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By: Steve Herman
Posted: January 31, 2012, from the January 2012 issue of GCI Magazine.
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In today’s lab, computer programs can be used to make important predictions of the properties of materials and mixtures. One program, for example, was designed for identifying the ideal solvent or solvent blend for polymers. Databases are also available to extend the applications into other personal care areas, such as fragrance or emollients. A well-designed software program goes a long way to determining what will or will not work, and makes predictions on many other properties, from vapor pressure to skin permeation.
A recent program commercialized3 by the late Johann Wiechers extends concepts and truths of how materials interact more specifically into cosmetic formulation, skin permeation, and the delivery of cosmetic and pharmaceutical actives. In “Formulating for Efficacy,” Wiechers concentrated on the solubility properties of the active and the vehicle.4 He identifies opposing solubility factors that allow the minimal amount of active to provide maximum delivery.
To be ideal, the outcome—the product—must meet three criteria: The active must be capable of penetrating human skin; the molecule must have the right activity profile; and it must be in the correct formulation. When the chemical structure of the active is entered into the software, an ideal set of formulation parameters is generated.
To Production; Scale-up
Using conventional methods, scale-up is a problem. Heating, cooling and mixing all change dramatically from a small beaker in the lab to a giant steam-jacketed kettle in production. Most companies have pilot plants to study the effect of larger equipment on the final product, a time-consuming and costly process. If formulation is undertaken with new tools—specifically, for emulsification—scale-up is no longer an issue. Using microchannel technology, the mixing process becomes an inherent component of formulation, equal in importance to the choice of emulsifiers. This approach was described in a recent article by Grace and Plonsker in GCI sister publication Cosmetics & Toiletries magazine.5
In the simplest configuration, two phases are pumped in. The external phase, usually water, flows through a channel, and the dispersed phase, usually oil, are pushed through a porous screen—which creates a steady stream of uniform small particles. The screen can be customized for different particle sizes, and the rate of flow can be controlled to create different product characteristics. Changing the flow and screen parameters changes the finished product, and, in this way, the device becomes an intrinsic part of the formulation.