Thursday, September 14, 2017
Why did I buy that again? Stearamidopropyl dimethylamine
What is this? It's a cationic or postively charged emulsifier that brings together water and oil to make an emulsion. It's positively charged, so we use it in conditioners to detangle, moisturize, condition, increase shine, and more.
What does it mean to condition our hair? A cationic quaternary compound or a positively charged compound adsorbs to the surface of your hair. This adsorption means the molecules accumulate on the surface of your hair in a process called substantivity. Our hair is negatively charged, so a positively charged ingredient will be attracted to the surface of our hair. Using a positively charged ingredient means our cuticle will lay down properly after washing, so our hair is less likely to tangle and more likely to shine.
Conditioner: What's that then?
Adsorbing and substantivity!
Quick summary of damaged hair
Stearamidopropyl dimethylamine is an amine with fatty chains added that becomes more cationic or positively charged when we reduce the pH. It's a good conditioner that prevents static, and will increase viscosity. It won't build up on hair, and it's said to help remove build up It can be used with cetrimonium chloride, another cationic ingredient, to become a good emulsifier. It's also used with behentrimonium chloride, a cationic ingredient that's a very close relative of behentrimonium methosulfate, the cationic ingredient in Incroquat BTMS-25 or BTMS-50 or Rita BTMS-225.
This ingredient works well with negatively charged surfactants, like those bubbly, lathery, foamy ones we use in shampoos, as it doesn't depress the foam or lather.
We have to alter the pH of this product with something like citric acid or lactic acid. As the pH decreases, the product becomes more cationic or positively charged, and it becomes more attracted to our hair making it a better conditioner. If you're using citric acid, you'll want a 5.88: 1 ratio (5.88 grams of SD to 1 gram of citric acid) or 3.7:1 ratio with lactic acid. The viscosity of the product can be different based on the acid you use. You're shooting for pH 4.5 to 5 as that's when it forms a cationic salt and becomes a proper conditioner. (It becomes a tertiary amine salt at this point.)
Related post: How to alter pH in our products
It works best when combined with a fatty alcohol, like cetyl alcohol or cetaryl alcohol, as this will boost the substantivity of your cationic ingredient to make it more conditioning. (I've found it used with stearyl alcohol, but I've never found this ingredient at any of our suppliers.) These also moisturize hair and increase the viscosity of the product.
How do we use it? Add it to the heated water phase of the product along with the acid you're using to decrease the pH. I've found I use about 1.1% to 1.2% citric acid to 5% stearamidopropyl dimethylamine to gett to pH 4.8 or so, but you'll have to see what your measurements might be and adjust your acid levels accordingly. Use your fatty alcohol in the oil phase of your product at anywhere from 1% to 7%, depending on how thick you want the product to be.
I'll be sharing some of the formulas I've been working on for ages with you tomorrow and next week.
As a note, I purchased mine from Making Cosmetics*. If you're using another version, please check what they suggest for usage rates and such as it may vary from supplier to supplier.
Handbook of Cosmetic Science & Technology
Chemists' Corner forum
Join me tomorrow for an awesome formula for a conditioner using this ingredient!