Stability of Depilatory cream

Hi everyone!
I've made a formulation about depilatory cream. The ingredients are:
Phase A:
Water    adj to 100%
EDTA      0.5
Glycerin  5
Xanthan  0.3
Phase B:
PARAFFINUM LIQUIDUM  5
Cetyl alcohol      3.5
Cestearyl alcohol  3
ceteareth 20      3.5
Dimethicone    2
Phase C:
NaOH   adj to pH = 12
Ca thioglycolate 8  (active 50%)
Perfume   0.3 - 0.4
and i have some problem about the stability of that cream. The cream will turn from white to yellow in the surface and the texture of the cream will unstable about 4 to 5 week in Accelerated test conditions. 
I don't have any idea to increase the stable time of this formulation. Please help me!!!


Comments

  • MetalizeMerzMetalizeMerz Member
    edited January 4
    What is the viscosity of your cream?

    The silicone content seems to be too high for 3.5% ceteareth-20 to work well.
    My addition opinion is adding bulky ingredients like Meagnesium Aluminium Silicate for enhancing viscosity (indirectly boosting stability).

    The decolouration from your product is from oxidation, please add antioxidant such as tocopherol if you have it.
  • Thanks for your comment. The viscosity of my cream is good and it can leave a layer when apply to the skin. i made some sample with no silicone in there and i got the same problem. It work but the stablity is unstable. 
  • chemicalmattchemicalmatt Member, Professional Chemist
    @NguyenDuy you are experiencing surface oxidation of the thiol reducing agent - so very typical of depilatories. The guts of your formula are pretty good though more mineral oil would be better. An anti-oxidant will not be of use since thiols ARE anti-oxidants (reducing agent, right?) That yellowing may be from iron or other multivalent metals in the water or your vessel. (Why we always passivate our SS blending equipment when using thiols) You already have EDTA (Na4?) so just deionize 99.999% and fill under a nitrogen blanket and no problemo. Never used xanthan gum as a rheological in a thiol system before. This should be fine without any, but Veegum would be a good choice as @MetalizeMerz suggests.   

  • @chemicalmatt thanks for your comment. 
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