The aforementioned anionic surfactants are all anionic surfactants with large output and wide use. The remaining varieties can be divided into two categories. One category has large output, but the characteristics of surfactants are not obvious. For example, lignin sulfonate ranks first in output after LAS. It is a by-product of the paper industry and is mainly used as a dispersant, flotation agent, and drilling mud additiveAgentand the forming of animal feedAgent. Its characteristic is that it does not reduce the surface flexural tension of water at low concentrations and does not form interface orientation and micelles.
The other type of products has a smaller output, but they all have certain special uses. Such as polyoxyethylene ether carboxylates, used in personal cosmetics and personal toiletries,
Nonionic surfactants
In nonionic surfactants, the hydrophilic group of the molecule is not an ion at all, but a polyoxyethylene ether Chain, that is, R—(OCH2CH2)20H. The oxygen atoms and hydroxyl groups in the chain have the ability to form hydrogen bonds with water molecules, making the compound water-soluble. The water solubility is closely related to the number of polyoxyethylene ether groups.
Nonionic surfactants have excellent wetting and cleaning functions, are compatible with anionic and cationic surfactants, and are not affected by calcium and magnesium ions in water. Due to the above-mentioned advantages, nonionic surfactants have developed rapidly since the 1970s. Its disadvantage is that they are usually waxy or liquid with low melting point, so it is difficult to formulate them into powder. Another disadvantage is that when the temperature rises or the electrolyte concentration increases, the solvation efficiency of the polyoxyethylene ether chain will decrease, and sometimes precipitation will occur.
Ethoxylation
The reaction of using ethylene oxide to introduce polyoxyethylene hydroxyl groups on the hydroxyl groups of fatty acids, alkylphenols or fatty alcohols is called ethoxylation. Alkaline catalysts, such as sodium alkoxide or caustic soda, are often used in production.
The third step is to control the reaction. It is a speed control stage, which varies depending on the groups on the hydroxyl groups of the raw materials. The reaction sequence is; ciscarboxylic acid>phenol>alcohol
If using phenol or carboxylic acid is a raw material, and further reaction will begin when all reactants are converted into monoadducts to increase the degree of polymerization. This phenomenon shows that phenol or carboxylic acid is more acidic than alcohol. This improves the reaction speed in the first step. Further increase in the degree of polymerization will continue until all the fed ethylene oxide has reacted.
Except for the reaction step of generating an adduct, which is related to the molecular structure of the raw material, the reaction speed of other reaction steps has basically nothing to do with the length of the carbon chain of the raw material. The speed of the ethoxylation reaction is also related to the alkalinity of the catalyst.
