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Home Cosmetic Science Talk Formulating Stability of Urea in Cosmetic Formulations

  • Stability of Urea in Cosmetic Formulations

    Posted by tecnico3vinia on November 25, 2021 at 7:14 pm

    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, 

    Graillotion replied 1 year, 1 month ago 5 Members · 9 Replies
  • 9 Replies
  • Graillotion

    Member
    November 25, 2021 at 8:08 pm

    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?

  • ngarayeva001

    Member
    December 1, 2021 at 5:35 am

    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.

  • ngarayeva001

    Member
    December 1, 2021 at 5:38 am

    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.

  • ngarayeva001

    Member
    December 1, 2021 at 5:39 am

    @Graillotion, sorry are you referring to sodium citrate?

  • Pharma

    Member
    December 2, 2021 at 8:31 pm
    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.
  • DaveStone

    Member
    December 3, 2021 at 11:28 am

    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.

  • ngarayeva001

    Member
    December 6, 2021 at 1:15 am

    @Pharma thank you! This is so cool!! I thought it just used in deodorants

  • Graillotion

    Member
    December 7, 2021 at 2:26 am

    @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.

  • em88

    Member
    January 5, 2022 at 3:29 pm

    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

  • Graillotion

    Member
    January 6, 2022 at 2:34 am

    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.