O/W emulsion at low pH

I'm making deodorant cream (O/W emulsion) for myself with alum (potassium aluminum sulphate) as active. Personally, I don't have problems with the low pH (approx. 2.5-3.0).
For as far as I know alum is unstable under higher pH conditions.
1. Would it be ok for the alum stability to raise the pH a little, to pH 3.5-4.0 (with NaOH)?
2. Preservatives might not be necessary at these conditions, but I like to be on the safe side. Would Phenonip at about 0,5% be a good idea at this pH?
3. I'm not sure if the emulsifiers I have can handle that low a pH.
Which one would be suitable:
- GMS + PEG 100 stearate
- Polyglyceryl-3 stearate
- Glyceryl stearate citrate
- GMS + Ceteareth 20
- Polyglyceryl-6 Stearate (and) Polyglyceryl-6 Behenate (Tegocare PBS 6)

Thanks in advance! :-)

Comments

  • edited March 11
    Btw: I used to make the deodorant cream by adding 5% alum to a standard lanette I cream:
    - purified water;
    - decyl oleate;
    - Lanette SX by BASF (cetearyl alcohol, sodium lauryl sulfate and sodium cetearyl sulfate);
    - sorbitol 70%;
    - sorbic acid.

    This is what I had in mind for future preparations (I'm not particularly fond of lanette cream):

    A )
    Distilled+deionized water ad 100
    Allantoin 0.35%
    Glycerin 2%
    Panthenol 1% skip panthenol to avoid hydrolysis?
    Caprylyl Glycol 0.3%
    Alum (KAlSO4) 5%
    (Should I add NaOH here to raise the pH to 3 before I add the Phenonip?)
    Phenonip 0.25%

    B )
    Glyceryl Stearate Citrate 2%    --> or GMS +PEG100 Stearate 4.5%
    Polyglyceryl-3 Stearate 2%      ----^
    Cetearyl Alcohol 2%
    Hydrogenated Vegetable Oil 2%
    Tocopherol 0.2%
    Isoamyl Laurate 6%
    Jojoba Oil 7%
    Phenonip 0.25%

    B1 )
    Sepimax Zen 0.85% (Polyacrylate Crosspolymer-6)

    C )
    Cyclopentasiloxane/Lexfeel D5 1%
    NaOH 18% q.s. -> pH 3.5-4.0??? -> stability alum, pH too high?
  • Cyclopentasiloxane/Lexfeel D5 1%
    NOT THAT. Please see recent posts about restrictions.
    Design of anti-aging creams, gels, and serums; shampoos; and therapeutic cosmetics. In-house label and box design capability.
  • @Belassi
    I know, I still have some left and it's for own use, I don't sell it.
    Lexfeel D5 isn't a silicone btw, it's a replacement.
  • Oh I see, a substitute!
    Design of anti-aging creams, gels, and serums; shampoos; and therapeutic cosmetics. In-house label and box design capability.
  • speaking from experience, you'll want a preservative to stop yeasts and moulds growing in it

    out of those emulsifiers, my personal choice would be a combination of GMS/PEG-100 stearate and polyglyceryl-3 stearate (high and low HLB, plus the GMS is acid-stable)
    UK based formulation chemist. Strongest subjects: hair styling, hair bleaches, hair dyes (oxidative and non-oxidative) I know some stuff about: EU regulations, emulsions (O/W and W/O), toothpaste, mouthwash, shampoos, other toiletries
  • I always thought Arlacel 165 was an HLB of 11 and Polyglyceryl-3 stearate (I have Dermofeel PS in stock was about an HLB of 9? That is a naroow, high range.
    markfuller@microformulation.com Microformulation.com Microformulation Cosmetic Consulting provides Custom Formulations for both large Commercial accounts as well as smaller entrepreneurs. We can provide Naturally compliant Formulations under the NSF, NPA, Whole Foods and USDA Organic Certifications.
  • @Bill_Toge @Microformulation
    Thanks for your help, I just made the cream this afternoon and it turned out great (for now that is). This is how I made it:

    A )
    Distilled+deionized water ad 100
    2%      Glycerin
    0.35% Allantoin
    0.3%   Caprylyl Glycol
    5%      Alum (KAlSO4)

    B )
    4%      GMS + PEG 100 Stearate (Tego Care 165)
    2%      Polyglyceryl-3 Stearate (Dermofeel PS)
    2%      Cetearyl Alcohol
    2%      Hydrogenated Vegetable Oil
    6%      Isoamyl Laurate
    7%      Jojoba Oil
    0.2%   Tocopherol

    B1 )   
    0.9%   Sepimax Zen (Polyacrylate Crosspolymer-6)

    C )
    1%      Cyclopentasiloxane
    0.5%   Phenonip

    The final pH was 3.2 without adjusting (turned out less acidic then I expected).
    I left out the panthenol to avoid acid hydrolysis.
    I put the Phenonip in the cool down instead of the water- and oilphase (because of the phenoxyethanol-emulsion stability we discussed in the other thread).
    Next time I make it I'll raise the cetearyl alcohol just slightly I think, for the rest viscosity/consistency is fine. Now I hope it remains stable for quite a while.
    Until I can get my hands on a stable salt like aluminum chlorohydrate, alum works just fine for me!
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