Does cocamidopropyl betaine deposit on hair because of being amphoteric?
July 9, 2018 6:30 AM Subscribe
In an FAQ about a laundry detergent (ECOS), I found an assertion that cocamidopropyl betaine deposits on clothing (due to clothing's negative charge). Is this true?
I know hair is negatively charged too, so if the above is true, I'm wondering if hair would also retain a residue of surfactant?
I'm a little concerned at the idea of residual surfactant on either my hair or my clothes, as I have sensitive skin that probably shouldn't be in contact with surfactant.
(See inside for a cut-and-paste of the assertion I found.)
What does it mean that ECOS™ Laundry Detergent has a built in softener?
Undesirable static cling, shock and pilling are caused by free flowing electrons, which are excited by rubbing/friction on the fabric. Generally, fabric softeners work by coating the fabric with electrically conductive, positively charged compounds that can absorb the negative charge of the electron. Because cocamidopropyl betaine is an amphoteric surfactant that has both a positive and negative charge, we are able to make this label claim. The positive charges of the surfactant act as softeners and have an electrostatic attraction to the negatively charged fibers on the clothing. When that happens it neutralizes the charge creating less static on clothing and leaving some of the residual surfactant on the clothing. This leaves a slight lubricity feel to the clothing giving you the softening feel.
What does it mean that ECOS™ Laundry Detergent has a built in softener?
Undesirable static cling, shock and pilling are caused by free flowing electrons, which are excited by rubbing/friction on the fabric. Generally, fabric softeners work by coating the fabric with electrically conductive, positively charged compounds that can absorb the negative charge of the electron. Because cocamidopropyl betaine is an amphoteric surfactant that has both a positive and negative charge, we are able to make this label claim. The positive charges of the surfactant act as softeners and have an electrostatic attraction to the negatively charged fibers on the clothing. When that happens it neutralizes the charge creating less static on clothing and leaving some of the residual surfactant on the clothing. This leaves a slight lubricity feel to the clothing giving you the softening feel.
Ok, so the other half of your question, you know, the one you asked first. I should clarify that my understanding of this is at a practical level, as I am learning about making my own shampoo and conditioner and personal products because I have sensitive skin and was running out of options. I'm not a chemist.
No, CAPB does not seem to build up on hair or even leave a signifigant residue. When it is in a shampoo, and acts positively charged because of the acidity, it is not strongly substantive to your hair. It increases mildness, which is the cosmetic industry's way of saying that it keeps other surfactants from being irritating or too powerful. When they say it is has anti-static qualities in products, it seems to be meant as relative to a formula that doesn't have it, not as an absolute. Nor as compared to a product that has an active ingredient with a stronger cationic charge or film forming properties.
It has been studied for decades, used in all kinds of products, and when people do react to products containing it, it has almost never been proven to be the cause. Though sometimes it has been impurities from the manufacturing process. So at least the odds are low that you will have a problem with it. Avoiding it completely in cosmetic products may be difficult, but not impossible. Avoiding it in laundry detergent should be easy.
I could not find any fabric softener formulations that contain it, but those kind of formulas are pretty rare anyway. I still think that ECOS could be using marketing chatter to make up for not being a very effective detergent. I'm sorry that I couldn't find you a better answer, but I don't have access to sources that could provide proof.
That mixture of surfactants from earlier has thickened to the point of being able to pick it up on a fork as an entire mass. I'm going to add some citric acid, water, and preservative to make it into shampoo.
posted by monopas at 8:32 PM on July 9, 2018
No, CAPB does not seem to build up on hair or even leave a signifigant residue. When it is in a shampoo, and acts positively charged because of the acidity, it is not strongly substantive to your hair. It increases mildness, which is the cosmetic industry's way of saying that it keeps other surfactants from being irritating or too powerful. When they say it is has anti-static qualities in products, it seems to be meant as relative to a formula that doesn't have it, not as an absolute. Nor as compared to a product that has an active ingredient with a stronger cationic charge or film forming properties.
It has been studied for decades, used in all kinds of products, and when people do react to products containing it, it has almost never been proven to be the cause. Though sometimes it has been impurities from the manufacturing process. So at least the odds are low that you will have a problem with it. Avoiding it completely in cosmetic products may be difficult, but not impossible. Avoiding it in laundry detergent should be easy.
I could not find any fabric softener formulations that contain it, but those kind of formulas are pretty rare anyway. I still think that ECOS could be using marketing chatter to make up for not being a very effective detergent. I'm sorry that I couldn't find you a better answer, but I don't have access to sources that could provide proof.
That mixture of surfactants from earlier has thickened to the point of being able to pick it up on a fork as an entire mass. I'm going to add some citric acid, water, and preservative to make it into shampoo.
posted by monopas at 8:32 PM on July 9, 2018
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I suspect that this blend is probably alkaline, even though there's less SCS than CAPB. The relatively large amount of CAPB is for viscosity. (Since I have CAPB and cocamidopropylamine oxide, I went and mixed them with the closest thing I have to SCS, sodium C14-16 alpha olefin sulfonate. The AO sulfonate is pH 8, at 40% dilution. The three liquids before blending are about the same viscosity as a fairly light oil or warm syrup. When I put them together to approximate the amounts that could be in the detergent, it turned into thick gel. The effect is probably more dramatic with SCS. I'll see what happens after I start diluting it.)
All three of the ingredients in the ECOS are really good at foaming, so if they're in a laundry detergent that requires even a quarter of a cup I suspect that it is probably very dilute. As in, you could probably safely use this as body wash or dish liquid in a pinch, though you probably wouldn't want to as it would feel unpleasant and the chemicals probably are not cosmetic grade.
I doubt that there's much residue left behind, and if you are concerned, adding an extra rinse would take care of it. The claims that they make looks like it was lifted straight out of the chemical manufacturer's marketing materials. It seems to be based on the research done for CAPB in shampoo and other cosmetic formulations. If you are interested in the Cosmetics Ingredient Review report on CAPB, scroll through the smaller of the two pdfs linked on this page. It is very dry and long. Descriptions of the human trials start on the 51st page of the pdf. Case reports start on page 56. Anyway, they found that very few people react to CAPB, even at much higher concentrations than would be left on your clothes after a poorly rinsed load of laundry. The CIR has a website for consumers, cosmeticsinfo.org, that has ingredients information without the bad science and hyperbolic tone of EWG (link is to the entry for CAPB, the search on the site is terrible, so google an ingredient name and cosmeticsinfo.org to actually find anything there).
I'd be more concerned that the ECOS wasn't strong enough to clean my clothes on a long term basis, or that using too much would create enough foam to trigger the foam sensor on my washer and make it angry. Or cause a leak.
posted by monopas at 4:18 PM on July 9, 2018