How does "no-rinse" detergent work?

October 16, 2022 6:04 AM

How do "no-rinse" hand laundry detergents (Soak, Eucalan) work on a chemical/physical/molecular level? DO they actually behave differently than other laundry detergents on a chemical level? Bonus: do the recipes for homemade no-rinse detergent (soap and methylated spirits, mostly--not what's in the commercial ones) successfully do this too?

I see Soak's website says: because Soak is a low-suds liquid, the dirt and detergent come out in the water, and whatever is left in the item evaporates and Eucalan says Eucalan is low-sudsing. But is there more to it than being low-suds?

posted by needs more cowbell to Home & Garden (7 answers total)

This piece on physics.aps.com has persuaded me that clothes should be rinsed after being washed with detergent. The clear water rinse actually helps to remove stains and dirt embedded in the clothing fibers.

The article doesn't answer the question you and I were wondering about...what happens when you don't rinse and just let the water evaporate after washing? How much detergent, dirt, sweat, body oil, deodorant residue, skin cells, remain on the clothes? The rinsing research by Dr Shin, et al., doesn't answer our question, but it does show that clothes can be cleaner after fresh-water rinsing.
posted by wryly at 7:43 AM on October 16, 2022

Oh, another thing: manufacturers of detergents can add ingredients that reduce suds, so lack of suds doesn't mean there's less residue.
posted by wryly at 7:45 AM on October 16, 2022

I've used both of these, usually for washing handknits. Eucalin has lanolin in it, so some residue is a feature for handknits.

With both of these I remember the amount I needed to use to be quite small to the volume of water, so I always assumed the need not to rinse is really related to how dilute they are in. I haven't used either in a while, I switched to using very dilute amounts of liquid castile soap, like dr bronners, because I found it worked as well and was less expensive.
posted by ice-cream forever at 9:30 AM on October 16, 2022

Could they be similar to the surfactants in micellar water? If so, the Lab Muffin explainer might help. But the answer there is there’s cleanser left on your face but it doesn’t bother most people’s skin.
posted by hydrobatidae at 12:14 PM on October 16, 2022

So looking at the ingredients of Soak, and also at the homemade recipe, the basics are, first, use fewer surfactants, and second, use alcohol as a solvent that will dissolve some soils but also evaporate. The surfactants don't evaporate, but they leave very little residue since there's such a low concentration of them.

I have definitely read that most people prefer a very sudsy soap or detergent since otherwise they think it isn't working, and as a result the manufacturers add much much more surfactant than they actually need. So step 1 for no-rinse detergent is just, don't do that.
posted by goingonit at 3:18 PM on October 16, 2022

I would have guessed dilution as well. You have like 1/1000 of stuff in the water/alcohol/whatever. When you squeeze that out of whatever you're washing there's just a tiny bit of the liquid left and an even tinier bit of stuff left in the fabric. Many extraction type processes work like that, the volume of the clean solvent plus the much smaller object that has bad stuff in it leads to the bad stuff going to equilibrium between the object and the solvent. Once you remove the object, much more of the stuff you didn't want is floating around in the solvent.
posted by zengargoyle at 7:57 PM on October 16, 2022

tl;dr: No-rinse laundry products/wool washes are just very dilute and should still be rinsed. However, they are not really the same as laundry detergents, which often contain enzymes and sequestrants/anti-deposition agents and other ingredients specific to machine washing. They're much closer to a simple body wash or shampoo.

Please don't use that DIY formula. It is old, and not in a good, classic way. You're better off using shampoo to clean wool. Though using very dilute soap might be better than using dishwashing liquid. Either way, rinsing is good.

RE: Methylated spirits aka denatured alcohol. There is no alcohol in Soak or Eucalan. Alcohol would serve no purpose, other than perhaps being a widely available self-preserving solvent for the soap flakes. If Eucalan was originally inspired by that blend, it has since been reformulated. Soak is using the word evaporate in reference to water. Very marketing.

Having used both Soak and Eucalan, I find them interesting. Now that ingredients lists are available for them, my long held suspicions have been confirmed.

Ingredients of Soak from their website, spelling mistakes are theirs: aqua, coco-glucoside, sodium cocamphoacetate, lauryl glucoside, glycerin, sodium cocoyl glutamate, sodium lauryl glucose carboxylate, glyceryl oleate, PEG-7 glyceryl cocoate, parfum, propanediol, ethylhexyl glyercin, potassium sorbate, tetrasodium EDTA, benzophenone-4, citric acid

If I didn't know what the product is, I would assume it was a body wash or baby wash. It contains a couple of gentle cleansing blends called Plantapon SF and Lamesoft PO 65, both commonly used in personal care products. Lamesoft PO 65 and PEG-7 glyceryl cocoate are both used in cleansing products to keep them from being too harsh (reduce irritation or increase mildness) and to leave behind a moisturized or conditioned feeling (sometimes called refattening). PEG 75 lanolin serves the same purpose in Eucalan.

Eucalan ingredients from their website, all parentheses and poor or misdirecting definitions contained within are theirs:
Essential Oil (where applicable) (Pure and natural eucalyptus, lavender, grapefruit or jasmine oils)
Ammonium Lauryl Sulphate (Vegetable-based soap)
Ammonium Chloride (Is a salt of ammonia; used as a thickener)
Cocamide MEA (Mild foaming agent and thickener derived from plant source)
Purified Water
Hydroxypropyl Methylcellulose (Thickener derived from plant source)
PEG 75 Lanolin (Naturally derived lanolin)
Methylchloroisothiazolinone (Preservative and antibacterial)

This list is quite similar to that of gentle shampoos or cleansers of ~30-40 years ago. Ammonium lauryl sulfate was considered the gentler alternative to sodium lauryl sulfate, which was (and is) a better cleanser than soap and less harsh than other surfactants commonly available at the time.

Neither ingredients list contains anything obvious that would control foaming. I suspect that claim is almost certainly founded in the low levels of surfactants.

For reference, liquid shampoo typically contains around 10-15% active surfactant matter (ASM), more or less, depending on surfactants used and type of shampoo. Facial cleanser is typically 10% or less. Body wash is usually 15-25%, but could be higher. I don't know what the ASM of the no-rinse washes are, but there are limits to concentrations for liquid surfactants, so I wouldn't expect the ASM of either to be above about 30%.

So yes, it is basically micellar water for textiles. It is lightly cleansing and refreshing, but it's not enough for really dirty things. It is safe to not rinse, but it's going to be less clean if you don't.
posted by monopas at 8:50 PM on October 17, 2022 [4 favorites]