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

MJLMJL Member
edited January 19 in Formulating
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? 

Comments

  • PharmaPharma Member, Pharmacist
    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.
  • MJLMJL Member
    edited January 19
    @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.
  • MJLMJL Member
     :'(  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? 
  • PerryPerry Administrator, Professional Chemist
    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 
  • MJLMJL Member
    Thank you, @Perry.
  • NeilLNeilL Member
    What preservative are using?
  • MJLMJL Member
    @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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