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Increased Opacity of Shampoo w/Thickeners & Oils
I’m hoping some of the experts here can explain a phenomenon that I have observed in my shampoo formulation trials. When I add thickeners (currently salt or glyceryl caprylate caprate), my shampoo remains clear. When I add essential oils (0.5%), it remains about 95% clear. However, when I combine the essential oils with a thickener, the solution becomes opaque. If I reduce the oil or thickener enough, it’s clear. What I’m trying to understand is the interaction between the thickener and oil… why are these ingredients clear (or mostly so) individually, but when combined the solution becomes opaque? What’s going on here? Thanks!
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9 Replies
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solubility issues
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As @Belassi says, solubility. The glyceryl caprylate caprate is only slightly soluble in water and the oils are only slightly soluble when combined with your surfactant. When you add them together the whole thing falls apart.
You need more surfactant or less oil or a solubilzing agent. -
Thanks for the answers.
@Perry - I have the same opacity issue when I use GCC as a thickener or salt. Does the salt also have a solubility issue? It’s clear until I add the oil (or the oil+surfactant is clear until I add the salt). -
Yes. When any salt goes into solution it dissociates into its ionic state. This means the ions are occupying spaces between the water molecules (this is a simplistic explanation) and so it becomes less easy to dissolve any other substance. For instance, even a very low proportion of salt - say 0.5% - makes it extremely difficult to dissolve NaOH, which is normally a very soluble substance.
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Secondly, if I read your original post correctly, you appear to be testing by adding the thickener / oils to the diluted surfactant mixture. This is much less likely to be successful. The correct procedure when adding an oil to a surfactant is to add it to whichever surfactant is the best emulsifier, in its UNDILUTED state. So for instance, I make a shampoo which is a combination of carboxylic acid, CAPB, and sodium cocoamphoacetate. Of the three, the last one is an excellent emulsifier and so my first process step is to mix that surfactant with the fragrance oil and stir until well emulsfied.
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@Belassi - Thanks for explaining the science behind the phenomenon. Yes, I’ve been adding the essential oils after cool-down to the diluted solution. I can certainly try to pre-mix the oils with the best emulsifier, but that brings up two questions: 1) What surfactants emulsify (or solubilize?) best? Is there a handy benchmark guide to determine which surfactants are best at this, or do I have to guess (and test)? 2) How would I pre-mix the oils with a surfactant if I need to apply heat? I add the oils to my cool-down phase because most of them have very low flashpoints and can’t handle high or even moderate temperatures.
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I would try premixing your essential oils with some Polysorbate 20 before addition.
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I use essential oils (tea tree, sage, lavender) at 0.4% in our most popular shampoo. I don’t have any problem achieving a clear shampoo; the surfactants are a blend, Plantaren APB, based of the ammonium anionic group. Good emulsifiers. Most surfactants are good emulsifiers but some less so, you have to try it and see. But frankly, I think your main difficulty is using low flashpoint EOs with a hot process. I use fragrance oil with our hot process shampoo, emulsify it in one third of the surfactant, and add that in to the mixed batch that’s just beginning to cool.
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@Belassi: Excellent, I will try that-thanks again! My formula has a good percentage of APGs (i.e. decyl glucoside) and sodium methyl cocoyl taurate. I don’t know how good they are as emulsifiers, but everything was fine until I tried to go above 0.3% essential oils. At 0.45%, it’s opaque. I’ll try your pre-mix method and see if it makes a difference. If not, I’ll try adding a better emulsifier.
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