Slow darkening in a phospholipid emulsion

AvickAvick Member
edited July 2014 in Formulating
Greetings, fellow formulators!

Ok, so here is my story for today--

I've created an emulsified product using phospholipid-based emulsifiers, and also including lysine, vitamin C, and several botanical oils and botanical extracts including St. John's Wort and arnica. The pH of the water soluble phase is around 5.5 (adjusted up with NaOH). I've been "field testing" this product, basically subjecting it to the abuse of life in the summer in the south, leaving it in my hot car, in the sun, etc. The emulsion is a lamellar one and although I have not seen signs of separation, I have noticed that the product darkens noticeably over a period of about 4 weeks.

The product is preserved with BHT as an antioxidant and benzylalcohol DHA as well as two essential oils (tea tree and peppermint) as anti-microbials. I have done simple dip-stick testing for on the most abused samples and they come out clean for total aerobic and yeasts and molds. What do you think could be causing the darkening?

Thanks for your spirit of collaboration!

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Comments

  • pmapma Member
    The vitamin C... It's very hard to avoid vitamin C oxidation. 
  • BobzchemistBobzchemist Member, PCF student
    edited July 2014
    "The vitamin C... It's very hard next to impossible to avoid vitamin C oxidation. "

    Fixed that for you... :)
    Robert Zonis, Sr. Formulation Chemist, Beaumont Products "All opinions and comments expressed are my own, have no relation to Beaumont Products, are fully copyrighted, and may not be used without written permission."
  • AvickAvick Member
    Haha, thanks you guys!
    :x
  • PerryPerry Administrator, Professional Chemist
    You'd better check your preservative system too.  That doesn't sound robust enough.
  • Hi
    Would you mind telling me where you obtained the phospholipid emulsifier?

    Thanks in advance
  • BobzchemistBobzchemist Member, PCF student
    Croda

    Resources of Nature 

    Lucas Meyer 

    also,plain lecithin.
    Robert Zonis, Sr. Formulation Chemist, Beaumont Products "All opinions and comments expressed are my own, have no relation to Beaumont Products, are fully copyrighted, and may not be used without written permission."
  • Yes, thanks Bob. I just saw this post. Lucas-Meyer has a great selection of phospholipid emulsifiers with great skin feel.

    @Perry, would you have any recommendations for a secondary broad-spectrum preservative? We haven't subjected it to challenge testing yet so I can neither confirm nor deny your allegations. ;)
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