phase separation in anhydrous scrub

Hello, I made an anhydrous body scrub that showed phase separation after stability test (1 month 35°C (control 25°C)+centrifugation 3000rpm/30min: phase separation, odour not comparable to standard and pH from 5.1 to 4.3 and viscosity decreased too), similar results with cycling of temperature (-20C/ 24h + 25C/ 24h).
I believe I made a mistake using that emulsifier, would just Sorbitan Olivate work better?, and that grape seed oil is too high and went rancid despite vitamin E? I appreciate very much any suggestion! Thanks!

The formula used:
A Butyrospermum Parkii (Shea) Butter 6.50
A Cetearyl Olivate, Sorbitan Olivate 3.40  
B Vitis Vinifera (Grape) Seed Oil 16.50
B Cocos Nucifera (Coconut) Oil 7.00 
B Kangaroo Flower Infused in Sunflower Oil 6.00 
B Simmondsia Chinensis Seed Oil 6.00 
B Macadamia Ternifolia Seed Oil 5.00 
B Kakadu plum seed oil 5.00 
C Naticide 0.60 
C Coconut Extract 0.20
C Mica 0.50 
C Vanilla Extract 0.10
C Tocopherol 0.20 
D Pumice powder 3.00 
D Salt 3.00 salt
D Kaolin, Australian clay 37,00 

Comments

  • AleHAleH Member
    edited August 12
    No comments? :( is it that it's not so clear why the instability? or that it's a very bad formula? :)

  • PerryPerry Administrator, Professional Chemist
    You have a lot of ingredients in your formula so any one of them can be a problem. The sorbitan olivate has an HLB of 4 and the Cetearyl olivate has an HLB of around 8. Your oils are somewhere around 7 so maybe your ratio is off but it may also be fine. I didn't do the exact calculations but it seems like you are in the ball park. It's possible you don't have enough emulsifier in there but it's not in there to make an emulsion, rather just to help the product get removed from the skin during use. 

    Most likely you do have too much grape seed oil. I'd swap it out with something that has fewer double bonds to oxidize. 

    Not sure about the clay thickener. That could be a problem. Also, the quality of the shea butter you use could be a problem. 

    Ultimately, you may have to do a formula knockout experiment to see what is causing the problem.
  • AleHAleH Member
    Thank you so much @Perry for taking the time to answer.
    I'm not understanding well why in this formulation I should balance the HLB (it is close to 200 in this case) if the idea of using the emulsifier is to structure a little and prevent the oils from leaking out of the mass, it's not a true emulsion. Obviously this is not working, I'm missing something! I've seen that an emulsifier w/o such as sorbitan olivate (olivem 900) works better, I'll try, but this has an even lower HLB so I would need to increase it with an increase in the consistency (I don't want to change consistency).
    Or would be better not to use an emulsifier and try to stabilize with a wax? in that case, it would be very difficult to remove from the skin during use  :s

    I'm going to do the formula knockout experiments but this instability is seen after 1 month at 35°C, there will be a faster way to realize?
    Thanks again!


  • Personally I'd scrap out the clay totally, and thicken with some waxes - beeswax would be ideal, 4-8% probably, and make up the rest with more oils. Clays can be so variable, and certainly from my experience of kaolin don't play nicely in anhydrous systems.

    Having said that, I"m guessing that the phase separation you're seeing is the solids sinking to the bottom and an oil phase on top? If that's the case you could probably get away with just thickening the formulation as is with a touch of high-melting point wax to the point where the viscosity is sufficient to overcome the effect of gravity - at least for an acceptable amount of time. Change in odour could be rancidity, could be the Kaolin. 
  • AleHAleH Member
    LincsChemist! Unfortunately, I made this formula for a client that wants a kaolin anhydrous scrub, I can't get rid of it, she wants that "muddy" sensation, do I have any option?
    Would you get rid of the emulsifier and change for waxes?
    Regarding "phase separation" that's what the stability report says, I also assumed the oils separating from the solids. Thanks again for your time!
  • @AleH

    Ah fair enough! Has she specified the Kaolin inclusion level? If not I'd still maybe drop it down a bit, 20% should be more than enough to feel muddy. 

    No I'd leave emulsifiers in, it'll probably be quite unpleasant to use without them but add some waxes as well. It might be useful to trial the wax levels without Kaolin to get to a firmish consistency that will suspend particulates.

    On a side note, I usually use Polysorbate 60 as the emulsifier for these sorts of products and it works quite well - I don't think you need to worry about matching the HLB of your oils and emulsifier system as you're not trying to make a stable emulsion. Something with a higher HLB (like the polysorbates) should interact more freely with the water in the shower when rinsing off. Doesn't fit very well with your natural looking formulation though!
  • AleHAleH Member
    Thanks @LincsChemist, your comments are very helpful!
    Now time to work on it! I'll design the experiments taking into account the suggestions and see what happens. Will there be any quick way to test? If not I will ask my client for patience! :)
    Yes, polysorbate 60 is not in the "natural" way but that gives me some ideas to try. Reviewing my notes I saw that I had already tried adding Sodium cocoyl isethionate and lauryl glucoside, improving a bit the rinsing but not the sweating of the samples. I'll keep working on it. Thanks!
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