Anonymous asked...Can i replace Laureth-4 for Laureth-3? I'm trying to do up a oil shower gel & i'm using MIPA –Laureth Sulfate as the suractant...
Great question! Let's take a look at what laureth-4 is, then figure out if it can be substituted by laureth-3.
Laureth-3 and -4 are ethers, subcategory alkoxylated alcohols. They are non-ionic surfactants and are ethoxylated alcohols. They may sometimes be called polyethylene glycol ethers or PEG ethers. These are produced by a reaction of a fatty alcohol with ethylene oxide. The name comes from the root of the fatty acid (laur, which comes from lauric acid), "eth" to indicate it has been ethoxylated, and the degree of ethoxylation (-3 or -4). You may see ingredients like oleth-5 (from oleic acid) or myristeth-7 (from myristic acid).
You might see other PEG ethers with names like laneth-16 (lanolin) or ceteareth-20 (cetyl and stearyl alcohol). These names are derived from the fat itself (lanolin) or the fatty acid.
We know these PEG ethers are emulsifiers, but the low ethoxylated ones tend to be solubilizers rather than emulsifiers. The higher the level of ethoxylation, the better they'll emulsify.
A solubilizer is something that makes an oil soluble in water. So when we use an emulsifying type ingredient in something like a shampoo, we're using it to make the oil dispersible in the water. Think of mixing polysorbate 20 with an essential oil to make a water based fragrance spray. We aren't expecting a lotion-type emulsification for this product, we merely want the oil to stay suspended in the water without forming a greasy mess at the top of the bottle.
So what is laureth-4? It's a non-ionic solubilizer with an HLB of 9.7. It's used at 1 to 5%. This is mostly for surfactants, but it can be used in lotions in combination with a low HLB emulsifier. Laureth-3 is also a non-ionic solubilizer with an HLB of 7.9 or 8.1 (depending where you find your information) that should be used at 0.5% to 5%. Both of these are able to thicken our surfactant mixtures.
Emulsifiers with an HLB of 8 to 10 will produce "stable milky dispersions" when not coupled with a low HLB emulsifier in an emulsion. In other words, if we use laureth-3 or laureth-4 in a surfactant mixture, it will solubilize our oils and possibly create a milky type consistency (not necessarily a milky
So can we substitute laureth-3 for laureth-4? Probably. They have the same kind of profile - they are both solubilizers (they are used to make oil dispersible in water), they will produce milky consistency emulsions, and they're intended for use in anionic surfactant products. Laureth-4 has more ethoxylation so it will be a better emulsifier, but if you're not using a ton of oils, laureth-3 will likely do the job!
Hope this answer helped!