Home Cosmetic Science Talk Formulating General Water based stick shrinking

  • Water based stick shrinking

    Posted by LabGuy on April 2, 2024 at 2:58 pm

    Hi all,

    I formulated a water based facial stick to provide blur/mattefying effects. After almost three months of accelerated stability testing at 45ºC it shrinked. A LOT. It started to shrink at 1 month and we knew that this was expected to some extent, but now ~60% of the mass was lost. Please see the formula below:

    • (1) Water - 67.5%
    • (1) Glycerin - 2%
    • (2) Sodium Stearate OP 100-V MB - 8%
    • (3) Microspheres (a blend of different microspheres such as silica, cellulose and mica) - 17%
    • (4) Niacinamide - 2%
    • (5) Polysorbate 20 - 2.5%
    • (5) 1,2-Hexanediol (and) Caprylyl Glycol - 1%

    I basically heat part 1 to 80ºC, then add sodium stearate and mix until it’s clear. After this I add the remaining ingredients one by one and mix for 5 minutes.

    I believe that this happended because a) the formula has high water content and b) we are not using an airtight packaging.

    However, I have to find a way to reduce the shrinking. I think that maybe incresing the glycol concentration (I’m working on a new version with ~30% Propanediol) and reducing the water content maybe can help, but I’m not sure.

    Does anyone have any idea of what I can do to solve this issue (reduce shrinking?)

    Look forward to hearing from you.

    Thanks 🙂

    LabGuy replied 1 week, 6 days ago 3 Members · 3 Replies
  • 3 Replies
  • chemicalmatt

    Member
    April 8, 2024 at 3:41 pm

    @LabGuy You are 100% correct, so I guess this means this post is self-correcting? You need to rebalance that polyol-water ratio closer to 3:2 of glycol: water and cut that glycerin with propylene, butylene or dipropylene glycol. That last one DPG being the best choice.

    • LabGuy

      Member
      April 9, 2024 at 7:27 am

      Thanks Matt!

      I already did a version with 30% Propanediol. Had to reduce Sodium Stearate also, cause as I increased the glycol concentration, the stick got harder. Now I’ll let it at 45ºC to see how it goes 🙂

      Why would you suggest cutting back glycerin though?

  • ChemistGuy

    Member
    April 8, 2024 at 8:15 pm

    Good luck

    • This reply was modified 1 week, 6 days ago by  ChemistGuy.

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