Cold process emulsions are possible with a selection of suitable ingredients. Prof Andrea Wanninger and her co-authors monitor emulsifiers, rheology modifiers and multifunctional blends. This first part of two focuses on O/W emulsifiers and their ingredients.
Benefits and limits of cold process emulsification have been discussed in a previous article (published in COSSMA 6/2023). To develop interesting skincare products that are well accepted and fulfil the intended claims, the selection of suitable cosmetic ingredients is limited and has some preconditions, especially when natural cosmetics are the aim.
In this article, the variety of suitable basic ingredients, which is nevertheless still huge, will be presented, focusing on emulsifiers, emulsifier blends, and rheology modifiers.
O/W Emulsifiers
There has been a remarkable shift and development of emulsifiers in the past ten years. Some time ago, emulsifiers were based either on polymer chemistry, silicone chemistry, or contain alkoxylated alcohols and phosphorous compounds1.
O/W Silicone emulsifiers and PhosphatesSilicone surfactants are based on polyether functional silicones, known as dimethicone copolyols. These are typically water-soluble and display a way of formulating clear-aqueous-based compositions. Silicone emulsifiers are liquid at room temperature2,3.Bis-PEG/PPG-16/16 PEG/PPG-16/16 Dimethicone and Caprylic/Capric Triglyceride is a silicone based nonionic O/W emulsifier. The silicone character enhances a long-lasting feeling of smooth skin. It can be used as a primary emulsifier with a use level of 1.5 – 3.0%. In cold emulsions a viscosity enhancing and stabilising system is needed. The emulsifier can be applied for sun care products, lotions, skin care creams and sprayable emulsions4.There is another silicone-based emulsifier which is interesting for cold process O/W emulsions. A blend consisting of Bis-PEG/PPG-20/5 PEG/PPG-20/5 Dimethicone, Methoxy PEG/PPG-25/4 Dimethicone and Caprylic/Capric Triglyceride delivers formulations leading to a smooth and velvety-silky skin feel. The product has a use level from 2.0 – 3.0%. A co-emulsifier is not necessary. Like for the former emulsifier, a viscosity enhancing and stabilising system is needed. Possible applications are sun protection as well as eye, face, neck, hand and foot care5.
Potassium Cetyl Phosphate is an anionic O/W emulsifier with applications in sun and skincare, colour cosmetics such as mascaras or foundations as well as hair care and cleansers. Used as main and co-emulsifier the use level is 0.5% as secondary and 1 – 2% as main emulsifier6.
Sugar emulsifiers
Sucrose esters provide an excellent touch and improve smoothness, emolliency and moisture level of the skin7. They have an interesting cooling effect. 2-3% Sucrose Stearate or Sucrose Palmitate can be used as primary emulsifier.
O/W emulsifier blends based on glycerin, Sucrose Laurate and Water with use levels of 2-10% function as natural oil thickening additives and cold emulsifiers. Caprylic/Capric Triglyceride (product 1), Caprylic/Capric Triglyceride and Sucrose Stearate (product 2) or Prunus Amygdalus Dulcis (Sweet Almond) Oil (product 3) may also be present in the blend. It is recommended that the O/W formulations are shaken or stirred before use8.
O/W Polyglyceryl Esters
The market offers quite a lot of polyglyceryl-based O/W emulsifiers. They include blends of Polyglyceryl-4 Laurate and Polyglyceryl-6 Laurate or Polyglyceryl-4 Laurate/Succinate and Aqua as well as Polyglyceryl-6 Oleate and Potassium Olivate, which are used in emulsions at 2 – 6%. These emulsifiers are palm oil-free and based on olive oil and sunflower oil9.The palm-free O/W emulsifier consisting of Polyglyceryl-4 Laurate and Polyglyceryl-6 Laurate is used in low viscosity lotions, sprayable or superfluid emulsions. It shows good compatibility with one-pot emulsions, liquid phases of different polarities as well as synthetic and naturally obtained thickeners. Furthermore, stable emulsions can be produced in a wide pH spectrum10.When using the O/W emulsifier of Polyglyceryl-4 Laurate/Succinate and Aqua in cold emulsification, the use of a co-emulsifier which is liquid at room temperature such as Sorbitan Laurate, Sorbitan Oleate or Sorbitan Isostearate is highly recommended. That co-emulsifier should be added to the oil phase in a ratio of 2:3 to 3:2 to the actual O/W emulsifier, whereby the total use level of the emulsifier blend in the emulsion should be between 3% and 8%. The emulsifier is highly compatible with oils of a wide polarity spectrum, is extremely electrolyte, pH and temperature tolerant and can be found in sunscreens and BB creams11.The O/W emulsifier