships between product properties (macroscopic, microscopic and molecular), and connecting them with product formulation and process variables (e.g. energy consumption, impeller type) is a key factor for creating a new product[4][5]. According to Pradilla et al.[6], scale-up factors as the tip velocity and pumping capacity of the impeller influence the amount of energy incorporated to an emulsion, leading to changes in microscopic (drop and drop size diameter) and macroscopic properties (rheology). In turn, rheological properties can be linked to textural properties of a cosmetic emulsion[7], highlighting the need of exploring the relationships between the mixing characteristics of impellers and textural properties of emulsions. The purpose of this work is to evaluate the effect of process variables such as the pumping capacity and tip velocity, quantifying the energy incorporated during the emulsification process, on macroscopic scale and microscopic scale properties of oil-in-water (O/W) cosmetic emulsions. In this study, the macroscopic scale is represented by rheological (viscosity and storage modulus) and textural properties (firmness, consistency and cohesiveness), while the microscopic scale corresponded to the drop size distribution and mean drop size. Additionally, the effect of process variables on the emulsions long-term physical stability was assed. All emulsions were prepared using a typical cosmetic formulation, including ingredients such as emollients, humectants, thickeners, preservatives and emulsifiers. Two formulation were used throughout the study. The first one had a dispersed phase concentration of 30% (w/w), while the second one had a dispersed phase concentration of 80% (w/w). For these emulsions, the impeller type, tip velocity and the impeller pumping capacity were varied during the mixing process. Three different impeller types were used for preparing the emulsions (propeller, hydrofoil and pitch blade 45°) at two different pumping capacity levels, modifying the impeller tip velocity. In all cases, the impeller to tank diameter ratio was kept at a constant value of 0.78. Results showed that, for a given tip velocity and pumping capacity values, these scale-up factors governs the drop formation within the emulsion at the viscous regimen of flow. These results enable to discuss previous proposed ideas reported by Pradilla et al.[6] for cosmetic emulsions design and cosmetic emulsions manufacturing scale-up processes.
REFERENCES
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[7] L. Gilbert, C. Picard, G. Savary, and M. Grisel, “Rheological and textural characterization of cosmetic emulsions containing natural and synthetic polymers: relationships between both data,†Colloids Surfaces A Physicochem. Eng. Asp., vol. 421, pp. 150–163, 2013.
