Essential Guide azelaic acid

Before adding the Oil Phase into the turboemulsifier you’ll use for the union of the phases, slightly heat the machine (35-45°C) to avoid thermal shocks. The union of the phases (Water Phase into Oil Phase) has to occur very gradually, from the beginning to the end of the process, mixing only with blades at middle-low speed, without the use of the turbine. The turbine has to be used only after the union at low speed for 5 minutes at most. Then slowly cool the cream. After 3 month of accelerated stability (40°C In the oven), the production of Whitening Cream is stable and without any precipitate. Azelaic acid loading for oil-in-water (O/W) emulsions is significantly lower compared to W/O-emulsions, while simultaneously avoiding crystallisation of Azelaic acid must be avoided. In O/W-emulsions non-ionic emulsifiers/emulsifier pairs must be used that form a liquid crystalline phase in the continuous phase of the emulsion (the water phase). There are numerous examples of emulsifiers that may be used. A small anthology, according to INCI, is given in table 14.

CETEARYL ALCOHOL / CETEARETH-6 / CETEARETH-25

STEARETH-2 / STEARETH-21

METHYL GLUCOSE SESQUISTEARATE / PEG-20 METHYL GLUCOSE SESQUISTEARATE

SORBITAN STEARATE / POLYSORBATE 60

SUCROSE STEARATE / SUCROSE DISTEARATE / CETEARYL ALCOHOL

CETEARETH-12 / CETEARETH-20 / GLYCERYL STEARATE

TABLE 14: Examples of emulsifiers

In these systems Azelaic acid is “dissolved” in the liquid crystalline double layer as described by Israelachvili, Ninham & Bingham (1976, Friberg & Shinoda). Numerous commercial examples of inclusion of physiologically active ingredients in the liquid crystalline double layer of emulsions have been reported. Processing is best done by combining the emulsifier pair and Azelaic acid at elevated temperature, followed by the addition of the water phase and the remaining ingredients of the oil phase. In many situations the use of a hydrocolloid is required as the mechanical strength of the liquid crystalline double layer is frequently insufficient, and that may lead to emulsion instability. The addition of a hydrocolloid does not necessarily leads to an increased viscosity. For the hydrocolloid choice polymers (rheology modifiers) resistant to electrolytes could be the most indicated.

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