Friday, February 26, 2010

E-mail question: Thickening surfactant systems

In this post, Naomi writes...If I don't have Crothix, could I substitute stearic acid? or Cetyl Alcohol? or another thickener - like Hydroxypropyl Methylcellulose? So, you add in Crothix for thickening purposes? What do you suggest as possible substitutes?

No, you can't use stearic acid or cetyl alcohol. They will eventually separate out and leave a gooey white mess at the bottom as they are not water soluble. So you'll want to use something water soluble like glycol distearate or PEG-150 distearate. Crothix was developed specifically to thicken surfactant blends, and it works really well (sometimes too well, creating Jell-O like substances! I suggest using the liquid because it's easier to control than the pastilles!)

You can use hydroxypropyl methylcellulose. As I've used this and wasn't really happy with it - it precipitated to the bottom, so I know I've done something wrong - I'd suggest consulting your supplier to find out how to use it. You can get pre-blended mixtures of this stuff (click here for more information from the Personal Formulator), which you would add at 5% in your surfactant mixture.

You could use something like carbomer for making gels. Here's a post I wrote on the topic a a while ago. Or you could thicken it up with some water soluble oils - they won't thicken as well as the other things I've mentioned, but they will increase the viscosity. Or you could use oils with polysorbate 80 in a surfactant mixture (like this body wash recipe here). Again, this won't thicken as much as the other suggestions, but it will thicken it up slightly.

You can also use salt to increase the viscosity of any anionic surfactant blend - this is called the salt curve. This is a tricky business and easy to mess up. Just add salt a bit at a time until it reaches the thickness you like. (Look for a post on this topic tomorrow morning...)

You can increase the viscosity of your surfactant mixtures by adding an amphoteric surfactant like cocamidopropyl betaine (I include this in all my recipes to increase mildness and add thickening). You can also make a thicker surfactant blend by reducing the water and increasing the surfactants. This will be more concentrated, and you'll need less. And you can use thicker surfactants. A mixture of something like SLeS, Plantapon, and cocamidopropyl betaine will be quite liquidy, while a mixture of something like BSB, LSB, and cocamidopropyl betaine will be quite thick.

You can also thicken your mixtures by including something like cocoamide DEA (I've been playing with this, and a post on this topic is coming shortly. See the picture to right - yeah, it's not pretty, but I stink at taking pictures!)

And finally, you can thicken your surfactant mixtures by choosing your essential or fragrance oils wisely. (Click here for a post on this topic). I have found that using a 2% mixture of half lavender, half rosemary thickens my bubble bath enough that I don't need to include any thickeners. Citrus based essential or fragrance oils work really well for thickening.

As a note, I'll be taking a closer look at surfactants in March, so keep a look out for that!


Susan said...

I am looking forward to your post tomorrow. I have tried using salt to thicken body wash. It worked really well but was more "murky" than the one thickened with crothix. Your post may help explain why.

Li said...

What about xantan gum, does that work?

Susan Barclay-Nichols said...

Xanthan gum could work in a surfactant based system, but it is dependent upon the amount of salt in it. I will write more about this shortly...

Tara said...

Susan, what do you think is the minimum amount of water you would need with surfactants?

Susan Barclay-Nichols said...

Hi Tara. I usually go for 50% water, about 40% surfactants, and about 10% other things like hydrolyzed proteins, glycerin, silicones, fragrance oils, panthenol, and preservative, depending on the creation. You can go lower to 30% surfactants if you want something thinner, or you could even go to 10% if you wanted to make something in a foamer bottle.

Anonymous said...

How does coco betaine thicken surfactants? It's much thinner than the other surfactants I use.


Marcus said...

In my understanding Cocomodioprpyl betaine works to thicken because of it's high salt concentration

Anonymous said...

I have a question about thickening surfactant products with stearic acid or cetyl alcohol. I want to make my own foaming bath whip, like the kind sold at Brambleberry and numerous other suppliers(I am trying to make something similar, although I have never used the original product. To me, buying a pre-made "base" kind of defeats the point of making my own products). The ingredient list is as follows:

Glycerin, Water, Sodium Cocoyl Isethionate, Sorbitol, Propylene glycol, Disodium Lauryl sulfosuccinate, Stearic Acid, Sodium Chloride, Diazolidinyl Urea (and) Iodopropynyl Butylcarbamate, Tetrasodium EDTA.

It's pretty simple, and I already have all the important stuff at home. But here are the problems I can see with the list:

1. Presumably the stearic acid is acting as the thickener and opacifier and is giving the formula the creamy texture. But what keeps this formula from separating without an emulsifier? They even tell you you can add up to 5% oils and not have separation. How is that possible? If it isn't possible, how could I make a product like this that would be stable? Could I perhaps substitute some emulsifying wax(or another emulsifier) for part of the stearic acid? Instead of using just stearic acid could I use 3 parts stearic acid to 1 part e wax? Or would adding a solubilizer like Polysorbate 80 help?

2. How on earth can there be more glycerine in the formula than anything else, including water? It seems like that would make for a very sticky product. I checked the ingredient lists of foaming bath whip at several different suppliers, and they were all the same, and all had glycerine as the first ingredient. My assumption is that the list is incorrect and that glycerin is quite a bit further down, past the water and SCI at very least. But I wanted to see if you had any thoughts on this.

As always, thanks so much for sharing your knowledge and experience with everyone. Your blog is absolutely brilliant.