Fatty acid isethionates and taurides (more about those tomorrow) are prepared by a reaction of a fatty acid chloride with sodium or ammonium isethionate which comes from the addition of sodium bisulphide (NaHSO3) and ethylene oxide. Generally, the fatty acid is coconut oil, hence the "cocoyl" part of the name.
Isethionates are considered exceptionally mild for skin, hair, and eyes, and are particularly tolerant to hard water. They leave behind a great skin feel - usually described as "silky" - and create really lovely foam, bubbles, and lather.
SCI is found in a solid form - prills (like Jordapon prilled), flakes, and noodles - whereas ACI is liquid. When you are melting SCI, there are a few things you can add to increase the solubility and melting time. You can add some anionic surfactants like the alkyl sulfosuccinates, alkyl ether sulfosuccinates, sodium or ammonium taurates (see tomorrow's post), acyl glutamates, or acyl sarcosinates. You can add the amphoteric surfactants like the betaines or hydroxysultaines. Or you can add some non-ionic surfactants like polysorbate 20 or 80, alkyl glucosides (like decyl glucoside), PEG glyceryl cocoates or PEG glyceryl laurates.
My first choice is always cocamidopropyl betaine because it increases the mildness of the surfactant mix! (As a note, I'm calling it cocamidopropyl betaine instead of coco betaine because they are, in fact, two different products. It's a pain to type, but it's a good thing to be accurate!)
Granules are generally just SCI, whereas the flakes or noodles may contain stearic acid, and the noodles may contain plasticizers like oils to keep their noodle-y shape. SCI granules are generally found as prills like Jordapon prilled (they prill it so it's less dusty, but it can still get up your nose, so wear a mask!) This product is 54% active and has a pH of about 6.
SCI loves being near stearic acid - you can add a lot to it before you ruin the lather and foam - and this is the secret of syndet bars like Dove. The moisturizing comes from the stearic acid. If you have the granules, feel free to add stearic acid to it. If you have the noodles, you may already have enough stearic in there, so you don't need to add more (having said this, you can add more if you like because moisturizing is a good thing!)
If you've tried making a shampoo bar with SCI, you'll notice there are sulfosuccinates (Bioterge 804), taurates (DLS mild), and an emulsifier (BTMS). These all help to increase the solubility of the SCI so it will melt better. (See above.)
How much SCI can you use? "The CIR Expert Panel concludes that SCI is safe for use in cosmetic formulations at concentrations of 47.5% in rinse off products, and at 17% in leave on products." So if you have Jordapon prilled SCI, you could use about 88% SCI in a shampoo bar. If you have other versions - for instance, 85% SCI, then you could use about 55% in a rinse off formula and still stay in the guidelines.
SCI noodles, flakes, and prills have a 2 year shelf life. ACI (liquid) has a shelf life of one year.
SCI is great for every skin or hair type. The dry type will enjoy the gentle cleansing and the creamy after feel. The oily type will enjoy these features as well. SCI is great for a cream cleanser - the oils won't mess with the lather too much - and body washes. The down side is that SCI will make it difficult to make a clear shampoo, body wash, shampoo, or facial cleanser.
ACI is also great for every skin type. It is substantive to skin, so it offers not only gentle cleansing and a creamy after feel, but it will offer some conditioning. Oily skin will benefit from the moisturizing without oils, while the dry type will appreciate the lack of tightness. Because it's a liquid, you can create clear surfactant mixes and don't need to worry about all that melting (although you'll still want to include the cocamidopropyl betaine for thickening and increased mildness).
Join me tomorrow for fun with taurates (also known as taurides).