Syneresis Problem Persists in Deodorant Formula

I have formulated an aluminum-free deodorant stick (solid) that is very effective at controlling odor, but I continue to have a syneresis problem despite increasing the amount of emulsifiers (both low and high HLB) and adding solubilizers. The ingredient list is as follows: 

Ingredients: Propanediol, Glycerin, Magnesium Hydroxide, Aloe Vera Juice, Sodium Stearate, Behenyl Alcohol, Arrowroot Powder, Castor Oil,  Cetearyl Alcohol, Glyceryl Stearate, Kaolin, Lavandula Angustifolia (Lavender) Oil, Citrus Sinensis (Orange) Peel Oil, Citrus Grandis (Grapefruit) Peel Oil, Juniperus Virginiana (Cedarwood) Oil, Polysorbate 20, Phenoxyethanol, Caprylyl Glycol

Because of the aloe vera juice, I have been using phenoxyethanol and caprylyl glycol as my preservative blend.  Is it possible that the syneresis problem is due to the fact that I'm using a preservative blend that is only recommended for low pH systems (my deo has a pH of about 10)? I just ordered and received a high pH preservative (phenoxyethanol with ethylhexylglycerin) that I'd like to try next, but I'm now wondering if a preservative is necessary. I notice that many aluminum-free deodorants on the market have a similar glycol/sodium stearate/botanicals ingredient list, but most of them do not list a preservative. My water phase (aloe) makes up only 17% of the total formula, and the glycols make up 55%. Would the high percentage of glycols, combined with the pH of ~10 discourage the growth of microbes? 

I am inclined to try the high pH preservative and possibly increase the emulsifiers yet again to see if my deodorant will stop sweating :-D, but I thought I'd see what you guys think first. Thanks in advance!

Comments

  • ozgirlozgirl Member, PCF student
    Not sure about your problem because I don't make sticks but ethylhexylglycerin is a deodorant active and may help boost the deodorant activity of your product.
  • MarkBroussardMarkBroussard Member, Professional Chemist
    @erindlea:

    Propanediol-based deodorant sticks simply don't firm up enough to eliminate syneresis.  It will always crumble with application.

    You would be better off switching to a wax-based (beeswax, carnauba, candellila) based formulation which would also allow you to eliminate the emulsifiers.
    Chemist/Microbiologist formulating in the Organic & Naturals arena under ECOCert/Natural Products Assn/Whole Foods/National Organic Program guidelines focused skincare & haircare products. 

    See website for details www.desertinbloomcosmeticslab.com
  • Thanks for the tip on the ethylhexylglycerin, ozgirl. That's a bonus!

    Mark, I've never had problems with crumbling. The deodorant glides on well and has a firmness and texture similar to most commercial stick deodorants. It is one of my best sellers. My original wax-based formulations were sticky and transferred oily residue onto clothing, so that's not an option for me. 

    I think I will reduce the glycerin and increase the kaolin to see if this helps. 

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