Friday, April 22, 2011

HLB system: An introduction

The next few days are going to be a blast from the past as we learn more about the HLB system. I've updated these posts with more information and ideas so it's not just a re-posting of something I wrote two years ago! 

When we're working with emulsification systems like e-wax or BTMS, we don't really think of how it's going to emulsify our product. We just add the required amount and poof! - we have lotion. If we want to create an emulsification system of our own, we need to turn to the HLB system for guidance! (Please click to see LabRat's amazing PDF on this topic, replete with all the HLB values for oil phase ingredients and emulsifiers! Download this and treasure it!)

For more information on how emulsification works, click here

The hydrophilic-lipophilic balance system (or HLB) was created by William Griffin the 1940s as a way of figuring out which emulsifier would work best with the oil phase of an emulsified product. All emulsifiers have a hydrophilic head (water loving) that is generally composed of a water soluble functional group and a lipophilic tail (oil loving) generally composed of a fatty acid or fatty alcohol.

The theory behind HLB is that emulsifiers showing greater solubility in water would be better for oil in water emulsifications; emulsifiers showing great solubility in oil would be better for water in oil emulsifications. The lower HLB valued emulsifiers are better in water in oil as they are more lipophilic; the higher valued HLB emulsifiers are more hydrophilic.

The solubility of a molecule means it will dissolve in the solvent and becomes part of a homogeneous solution. It generally increases with temperature, hence the reason for heating and holding our lotion ingredients. And most emulsifiers we use are in a pellet or flake form, so heating is the only way to incorporate it into a liquid environment.

The HLB value of an emulsifier is determined by the hydrophilic portion of the surfactant. The equation is as follows - HLB = % hydrophilic portion by weight of the molecule divided by 5. (We don't need to know this to use the HLB system, but I'm the kind of girl who has to know everything, so I thought I'd include it for like minded people!) So the higher the number, the higher the portion of the molecule is hydrophilic, and the more water soluble it will be. The lower the number, the less water soluble and more fat soluble it will be. 

Take a look at this polysorbate 80 molecule (HLB 15). Based on this number, we should expect this is to be an emulsifier that would be better suited for oil in water emulsifications because it has such a high HLB number. (And from experience, we know polysorbate 80 is well suited for adding oil to watery things like toners or facial cleansers - not a lot of oil, but enough that we want it not to float on top of the product!) We don't see any fatty acids or alcohols on this chain, so it's going to be a hydrophilic emulsifier with a high HLB value.

Other high HLB emulsifiers include ceteareth-20 (HLB 15.2), Oleth-10 (HLB 12.4), and polysorbate 20 (HLB 16.7).

Glycol stearate has an HLB of 2.9, which means it is a lipophilic emulsifier that would be better suited for water in oil emulsifications due to its low HLB number. Sorbitan stearate (HLB 4.7), glycol distearate (HLB 1.0), and glyceryl stearate (HLB 5.8) are all examples of low HLB emulsifiers.

So how do we use the HLB system to create an emulsifier? We work out the math (I heard some of you shriek there, but if you can remember your elementary school math for figuring out percentages, you'll be fine!) by figuring out the required HLB of our oil phase and the HLB values of our emulsifiers to get a number that matches. (That's for tomorrow's post!)

You will never use one emulsifier alone for a lotion - you might for bubble baths and body washes (glycol distearate to pearlize them), perfumes or toners (polysorbate 20 or 80 to disperse the oils), and so on, but for a lotion, we require a complete emulsification system!

We want to combine a low HLB emulsifier (the one that loves oil more) and a high HLB emulsifier (one that loves water more) at a level that will match the HLB of our oil phase. And we'll want to add enough of these emulsifiers to ensure we get proper, stable emulsification of our product. (I've seen it suggested that you start at 2% and at 4% emulsifiers in your lotions. I'm going to suggest 4% for now to ensure we have enough in the lotion to be successful.)

Please note, there is no hard and fast rule for how much HLB emulsifier to start off with in a recipe. LabRat used to suggest 2% but I like to use 4% or 5%. This is not like Polawax - there is no suggested rate, it's all about trial and error. You will see different amounts of emulsifier used in different recipes. If you're going to use the HLB system, be prepared to work on the calculations for each recipe and the possibility that you haven't used enough emulsifier. This is why I suggest 4% or 5%. 

Join me tomorrow for more fun with the HLB system with a demonstration of how it works (or you can read ahead to this older post if you can't wait, but there will be more added tomorrow!) 


Katie said...

So when is the exam? And is it multiple choice? :)

Honestly, it is amazing how much I have learned from you in the past few months! When I first found your site I shied away from the posts about HLB because it felt way over my head. Today I just drank it up and even went to look at some of the old HLB posts! Thanks, Swift! Have a good weekend!

Will said...

Oh great, this is where I get to feel stupid.

This time I really try to understand.

Good piece.


Ellbie said...

Thanks Susan,

Very well written so even I can understand. Also, thanks for looking into the Aveda shampoo formulation, I have been away and doing a lot of catching up today. There are SO MANY products I want to make, just need to find some extra bucks for the supplies.


Susan Barclay-Nichols said...

Hi Katie! There isn't an exam (and I don't do multiple choice!), but tomorrow I will be posting a recipe that I'll encourage you to figure out on your own (the answers will be posted the next day).

Don't feel stupid! We all didn't know something at one time! Just go into every situation being curious and you'll learn it! I didn't think I could ever be interested in chemistry and now look at me - okay, that's probably a bad example because I'm slightly obsessive compulsive, but you get the idea!