Stability of Urea in Cosmetic Formulations

Hi there,

I found out that is quite difficult to stabilize urea in cosmetic formulations. Sometimes it can lower the viscosity of emulsions and it also can increase the pH of the cosmetic system after some time, and above pH 7 sometimes there's liberation of ammonium. 

After some research I found out that is necessary to have a buffer solution to prevent pH alteration, but I am a little confused about it. Do I really need to prepare a buffer solution or just a pH adjuster (e.g. citric acid, alctic acid, sodium hydroxide) can already fix the problem? How can I prepare a buffer solution? Do I need to calculate something? I'm having trouble understanding it.

Also, anyone has any more tips about working with urea?

Thanks in advance!

Kind regards, 

Comments

  • GraillotionGraillotion Member
    edited November 2021
    Try searching triethyl citrate in relation to urea....that might get you on a path. :)  (And use the lactic acid.)

    Since you did not list the formula...difficult to give any better kind of answer.  Do you have some liquid diol/polyol as part of the formula?

  • You need to estimate ph of buffer solution using Henderson-Hasselbalch equation. There are calculators online http://calistry.org/calculate/ph-buffer-Henderson-Hasselbalch

    Although, I think it’s easier to stick it into Excel and let it do the job (calculating logs etc). All input are available online, you need to convert amounts of acid and conjugate base to moles (also available online). I use lactic acid buffer.
  • Another alternative is w/o emulsion instead of o/w. pH of w/o doesn’t drift. Having said that w/o are tricky and it’s easier to figure out henderson-hasselbalch equation.
  • @Graillotion, sorry are you referring to sodium citrate?
  • PharmaPharma Member, Pharmacist
    He's referring to triethyl citrate. It's not an acid but a tripple ester of citric acid with ethanol. Once pH increases, it hydrolyses turning into citric acid. This in turn brings the pH back down (and also stopps hydrolysis).

    w/o emulsions also have a pH which can (and will) drift when using enough urea. Unfortunately, there is no benefit from using this type of emulsion when it comes to stabilising urea. I tried making w/o emulsions with 40% urea... was fun but didn't work out (emulsion instability, not chemical instability). Urea is the same b*+ç# as always and heavily interferes with HLB/HLD calculations/estimations and oil phase integrity/stability.
  • I'm using citric acid + sodium citrate to buffer urea. I added too much citric acid the PH went down to 5-5.5. So then I added the citrate to get it up to 6. I don't know if that's the way to do it. I've never come across documentation explaining how to use a buffer, that is, how much of each to add.
  • @Pharma thank you! This is so cool!! I thought it just used in deodorants
  • GraillotionGraillotion Member
    edited December 2021
    @Pharma thank you! This is so cool!! I thought it just used in deodorants
    It will be a cornerstone of our next deodorant project...hehehe...  

    But Chemical Matt turned me on to TEC way back when... I was making mosquito lotion....and needing to extend fragrance/solubilize EO's. 

    Now that I am using a lot of HydroVance....I am also using TEC in about everything. 

    Such a diverse ingredient...can't live without it now.
  • em88em88 Member
    Pharma said:
    He's referring to triethyl citrate. It's not an acid but a tripple ester of citric acid with ethanol. Once pH increases, it hydrolyses turning into citric acid. This in turn brings the pH back down (and also stopps hydrolysis).

    w/o emulsions also have a pH which can (and will) drift when using enough urea. Unfortunately, there is no benefit from using this type of emulsion when it comes to stabilising urea. I tried making w/o emulsions with 40% urea... was fun but didn't work out (emulsion instability, not chemical instability). Urea is the same b*+ç# as always and heavily interferes with HLB/HLD calculations/estimations and oil phase integrity/stability.
    I have read a few articles about using triethyl citrate to stabilize urea. I would give it a shot. Do you have any suggestions regarding any ratio TEC/Urea?

    Thank you
  • em88 said:
    Pharma said:
    He's referring to triethyl citrate. It's not an acid but a tripple ester of citric acid with ethanol. Once pH increases, it hydrolyses turning into citric acid. This in turn brings the pH back down (and also stopps hydrolysis).

    w/o emulsions also have a pH which can (and will) drift when using enough urea. Unfortunately, there is no benefit from using this type of emulsion when it comes to stabilising urea. I tried making w/o emulsions with 40% urea... was fun but didn't work out (emulsion instability, not chemical instability). Urea is the same b*+ç# as always and heavily interferes with HLB/HLD calculations/estimations and oil phase integrity/stability.
    I have read a few articles about using triethyl citrate to stabilize urea. I would give it a shot. Do you have any suggestions regarding any ratio TEC/Urea?

    Thank you
    I use HydroVance...which is not exactly the same animal...The mfg formulas I found...were running .2 to .3%.  But TEC is a nice ingredient...and actually a nice emollient....so maybe a little more is better.  I have a delightful deo formula...and it uses a full 5% of TEC.

    Aloha.
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