Ingredients for Cold Emulsification - Part Two

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.

W/O Emulsifiers

W/O emulsions exhibit significant potential in cosmetic applications. They demonstrate complete compatibility with the skin’s natural hydrolipidic film. These emulsions effectively protect against transepidermal water loss without causing occlusion, thereby contributing to skin moisturisation. Additionally, they possess excellent coverage properties, enhancing cutaneous protection. Furthermore, they naturally exhibit water resistance, ensuring extended durability for sun protection and makeup products.1

W/O Silicone emulsifiers

Cetyl PEG/PPG-10/1 Dimethicone is a silicone-based non-ionic emulsifier used in low concentrations between 1,5 – 2,5%. Its polymeric and polyfunctional structure ensures high heat and freeze stability, making it suitable for various applications. It is compatible with all kinds of cosmetic oils, which allows formulators to create cosmetic products with diverse textures. It also exhibits excellent compatibility with substances possessing specific properties, such as UV filters, plant extracts and antiperspirants, providing enhanced sun protection in sunscreen formulations and benefiting from natural ingredients. It’s designed for cosmetic creams and lotions. When used in cold emulsification, typically 1% of Polyglyceryl-4 Isostearate is added2. 

W/O Polyglyceryl esters 

W/O emulsifiers for cold emulsification are often polyglyceryl-derived esters. Some traditional examples are Polyglyceryl-2 Diisostearate and Polyglyceryl-3 Polyricinoleate3. 

The following W/O emulsifiers are ideal for cold processing and are usually used in concentrations between 2–6%. Polyglyceryl-2 Dipolyhydroxystearate can be used as an O/W co-emulsifier in low concentrations, as a primary W/O emulsifier in 4–5% or in combination with 1% Polyglyceryl-3 Diisostearate4.

The next emulsifier is also derived from renewable sources, namely olive oil and vegetable glycerin. The blend of Olive Oil Polyglyceryl-6 Esters (and) Polyglyceryl-6 Pentaoleate creates a liquid crystal reticular system that restricts agglomeration and coalescence, resulting in stable emulsions and enhancing moisturisation. Polyglyceryl-4 Olivate/ Polyricinoleate has moisturising and pigment wetting properties and is used in 2–4%5. Polyglyceryl-3 Sorbityl Linseedate is derived from transesterifying polyglycerin and sorbitol with fatty acids sourced from linseed oil. What sets this emulsifier apart is its ability to form W/O emulsions without additional co-emulsifiers or stabilizers6. 
Polyglyceryl-6 Polyhydroxystearate (and) Polyglyceryl-6 Polyricinoleate is mainly designed for pigmented color or sunscreen formulations because it is an excellent dispersant for powders7. The blend of Polyglyceryl-4 Oleate (and) Polyglyceryl-6 Oleate (and) Polyhydroxystearic Acid demonstrates a new emulsion concept as it creates a water-and-oil fusion and allows total control over the emulsion’s final viscosity due to its ability to accommodate up to 80% of the internal water phase8. In addition to that, Polyglyceryl-3 Diisostearate1 and Glyceryl Oleate (and) Polyglyceryl-3 Polyricinoleate (and) Olea Europaea (Olive) Oil Unsaponifiables 9 are natural emulsifiers which offer compatibility with various oils, allowing the creation of different textures. They are used in multiple products, including baby care formulations and water-proof products like sunscreens and makeup.

Polyglyceryl-4 Diisostearate/Polyhydroxystearate/Sebacate (and) Caprylic/Capric Triglyceride (and) Polyglyceryl-3 Oleate (and) Diisostearoyl Polyglyceryl-3 Dimer Dilinoleate is a PEG-free emulsifier blend derived from vegetable raw materials. Due to its high molecular weight and polymeric and polyfunctional composition, it provides excellent stabilisation for various formulations. It can be used in concentrations between 1.5–5%. Thanks to its high molecular weight, it can accelerate water uptake during processing or enhance the wetting of pigments when combined with a low molecular weight co-emulsifier. It offers versatility in terms of oil phase content, enabling the creation of quick-breaking emulsions with 10 % oil phase or sprays with up to 50% oil phase. It offers high compatibility with organic and inorganic UV filters, making it suitable for formulating color cosmetic products. One notable advantage of this emulsifier is its ability to be used in W/O sprays and aerosols10. 

