Monday, April 12, 2010

Surfactants: Alkyl-aryl sulfonates

The linear alkylbenzene sulfonate (LAS) is one of the most widely used detergents, but its use in personal care is very limited. It has a very low compatibility with skin, and is usually only used in anti-seborrheic or very oily skin cleansers.

This picture is of sodium linear alkyl benzene sulfonate.

It has good detergency and foam properties, but because it strips away so much oil, pretty much every skin type (except the extremely, almost medically too much oily skin) will feel dry and tight after using it. The main purpose of this ingredient is dishwashing liquid or all purpose cleansers.

It has a pH around 7.5, so it's almost neutral. The product I found from Stepan (Bio-Soft D Series) comes in a 38% to 55% active liquid form. These would be fabulous for cleaning products for your home. They are very biodegradable, and they play well with other surfactants.

Let's take a look at how to incorporate one of these surfactants into a cleaning product! (From this post...d-Limonene in your cleansers). To learn more about d-Limonene, please visit this post - d-Limonene: Awesome cleaning power!

5% d-Limonene
5% polysorbate 20
5% Amphosol CG or cocamidopropyl betaine
5% anionic surfactant of choice - an alkyl-aryl sulfonate, SLeS, Bioterge 804, Bioterge AS-40, castille soap, or decyl glucoside
79 to 79.5% water
0.5% to 1% preservative

Mix the polysorbate 20 and d-Limonene together in a small container. In another container, mix the surfactants together - try not to get too much foam - then add the surfactants and preservative and mix together again. Add the polysorbate 20 and d-Limonene, and package in a spray bottle.

This won't be too foamy as the d-Limonene is an oil and the polysorbate 20 is a solubilizer, and neither of these play well with surfactants! So we're using their natural de-foaming and de-lathering abilities to creating a surfactant based cleanser that won't foam up too much!

You could also create a lovely foaming hand wash like this one with these surfactants. I'd suggest replacing the BSB with the alkyl-aryl sulfonate. You don't need a lot to make a difference!

Check out this package of recipes from Voyageur Soap & Candle for green cleaning products. You could replace the liquid castille soap in any of these recipes for your alkyl-aryl sulfonate. You could make a dishwashing liquid with it - try it at 15% to 20% to start - with some d-Limonene and a nice moisturizing ingredient for your hands.

Join me tomorrow for fun with sulfosuccinates (why do I always feel like Sylvester the Cat when I say that?).


Robert said...

There's an important distinction between alkylaryl sulfonate and alkylbenzene sulfonate. ABS could also be called and alkyl phenyl sulfonate, the important point being the direct sulfonation of the benzene ring. An aryl sulfonate, by contrast, has the sulfonate moiety on the end of an alkyl group. "Aryl" could also be called "phenylalkyl". So alkylaryl sulfonate is like an alkylbenzene sulfonate with the benzene "bead" slid partway up the "string" from the sulfonate end.

(Maybe in formal terms, "aryl" is a general term that includes "phenyl", but in surfactants it's used to distinguish them.)

It wouldn't matter if it didn't have consequences, but the alkyl aryl sulfonates are more irritating than the alkyl benzene sulfonates. So while alkyl benzene sulfonates have had use in toiletries -- less these days than in the 1960s, when the supermarket bubble baths were close to high-suds laundry powders in formula -- to my knowledge the alkyl aryl sulfonates have never had such use and people would be nuts to use them that way. The particular ingredient SDBS (sodium dodecylbenzene sulfonate) has been in fairly recent use still in some powdered "family" bubble baths (with other surfactants and a lot of inert filler), a few oily hair shampoos (with other surfactants aplenty), and way down the list of ingredients in some "flavors" of Dove/Caress bar (maybe as a processing aid for incorporating some other ingredient, just guessing).

For a while the term "ABS" was used in distinction to "LAS" (linear alkylate sulfonate), the latter having a linear alkyl group, but now that that biodegradability issue is long past, the better descriptive term "ABS" has come back to cover it, and everyone knows the alkyl moiety is linear.

Susan Barclay-Nichols said...

Very nice! Thanks, Robert. I couldn't find much about these surfactants as they don't tend to have a lot of use in personal care products - with the exceptions you mention - so I really appreciate this information!

Great to have you as a reader and (I hope) regular commentator given your educational background and extensive experience with personal care products!

Bob Goodman said...

Thanks, Susan, but I think your total experience in "personal care products" is likely greater than mine. I just know a lot about a few things, and a lot of technical details and theory regarding others, some of which is useful in that field.

Robert said...

I recently learned that the sodium dodecylbenzene sulfonate in Dove was to increase its lathering, not as a processing aid. Lately on Dove & Caress bar labels I've seen that ingredient alternating with a sodium alpha olefin sulfonate and cocamidopropyl betaine. If I had to choose between those formulas at the same price, I'd always take the one w cocamidopropyl betaine; SDBS would be my last choice of those 3.