EMULSIFIERS
Cosmos definition of natural It is worth pointing out here that the definition of natural varies considerably depending on the certification body. There are many common elements, but it is not a universal list of requirements. According to Cosmos3
, the definition of
natural is: Physically processed agricultural ingredients, eg oils (non-toxic, non GMO, non endangered, non animal tested)
Derivatives from unharmed animals allowed (eg. beeswax, lanolin)
Extracts are allowed, but must not use synthetic organic solvents
Chemically processed ingredients are allowed, subject to certain processes (esterification, alkylation and hydrogenation are allowed) as long as starting materials are naturally derived
No irradiation or chemical treatments allowed
In terms of emulsifiers, this narrows the field down considerably as chemical transformations such as ethoxylation are not permitted. However, as esterification is allowed we can still create molecules containing a lipophilic group and a hydrophilic group, which is permitted under Cosmos.
Types of natural emulsifier There are actually not many different types of natural emulsifier, as the restrictions placed on what is permitted results in a limited pool of candidates. There are also not many physically processed naturally occurring emulsifiers, so most of the commonly used natural emulsifiers have been synthesised from natural starting materials. According to Cosmos this is allowed (but some purists may not agree).
Some examples of chemically processed natural emulsifiers: Sucrose Esters Polyglycerol Esters Glucosides Sodium Stearoyl Lactylate Potassium Cetyl Phosphate Sorbitan Esters Cetearyl Olivate Stearic Acid Glyceryl Stearate Citrate
Some examples of physically processed natural emulsifiers: Quillaja Extract Yucca Extract Lecithin Beeswax Soapwort Extract Soapnut Extract Lanolin Egg Yolk
Figure 3: Microemulsion.
It is common practise to combine two or more emulsifiers together, and also with fatty alcohols and glyceryl stearate (to promote liquid crystals), this gives a more complete package for the formulator. We are now going to examine three of
the above emulsifiers in more detail: sucrose esters, polyglycerol esters and quillaja extract.
Sucrose esters These take the form of a hydrophilic sucrose molecule to which one or more lipophilic groups have been grafted onto it by esterification onto the numerous hydroxyl groups.4
The lipophilic groups are
normally fatty acids derived from coconut or palm oil. The advantages of sucrose esters over other emulsifiers are many. They are very safe, used in food, and are mild to skin. They also have very favourable INCI names where it is easy to see the natural origin of the molecule. Depending on the type of sucrose ester they are fairly easy to use as long as the rules are followed. Getting a good texture
and body to emulsions is something that can be a challenge, but the experienced formulator can use tricks to improve body (by using fatty alcohols) and increase viscosity (by using thickeners). One reported problem is that viscosity can change over time, however the manufacturing method can help this. Some examples of sucrose esters
are: sucrose laurate, sucrose stearate, sucrose distearate, sucrose tristearate, sucrose cocoate, all with varying HLBs from 1 to 16.
Simple cream 1 In this very simple system (Formulation 1), a high HLB sucrose ester is combined with a low HLB one. This ensures maximum packing at the interface and improves stability and texture.
Polyglycerol esters These have a chemical similarity to PEG- based emulsifiers – except the hydrophilic part is natural. Glycerol molecules will easily join together via their hydroxyl
Table 1: Synthetic versus natural emulsifiers. Synthetic
• (Usually) Low odour and colour • Predictable results, very reproducible
• Can accurately predict HLB Value • (Usually) Cheap
• Can be irritant to skin (especially PEGs) • Unattractive INCI name
• Cannot be used in organic products • Range of textures can be achieved
• Becoming less favourable to consumers Natural • Often odour and colour problems
• Can be batch to batch variation, unpredictability and reproducibility problems
• Cannot always predict HLB Value • Can be expensive
• Normally perceived as mild to skin • Attractive INCI name
• Can be organically approved
• Can be difficult to achieve a good texture, and texture can change over time
• Becoming more favourable to consumers February 2016 PERSONAL CARE 57
n Surfactant: forms the interfacial film
n CoSurfactant: ensures flexibility of interfacial layer and reduces the interfacial tension
Hydrophilic phase
Hydrophobic phase
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