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Stearic acid neutralization in emulsions
Please help me understand something by filling in the blank: Stearic acid requires something alkaline to neutralize it, otherwise ____________.
I read a post (can’t remember which one) that I “believe” @Microformulation mentioned that if you use emulsifying Wax in the emulsion you should be ok. Maybe it wasn’t @Microformulation but it was one of the forum gurus… I want to make a cream using both ewax wax, plus the stearic acid to thicken.
Thanks a bunch!
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21 Replies
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I think you are confusing stearyl alcohol with sterates. If you neutralize stearic acid you get a hard soap. Stearyl alcohol is usually combined with ewax for viscosity.
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@DAS, no I’m not confusing it with Stearyl alcohol but perhaps I’ll consider using it instead. In my sentence above where I asked to fill in the blank, I was actually paraphrasing something @Perry told someone in a recent post titled Best Way to Use Stearic Acid (Mar 20th). I’m trying to find out what negative effects it would have on the emulsion if you don’t neutralize it.
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This isn’t very, uh, scientific but I have stearic acid in a mascara I make and I do neutralization as the very last step. Before neutralization the mascara looks very rough and bumpy, and after neutralization it’s very smooth and creamy. Very interesting to watch. So there are at least some texture benefits to neutralizing.
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@gld010, interesting. Thank you
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I recall the thread, but I didn’t make the statement.
That said, there are countless Formulations where Stearic acid is used to build viscosity with a softening effect without neutralizing the product.
“Stearic acid is one of the most widely used ingredients in cosmetics. A basic thick cream can be formulated using stearic acid…”
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Thanks for clarifying @Microformulation. I’ve used it in the past to make creams and lotions but never neutralized it. Thanks for confirming it’s not necessary for my purposes. And thanks for the link as well!
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It is still not my favorite as it contributes to the soaping in some cases. I have moved onto Ceateryl Alcohol more often for this purpose.
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@Microformulation I’m using ewax with Cetearyl Alcohol and Poly-20. Would u still use additional Cetearyl in this case or perhaps stearyl alcohol as @DAS mentioned?
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Honestly, if you are using a nonionic emulsification system such as that I would add more or less depending on the desired final viscosity. Now, I usually have a Brookfield measurement of a standard and use that to determine how close I have hit the desired viscosity. It is pretty straightforward in that case.
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Ok cool thanks!
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for what it’s worth, I did an extensive experiment a few years back and found that cetyl/stearyl alcohols increase the viscosity of the proruct at low shear (i.e. make the product more rigid and less fluid), while stearic acid increases the viscosity at high shear (i.e. makes the product feel more ‘creamy’)
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Interesting. How about skin feel? Cetearyl alcohol has always been purported to show more “slip” and less soaping.
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I think the combination tanelise used in March 22 is fine. If you like to use Stearic Acid, you need to have really good heating system and when you add the oil phase (with stearic acid) to the water phase you need to keep the temp. in the same emulsification range for 20-30 min. You may need, also, to use a good homogenizer. You may check your manufacturing settings to know whether they can go up by temp to 75-80 C. because the melting point of stearic acid is approximately 70C
https://en.wikipedia.org/wiki/Stearic_acid
So, you need to go above the melting point by 5-10 C to avoid getting surprises in the stability testing -
@Microformulation I found cetyl/stearyl alcohols thin very readily under shear, and don’t contribute much to the skin feel of the product
@JOJO91343 is this assertion based on your personal experience?
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@JOJO91343 Thanks for the formulation tips. Ive used Stearic acid in the past so I’m familiar with it’s melt point etc. I’ve got a Silverson which creates emulsions before you can blink your eye but honestly I don’t know if mixing for 30 minutes would be over-kill or not.
@Bill_Toge , I’ll be putting your suggestions/comments to the test soon. Thanks for all the input.
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@Bill_TogeI observed the shear thinning of Cetearyl alcohol in past Formulas. However, like many fatty alcohols, I saw rebound from this effect at 24-48 hours. Anyone who has ever seen one of these products thicken post manufacturing can weigh-in on this effect.
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For Stearic Acid, you may use 20 min. for homogenization with the water phase, as long as the temp dose not drop. When you can cool the emulsion, it should be very fast (preferably bu ice) in the lab. You may switch to medium - low homgenization when the temperature go down to 60c till RT.
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Sorry, you may use 20 min, for mixing on High Shear (Not Homogenization) with water phase, etc..till the end of the post (Re: JOJO91343 AT 10:38pm)
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You can use the homogenizer, if the emulsion is still thin at room temp (at the end of the emulsification). If you can leave it overnight, it may thicken up over night based on the concentration of the the emulsifying agents (including Stearic Acid) you have
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Yes, I noticed the rebound effect of cetearyl alcohol
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This is one of the formulas I passed by which contains even Stearate (not directly stearic acid). The formulator in this formula has to heat the Stearate (Oil Phase) up to 80C
https://www.ulprospector.com/documents/1138916.pdf?bs=1254&b=203494&st=1&sl=59688265&crit=a2V5d29yZDpbc3RlYXJpYyBhY2lkIGZvcm11bGFzXQ%3d%3d&k=stearic|acid|formulas&r=na&ind=personalcare
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