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Home Cosmetic Science Talk Formulating Magnesium sulfate makes my emulsions fail

  • Magnesium sulfate makes my emulsions fail

    Posted by pccochran on October 30, 2019 at 9:28 pm

    Hello everybody. My name is Craig, and I make body
    emulsions in Georgia. My current method is to make a base o/w emulsion and use
    this to create a variety of different finished products. This base emulsion is
    smooth and stable, and it will accept just about any active ingredient (e.g.,
    taurine, benfotiamine, leucine, resveratrol, vitamin D3, melatonin, etc). This
    is the recipe for the base emulsion:


    • Distilled water - 63.00%
    • Glycerin - 4.50%
    • Hydroxyethyl cellulose - 0.75%
    • Phenonip - 1.00%            

    OIL PHASE          

    • Flaxseed oil - 8.88%
    • Avocado oil - 8.88%
    • Isopropyl myristate - 4.00%
    • Emulsifying wax NF - 7.00%
    • Vitamin E Tocopherols - 1.00%

    EMULSION PHASE           

    • Fragrance - 1.00%

    Recently I created a batch of body cream with 10% magnesium
    sulfate. Powders like this are folded into the base emulsion, then homogenized at very low sheer. Within a day, the mag emulsion started to separate, with a portion of the water
    phase settling on the bottom of the jar. Does anybody know why the magnesium sulfate
    is causing the emulsion to fail? I made a 2nd batch with a more
    incremental addition of magnesium, but it also separated. Any advice you can
    provide is greatly appreciated.

    pccochran replied 3 years, 6 months ago 5 Members · 8 Replies
  • 8 Replies
  • EugeneL

    October 31, 2019 at 6:04 pm

    It’s typical for high amounts of electrolytes to destabilize W/O emulsion. Although HEC is fairly electrolyte tolerant, is it possible that the system is too overloaded? what was the incremental amount of MgSO4 added in the second batch?

  • chemicalmatt

    November 1, 2019 at 7:09 pm

    I doubt that system would hold up with even 1.0% MgSO4.  Divalent electrolytes are particularly adept at destabilizing.

  • Pharma

    November 1, 2019 at 7:55 pm

    Emulsifying wax NF per se shouldn’t be too much of a problem since it’s non-ionic but the fairly small quantity of true surfactant in the mixture (Polysorbate 60) is low and it’s just one single surfactant; hence it’s prone to ‘surface charge neutralisation’ by MgSO4. I suppose you should be able to find a work-around probably by adding a co-emulsifier. Maybe try a sorbitan ester and some fatty alcohol?

  • Bill_Toge

    Professional Chemist / Formulator
    November 1, 2019 at 8:45 pm
    instead of emulsifying wax NF, try an emulsifier with an electrolyte-tolerant co-emulsifier with a long chain, e.g. PEG-100 stearate or polyglyceryl-6 behenate
    alternatively, instead of magnesium sulphate try using magnesium oxide (less water-soluble)
  • Pharma

    November 2, 2019 at 8:31 am
    Emulsifying wax NF should be electrolyte tolerant and has a relatively long chain ;) . But using either of the two proposed ones in addition might actually work (try and see).
    Magnesium oxide will form magnesium hydroxide in water and this is alkaline. Neutralising it will result in a soluble magnesium salt. Since magnesium ions are usually the culprit, using magnesium lactate or the like is pointless unless one were to use a cationic emulsifier.
  • pccochran

    November 7, 2019 at 6:52 am

    Thank you for all the excellent advice. I think a co-emulsifier is a logical next step. 

    But here’s another mystery. In the last couple of days I made a batch of cream that included 7.5% magnesium sulfate and 7.5% taurine. The taurine seems to “protect” the emulsion and it is still very robust. I’ve noticed a similar effect with taurine emulsions that are subjected to high heat for multiple days — they don’t separate. Why would taurine have that kind of preservative effect? 

    Taurine has some negative side effects in this particular case, but there’s no doubting its ability to strengthen an emulsion. 

  • Pharma

    November 7, 2019 at 6:52 pm

    pccochran said:

    …Why would taurine have that kind of preservative effect? … 

    It is likely the coincidental result of ionic strength, ion type, buffer capacity, and probably pH which has an impact on Debye length, Zeta potential, and electrical double layer which in turn affect emulsion stability.
    Taurine being a zwitterionic aka inner salt makes it likely (but not obligatory) that it’s addition can reduce adverse effects of other salts on emulsion stability.
    Given the high electrolyte concentration, I’m not sure how well predictions are possible and how far it’s just a lucky find.
  • pccochran

    November 9, 2019 at 4:47 pm

    Thank you, @Pharma. Your response is very helpful.