BTMS exfoliating moisturizer emulsion went grainy and separated - likely culprits? Full formula incl

edited April 12 in Formulating
Here's the basic formula, I only had a hand immersion blender as my overhead mixer is being repaired so for this first atempt so I was not able to do low speed mixing during cool down and after adding the final phase which could have lead to inadequate formation of lamellar phases - BTMS is AFAIK a liquid crystal emulsifier. I've wanted to test how it feels in a moisturizer formula for some time now.

Method

1. Heat phase A to 70C
2. Mix B1 and B2 separately until homogenous. Add B1 to B2 under high shear mixing. Heat to 70C.
3. Add A to B under stirring and mix with high shear mixing for 3 minutes.
4. Cool to 40C, add phase C under high shear mixing for 1 minute. Bottle.
Final pH 3.8

Ingredient INCIPhase%
Capric/Caprylic TriglyceridesA5.0
Behentrimonium Methosulfate, Cetearyl Alcohol (BTMS 25)A5.0
Glyceryl StearateA3.0
Salicylic Acid A2.0
Cetyl AlcoholA2.0
Stearic AcidA1.0
WaterB163.5
Lactic AcidB15.6
TriethanolamineB12.6
GlycerinB25.0
Hyaluronic Acid (Low MW)B20.2
Xanthan GumB20.2
NiacinamideC12.0
Dimethicone (CPS1000)C22.0
Phenoxyethanol, Caprylyl GlycolC21.0

Result
Salicylic Acid did not entirely solubilize in the oil phase, possibly at least in part due to lack of stirring. Not entirely unexpected.

The end formula formula was watery, too thing for a lotion - likely used too little BTMS, Glyceryl Stearate, Cetyl Alcohol and Xanthan Gum to make a cream. That said, skin feel and effects are good. After a few hours a water phase separated out on the bottom.

Let me know what you think are the culprit(s) for the curdling and separation, I'm thinking of increasing what I mentioned above, along with low shear stirring during cool-down and after adding phase C. There could also be some ionic interference going on with the BTMS but I'm not experienced enough with it to know what it could be. It's been a while since I've formulated myself so a bit rusty, also I'm lacking experience with silicone and I'm not sure It needs anything extra to stably incorporate Dimethicone.

HLB values shouldn't matter too much with BTMS, but they shouldn't be too far off a classic calculation.

Lastly if you have experience with Niacinamide stability at relatively low pH I'd be curious to know about it. It's optimum solution stability is around pH 6. It can hydrolyze and form nicotinic acid at higher or lower PH, but not sure if at a significant enough rate to worry about esp if making a (eventually) thick cream.


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Comments

  • Also FYI if you want to post formulas it works fine to copy directly from google sheets.
  • xanthan gum is anionic, it's not compatible with quats

    also, I'd get rid of the glyceryl stearate; BTMS/cetearyl alcohol is sufficient to form an emulsion, and in my experience with cationic emulsions, some non-ionics can thin this kind of product (not sure why, but it's something I've observed with ceteareth-20 as well)
    UK based formulation chemist. Strongest subjects: hair styling, hair bleaches, hair dyes (oxidative and non-oxidative) I know some stuff about: EU regulations, emulsions (O/W and W/O), toothpaste, mouthwash, shampoos, other toiletries
  • Thanks Bill! I was not aware about xanthan gum being incompatible, will exclude, this is my first time testing BTMS so not surprised I'm missing something. 

    I've seen glyceryl stearate used in similar formulas, I guess it's a good candidate to test with and without, I agree it should work fine without it.

    Think excluding those two + increasing mixing time during emulsification and cooldown will do the trick or does it likely need more BTMS?

  • Other changes

    Move dimethicone and the preservatives to the heated oil phase (both should tolerate 70C). Move Niacianmide to B2 (it's also ok with 70C). 
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