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pH strips and natural preservative system
Hello..I have made a lotion with the ingredients
listed below:1) Cold pressed vegetable oil mix – 15.5%
2) Stearic acid - 6.5%
3) T.E.A. - 1%
4) Glycerin - 5%
5) Aloe vera juice - 10%
6) Sodium benzoate - 0.35%
7) Potassium sorbate - 0.35%
BHT - 0.5%9) Benzyl alcohol - 0.2%
10) Essential oils - 1%
11) Deioninsed water - 61%
I took below 3 samples (10% solution samples) of this lotion for pH testing:
1) The original formula
2) The original formula + 10 drops of citric acid solution (40%)
3) The original formula + 30 drops of citric acid solution (40%) - At this point I could see the lotion separating into small globules.
I was using pH strips of Merck and they seemed to indicate
that all 3 samples I took are quite high pH, nearly 7.My questions:
A) Are pH strips accurate?
I understand that my preservative mix – sodium benzoate,
potassium sorbate and benzyl alcohol – needs a low pH (~5) to be active against
microbes. How do I reduce the pH of my lotion without causing
it to separate? Will increasing the quantity of stearic acid + TEA help?C) Will the preservatives in this lotion not work
at all, or can I put some shelf life on it – even if a short one
like 2-4 months? -
8 Replies
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A) no
no - TEA is a base
C) no the preservatives won’t work but a high pH could. (> -
There are no emulsifiers in this formula, I don’t see how it could possibly work.
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1) TEA Stearate, made from reacting TEA with Stearic Acid, is an emulsifier, (not a very good one) but it only forms/reacts at temperatures above 70-75C. Are you are processing at that temperature? How have you determined how much TEA to use?
2) TEA Stearate is a soap, just like sodium, magnesium and potassium stearates are soaps. They are formed through an acid-base reaction. The reaction reverses/falls apart at pH’s below about 8. There is no way around this.
3) It is not chemically possible for your lotion to exist in a stable form below pH 7. Therefore, your preservative mix – sodium benzoate, potassium sorbate, and benzyl alcohol - is completely unsuitable for your product. You will either have to use a different preservative mix, or a different emulsifier. Sorry, but there’s no other way to fix this. -
- The stochiometry for TEA STEARATE is way off and you need 3.25 percent TEA to use TS as a emulsifier with 6.5 stearic.Your preservative system will not work using TS suggest new formula using polymeric emulsifier as a start.Also ending up with about 10 percent soap as TS is way too high for skin.
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^^^ Both the above. Use better technology as DrBob suggested.
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Thank you very much for your comments @Belassi @Bobzchemist @DRBOB@VERDIENT.BIZ @David
I can’t understand though how this lotion was working..I’ve been using it for few months now, though consumed it within 3-4 weeks of making.1) Can you please suggest a suitable emulsifier keeping the rest of the formula constant? Will help to get a few options as availability may become an issue (I’m based in Mumbai, India).
2) And the recommended dosage for each? Let me mention here that I am trying to create a body lotion that flows, not a heavy cream.
3) One last question: If pH of TEA stearate emulsions is so high, how was it traditionally used for leave-on creams? Does applying a pH of 8+ on skin regularly not cause skin damage?~Thanks!
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@Bobzchemist Yes, I am mixing at 70 degrees C. I do not want a high pH formulation as I want to make a product suitable for kids and people with sensitive skin. So I’m guessing a pH of 5.5 to 6 would be ideal?
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Can you get Ultrez 10 and xanthan gum/If so take out stearic acid and use 1/0.3 ratio of U-10/XG neutralizing using 1;1wt/wt ratio of TEA to Ultrez to Ph 5,5-6 to get lotion consistency you want.You can then use the formula as is including preservative system.Heat both water and oil phases to 70-75C and add oil to water.
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