Fatty Acid, Methyl Ester, and Vegetable Oil Ethoxylates

Soap is the first and oldest example of a biobased surfactant. Soap is prepared by saponifying fats and oils with caustic. Soap has been used for over 4500 years for personal cleaning and washing of clothes. In personal cleaning products, the high pH of soap can irritate the skin and eyes, and soap also suffers from sensitivity to salinity and hard water ions. With the advent of modern industrial chemistry, the reliance on soap has declined. Fatty acid ethoxylates (FAEs) are prepared by reacting fatty acids with ethylene oxide or polyethylene glycol (PEG). Both reactions produce a mixture of ethoxylated fatty acid, bis fatty acid ester, and PEG. FAE can be used in neutral pH and is relatively insensitive to hard water ions but suffers from low yields due to the transesterification reaction. Methyl ester ethoxylates (MEEs) were originally developed to improve the efficiency of FAEs. Reacting fatty acid methyl ester with ethylene oxide using a calcium- or magnesium-based catalyst or esterification of fatty acids with polyethylene glycol methyl ether (MPEG) produces MEE high yields. MEE is soluble at neutral pH and shows favorable detergency but suffers from hydrolytic stability issue in alkaline solution and does not build viscosity in low active formulations through the salt effect. Vegetable oil ethoxylates (VOEs) are made by direct ethoxylation of triglycerides or transesterification of triglycerides with ethoxylate glycerin. VOE show good surface activity and are exceptionally mild to skin and eyes. VOE is used primarily in personal care as emollients and foam boosters in rinse off products.