68 COLOUR COSMETICS
Stabilising W/O emulsions with pigments, naturally
n Flora Bollon – Gattefossé, France
Despite the growing interest of consumers in natural makeup and sun care, brands struggle to develop effective and sensory products. The blame is laid on the insufficient supply of ingredients, which does not make it possible to solve recurrent problems of stability of this kind of formulations. In response to these challenges, Gattefossé launched Emulium®
Illustro
(INCI: Polyglyceryl-6 Polyhydroxystearate (and) Polyglyceryl-6 Polyricinoleate), an innovative W/O emulsifier of natural origin. Emulium Illustro (now referred to as “W/O emulsifier”) has been designed principally for use in pigmented formulations.
Challenges of natural formulation Over the last decade, skin care has gone natural, progressively but with great success. It is undeniable that natural skin care today is as performant, sensorial and pleasant to use as synthetic skin care, indeed more so. This achievement has been obtained as a result of research carried out by scientists across the board, from raw materials to formulation. Colour cosmetics and sun care are a
different story altogether. Complex to formulate and stabilise, heavily reliant on silicones and synthetic polymers, these cosmetic products are rarely natural. Despite a growing consumer interest for silicone-free, natural cosmetics, water-in- silicone (W/Si) formulations remain undisputed leaders in makeup and sun care applications.
Making high performance makeup
products without using synthetics is difficult. Most makeup and sun care products employ a W/Si composition, a structure that performs well, bringing good stability and smooth and easy application of pigments to the skin. The end result is perfect, with long lasting and water resistance properties. Natural ones are more often based on oil-in-water (O/W) compositions similar to those used in skin care. The challenge for such formulations, besides stability and in particular for high pigment levels, is a
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tendency to caking with a dry, uncomfortable feel. The water-in-oil (W/O) structure appears to give superior results in terms of coverage and comfort. Yet silicone-free and PEG-free inverse emulsifiers are rare. The few examples that exist have not been designed for pigment carrying systems and are difficult to stabilise. They require the addition of synthetic stabilisers and/or a co-emulsifier, with an impact on naturality and sensory properties.
Stability issues due to pigments One of the main causes of destabilisation of makeup and sun care formulas is the presence of pigments which influence the integrity of the final emulsion.
OH
HO O
O O O O
O O
O OH O O
Pigments are solid particles which are insoluble in water and oil. The main pigments used in cosmetic products are titanium dioxide (CI 77891), red iron oxide (CI 77491), yellow iron oxide (CI 77492), and black iron oxide (CI 77499). They appear in the form of dry powders and tend to form aggregates, which are difficult to separate.
Some techniques can be used to break these agglomerates. The first one is to use a strong agitation to break them up physically, but it is not enough to avoid reagglomeration. The use of a wetting agent is therefore necessary to prevent this phenomenon, by adsorbing on the surface of the pigments. It also helps to reduce the amount of mechanical energy needed to make the dispersion. The other technique is to use treated pigments which are more hydrophobic and less reactive than untreated pigments.
O HO O O O HO O O
Pigments at the heart of creation Anyone who wishes to develop an ingredient dedicated to formulations containing pigments must place pigments at the centre of the process. Gattefossé has applied its strong knowledge in lipid chemistry to the development of its latest W/O emulsifier. Guided by colour formulation experts, pigments were placed at the heart of the research from day one. The emulsions were constructed around pigments, taking into consideration different types of coating and uncoated materials. Among the steps: l Reverse engineering of performant W/Si and PEG-based systems to understand exactly how they work at the water-oil interface
OH
l Construction and trials in formulation of prototypes based on building-blocks composed of fatty acids and polyglycerol of variable chain length and composition
l Determination of HLB using the PIT- slope method
Figure 1: Schematic representation of the main structure of the W/O emulsifier.
l Conception and patenting of a unique composition that has a determining role on the performance of the ingredient
September 2019
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