Ethoxylation
- Also known as
- ethoxylated, ethoxylates, ethylene oxide
Ethoxylation is a chemical reaction that adds chains of ethylene oxide units to a molecule, such as a fatty alcohol, to make it more water-attracting. It is the main route to many nonionic surfactants and to ingredients such as sodium laureth sulfate.
What is ethoxylation?
In ethoxylation, a starting molecule with a reactive hydrogen, typically a fatty alcohol, fatty acid, amine or alkylphenol, reacts with ethylene oxide. Each reaction adds a unit of ethylene oxide, and the process continues to build a chain. The chain is water-attracting, so the result is a molecule with an oily tail and a water-loving head: a surfactant.
Ethylene oxide is a flammable, toxic gas, and ethoxylation is carried out in closed industrial reactors under controlled conditions.
What ethoxylation produces
- Alcohol ethoxylates, a major class of nonionic surfactants.
- Ethoxylated sulfates, such as sodium laureth sulfate, made by ethoxylating and then sulfating a fatty alcohol; see sulfate-free surfactant.
- Polysorbates and other ethoxylated emulsifiers.
- Polyethylene glycols used in many formulations.
By controlling the length of the ethylene oxide chain, manufacturers tune how water-soluble a surfactant is, its hydrophilic-lipophilic balance, and its cloud point.
Concerns
- 1,4-dioxane. Ethoxylation can create trace 1,4-dioxane as a byproduct, which manufacturers remove to varying degrees.
- Ethylene oxide itself is classed as a carcinogen, so handling and emissions at production facilities are regulated.
- Carbon source. Ethylene oxide is usually made from petrochemical ethylene, so an ethoxylated surfactant built on a plant-derived fatty alcohol is only partly biobased; see biobased content.
These concerns have driven interest in non-ethoxylated alternatives, including sugar-based surfactants and biosurfactants.
Frequently asked questions
Ingredients such as sodium laureth sulfate, with “eth” in the name, or those containing “PEG” or ending in “-eth,” have typically been made by ethoxylation.
Ethoxylated surfactants are widely used and regulated. The main concerns are trace 1,4-dioxane, which can be controlled in manufacturing, and the hazards of ethylene oxide at production sites.
Sources
- Surfactants and Interfacial Phenomena, 4th edition, M. J. Rosen and J. T. Kunjappu, Wiley, 2012
- 1,4-dioxane technical fact sheet, U.S. Environmental Protection Agency