In W/O formulations, the choice of stabilisers is crucial. Typically, Magnesium Sulfate or Sodium Chloride is added to the aqueous phase, but Zinc Sulfate may be preferred in some cases. In the oil phase, Zinc Stearate helps a lot. It has to be readily dispersed before adding the aqueous phase.

Rheology modifiers 

In emulsions that are produced in a hot or hot/cold process, solid, wax-like ingredients are parts of stabilising lamellar gel structures or oleogels. Therefore, in the cold process a different formulation world is present. While W/O emulsions can be stabilised by a high internal phase and the viscosity can be increased to cream consistency, O/W emulsions have to be formulated with rheology modifiers such as water-based thickeners11. In recent years, Carbomer and other types of polyacrylates have been more and more replaced. Different classes of rheology modifier can be used such as cellulose derivatives e.g.  Microcrystalline Cellulose and Cellulose Gum, starch derivatives e.g. Hydroxypropyl Starch Phosphate alone or in combination with Sodium Starch Octenylsuccinate which then does not only increase the viscosity but can act as a primary O/W emulsifier in 1.0 – 6.0%12. Gums can be extracted from Irish Moss (Chondrus Crispus Extract) which then contains carrageenans and proteins or be prepared by fermentation as Xanthan Gum or Sclerotium Gum. Tara Gum (Caesalpinia Spinosa Gum) is also common and compatible with synthetic polymers. Those gellants are often found in blends which sometimes exhibit a stunning skin feel. In carrageenans, the iota, kappa and lambda types have to be distinguished as they exhibit different viscosity build-up and behavior.

Although sprays and liquid emulsions to light creams can be stabilised, there are some limitations in cold emulsification. At high concentrations of water-based thickeners pilling on skin can be observed and high viscous creams cannot be produced. Bentonite or Magnesium Aluminum Silicate can be used alone or to support organic thickeners.14

Conclusion

The ingredient base for cold emulsification processes has changed over the years. Especially, different types of polyglyceryl or sugar-based emulsifiers and biobased gums, starch and cellulose derivatives are applicable.

Acknowledgements

The authors wish to thank Dr Corinna Fetsch for her contribution.

References:

 1 Plurol Di Isostearique - Cold Process W/O Emulsifier - An advanced approach to continuous oil phases, Gattefossé (2001).

 2 Abil EM 90 - Technical Information, Evonik Nutrition & Care GmbH (2016).

 3 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).

 4 Dehymuls PGPH and Lameform TGI (BASF).

 5 Olivatis 12 C, Medolla Limited (2016); Olivem 2090, Hallstar Beauty

 6 Ewocream - W/O skin shield - Flyer, Sinerga S.p.A. (2022).

 7 Emulium Illustro - Pigment empowered, Gattefossé (2019).

 8 PolyAquol-VO4 - Technical Data Sheet, Innovacos Corporation (2022).

 9 Matsui et al. Physiological and lifestyle factors contributing to risk and severity of peri-orbital dark circles in the Brazilian population. An Bras Dermatol. 2015; 90(4):494-503.

10 Personal Care Emulsifiers - Uncover the Secret Code of Beauty - Emulsifier Guide, Clariant (2014).

11 ISOLAN 17 MB - Technical Information, Evonik Nutrition & Care GmbH (2019).

12 A. Wanninger et al: Natural Water-based Thickeners, COSSMA 4, 22-24 (2019).

13 https://www.ulprospector.com/en/eu/PersonalCare/Detail/117838/5315352/StarDesign-Power (14.06.2023).

14 Vanatural, Veegun, Vanderbilt Minerals LLC.