made of Polyglyceryl-6 Oleate and Potassium Olivate is also used in low viscosity emulsions and can also be used in cold emulsification without any loss of efficiency. The emulsion is stable, fresh and offers a pleasant feeling of lightness when applied to the skin – even when large amounts of emollients are present. The best performance of the O/W emulsifier can be ensured at medium or high polarities. Another advantage is that remarkably simple stirring and homogenisation equipment can be used for production12.The pure anionic, natural O/W emulsifier Glyceryl Citrate/Lactate/Linoleate/Oleate is applicable as main emulsifier with a use level from 1 – 3% or as co-emulsifier with at 0.5 – 2%. It can form a variety of product textures from a low viscosity milk for sprayable applications to lotion-like emulsions to high viscous creams depending on the applied concentration. Cold emulsions can be easily produced by preparing each phase separately and mixing the phases afterwards. After homogenisation only a check of the pH is necessary and the emulsion is ready to use13.Another interesting O/W emulsifier is a mixture of Glyceryl Citrate/Lactate/Linoleate/Oleate, Polyglyceryl-4 Cocoate, Polyglyceryl-3 Caprate, Glyceryl Caprylate. It is 100% natural, produces stabile emulsions for oil phases ranging from 5 – 40%, processable at room temperature and low shear rates without viscosity build-up. The typical dosage is 1 to 8%. If applied in lower concentrations, the emulsifier forms a liquid milk with many possible applications e.g. as hair conditioner, and products for body and face care. Furthermore, it works well in sprayable natural cosmetic applications, but also in wet wipes solutions14.The mix of Glyceryl Oleate Citrate and Caprylic/Capric Triglyceride is an easy processable liquid emulsifier applicable for O/W skin and sun care creams and lotions. Used with a typical dosage of 2 – 4%, the emulsifier is able to stabilise emulsions with low and high oil content ranging from 10 – 40% of both polar and non-polar oils. In the emulsifying process it is possible to add it to the aqueous phase first but preferably to the oil phase of the emulsion. The emulsifier has various applications. It is recommended for sensitive skin and is also approved as food emulsifier15.In addition, a mixture of Sorbitan Laurate, Polyglyceryl-4 Laurate and Dilauryl Citrate is a suitable O/W emulsifier for lotions and sprays. The suggested use level is between 1.5 – 2.5%. This mild emulsifier is based on vegetable raw materials. The emulsion can either be processed using a homogeniser or by intensive stirring. Considering both options, it is suggested to add the emulsifier to the oil phase, followed by combining the aqueous phase and the oil phase. When using this blend, no further co-emulsifier is needed16.
The emulsifier consisting of Lauryl Glucoside, Polyglyceryl-2 Dipolyhydroxystearate and Glycerin offers a wide range of applications in the field of skin care emulsions. It is especially suitable for low-viscous lotions and sprays. The ingredients are based on naturally occurring raw materials. Typical use levels are 2.0–4.0%17.
Acyl Glutamates
Sodium Stearoyl Glutamate, a solid anionic emulsifier, is used in 0.5 – 1%. Sodium Cocoyl Glutamate (and) Disodium Cocoyl Glutamate, a mild anionic surfactant, can be applied at 2%.References:1. P. Tsolis, M. Ingrassia: Approaches to Cold-process Formulations (2014), https://www.cosmeticsandtoiletries.com/formulas-products/skin-care/blog/21837783/approaches-to-cold-process-formulations (14.06.2023).2. E. D. Goddard, J. V. Gruber,Principles of Polymer Science and Technology in Cosmetics and Personal Care, 1999, p. 297.3. https://foreverest.net/news-list/silicone-emulsifiers-and-formulation-techniques-for-stable-aesthetic-products (14.06.2023)4. ABIL Care 85 MB TDS (Evonik)5. ABIL Care XL 80 MB TDS (Evonik)6. amphisol-k_brochure_2021-03.pdf (dsm.com)7. https://www.sisterna.com/personal-care/application-concepts/cold-emulsifier-for-ow/ (14.06.2023)8. SUCROSE LAURATE – Inhaltsstoff INCI Beauty9. Polyglyceryl-4-Oleate (brennessel-muenchen.de)10. PolyAquol LW (alexmo-cosmetics.de)11. NatraGem E145 NP | Croda Personal Care12. OLEAMULS LOW emulsifier ingredient- greengredients13. IOI_Leaflet_IMWITOR_V4.pdf (ioioleo.de)14. IMWITOR liteMULS.indd (chemical-centre.com)15. COS1106_14_ProdSymrDracorin_GOC.pdf (cossma.com)16. [TEGO Care LTP Cold processable PEG-free O/W Emulsifier TDS]
17. Eumulgin VL 75 (BASF)
PART TWOfollows in COSSMA 9/2023 |
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Prof Dr Andrea Wanninger
Professor of Organic Chemistry, ILOC Institute of Coatings and Surface Chemistry, Krefeld, Germany