Home Cosmetic Science Talk Formulating What reaction is happening here btwn my surfactant and citric acid?

  • What reaction is happening here btwn my surfactant and citric acid?

    Posted by MJL on January 19, 2020 at 6:39 pm

    Hi. I am mixing together distilled water, sclerotium gum, and sodium cocoyl glycinate. The mixture is completely clear, and gel-like (smooth and “gliding” feeling). When I add a tiny amount of citric acid to adjust the pH, as I stir the product, it starts turning white/opaque and results in a kinda thin, “milky” look and slightly denser, less “wet”/glide-y feeling (if that even makes sense); less “gel” feeling, anyway. The product then remains this way for the rest of its “shelf” life (not selling it, just for personal use). 

    Does anyone know what reaction is happening in this case, and is it affecting the properties of the surfactant and/or final product? Or is it simply cosmetic? 
    MJL replied 4 years, 6 months ago 4 Members · 7 Replies
  • 7 Replies
  • Pharma

    Member
    January 19, 2020 at 7:04 pm
    You’re probably producing cocoyl glycine which is no longer a high HLB anionic sufactant but a low HLB non-ionic one which also lost most of its surfactancy.
    At a rough estimate, this starts happening at a pH below ~4.5 (really starting to get problematic below pH ~2.5) -> at a higher pH, you should be fine and it’s likely something else.
  • MJL

    Member
    January 19, 2020 at 10:21 pm

    @Pharma Thank you for this information. My pH does often drop to about 4.5-4.8 when I first adjust with the citric acid, though not below that. My preservative brings it back to around 5.0-5.5. I guess in the future it would be worth it to try to avoid getting as close to the 4.5 range while I am formulating. Hopefully this will help. Thank you again.

  • MJL

    Member
    January 20, 2020 at 8:11 am

     :'(  Still got clouding as soon as pH gets around 7.5. Any lower and the milky/opaque characteristic(s) are back. Hmm… 

    I definitely observed the citric acid reacting with the surfactant in some kind of way…

    Anyone know of any ways to remedy this? Is there another pH adjuster that would be better? 

  • OldPerry

    Member
    January 20, 2020 at 1:55 pm

    Yeah, you could try a different acid. HCl, acetic acid, phosphoric acid. Or try adding the citric acid as a solution (20% aqueous) instead of directly as crystlas.

    You might also consider adding some Cocamidopropyl Betaine 

  • MJL

    Member
    January 21, 2020 at 3:25 am

    Thank you, @Perry.

  • NeilL

    Member
    January 21, 2020 at 9:34 am

    What preservative are using?

  • MJL

    Member
    January 21, 2020 at 5:50 pm

    @NeilL  Leucidal SF Complete, but this reaction btwn the surfactant and citric acid is taking place before I have added the preservative, and there are no changes for the better or worse after adding the preservative.

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