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How much do your creams & lotions thicken over a few days?
Recently I am finding that many of our formulations are almost doubling in viscosity over 2 to 4 days after a sample is made.
I am wondering if this is common to others too? We have some samples recently that started out same day pourable as a milk shake and then set up to the point where it won’t pour at all in 2 or 3 days.
The base of most of these usually contains
Water, Prop Glycol, PEG-40 Stearate, Cetyl Alcohol, GMS 165, oils, Isopropyl palmitateWhat is your experience as far as lotion or creams thickness over a few days time?
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23 Replies
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@DavidW I think in many more discussion previous to this, it has been pointed out by many learned chemists here that Cetyl Alcohol is the main culprit which leads to this thickening of emulsion on standing. Try to either cut down or eliminate just to confirm the fact.
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Yes, in most the cases Cetyl or Cetearyl Alcohols are a culprit. However you may try to stir it slow in a few days - it helps with many formulations to get the same viscosity you have achieved initially.
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Does anyone know why cetyl/cetearyl alcohol is the culprit? What is chemically happening? I have seen this trend myself but it hasn’t occurred to me yet why.
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slow crystal formation at RT
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I have read in some article that single fatty alcohol would crystallize more compared to a mixture of fatty alcohols. A mixture would give you a more amorphous and stronger structure, this was pertaining to some candle patent but I am guessing that it might be applicable to emulsions as well.Though I use a mixture of fatty alcohols in my emulsions but honestly never ever thought of this crystalline and amorphous part.Correct me if I err.Cheers
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@milliachemist u mean cetyl alcohol thicken the emulsion after several days, but mixture of cetyl alcohol and stearyl acohol dont thicken it?
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The purer the fatty alcohol is, and the tighter the carbon chain length distribution is, the more it will develop crystals in an emulsion. The interaction between/among crystals is what causes the viscosity to increase in the way David describes it.Mixing cetyl and stearyl alcohols will inhibit some, but not all, of that crystal formation. There are ingredients that will completely inhibit crystallization.
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Thank you all for your responses. This is very interesting. And believe it or not, after being in the industry for 29 years I am just now realizing this.
So what do you all use in place of Cetyl or Cetearyl alcohol in order to thicken a product but not have this occur over time?
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I would add some liquid caprylic alcohol to inhibit crystalization without changing skin feel. (INCI may be Caprylyl Alcohol.)
KAO, P&G, and Sasol North America all make this material.Alternatively, using Behenyl Alcohol instead of cetearyl should work better.This lit may help: -
@Bobzchemist Very interesting and useful link.
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When you say that Behenyl Alcohol should work better, does it mean that in this case as well the chances of crystallization exist??? Like Cetyl this is also a saturated alcohol and with a longer C chain, or the curious case of Cetyl differs from formula to formula???
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It’s been my experience that Behenyl doesn’t crystallize nearly as much. I’m not sure why - it could just be because the grades I’ve used haven’t been very pure.
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That purity part makes it all too plausible, indeed how we say it - self explanatory.
Thnx @Bobzchemist
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Bob thanks for the info and the link.
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IIRC few days back we had a query (on chemistscorner.com) for Caprylyl Alcohol being used as a preservative but overall reducing the emulsion viscosity as well. So I suppose this is where it can come into play as a preservative plus viscosity regulator in cetyl alcohol based emulsions. Maybe disrupting the formation of crystalline structure, who knows!!!!!
This means certain other glycols can be used as well to regulate the viscosity in emulsions if incorporated and chosen wisely. -
I have noticed many times that adding PEGs or even Alkyl PEG Ethers help to solve the problem in some formulations.
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@vitalys I noticed this in my normal salt based shampoo when I added DPG and it became water thin.
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To refer this back to the one-pot emulsification post a bit ago, this is one of those situations where using a one-pot process can be a drawback. It’s important in terms of preventing crystallization to get the cetyl, stearyl, and other fatty alcohols mixed together well before emulsification, otherwise you run the risk of having droplets of mostly pure fatty alcohols lurking in your system, ready to crystallize as soon as they are left alone to accomplish their dastardly deeds.
You can attempt to avert this cruel fate by mixing/homogenizing at high temperatures for extended periods of time, but at some point the costs of doing so exceed the costs of using an auxiliary kettle to heat your oil phase in separately.(No, I don’t know why the purple prose crept in. We may just be getting too close to Halloween…) -
We always make our products in 2 phases.
One thing we did that was interesting (I knew of this but forgot). Took out cetyl alcohol totally. We had polyquat 10 in the formula, about 0.4%. After the emulsion and after cool down we added about 0.3% SLS to see if it helped the emulsion any. Upon addition it thickened the product. It is the combo of polyquat 10 and SLS
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David, that’s interesting experience, thank you!
Bobzchemist, It was nice purple prose
-idiomatic and simple explanation -
@Bobzchemist - I recently created a formula with approx. 7% Cetearyl & Cetyl Alcohol and used a Caprylic Acid combination at 1% as a preservative and it Did Not thicken, I was wondering why because some “lotion” formulas have thickened over a week or more with just 3-4 % C. Alcohols. I happened to use this preservative as a fluke with intentions of not reordering it, now it’s a Keeper!
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@Ajm Think it has been clarified in some other posts too that the crystallization of the fatty alcohols that takes place over a period of time has been nipped in the bud by the magical herb used by you.
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BobZchemist,
Is using Behenyl Alcohol instead of Cetyl Alcohol a direct replacement or is it formulation dependent?
Thanks
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