Auto-emulsifying polymer bases in cold conditions. Maximum moisture and emollient power of application.

Emulsions are colloids consisting of the mixture of two immiscible fluids. Stability is conferred upon an emulsion by different variables such as its temperature, composition and micelle formation. Oil and water are the main components of emulsions in cosmetics, although there are other dispersed hydrophobic and hydrophilic components respectively.

As they are immiscible liquids, they need surfactants or emulsifiers that cleave to the interface created, reducing the surface tension and making the formation of emulsion possible. They could also need the addition of polymers that reticulate the continuous phase by forming a three-dimensional get network which facilitates dispersion and reduced globule mobility.

Conventional emulsions can be classified as:
• oil/water (O/W): oil droplets dispersed in water.
• water/oil (W/O): water droplets dispersed in oil.

Other possible emulsion forms often found on the market are the multiples and silicates, such as water/oil/water (W/O/W), oil/water/oil (O/W/O), water/silicone (W/Si) and silicone/water (Si/W) emulsions, among others.

Oil/water emulsions are the emulsions found most commonly in the area of cosmetics, found in the form of creams and lotions, differing as to oily composition and viscosity. Oil/water emulsions, along with the others, tend to be thermodynamically unstable. Stabilizing and emulsifying agents create stability through the emulsion-forming process. At the beginning of the process to form an emulsion, breaking the dispersal stage leads to an oil/water interface. This is mainly established against an immediate coalescence by the emulsifier. The stabilizing agents take longer to adhere to the interface, but have a greater propensity to stabilize the system and guarantee a longer use-by date.

The conventional way in which cosmetics emulsions are prepared is via a heat process. In the attempt to stabilize these emulsions, polar and non-polar phases are heated and combined with the use of high-speed agitation and the use of surfactant agents. This process takes time, energy and specific equipment. For these, and other, reasons a ‘cold’ process for the preparation of cosmetics emulsions has been of great commercial interest in the attempt to create emulsions of the same quality but with a reduced process cost in comparison to heat-processed emulsions.

The use of surfactant agents is the most common method for stabilizing cold-processed emulsions. There are, however, few liquid emulsions able to be cold processed that guarantee a good stability and feel to the emulsions. The use of rheology modifiers to bring structure to the emulsion’s aqueous stage is another option for stabilizing these emulsions. Their use facilitates dispersion, jellifying the emulsion’s continuous phase and increasing the product’s stability, and, ultimately, its shelf life.

The most common forms of instability seen in emulsions are coalescence, flocculation, creaming and Ostwald ripening. Coalescence is an irreversible grouping of the dispersal phase, in which the globules group together, breaking the surface and forming one sole globe. Flocculation is the union of the dispersed globules without any breaking of the surface – any agitation may reverse the process and the emulsion remain unstable for some time. Creaming is the separation of the dispersal and continuous phases via the effect of gravity. This occurs when there is a significant difference of density of phases. Ostwald ripening is a mechanism that promotes the increase of major globules and the reduction of the minor globules. This is connected to greater solubility of the dispersal phase for the smaller globules: the greater the interfacial curvature of the globule, the greater its solubility in the continuous phase.

Avoiding all these forms of instability is a difficult task and the association of different mechanisms of action enables these difficulties to be overcome more efficiently. In this way, the association of a pre-defined lipid network, a thick polymer structure and composites that reduce the interfacial tension of dispersed globules can stabilize high oil charges without compromising the look or feel of the emulsions. This association is known as Organogel.

Organogels are defined as viscoelastic and thermo-reversible materials where an organic fluid is immobilized by a three-dimensional crystalline gel network formed by the physical or chemical interaction of the molecules of a structuring agent that prevents leakage of the non-polar external phase. In other words, organogels are materials with the rheologic characteristics and properties of a solid, but that contain, in their majority (around 98%), an organic liquid.

The structuring agents are composed so that, when solubilized in comestible oils, they undergo a molecular ‘self-orientation’, creating a get network able to sustain a great volume of liquid. The structure of the gel network formed is quite specific for each structure. Crystalline structures, with controlled temperature and process, can form crystalline networks, with crystals of varying magnitudes, shape and resistance. The use of this technology helps in the stabilization of high concentrations of the oily phase using oily components used routinely in the cosmetics area, thus forming emulsions of a greater stability.

The association of cetearyl alcohol (and) ceteth-20 (and) glyceryl stearate (and) PEG-40 hydrogenated castor oil (and) polyacrylic acid (and) caprylic acid + excipients is designed to form cold emulsions with high oily phase concentrations, such as sunscreens. One of the major difficulties of sunscreen formulations is the stability of the high oil charge that can affect not only the emulsion’s stability but also its feel. Based on organogel technology to structure the combined oils with the addition of coadjutant composites, this product is designed to develop highly stable emulsions, the result of the ability to structure both oil and water phases, of cold-processed emulsion.

The association of helianthus annuus seed oil (and) polyacrylic acid (and) glyceryl stearate (and) candelilla wax + excipients is designed to facilitate the preparation process of oil/water emulsions. This is also developed from organogel technology, based on the ability to structure the water and oil phase of an emulsion. This double structuring, associated to an increase viscosity of the water and oil phase, makes it possible to increase the stability of the system against the coalescence of the globules without the need to use surfactant agents in the formulation, or high-speed agitation in the process. The product’s main advantage is its simple application that works via incorporating the oil phase in the water phase. The oil and water phases have added to them other components present in the formation.

Thus, we can conclude that we have today cosmetics ingredients which are easy to manufacture, as they are manipulated using cold systems, and whose formulations are easy to stabilize, as they withstand a greater quantity in the lipid stage.

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