What are surfactants?
The term surfactant derives from the words surface active agent and they work by reducing the surface tension between two things that don’t usually mix, like oil and water, making it easier for them to be next to each other. For example, when you shake a bottle of oil and water, little droplets of oil are briefly dispersed into the water but eventually separate into two layers. But introduce a surfactant in the mix, and the droplets will be smaller and more stable—meaning the whole thing will stay mixed longer.
Surfactants can be used as detergents, wetting agents, emulsifiers, foaming agents, or dispersants.
Surfactants are amphiphilic meaning that they have a hydrophobic (water-hating) tail and a hydrophilic (water-loving) head. The hydrophobic tail of each surfactant surrounds and traps dirt, grease and soils. The hydrophilic head is surrounded by water. When the surfactant concentration reaches a certain level the individual molecules start to group together into spherical structures called micelles, where all the tails point to the centre and all the heads are on the outside of the sphere. Dirt and grease is trapped amongst the hydrophobic tails and this is how surfactants work as detergents to clean. See image
What are surfactants used for in personal care?
The three main functions of surfactants in personal care are detergency, foam generation and emulsification (mixing two immiscible substances).
We described about how the detergency (cleaning) works above – by trapping the dirt in structures called micelles. Interestingly the very property that makes them great at remove grease and dirt is also responsible for the ‘stripping’ feeling we sometimes experience after using soaps and shower gels. Unfortunately, most surfactants don’t discriminate between the oils, sebum and dirt we want to remove and the lipids (fats) that are an essential part of the skin’s make up. And this is where skin irritation can occur if the surfactants are not sufficiently mild.
When it comes to foam, this is where we see the surfactant lowering the surface tension between a liquid and a gas – usually the liquid is water and the gas is the air that’s in the bubbles. Some surfactants create a very stable dense creamy foam and some produce larger ‘lacy’ bubbles which disappear more quickly.
This emulsifying property of surfactants make them essential in cosmetics. They can be used to blend oil and water in products like lotions and creams as well as being solubilisers for fragrances and preservatives into water.
What are biosurfactants?
Traditionally the tail portion of surfactants is made from petrochemical sources, and more recently from plant derived oils such as palm and coconut. However, there’s a new kid on the block – biosurfactants.
The industry defines biosurfactants as natural surfactants excreted by an organism. Biosurfactants are amphiphilic compounds (just the same as their chemical counterparts) but they are synthesised from microorganisms. These compounds demonstrate
- high biodegradability
- low toxicity
- effectiveness at extreme temperatures or pH values
- environmental remediation capability
- low aquatic toxicity
- gentle on skin
- impervious to hard water
- good availability of non-tropical renewable resources
- low carbon footprint
Some of the biosurfactant classes are shown in the table. Of these, the sophorolipids and rhamnolipids are the ones making their mark on the personal care market.
Sophorolipids: produced by yeasts which occur naturally in the honey made by bumblebees
Rhamnolipds: fermentation of sucrose
Research has shown that rhamnolipids are more hydrophilic while the sophorolipids are more hydrophobic. Therefore, rhamnolipid and sophorolipid biosurfactants in mixtures showed robust performance.
|Glycolipids||Rhamnolipids||P. aeruginosa and P. putida||Bioremediation|
|P. chlororaphis||Biocontrol agent|
|Bacillus subtilis||Antifungal agent|
|Sophorolipids||Candida bombicola and C. apicola||Emulsifier, MEOR, alkane dissimilation|
|Trehalose lipids||Rhodococcus spp.||Bioremediation|
|Tsukamurella sp. and Arthrobacter sp.||Antimicrobial agent|
|Mannosylerythritol lipids||Candida antartica||Neuroreceptor antagonist, antimicrobial agent|
|Kurtzmanomyces sp||Biomedical application|
|Lipopeptides||Surfactin||Bacillus subtilis||Antimicrobial agent, biomedical application|
|Lichenysin||B. licheniformis||Hemolytic and chelating agent|
Historically scale-up of production has hindered the wider uptake of biosurfactants however market leader Evonik, Jeneil Biotech and Holiferm have cracked the problem and can offer commercial-scale volumes.
At XCellR8 we talk a lot about mildness to skin and these compounds are incredibly exciting from that perspective. We recently wrote a blog about our work using the XtraMild test with Holiferm to help them show just how mild their sophorolipids are.
Formulators will undoubtedly still be getting to grips with working with these new compounds in personal care products, and it may be that we see blends of chemical- and biosurfactants either as a transition or longer term – in any case the potential the myriad benefits that the biosurfactants bring will be felt.
For more info, contact us today.