The ABC to HLB - Creating Dream Creams and Luscious Lotions

Anyone who has tried to wash a greasy pan without using detergent will know that oil and water don't mix in fact they detest each other so much that they usually require chemical mediation. You may beg to differ and tell me that it is perfectly possible to get oil and water to mix and you would be right for a while but it doesn't take long before they go their separate ways and spelling devastation for your formula.

Without going into a detailed chemistry lesson water likes to bond with water and oils like to bond with other oils due to special internal forces. The strong bonds that exist within each separate phase can be broken if you put some energy into the system (for example by homogenizing or stirring at high speed for a while) but when you stop stirring the little balls of oil and water soon start to coalesce and grow and before too long you have your two phases again. This can be slowed down physically by adding something that acts as a barrier - a thickener or suspending agent may do this job nicely and may result in a product that is stable for months or more but this only tends to work where the difference between the phases is very large - say 95% water, 5% oil. So, what most people do is opt for an emulsifier and this is where chemical mediation comes in.

There are lots of different emulsifiers but the general principal remains the same. They have one end that likes water and another end that likes oil. This dual-personality means that they grab hold of water droplets with one arm and oil with the other helping to form the emulsion of your dreams!

The HLB scale (which goes from around 4-18) was originally established to help classify ethoxylated emulsifiers and is applied to non-ionic emulsifiers. Matching the HLB of your ingredients to the emulsifier via a few simple calculations gives you a good starting point for a formulation. While the system isn't fool proof (it doesn't always work) it is regularly used to help select a wide variety of different emulsification systems and remains a good starting point, especially for those new to formulating. The classifications run like this:

To work out which HLB you need to make an emulsion you need to do the following.

1. Find out the HLB of each of the main ingredients in your oil phase. For example: Beeswax HLB 12, Almond Oil HLB 6, Isopropyl Myristate HLB 11.5.
2. Work out each ingredients contribution to the total HLB for the oil phase. To do this you need to know how much oil is in your oil phase:

So, the oil phase makes up 20% of the formulation so: HLB / TOTAL % OF OIL PHASE * % FOR THAT INGREDIENT.
Example - Beeswax: 12/20 * 5 = beeswax accounts for a HLB of 3 in this formulation.
Almond Oil 6/20 * 10 = Almond Oil accounts for a HLB of 3 in this formulation.
Isopropyl Myristate 11.5/20 * 5 = Isopropyl Myristate accounts for a HLB of 2.88.

The total HLB for this formulation works out at: 8.88 so you would choose emulsifiers with a HLB of between 8 and 9.

Now that you have identified your products HLB best practice takes two emulsifiers and blends them to form a stable emulsion. This is because it increases the complexity of the two phases and makes then just a little less likely to split. Different emulsifiers will have different sized 'middles' and this too can add to the stability - very long chain emulsifiers can tangle up in the formula providing a physical as well as chemical barrier between phases.

Finally you will be wondering what percentage of emulsifier is required. Unfortunately this is not covered in the HLB system so a general rule of thumb applies. Your emulsifier will generally make up between 2-7% of your formulation. Getting it right in your formula may take some development time but it is worth persisting with as once you crack the code you are on the road to riches with your own beautiful creams and lotions.

Take care and have fun with your formulations and remember that New Directions offers a consultancy service to help iron out any specific problems or questions that you might have. Creating a stable emulsion can be quite tricky so don't expect to solve the problem in a day, especially if you are going for a 'niche' product such as an organic or cosmaceutical.

Amanda Foxon-Hill

29 November 2010