Nonionic surfactants have covalently bonded oxygen-containing hydrophilic groups, which are bonded to hydrophobic parent structures. These Nonionic surfactants, are not ionized in water, and contain both hydrophilic groups (e.g. oxyethylene-CH2CH2O-, ether groups, hydroxyl group -OH or -CONH2 amide group, etc.) and lipophilic group (e.g., hydrocarbons which can be natural fatty alcohols or synthetic alcohols, acids or glyceryl esters/oils). The water-solubility of the oxygen groups is the result of hydrogen bonding. Hydrogen bonding decreases with increasing temperature, and the water solubility of Nonionic surfactants therefore decreases with increasing temperature. This result in formation of a milky/cloudy emulsion called the cloud point of surfactants. This property is very essential for determining the optimum use of Nonionic surfactant in formulations at elevated temperature especially in cleaning formulations like detergents, CIP etc.
As discussed above Nonionic surfactants have a unique property called a cloud point. The cloud point is the temperature at which the Nonionic surfactant begins to separate from the cleaning solution, called phase separation. When this occurs, the cleaning solution becomes cloudy. This cloud point is therefore considered the temperature for optimal detergency. For low foaming cleaners, optimal detergency is at the cloud point; for foaming cleaners optimal detergency is either just below the cloud point or at the start of the cloud point. The agitation of low foaming cleaners is sufficient to prevent phase separation. The temperature of the cloud point depends upon the ratio of the hydrophobic and hydrophilic portions of the Nonionic surfactant. Some cloud points are at room temperature while others are very high. Some Nonionic surfactants don't have a cloud point because they have a very high ratio of hydrophilic to hydrophobic moieties.
Nonionic surfactants are less sensitive to water hardness than anionic surfactants, and they foam less strongly. The differences between the individual types of Nonionic surfactants are slight, and the choice is primarily governed having regard to the costs of special properties (e.g., effectiveness and efficiency, toxicity, dermatological compatibility, biodegradability) or permission for use in food. In areas with hard water (high mineral content), Nonionic surfactants are more heavily marketed, as they are less likely to form a soap scum. The Nonionic surfactants are less likely to cause skin irritation, but this is associated with a less potent cleaning ability. Most cleaning products are manufactured as a blend of anionic and Nonionic surfactants to balance out the cleaning potential with the risk of skin irritation.
The aqueous solution of Nonionic surfactants has poor foaming capability with the foam being not stable as well. This is due to that each molecule of the Nonionic surfactant has relatively large surface area and the interface being in uncharged foam. Polyoxyethylene has long chain and uniform molecular weight distribution. The lipophilic group has long chain and also contains branched chain. The presence of the polyoxyethylene -polyoxypropylene copolymer both has a great impact on the foaming of the Nonionic surfactants. Owing to the presence of the polar portion and non-polar portions existing in their molecular structure, they have large surface activity. Such kind of active agents can be divided into the ester type (e.g. polyoxyethylene fatty acid esters, sorbitan fatty acid esters anhydrides), ether type (e.g., polyoxyethylene alkyl ether, polyoxyethylene alkyl phenol ether), amine type (such as polyoxyethylene fatty amine), amide type (such as polyoxyethylene alkyl amide) and mixing type (such as sorbitol anhydride fatty acid esters, polyoxyethylene ether). In the field of oiling, Nonionic surfactants are mainly used in foaming, emulsifying, anti-wax, anti-corrosion, retarder, production increase of oil wells, intensified injection of injection wells as well as improving oil recovery and so on.
Nonionic surfactants are neutral, they do not have any charge on their hydrophilic end. Therefore, Nonionic surfactants are very good at emulsifying oils and are better than anionic surfactants at removing organic soils/grease. The combination of Nonionic and anionic surfactants are frequently used together to create dual-action, multi-purpose cleaners that can not only lift and suspend particulate soils, but also emulsify oily soils. Most cleaning products contain Nonionic surfactants (emulsifiers and detergents), anionic surfactants, or a mixture of both in their composition.
Certain Nonionic surfactants can be non-foaming or low-foaming. This makes them a good choice as a ingredient in low-foaming detergents. Examples of some common nonionic surfactants include ethoxylates, alkoxylates, and cocamides.
If anionic surfactants are the most popular, Nonionic surfactants are a close second, widely used in a range of cleaning, personal care, and disinfectant products as well as industrial processes. The most common anionic surfactants are: Cocamide monoethanolamine (Cocamide MEA), Cocamide diethanolamine (Cocamide DEA), Fatty alcohol ethoxylates, Amine oxides, Sulfoxides. The group of Nonionic surfactants represents the second, by volume, most relevant group of surfactants used in cleaning products. Its most important representatives are by far the alcohol ethoxylates (AE) while other groups like alcohol alkoxylates (EO/PO adducts), fatty acid alkanolamides, alkylamine oxides and alkyl polyglucosides (APG) play a less ubiquitous role.