Stearamidopropyl dimethylamine as conditioner emulsifier

Hi everyone, Amaris here. I'm a home crafter from Canada with a bunch of years as a soap maker and an okay understanding of chemistry under my belt. I was hoping someone would be able to help me out with a few questions I have about using stearamidopropyl dimethylamine in a conditioner. I've scoured the internet and have come up lacking.

First of all, I'd like to establish that SD is usable as a stand-alone emulsifier in a conditioner. I have an ingredient list from a discontinued conditioner that I'd like to recreate in which SD is the only emulsifier listed, so I think it should work. However I have had other DIYers tell me that it can only be used as a co-emulsifier alongside BTMS or cetrimonium chloride or etc.

Secondly, is there any consensus on what phase to put SD in? There is conflicting information all over the web. The DIY supplier I bought mine from says it is oil soluble, but another big supplier says it is water soluble. I have also found sample formulas from manufacturers that vary in which phase it goes in. My understanding of the chemistry is that SD is water soluble once neutralized into a salt using an acid. Is it oil soluble prior to neutralization?

Finally, if anyone has any tricks for working with SD in a conditioner, I'd be eternally grateful. I know it's not a super strong emulsifier, and that I should keep my dimethicone levels fairly low, but are there any incompatibilities with common conditioner ingredients or preservatives?

Thanks so much to everyone who contributes to this fantastic resource!

Glam

Comments

  • chemicalmattchemicalmatt Member, Professional Chemist
    Actually Glam, SD is a very good emulsifier - only when acidified into a tertiary amine salt to about pH 5 -  but especially so when used in conjunction with alkyl quats such as CETAC, STEARAC and BEHENTAC, etc.  Be advised you will obtain sharply different viscosity and stability outcomes depending upon the organic acid used.  If you can afford glutamic acid that will work best, but good old inexpensive lactic acid 88% works nicely too. Regarding dimethicone emulsification: the SD/behenyl quat (use the chloride not the TMS analog) system you are trending toward is perhaps the best vehicle to use for that ingredient, even with the 10,000 CST DMC.  Happy trails. 
  • BartJBartJ Member
    Matt, could you please share a few thought on why you recommend chloride rather than TMS for Behenyl and it's work with silicones?

    So far I only used the BTMS variants without a reason to complain. Very curious of your opinion.
  • Thanks so much for the replies.

    I've done some experimenting since I posted my questions. I've been able to get a stable emulsion with 3% SD, 7% cetearyl alcohol, 1% citric acid, and q.s. water with 0.2% powdered Germall Plus, 2% liquid panthenol, and 0.2% fragrance added at cool-down. Now I just have to try to get 0.5% dimethicone (350 cst, as that's all I have) and ~3% cyclomethicome in there and I'll more-or-less have what I'm looking for! pH is about 4.5.

    I think I initially had stability problems due to insufficient citric acid, and possibly also thanks to Optiphen Plus destabilizing the emulsion...
  • PerryPerry Administrator, Professional Chemist
    You don't really need that much Panthenol. You should try the formula with and without. I bet you won't notice a difference.
  • Thanks Perry, you're right. My supplier recommends 0.1-0.5% for hair applications. I must've been thinking of the higher percentages recommended for skin applications. :smile: 
  • chemicalmattchemicalmatt Member, Professional Chemist
    Bart, partly charge-mass ratio granting greater emulsifier range and cationic conditioning on the hair; but mostly because it's much less expensive.  Croda has enough money already, don't you agree?
  • BartJBartJ Member
    They say things happen for a reason. Thank you Matt, BTCL's on order.
  • I was wondering which nitrogen gets protonated first when forming the cationic form of stearamidopropyl dimethylamine? Can anyone please help?

  • The second tertiary amine nitrogen(dimethylamino) gets protonated:the first is an amide stearamidopropyl and does not protonate.
  • faithiefaithie Member
    How much oil could I use with SD-3 and cetearyl-7?
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