Valerie George03.02.22
This month, I give formulation advice on maintaining viscosity in an acrylate-based system and insights on raw material selection. Have a formulation question? Email me: askvalerie@icloud.com.
Dear Valerie: I overheard a chemist in my lab telling another chemist he needed PEG-8 stearate but could only find PEG-8 distearate, which they would use instead. What does the additional “stearate” do and will this be an issue?
—The Replacement
Dear Replacement:
I’m not sure what emulsion your co-worker is making, but I do know he’s making a big mistake! Well, he’s making a mistake big enough that he’ll wish he just took the time to find the missing ingredient. These two ingredients are not close enough to be used interchangeably. PEG-8 stearate is an oil-in-water emulsifier, whereas PEG-8 distearate is a water-in-oil emulsifier. That extra stearate in the “distearate” is a lipophilic moiety, so its presence makes it more oil-loving than using the stearate version. This is reflected in the HLB values of both compounds. The HLB value drops from approximately 11 to 8 in comparing PEG-8 stearate versus PEG-8 distearate.
Likewise, when comparing glycol stearate to glycol distearate, distearate has a lower HLB value than the stearate due to the additional stearate molecule. The HLB value for the distearate is approximately 1, and stearate’s HLB is approximately 4. Because there is a glycol instead of a PEG-8 moiety, these compounds overall are more lipophilic and can be used in both oil-in-water and water-in-oil systems. Both act as emulsion stabilizers, and from that perspective, they can be used interchangeably with some slight variation in end viscosity and feel. However, it’s still not recommended! Glycol distearate lends a pearlescent appearance to emulsions due to the packing of the distearate molecules. Glycol stearate does not lend this effect, and anyone is bound to notice a difference when looking at your elegant cream.
Dear Valerie: I’m making a hand sanitizer with polyacrylate crosspolymer-6 and I wanted to add a tiny bit of cocamidopropyl betaine. When I did this, everything turned to water, and I completely lost viscosity. Why did this happen? Can you fix it by adjusting the pH like you can with carbomer?
—Keep It Clean
Dear Keep It Clean:
Acrylate polymers are notorious for being sensitive to electrolytes. While polyacrylate crosspolymer-6 is noted by the manufacturer to have “extreme resistance to electrolytes up to 10%,” the reality is that 10% is not always realized depending on the formulation. Cocamidopropyl betaine can not only have a net charge depending on pH, but it also contains up to 6% sodium chloride or more. You won’t be able to adjust the viscosity by playing with pH because polyacrylate crosspolymer-6 is a pre-neutralized polymer that does not rely on an alkali to open the polymer for viscosity building. Skip the cocamidopropyl betaine for something that’s salt free.
Dear Valerie: If you had to carry just one fatty alcohol, which one would you keep at your bench? Our facility is in a very remote place and it’s getting more expensive to bring items in. Is there one fatty alcohol that seems to do it all—thickening, stability, good skin feel? I thought it would be easier to just carry one.
—Fatty Alcohol Favorites
Dear Fatty:
An intern once asked me why I reach for one fatty alcohol over the other. In Mr. Miyagi fashion, I directed her to whip up four lotions to see the difference for herself, each with cetyl, stearyl, behenyl and cetearyl alcohols. My older chemists peered over with a look that read both scoff and interest, waiting for the outcome of the intern’s labors.
A fatty alcohol should be chosen with consideration, yet they may be one of the ingredients that chemists least think about. Regarded as commodities, fatty alcohols are often used to provide structure in an emulsion, which in turn builds viscosity and provides stability to a formula. While they all can impart these attributes to some varying degree, one differentiating point between fatty alcohols is what the consumer feels on pick up, application and end skin or hair feel.
What did the intern discover? Cetyl alcohol is the lightest of them all. It provides excellent thickening and stability to formulas but can still leave a lotion feeling light. Stearyl alcohol yielded a more compact cream that was denser than the one with cetyl alcohol. Cetearyl alcohol fell expectedly between cetyl and stearyl alcohols, as we used a cetearyl alcohol that was equal parts cetyl and stearyl. Behenyl alcohol was the most luxurious of them all, feeling denser and heavier than stearyl. It spread beautifully but had quite a bit of that characteristic fatty alcohol “afterglow” on application that required extensive rubbing.
Knowing this, is it possible to just choose one? I suppose it is, if you can compensate for the attributes that the others provide at an economic price. For example, if you only carry cetyl alcohol but must create a luxurious face cream, you will need to compensate for the creaminess that stearyl alcohol imparts compared to cetyl alcohol. Sometimes I find that cetyl alcohol can feel a little too cheap, so cetearyl alcohol is often the best bet. It’s not too light, nor too heavy.
Be cautious, however, because not all suppliers of fatty alcohols are the same. Cetyl alcohol is a C16 alcohol derived from palmitic acid. Stearyl alcohol is a C18 alcohol derived from stearic acid. None of these are pure compounds, and some suppliers have varying compositions of 10% or more. Cetearyl alcohol is a little tricky because every supplier offers varying ratios of cetyl:stearyl in 70:30 or 30:70 or 50:50. Once you qualify a supplier of your fatty alcohol, don’t treat it like a commodity. Validate every new source you’re considering.
What did my older chemists did learn that day along with the intern? That having patience to conduct tedious work on the bench can reveal a lot about the simplest things!
Valerie George
askvalerie@icloud.com
Valerie George is a cosmetic chemist, science communicator, educator, leader and avid proponent of transparency in the beauty industry. She works on the latest research in hair color and hair care and is the co-host of The Beauty Brains podcast. You can find her on Instagram at @cosmetic_chemist. Do you have a formulation question you want answered? Email her at the address above.
