Polyethylene glycol (PE) type nonionic surfactants can be classified according to the type of hydrophobic group, including long-chain fatty alcohol polyoxyethylene ethers, alkylphenol polyoxyethylene ethers, fatty acid polyoxyethylene esters, polyoxyethylene alkylamines, polyoxyethylene alkylamides, and polyethers.
Long-chain fatty alcohol polyoxyethylene ethers
The hydrogen atom on the hydroxyl group in long-chain fatty alcohol molecules is an active hydrogen atom, and ethylene oxide is an active compound that can replace the hydrogen atom. They readily react and polymerize into ethers.
In fact, the addition of ethylene oxide proceeds gradually, first adding one ethylene oxide molecule, then adding a second, third, and so on. Optimal detergency is observed after adding 10-15 molecules. Commonly used long-chain fatty alcohols include lauryl oleyl alcohol, palmitol, stearyl alcohol, cyclohexanol, and terpene alcohols. These surfactants have high stability, good biodegradability and water solubility, and excellent emulsifying, wetting, penetrating, dispersing, and solubilizing abilities. They are commonly used in laundry detergents and shampoos. Alkylphenol polyoxyethylene ethers are produced by the addition reaction of alkylphenols with ethylene oxide. Commonly used phenols include octylphenol and nonylphenol. When nonylphenol is used, the product formed by the addition of 4 molecules of ethylene oxide is insoluble in water; the product formed by the addition of 6 or 7 molecules of ethylene oxide is completely soluble in water at room temperature; the product formed by the addition of 8-12 molecules of ethylene oxide has good wetting, penetrating, and detergency, and also has good emulsifying power, making it suitable for use as a detergent and penetrant; the product formed by the addition of more than 15 molecules of ethylene oxide has no penetrating or detergency, but has good emulsifying and dispersing power, making it suitable for use as an emulsifying dispersant, leveling agent, and retarding agent. Alkylphenol polyoxyethylene ethers have high chemical stability and are not easily destroyed by strong acids or alkalis even at high temperatures, and their biodegradability is poor. Therefore, their demand is gradually decreasing, and they are mainly used in acidic and alkaline detergents for metals, with less use in household detergents.
Fatty acid polyoxyethylene esters
Fatty acids react with ethylene oxide in the presence of a catalyst to form fatty acid polyoxyethylene esters. The more carbon atoms in the fatty acid, the lower its solubility and the higher its cloud point, except for fatty acids containing hydroxyl groups or unsaturated fatty acids. The effect of the number of added ethylene oxide molecules on the ester is similar to that of fatty alcohol polyoxyethylene ethers. For example, fatty acids with 12-18 carbon atoms bonded to 12-15 ethylene oxide molecules have excellent detergency, while those with fewer than this number, such as 5-6 ethylene oxide molecules, exhibit oil-soluble emulsifying power. This type of surfactant has lower penetrating and detergency than polyoxyethylene ethers of fatty alcohols and alkylphenols, and is mainly used as an emulsifier, dispersant, fiber oiling agent, and dyeing auxiliary agent.
Polyoxyethylene alkylamines
Alkylamines undergo an addition reaction with ethylene oxide to produce two reaction products. Similar to the three nonionic surfactants mentioned above, when the number of ethylene oxide additions in the polyoxyethylene alkylamine molecule is small, it is insoluble in water but soluble in oil. However, due to its organic amine structure, it is soluble in acidic aqueous solutions. Therefore, polyoxyethylene alkylamines possess some characteristics of both nonionic and cationic surfactants, such as acid resistance but poor alkali resistance, and bactericidal properties. When the number of ethylene oxide additions is large, its nonionicity increases, and it does not precipitate in alkaline solutions, exhibiting good activity even in alkaline solutions.
Due to the increased nonionicity and relatively decreased cationicity, it exhibits compatibility with anionic surfactants and can be used in combination with them. Because this surfactant combines nonionic and cationic properties, it is commonly used as a dyeing auxiliary agent and in rayon production to enhance the strength of regenerated fiber yarns. It also helps maintain the cleanliness of spinneret orifices and prevent dirt deposition.
Polyoxyethylene alkylolamides
Alkylolamides undergo an addition reaction with ethylene oxide to form polyoxyethylene alkylolamides. These nonionic surfactants possess strong foaming and stabilizing properties, and are therefore commonly used as foam promoters and stabilizers. Some also exhibit good detergency, solubilizing, and thickening effects. An early product of this type is lauroyl diethanolamine, which is synthesized by heating lauric acid and diethanolamine under nitrogen protection. Lauroyl diethanolamine is insoluble in water; it only exhibits good water solubility and detergency when combined with one molecule of diethanolamine to form a complex. It can be used as a foam stabilizer in detergents, as well as an emulsifier, rust remover, and dry cleaning soap. The stability and hydrolysis resistance of this surfactant are superior to those of fatty acid polyoxyethylene esters.
Polyethers
Polyether products are a general term for a series of products copolymerized with propylene glycol as a starting agent and various polyoxypropylene-ethylene oxides of different relative molecular masses. The relative molecular mass of polyethers can reach several thousand or more, significantly higher than that of ordinary surfactants, therefore they can also be classified as high molecular weight surfactants. Polyethers have unique properties; they are generally non-hygroscopic, soluble better in cold water than in hot water, and concentrated solutions are gel-like. They are also soluble in aromatic hydrocarbons and chlorinated organic solvents. Polyethers have low toxicity and low foaming power; polyethers with a relative molecular mass of 2000-3000 have good detergency; higher relative molecular masses have better dispersing power. In addition, polyethers have strong emulsifying power, so they can be used in low-foaming detergents, emulsifiers, defoamers, as well as fabric leveling agents, antistatic agents, metal cutting coolant lubricants, and binders. They have even wider applications in some specialized fields.
