Wednesday, April 7, 2010

Surfactants: Carboxylates

Carboxylates are produced by the alkaline hydrolysis or saponification of animal or vegetable fats and result from the neutralization of fatty acids. They are extremely soluble in water up to C18 (or 18 carbons), and are insoluble over C20. If you use an unsaturated oil or butter to produce these surfactants, you might see some oxidation, demonstrated by a rancid smell and yellowing of the product. They aren't great in hard water, and their main use is in skin cleansers (bars or liquids).

Yep, I'm talking about cold process soaps! Take some animal or vegetable fats, add some sodium or potassium hydroxide and you've got a wonderful creation that is soluble in water! (And remember, I don't make CP soap, so please don't ask me any specific questions - I know the chemistry, not the process!)

Isn't this chocolate chip soap from ForgetMeNot soaps adorable? Thanks for the use of the cute picture!

There are two major sub-types of carboxylates, ester carboxylates and ether carboxylates.

Ester carboxylates can be made in a variety of ways. They could be condensation reactions between an alcohol with a polycarboxylic acid (like tartric or citric acid) or a hydroxy acid (like lactic acid) and carboxylic acid. They are good foamers and have substantive properties to hair and skin, which makes them great choices for body washes or shampoos. If you combine them with ethyoxy sulfates (AEOS - more to come about those shortly), they reduce skin irritation from surfactants. Some can act as humectants - those from lactic acids - so they're great for body washes!

Ether carboxylates are made from a reaction of sodium chloracetate with ethoxylated alcohols. They are more soluble in water and less sensitive to hard water than cold process soaps. They show good wetting and foam stability, and impart mildness and creaminess to your products. They leave behind a conditioned feeling because they are substantive to skin and hair. They are great in combination with alkyl ether sulfates (like sodium laureth sulfate) and make great shampoos because they are so compatible with cationic ingredients (like our cationic polymers, Honeyquat or polyquat 7).

Where can you get these wonderful surfactants? Using a cold process bar or liquid soap - like castille, for instance- will give you all the goodness of carboxylates.

And Plantapon LGC Sorb uses sodium lauryl glucose carboxylate and lauryl glucoside in combination to give you the mildness of the alkyl polyglucoside (APG) with the conditioning nature of the carboxylate. (Apparently this surfactant works well with disodium cocoamphidiacetate.)

BSB (Stepan, found at Voyageur) contains sodium laureth-13 carboxylate, which explains why it feels nice on your skin after a bubble bath or body wash! (BSB INCI: PEG-80 Sorbitan Laurate, Sodium Trideceth Sulfate, Cocamidopropyl Betaine, Disodium Lauroamphodiacetate, PEG-150 Distearate, Sodium Laureth-13 Carboxylate, Quaternium-15). Oh, there's that disodium lauroaphodiacetate!

Join me tomorrow for fun with sulfates!


Topcat said...

I was reading your introductory paragraph and thinking to myself "she could almost be talking about CP here" you were ;) Forget Me Not Soap has beautiful products; that choc chip soap looks edible! :)

Tara said...

If you are talking about liquid soap, it is actually not cold process, but hot process. Cold process soaps are generally bar soap (which I have heard of some people using to clean their hair with); but bar soap can also be made with a hot process method. I think it is pretty much impossible to make liquid soaps with a cold process. To distinguish, I would go with potassium hydroxide (KOH, or liquid soap) or sodium hydroxide (NaOH or bar soaps) in order to clarify :)