Dear Valerie: I overheard a chemist in my lab telling another chemist he needed PEG-8 stearate but could only find PEG-8 distearate, which they would use instead. What does the additional “stearate” do and will this be an issue?
—The Replacement
Dear Replacement:
I’m not sure what emulsion your co-worker is making, but I do know he’s making a big mistake! Well, he’s making a mistake big enough that he’ll wish he just took the time to find the missing ingredient. These two ingredients are not close enough to be used interchangeably. PEG-8 stearate is an oil-in-water emulsifier, whereas PEG-8 distearate is a water-in-oil emulsifier. That extra stearate in the “distearate” is a lipophilic moiety, so its presence makes it more oil-loving than using the stearate version. This is reflected in the HLB values of both compounds. The HLB value drops from approximately 11 to 8 in comparing PEG-8 stearate versus PEG-8 distearate.
Likewise, when comparing glycol stearate to glycol distearate, distearate has a lower HLB value than the stearate due to the additional stearate molecule. The HLB value for the distearate is approximately 1, and stearate’s HLB is approximately 4. Because there is a glycol instead of a PEG-8 moiety, these compounds overall are more lipophilic and can be used in both oil-in-water and water-in-oil systems. Both act as emulsion stabilizers, and from that perspective, they can be used interchangeably with some slight variation in end viscosity and feel. However, it’s still not recommended! Glycol distearate lends a pearlescent appearance to emulsions due to the packing of the distearate molecules. Glycol stearate does not lend this effect, and anyone is bound to notice a difference when looking at your elegant cream.
Dear Valerie: I’m making a hand sanitizer with polyacrylate crosspolymer-6 and I wanted to add a tiny bit of cocamidopropyl betaine. When I did this, everything turned to water, and I completely lost viscosity. Why did this happen? Can you fix it by adjusting the pH like you can with carbomer?
—Keep It Clean
Dear Keep It Clean:
Acrylate polymers are notorious for being sensitive to electrolytes. While polyacrylate crosspolymer-6 is noted by the manufacturer to have “extreme resistance to electrolytes up to 10%,” the reality is that 10% is not always realized depending on the formulation. Cocamidopropyl betaine can not only have a net charge depending on pH, but it also contains up to 6% sodium chloride or more. You won’t be able to adjust the viscosity by playing with pH because polyacrylate crosspolymer-6 is a pre-neutralized polymer that does not rely on an alkali to open the polymer for viscosity building. Skip the cocamidopropyl betaine for something that’s salt free.
Dear Valerie: If you had to carry just one fatty alcohol, which one would you keep at your bench? Our facility is in a very remote place and it’s getting more expensive to bring items in. Is there one fatty alcohol that seems to do it all—thickening, stability, good skin feel? I thought it would be easier to just carry one.
—Fatty Alcohol Favorites
Dear Fatty:
An intern once asked me why I reach for one fatty alcohol over the other. In Mr. Miyagi fashion, I directed her to whip up four lotions to see the difference for herself, each with cetyl, stearyl, behenyl and cetearyl alcohols. My older chemists peered over with a look that read both scoff and interest, waiting for the outcome of the intern’s labors.
A fatty alcohol should be chosen with consideration, yet they may be one of the ingredients that chemists least think about. Regarded as commodities, fatty alcohols are often used to provide structure in an emulsion, which in turn builds viscosity and provides stability to a formula. While they all can impart these attributes to some varying degree, one differentiating point between fatty alcohols is what the consumer feels on pick up, application and end skin or hair feel.
What did the intern discover? Cetyl alcohol is the lightest of them all. It provides excellent thickening and stability to formulas but can still leave a lotion feeling light. Stearyl alcohol yielded a more compact cream that was denser than the one with cetyl alcohol. Cetearyl alcohol fell expectedly between cetyl and stearyl alcohols, as we used a cetearyl alcohol that was equal parts cetyl and stearyl. Behenyl alcohol was the most luxurious of them all, feeling denser and heavier than stearyl. It spread beautifully but had quite a bit of that characteristic fatty alcohol “afterglow” on application that required extensive rubbing.
Knowing this, is it possible to just choose one? I suppose it is, if you can compensate for the attributes that the others provide at an economic price. For example, if you only carry cetyl alcohol but must create a luxurious face cream, you will need to compensate for the creaminess that stearyl alcohol imparts compared to cetyl alcohol. Sometimes I find that cetyl alcohol can feel a little too cheap, so cetearyl alcohol is often the best bet. It’s not too light, nor too heavy.
Be cautious, however, because not all suppliers of fatty alcohols are the same. Cetyl alcohol is a C16 alcohol derived from palmitic acid. Stearyl alcohol is a C18 alcohol derived from stearic acid. None of these are pure compounds, and some suppliers have varying compositions of 10% or more. Cetearyl alcohol is a little tricky because every supplier offers varying ratios of cetyl:stearyl in 70:30 or 30:70 or 50:50. Once you qualify a supplier of your fatty alcohol, don’t treat it like a commodity. Validate every new source you’re considering.
What did my older chemists did learn that day along with the intern? That having patience to conduct tedious work on the bench can reveal a lot about the simplest things!
Valerie George
askvalerie@icloud.com
Valerie George is a cosmetic chemist, science communicator, educator, leader and avid proponent of transparency in the beauty industry. She works on the latest research in hair color and hair care and is the co-host of The Beauty Brains podcast. You can find her on Instagram at @cosmetic_chemist. Do you have a formulation question you want answered? Email her at the address above.