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Preservative questions
I’m still having a lot of doubts about preservatives…
How do you deal with (partial) hydrophobic preservative(s) (blends)?
For example, phenoxyethanol is added to the cooling down phase, due to its volatility, but won’t it migrate to the oil phase instead of being active in the water and oil/water interphase?
* I want to try a few blends, but am not 100% sure in which phase to put them or to pre-mix with a water miscible solvent first:
Blend 1: phenoxyethanol (90%) + ethylhexylglycerin (10%);
Blend 2: 68% Benzylalcohol
26% Methylparaben
6% Propylparaben
0,1% BHT (to inhibit benzyl alcohol from oxidizing).* I know non-ionic surfactants can deactivate some preservatives, like phenoxyethanol, parabens. But inspite of that, I see them combined all the time. Is this really something to worry about? Or is this only with polysorbates?
* And last but not least: packaging.
I read that low to medium density polyethylene is able to absorb parabens from a formulation and benzyl alcohol and phenoxyethanol are known to interact with polyethylene and polystyrene.
But aren’t most packages made of polyethylene?
What are your thoughts on this?Thank you!
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20 Replies
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phenoxyethanol and benzyl alcohol are water-soluble, though sparingly so - very little of either will partition into the oil phase, so the answer is put them in the water phase
substantially water-soluble ethoxylated surfactants, e.g. SLES, can reduce the activity of some preservatives; they won’t deactivate them outright
regaring packaging, I’ve never seen any of these phenomena occur in practise; this appears to be one of those urban myths that has somehow become received wisdom despite not having a shred of evidence to support it
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Parabens can be inactivated by polysorbates via micelle binding.
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The “myth” that parabens get absorbed may come from food industry where migration of chemicals from /into plastic packaging is important as they can end up in the food. However, that all parabens somehow will migrate into the packaging is not realistic.
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@Bill_Toge
So it doesn’t have to be added to the cooling phase due to its volatility?
Both blends I mentioned can be added to the water phase as well, I reckon?
Glad to read that whole packaging thing is an unsupported urban myth. You’re right, I never see links to researches when they state those interactions.Thanks everyone!
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@Doreen81 it has a boiling point of 247 °C at atmospheric pressure, so it’s not particularly volatile
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So is there any truth to phenoxyethanol being inactivated by polysorbates? I know this has been around for a while but I’ve never seen any data.
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@Bill_Toge
You’re totally right, silly me! I think I got confused because of this sentence “Phenoxyethanol has the advantage that it is slightly volatile so it will protect the “head space” or vacant air space above the product in the bottle.” on the site of Making Skincare. -
@Bill_Toge
About the supposed volatility of phenoxyethanol.
My supplier of phenoxyethanol keeps on saying that it is volatile, that I shouldn’t look at the boiling point, but the vapor pressure.
He also says that if it wasn’t volatile, I wouldn’t be able to smell its slight flowery scent.
But if I look up the vapor pressure and compare it to a volatile like petroleum ether and a non volatile, like say glycerin, its vapor pressure is indeed more comparable to that of a non volatile.
At the Making Skincare site of Jane Barber they also speak of the volatility of phenoxyethanol, that it “will protect the vacant air space above the product in the bottle”.
I’m confused at which phase to add it. I usually add up to 0,5% to the heated water phase (>70C).Would you help me with this? Thanks!
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@Doreen technically it is, but the question is how volatile
in this paper, the authors recorded the vapour pressure of phenoxyethanol as 0.7 mmHg at 84.5°C and 19.4 mmHg at 135°C
for comparison, the vapour pressure of water at 85°C is around 430 mmHg (and atmospheric pressure at sea level is around 760 mmHg)
although its vapour pressure is very low at room temperature, the fact it can be smelt implies the human nose is very sensitive to it
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@Bill_Toge
Exactly. I see I forgot to mention that the supplier disagreed on me calling it slightly volatile. He recommended to put it in the cooling down phase because he’s somehow convinced the volatility is way higher.
I’ll forward this paper to him.
Glad to see I can keep adding it to the heated water phase.
Thanks for your help, Bill! -
https://knowledge.ulprospector.com/2532/pcc-phenoxyethanol-globally-approved-preservative/
Per George Deckner who is eminently knowledgeable, it is stable at temperatures >100C. In fact, the Technical Rep from Schulke once recommended adding it prior to heating as it will be more effective at the phase borders.
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@Microformulation
Thanks!! -
apropos of nothing, the human nose is extraordinarily sensitive to grapefruit mercaptan; it can be smelt in the parts-per-billion range
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OMG Bill. You have reminded me of my experiences trying to teach organic chemistry to High School students here in Mexico.
I had inherited a number of interesting components from the previous incumbent, so I was able to synthesise compounds such as methyl salicylate, etc. and everything went well until the day I decided to teach my class about fragrances. (This is long before I got the idea to be a cosmetic chemist).
Knowing a bit about it, I prepared for the class by opening all the windows and doors, and turning on the overhead fans.
“Today,” I began, “We are going to make some very fine fragrances that you’ll love. And the really interesting thing is that the main ingredient smells the opposite. Quite bad actually.”
About 10 seconds after I took the lid off the container of butyric acid, all the girls screamed and ran out of the lab, and the boys backed out of the room shaking their heads. I was unable to get them to tolerate the smell while we did the synthesis. -
Low molecular weight amines will clear the room in a flash!
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we have a container of sodium hydrosulphite in the lab… it’s the worst-smelling thing on site (even worse than the thioglycolic acid we use in perms), and because of this I’ve nicknamed it the Tub Of Death
the smell is so vile the technicians won’t even go near it
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@Bill_Toge
Re: phenoxyethanol. I was just reading the data sheet of Tego Care PBS 6 of Evonik Industries. This is what they suggest:“Perfume, temperature-sensitive substances or
electrolyte-containing ingredients are preferably
added at 35 - 40 °C. Phenoxyethanol-containing
preservatives should be incorporated at this
temperature, as well. Since phenoxyethanol is an
amphiphilic molecule it can interfere with the
emulsification process when added directly to the oil
or water phase.”
I would like to know your expert opinion (and/or from others) on this! -
I have heard multiple opinions on this.
It is common knowledge (anecdotal) from many Formulators that Phenoxyethanol (Euxyl PE9010 with Ethylhexylglycerin) will destabilize an emulsion if added in the initial water phase. So, for years I have (and continue to add it post-emulsification when the bulk reaches <40C. This with a chelant(I always use one) and I have never had challenge test failures I can recall.
On the other side of the coin, I have heard Technical from Schulke speak numerous times and they will sometimes endorse adding it at the initial heated phase since they feel it is more effective at the phase boundaries. However, being pragmatic and getting good results (as outlined in the paragraph above), I take the approach “If it isn’t broke, don’t fix it.”
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this is another example of received wisdom where (apparently) nobody has asked why or how it occurs, or tried it for themselves to see whether or not it’s true
personally, I have never witnessed it, and my view is that if an emulsion can be destabilised by something as inert and sparingly soluble as phenoxyethanol, it’s nowhere near robust enough to be fit for use in a consumer product
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I tried it for myself in a knock-off of a failed emulsion and Idid see thet it was causing the instability.
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