How to add essential oils into your cleaning products.
If the thought of lazing around in your very own ‘hand-made’ spa-at-home excites you then read on. We want to help you turn your basic and boring old shampoo or bubble bath base into a feast for the senses! All you need is some base (see the New Directions website for a basics range that is available via mail order), some essential oils and a little bit of chemical know-how……
We’re talking essential oils and delving into a little of the how and why to ensure that your sweet smelling dreams come true time after time!
Before we get into the oil side, let’s take a closer look at some surface chemistry and discover a little more about the chemistry of clean.
What is a shampoo / body wash made of?
A basic shampoo or body wash can be made with a cleansing agent, known as a surfactant, distilled water and preservative. However, this will not make the best shampoo or body wash. By using additional ingredients, the shampoo/body wash can be given different characteristics to make each one suitable for different hair or skin types.
It is important to note that the key ingredient is the surfactant.
What is a surfactant?
A surfactant is a chemical that stabilizes mixtures of oil and water by reducing the surface tension at the interface between the oil and water molecules. To put this in other words, the surfactant acts as a sort of chemical mediator or bridge builder. Because water and oil do not dissolve in each other a surfactant has to be added to the mixture to keep it from separating into layers.
Surfactants have a hydrophobic (water hating) tail and a hydrophilic (water loving) head. As can be seen from Diagram 1, the hydrophobic tails move to the centre to get away from the water and the hydrophilic heads turn to the outside to get nearer to the water.
Surfactants form micelles in these types of systems.
What is a micelle?
Micelles are a group of surfactant molecules dispersed in a mixture.
To get the micelles to form, we need two things – we need to add enough surfactant to get to the right critical micelle concentration (CMC) for the specific product, and we need to reach the critical micelle temperature. It can be hard to work out the optimum point for your surfactant blend but for most applications that isn’t a real problem as the product will still function well at either side of the CMC.
These micelles are important, as they are what create an emulsion in a formula.
In mixes such as shampoo’s and body washes, these micelles are what creates the viscosity of the product and what emulsifies oils (such as fragrance, essential oils or specialty oils).
What can cause such mixtures to thicken / thin / separate?
Where you have a standard, salt-thickened surfactant system the micelles are generally arranged in rods close to their critical micelle concentration. This is the point where they need the least amount of energy to stay happy – their lazy place! Happily this is also the point where they work best.
Fragrance oils will often react differently with the surfactants and can sometimes cause the mix to become too thin. This is usually only a problem when you are using lots of fragrance – say over 2%, most formulations require only 0.5-0.8% fragrance to get a good result. Each fragrance oil may require a variation in the basic formula so it is important to carry out stability and performance testing every time you make a change.
Adding Essential Oils
When you add essential oils into this micelle structure you ‘stress’ it a little. The free surfactant in the bulk water will either solubilise or break the oil down depending on the surfactant HLB but after a certain point the micelle structure will collapse. This can happen for a number of reasons:
1) Any water based surfactant system will have a limit to how much oil it can accommodate before it get’s defoamed.
2) The complex aroma chemistry of essential oils has a detrimental effect on micelle packing. As each essential oil is different, some will be tolerated better than others.
Essential Oils that do not seem to have any significant effect on surfactants are:
The citrus essential oils have a tendency to “thin-out” the shampoo/body wash.
To overcome this, It sometimes helps to add the fragrance or essential oil to a small amount of solubiliser such as polysorbate 20 or PEG 40 castor oil, mix well, and then add it to the shampoo/body wash mix. If you want a natural solution you could try our vegetable derived decaglyceryl monolaurate as this has proved to work well in some formulations.
Wondering how much solubiliser to use? Well, you usually have to add it at a ratio of approx 3 solubiliser to 1 part essential oil but that won’t work with every solubiliser/ oil combination so be prepared to have a few goes. When it works, the micro-emulsion will be totally clear and should improve both foaming and stability.
Another option could be to add a polymeric thickener to the surfactant blend that would act like a spiders web and trap the little oil drops throughout the mixture making it less likely to collapse. Xanthan gum is probably the easiest and most cost-effective solution.
Essential Oils or Fragrance Oils can be added according to personal preference – but we generally recommend addition of no more than 1% or so as adding more can lead to sensitivity issues and that is a much bigger problem than having a thin shampoo!
Experiment with your shampoo/body wash and different fragrances to make sure you get the effect you want and if you are still having problems, speak to our team of experts who may be able to work with you to find a more robust solution.