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Water based stick shrinking
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 🙂
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3 Replies
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@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.
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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?
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Good luck
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