Unstable emulsion advise/troubleshooting ideas

Hi folks. Maybe something stands out for you in this formula that is simple to fix? 
Freeze-thaw performs well and stable at room temp but once I let it warm up to ~40C, it separates. 

An important caveat: I used regular home stick blender for 2-3 min high sheer blending and the rest was mixing by hand during the cooling phase (this is when Phase 3 was incorporated), so perhaps mechanics are to blame?
The product ended up with lots of small visible bubbles. 
I also tried the same formula with a different emulsifier (Cetearyl Alcohol & Glyceryl Stearate & Coceth-20) and managed to not have bubbles but similar performance on stability (separates when warmed up). 



In terms of HLB value, I was targeting 11.9 since some sources put olive squalane at 11 while others at 12-12.9 HLB.
Phase 1Water53.90%
Sodium phytate0.10%
glycolic acid (GA)6.00%
lactic acid2%
Salicylic Acid2%
Propanediol6%
L-arginine (up to pH 3.9. appr. 7%)
Phase 2
olive squalane15.0%
Montanov 68 (Cetearyl Alcohol (and) Cetearyl Glucoside)4.5%
Behenyl Alcohol2.50%
Phase 3
Leucidal6%
Gorgonian extract2.0%

Comments

  • I have to add this about separation when heated: it could be easily "emulsified" again when just stirred (in both cases), and once it cools down it looks fine again. HMMMMM...
    Technically, coalescence would be irreversible, right? So it's not it? Maybe just oil separating?

    Should I increase the emulsifier? Or maybe increase the oil phase proportion? Up to 25%?

    FYI Montanovs' pH range is 3-12. 

    Now, the whole anionic/cationic/zwitterionic thing - that I don't know how to think about. Technically, Montanov is good with cationic ingredients but I can't find anything on zwitterionic ingredients that (as I was explained earlier) form here when Arginine interacts with acids.



  • AVisotsky said:
    I have to add this about separation when heated: it could be easily "emulsified" again when just stirred (in both cases), and once it cools down it looks fine again. HMMMMM...
    Technically, coalescence would be irreversible, right? So it's not it? Maybe just oil separating?

    Should I increase the emulsifier? Or maybe increase the oil phase proportion? Up to 25%?

    FYI Montanovs' pH range is 3-12. 

    Now, the whole anionic/cationic/zwitterionic thing - that I don't know how to think about. Technically, Montanov is good with cationic ingredients but I can't find anything on zwitterionic ingredients that (as I was explained earlier) form here when Arginine interacts with acids.




    Hi there,

    There are a few reasons I can think of:

     - Although 40°C is not quite the melting point of some of your emulsifiers, it may be enough to soften and destabilise them.

     - You have no thickeners in the formulation, so all of its viscosity probably comes from the emulsification itself, which means that when the emulsification fails, there is no "backup" to help hold it together.Your olive squalene is going to decrease in viscosity even if it is liquid at room temperature, so the product will lost viscosity this way too.

     - Your mention of stirring by hand after blending may be to blame if it's not very thorough. Consider the implement you're using - something with more surface area (e.g. wooden spoon vs dessert spoon) is going to move the mixture more efficiently and keep the emulsion stable whilst it cools.

    I would suggest:

     - Introducing a liquid emulsifier (perhaps replacing one of the two you're already using as three might be excessive) which means that it will act the same at room temperature as it will at 40°C = no instability surprises because it can't melt.

     - Introducing a thickener to the water phase such as hydroxyethylcellulose at about 0.3-0.5%. Add it to your water phase and allow it to disperse before heating and it will help to keep all those emulsified oil droplets suspended.

  • Thank you so much for your analysis!
    I was just putting Hydroxypropylcellulose on my shopping list as I read this :)
    I will check for liquid emulsifiers as well. 

    Yes, I use a spatula for the cooling phase, I'll pay more attention during the next trial batch. 

    Thanks again, for taking the time to provide your suggestions. 
  • @AVisotsky when you introduce phase B into phase A does it immediately turn into a white liquid or do you need to stir/shear?

    The reason I ask is, if it doesn’t automatically turn white, you don’t have enough (or the right) emulsifier/surfactant to break the surface tension between the oil phase and the water phase, so you require plenty of shear to keep the two combined until the “waxes” start to solidify. And then it’s only pseudo-stable, an increase in temperature breaks it easily given that you don’t have any rheology modifiers (Xanthan Gum is great for this) to prevent micelles from moving and coalescing.

    At any rate, to reduce impact of temperature on the texture of your lotion/cream, you should always have a water phase thickener in there. Even if your emulsion is stable. Otherwise you’ll pump out lotion when cooler, and ”milk” when it’s warmer. It will also reduce the amount of emulsifier you will need.

    I experimented with a lotion with no water thickeners, and it was stable. I was able to even melt it back to liquid and it remained stable. But obviously the viscosity fluctuation was less than desirable. 
  • Got ya. I was reading this technical explanation that helps understand the mechanics, exactly what you just said: either even out the viscosity or power through with EM/sheer. Makes sense, thank you for taking the time to explain.

    I'd like to stay away from gums, are there are other viscosity modifiers besides Hydroxypropylcellulose that you know? 
    Thank you so much for sharing your thoughts and experience.
  • letsalcido It's a good question. If I remember correctly, it turns white once I start the blender, it just loses translucency once mixed. 
    Perhaps, need to try a thickener and increase Montanov a bit? I do like the sensorial properties of Montanov 68 emulsions. It would be great to keep it.
  • @AVisotsky I’m not super experienced in cosmetic ingredients. But any water gelling agent would help: carbomers, acrylic based polymers/copolymers, natural gums, modified celluloses.

    It will all really depend on the texture you want to achieve. Are you looking for more of a water gel cream feel? Go with acrylic polymers and copolymers. If you want something with a bit more “flow” like a lotion packed in a pump bottle, then gums or modified celluloses. Or combine a couple different things to achieve the rheology you’d like.

    In terms of stability, you just want the water phase to “move less”, the rest is just how you want it to feel.
  • ozgirlozgirl Member, PCF student
    The BASF equivalent to Montanov 68 is Emulgade PL68. Emulgade PL68 is always used in combination with a second emulsifier (Usually Emulugin SG - Sodium Stearoyl Glutamate) in the BASF starting formulations.


  • @letsalcido this is very helpful. How do one decides on the optimal viscosity of the water phase? 
  • @ozgirl thank you, I used behenyl alcohol since per Montanov's formulating guide they recommend fatty alcohol as a co-emulsifier. I'll look into alternatives to that if my experiment with viscosity fails :)
  • @AVisotsky trial and error: stability testing and skin feel. Also looking at what other people are doing can give you a good idea (for example, Xanthan Gum 0.1-0.5% normally used in lotions and creams).

    It all really depends on your product, the characteristics you want it to have and how stable it is from your own testing.

    Maybe someone else here has more precise guidance.

  • letsalcido  :) The trial approach works for me :) Thank you!
Sign In or Register to comment.