EMULSIFIERS
Formulation 1: Simple cream. Ingredient
Phase A Water
Sucrose Stearate (HLB 16) Glycerine
Xanthan Gum
Phase B Abyssinian Oil
Sucrose Tristearate (HLB 3) Phase C
Preservative, fragrance %
74 3 5 1
15 2
qs
Procedure: Mix together phase A and heat to 75˚C until homogenous. Mix together phase B and heat until homogenous. Add phase B to phase A with rapid stirring for 5 minutes. Once cooled, add phase C.
Appearance: Smooth white cream
groups to form chains of up to 10 and possibly more. This entity can then be combined with fatty acids via esterification to produce emulsifiers. Generally, the more glycerol molecules you join together, the bigger the hydrophilic part will be and the higher the HLB will be. Therefore polyglyceryl-6 distearate has a higher HLB (approximately 16) than polyglyceryl-3 diisostearate (approximately 4.5). Again these are widely used in the food industry and are very mild and safe. They have a light feel on the skin, and are easy to use, some of them being liquid and some solid.5
Simple cream 2 In Formulation 2, the polyglycerol ester is acting as the sole emulsifier, and as it has a high HLB it forms an oil-in-water system easily.
Quillaja extract This ingredient is a water-based extract made from the whole biomass of the quillaja tree (Quillaja saponaria), which grows native in Chile.6
Creaming – when the oil droplets rise to the top of the emulsion
Sedimentation – a substance in the formulation drops out and forms a solid on the bottom
Phase inversion – the emulsion changes from w/o to o/w or vice versa
Flocculation – where oil or other particles stick together in lumps
Coalescence – oil particles join together to make bigger particles or a continuous layer
Ostwald Ripening – where oil particles gradually get bigger over time
When trying to overcome problems such as these, the main principle is to prevent oil droplets coming together and also floating to the top of the emulsion. In water-in-oil systems, the water droplets need to be kept suspended.
These giant trees
produce a high concentration of saponins in their bark, wood and leaves, which act as a detergent/ emulsifier (Formulation 3). The material is very natural, minimally processed and can also be obtained in an organic grade. It is also palm-free, a big current trend.
Stabilising natural formulations
When trying to stabilise natural emulsions, the same rules apply as with synthetic formulations. However, the range of ingredients used to solve the problems will be narrower as the formulation still needs to be natural. The most common causes of instability in emulsions are:
58 PERSONAL CARE February 2016
One of the main methods of improving the stability of oil-in-water emulsions is to thicken the water phase of the formulation. This prevents the oil droplets from coming together and prevents mobility of ingredients. One of the most popular thickeners for emulsions is carbomer, however under natural formulating rules this cannot be used. Good natural alternatives are xanthan gum, cellulose based thickeners, modified starch and some clays. To improve stability of both w/o and o/w emulsions the oil phase can also be thickened, again this is to prevent movement of droplets. For this, natural waxes could be used.
Other factors to take into consideration when looking at stability include the emulsifier – is the right HLB combination being used? Consider combining high HLB/low HLB and ensure the right level of emulsifier is used as the oil/water
interface may not be covered sufficiently. There may also be a problem of incompatible ingredients which are causing flocculation or sedimentation. Possible candidates here are salts, preservatives, high/low pH ingredients or perfumes. Of course it is always recommended to carry out full stability testing on any formulation, which as an absolute minimum is 3 months storage at 40˚C.
Conclusion
It is possible to make elegant and stable emulsions using natural emulsifiers, provided a few rules are followed. It is always a good idea to survey the market to select emulsifiers that suit the type of formulation being made, and bear in mind there are many commercial blends that have taken away much of the guesswork so that a stable emulsion can be made every time. If instability or an unfavourable texture results, the formulation needs to be revisited to see if there are any incompatibilities or omissions. Finally it is worth pointing out that the current trend for natural formulations continues and does not show any signs of retreating, therefore perseverance in this field is advantageous.
PC
References 1
2
Klein K. Liquid crystals and emulsions: a wonderful marriage. Cosmetics and Toiletries 2002; 117: 30-4.
‘The HLB System’ 1976. ICI Americas Inc. Revised March 1980.
3 ‘Cosmos – Standard’.
www.cosmos-standard.org/ docs/COSMOS-standard-final-jan-10.pdf
4 Mitsubishi-Kagaku Food Corporation
www.mfc.co.jp/english
5 Gattefosse SAS.
www.gattefosse.com 6 Desert King International, Chile.
www.desertking.com
Formulation 2: Simple cream. Ingredient
Phase A Water
Glycerine Xanthan Gum
Phase B Abyssinian Oil
Polyglyceryl-6 Distearate Phase C
Preservative, fragrance %
74 5 1
15 5
qs
Procedure: Mix together phase A and heat to 75˚C until homogenous. Heat phase B to 75˚C. Add phase B to phase A with rapid stirring for 5 minutes. Once cooled add, phase C.
Appearance: Smooth white cream
Formulation 3: Simple cream. Ingredient
Phase A Water
Quillaja Extract Glycerine
Xanthan Gum
Phase B Abyssinian Oil Phase C
Preservative, fragrance
%
74 5 5 1
15 qs
Procedure: Mix together phase A and heat to 75˚C until homogenous. Heat phase B to 75˚C. Add phase B to phase A with rapid stirring for 5 minutes. Once cooled, add phase C.
Appearance: off-white smooth cream
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