Emulsifiers are a group of materials that have expanded in type and functionality in recent years as suppliers endeavour to fill the various niches created for cosmetic products. John Woodruff reports
At one time it seemed that triethanolamine stearate, self-emulsifying glyceryl monostearate and sorbitan esters and their ethoxylated counterparts were going to dominate emulsion formulation forever. But then came a realisation of the benefits of liquid crystal structures and a demand for emulsifying high silicone-content products for cold processing and for non-ethoxylated materials, preferably of natural origin.
Silicones are one of the most popular groups of materials used in cosmetic formulation but bring their own problems of compatibility with other ingredients and difficulties in emulsification.
Dow Corning has produced a quick guide to silicone emulsifier selection based on inputting answers to various criteria. Altogether Dow Corning has nine possible silicone based emulsifiers. All contain polyethylene glycol with varying degrees of ethoxylation, the simplest of which is ES-5612 Formulation Aid, PEG-10 dimethicone. It is recommended for preparing water in silicone (w/si) or water in silicone in oil (w/si/o) emulsions and is suitable for cold processing. The most recent introductions from Dow Corning are ES-5226 DM and ES-5227 DM. Both contain the silicone polyether PEG/PPG-18/18 dimethicone and are recommended for preparing low to medium viscosity w/si emulsions. ES-5226 DM is a 37.5% dispersion of PEG/PPG-18/18 dimethicone in a low viscosity, volatile dimethicone fluid and ES-5227 DM is a 25% dispersion in a low viscosity, non-volatile dimethicone fluid.
Shin-Etsu Chemical Company is a Japanese supplier of silicones of every description. For preparing w/o emulsions it recommends KF-6005, which is a 100% active polyether modified silicone fluid [INCI: PEG-9 dimethicone]. Its low molecular weight is beneficial in that it can stabilise high internal phase emulsions of low viscosity without sacrificing stability. It has excellent aesthetics with light and silky skin feel, and ambient processing is possible if all ingredients are liquid. Also from Shin-Etsu is KF-6050L, a linear w/si emulsifier [INCI: Dimethicone, PEG/PPG-18/18 dimethicone] that shows good compatibility with cyclomethicone and dimethicone of low viscosity and with KSG-210.This latter material is a crosslinked elastomer emulsifier [INCI: Dimethicone/PEG-10/15 crosspolymer, dimethicone] that enables the formulation of unique textures of w/si emulsions containing up to 90% water.
Kodasil 451S from Koda is described as a new and unique silicone that incorporates a dimethicone copolyol into its crosspolymer network [INCI: Dimethicone, phenyl trimethicone, cyclopentasiloxane, dimethicone/vinyl dimethicone crosspolymer, PEG/PPG 20-15 dimethicone]. Due to the immediate availability of the copolyol, low temperature emulsification is possible and the copolyol/crosspolymer network allows the use of a high water load in w/si emulsions.
Chemsil Silicones simplifies the use of silicones by providing product bases such as Gelaid CPE to which formulators are encouraged to add water and water-soluble actives to formulate stable, elegant emulsions. Its properties can be further modified by the addition of esters, natural oils and mineral oil. Gelaid CPE is a mixture of cyclopentasiloxane, dimethicone/vinyl dimethicone crosspolymer and hydroxyethyl acrylate/sodium acryloyldimethyl taurate copolymer and it is suitable for cold processing. Gelaid CPE-CF is similar but without cyclomethicone.
Polymeric emulsifiers have been slowly establishing themselves with formulators. They do not form true emulsions in that the dispersed oil droplets are stabilised by the polymer matrix. They have the advantage that emulsions prepared using them are almost immune to temperature fluctuation. Also they can be added at any stage of the processing operation, they thicken as well as emulsify and they are suitable for cold processing. To satisfy this trend Croda Europe has relaunched its acrylic based emulsifiers under its ViscOptima brand name.
ViscOptima LV [INCI: Sodium polyacrylate, isotridecyl isononanoate, trideceth-6] gives instant and efficient thickening at low inclusion levels and emulsifies up to 20% oil and silicone. When a higher oil or silicone content is required, ViscOptima SE [INCI: Sodium polyacrylate, ethylhexyl cocoate, PPG-3 benzyl ether myristate, polysorbate 20] is recommended. Up to 30% oil or silicone can be included in the formulation without the need for additional emulsifiers. ViscOptima SE and ViscOptima LV can also be used as aqueous phase rheology modifiers and emulsion stabilisers in traditional emulsions containing conventional emulsifiers. They will create a higher viscosity, a higher yield point, a different texture on the skin and improve the stability of the emulsion.
Rockwood Additives has developed a cold process method to produce surfactant free Pickering emulsions, stabilised using low concentrations of colloidal sized particles of Laponite ED. O/w and w/o systems can be prepared with emulsion droplet particle sizes ranging from a few microns to a few millimetres using a variety of oil types of different polarity, from silicone oils and non-polar hydrocarbons through to polar alcohols. Laponite ED [INCI: Lithium magnesium sodium silicate] is a high specification Laponite grade that is dispersed in the oil phase and the water phase then added with high shear mixing, creating a thickened emulsion.