Salicylic acid solution cloudy with polysorbate 20 during processing

Hello,

Thanks to the many questions and answers I found using the search feature, I was able to come up with this simple formula and process for a salicylic acid toner. However, I have come across an issue, and I am wondering if I can get some help with this formula or process. One other person already asked this but never returned with feedback. I have tried the suggestions offered in that thread, but nothing has worked.

My simple toner turns cloudy the moment I add polysorbate 20. 24 hours later - it appears clearer, but I noticed a gel-like sediment at the bottom, which I think is the polysorbate 20. When I agitate the solution, it is cloudy again. The final pH is 3.55 without any adjusting. Here are the two versions I have tried so far.

Version 1

Ingredients

Water qs
Sodium Citrate 1%
T. EDTA 0.1%
1,3 Propanediol 13%
Propylene glycol 12%
Salicylic acid 2%
Polysorbate 20 2%
Sodium Benzoate 0.3%

Version 2

Same as version 1, except Propanediol increased to 16% and Propylene glycol 14%.

Process

1. Add Sodium citrate and Sodium Benzoate to water and heat to 75c
2. Add Salicylic acid to glycols, mix until clear and then heat to 75c
3. Add Salicylic solution to water slowly, before the temperature reduces to <70c - (the solution is clear)
4. Add polysorbate 20 (This is when it turns cloudy)

Both processes resulted in a cloudy solution which gradually becomes clear with a gel-like sediment at the bottom. Anyone know what might be happening here? Thank you
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Comments

  • chemicalmattchemicalmatt Member, Professional Chemist
    First, propanediol is virtually same as propylene glycol, and is not as good a solvent so DEL 1,3, propanediol and reduce your cost, improve your product. Likewise for sodium citrate and EDTA; both are chelants so go with one or the other, EDTA being my choice. Next: why do you need Tween 20 in here? I do not see a fragrance oil to solubilize. Leave it out, problem solved. My guess is the citrate is salting out your surfactant causing the cloud. Should you somehow need to employ a surfactant, use the glycereth-XX PEG's (i.e. glycereth-26) instead. These aid solvation of SalAcid while acting as solubilizers same time - double duty! 
  • I guess Polysorbate is here as a surfactant and it reduces chance of recrystallization? I usually use CAPB and it causes no issues. I don’t use sodium citrate though just edta.
  • toketsutoketsu Member
    edited November 18
    There is a study called "Mixed solvency approach", it describes synergy between solvents. There is SA used as a model poorly soluble ingredient. So I guess you are following their method - combine sodium citrate, propylene glycol and polysorbate to get synergy of solvents.

    For commenters above: sodium citrate is a hydrotrope used in many products to dissolve SA (or better to prevent recrystallization), it is not used as a chelator here (reference: Application of Sodium Citrate As Hydrotropic Agent In Spectrophotometric Analysis of Salicylic Acid)
  • Thank you all for your responses!

    @chemicalmatt the polysorbate 20 is in there for two reasons; 1. To lower surface tension to make the solution more readily wetten skin, and 2. As @ngarayeva001 mentions to reduce the chance of recrystallization.

    @toketsu, yes that's right! that's the approach I was going for. 

    An update on how the samples are looking - I increased the pH of both samples to closer to 4. Sample 1 with 25% glycols is clearer but still a little cloudy, pH 3.8. Sample 2 with 30% glycols is completely clear, I actually got this one to pH 4.1.

    I am going to do two more trials - one with sodium citrate and the other with t.edta . I'm trying to get my hands on some butylene glycol so that I can use propylene/butylene mix.

    @ngarayeva001 how much polysorbate do you recommend? I would like to minimize ingredients as much as possible. Also, what's your ideal pH for stability and do you use NaOH as a buffer?
  • MarkBroussardMarkBroussard Member, Professional Chemist
    @ccchem

    You'll have better results using Cocamidopropyl Dimethylamine as opposed to Polysorbate 20.  Also, you don't need both EDTA and Sodium Citrate, Sodium Citrate alone will function both as a chelator and help prevent recrystallization.  Finally, why use an ionic/salt preservative ... Sodium Benzoate?  Better to go with Phenoxyethanol or Phenoxyethanol/EHG that won't salt-out with the salicylates.  As you have learned, your glycols need to be in the 30% to 40% range.
    Chemist/Microbiologist formulating in the Organic & Naturals & Clean Beauty arena under ECOCert/Natural Products Assn/Whole Foods/National Organic Program/Clean At Sephora/Credo Clean guidelines focused skincare & haircare products. 

    See website for details www.desertinbloomcosmeticslab.com
  • ccchemccchem Member
    edited November 23
    @MarkBroussard Thank you for your comment. Unfortunately, I do not have Cocamidopropyl Dimethylamine on hand, so the polysorbate will have to do for now. Apart from Cocamidopropyl Dimethylamine, are there any others you recommend - that are better than Polysorbate 20 or 80?

    Thanks for the tip on Sodium Citrate and preservation, I'll go with the citrate alone and switch to Phenoxyethanol/EHG.

    On the glycols - I was really hoping to get good stability at <30% input. Looks like there's no way around this!

    I'll be back with results once I test another sample with these tips.

    Thank you all

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