emulsion help

How would these ingredients form an emulsion if glyceryl stearate (HLB ~ 3.8) is being used to emulsify lanolin (rHLB ~ 10) and stearic acid (rHLB ~15)? Or would this be w/o emulsion because of the low HLB of the emulsifier?

Active ingredients: menthol 10%; methyl salicylate 15%. Inactive ingredients: citric acid, glyceryl monostearate, lanolin, methylparaben, propylene glycol, propylparaben, purified water, stearic acid, trolamine.

Comments

  • letsalcidoletsalcido Member
    edited June 26
    There is less water than glyceryl stearate and lanolin, if in the right order. This is definitely w/o in that case.

    Maybe someone experienced will be able to tell for sure.

    If you have a sample of this product, does it “dissolve” in water or just floats?
  • mhart123mhart123 Member
    @letsalcido for otc labeling, the inactive ingredients can be listed in alphabetical order so that makes it a little trickier when trying to determine use level. I do not have a sample of the product yet but when I get it, I will try that out.  
  • PharmaPharma Member, Pharmacist
    Mixing stearic acid with trolamine results in TRIS stearate, a soap or in other words a high HLB emulsifier.
    Just based on composition, it can be either. Lanolin does bind water nicely and 25% oil soluble actives... a water saturated 'oil' would be my guess.

  • mhart123mhart123 Member
    Thanks @Pharma, I did some searching on here through older posts and found that the trolamine would I guess kind of activate the stearic acid and help with the emulsification.

    I mixed trolamine into the water (pH was 8.5) before adding the oil to the water phase and the emulsion turned out better then my previous tries, however it was still pretty thin.  Then with the addition of citric acid the oil separated out (pH 6.9). I will check to see what the pH of the competitor sample is when I receive it, but are there pH limitations for the stearic acid/trolamine combo?
  • PharmaPharma Member, Pharmacist
    If you add too much citric acid (or any acid), pH drops and reverts TRIS stearate back to non-emulsifying stearic acid.
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