There are numerous types of surfactants. Ranked by output, anionic surfactants account for 56%, nonionic surfactants 36%, amphoteric surfactants 5%, and cationic surfactants 3%..
2.Anionic Surfactants
2.1 Sulfonate-type Anionic Surfactants
Common types of such surfactants include sodium linear alkylbenzene sulfonate and sodium alpha-olefin sulfonate.
Sodium linear alkylbenzene sulfonate, also known as LAS or ABS, is a white or pale yellow powdery or flaky solid soluble in water. It exhibits poor water solubility at low temperatures with a solubility below 3 in water at room temperature, yet it boasts excellent solubility in compound surfactant systems. It features good stability against alkalis, dilute acids and hard water, with a decomposition temperature of 240℃. Its irritation index of 10% solution is 5.0, the microbial degradation rate ranges from 80% to 90%, and the LD50 value is 1300 to 2500 mg/kg.
Sodium alpha-olefin sulfonate is abbreviated as AOS. When the active substance content is between 38% and 40%, it appears as a yellow transparent liquid and is highly soluble in water. It maintains favorable stability across a wide pH range; after being stored for three days at 30℃ under pH values of 2, 4 and 10 respectively, its hydrolysis rate remains zero in all cases. It causes mild skin irritation, achieves a 100% microbial degradation rate, and has an LD50 value of 1300 to 2400 mg/kg.
Generally, LAS is rarely used in shampoos and body washes, and is mainly applied in laundry liquid detergents and dishwashing liquids. In dishwashing liquids, LAS can account for approximately half of the total surfactants, while its proportion in laundry liquid detergents can be adjusted within a wide practical range.
LAS gains favorable water solubility mainly at relatively high temperatures such as 60℃ and when compounded with certain other surfactants. A typical ternary compound system “LAS-AES-FFA” is widely adopted in dishwashing liquids, and the compound system “LAS-soap base-η·SAA” is commonly used in laundry liquid detergents. It is noteworthy that direct compounding of LAS with nonionic surfactant alkylol amide often fails to achieve ideal effects; the “LAS-FFA” system is unstable with low viscosity and presents a white milky appearance.
LAS ranks first in output with an annual production volume of 290 kilotons and is the most inexpensive synthetic surfactant. It has the lowest price among the top five high-output synthetic surfactants, and its price is comparable to that of soap bases (fatty acid soaps) among conventional anionic surfactants. LAS is distinguished by excellent stability, strong detergency and low cost, while its prominent disadvantage is relatively high irritation.
Among all sulfonate surfactants, AOS delivers the optimal comprehensive performance. It inherits and further enhances the merits of ordinary sulfonates while avoiding their inherent drawbacks. As one of the major primary surfactants, AOS is widely used in shampoos and body washes, and its application in other liquid detergents will gradually expand along with the localization production and consequent price reduction.
AOS possesses outstanding advantages including superior stability, excellent water solubility, good compatibility, low irritation and ideal microbial biodegradability. Its main downside is that it is relatively expensive among all anionic surfactants.
2.2 Anionic Surfactant Sulfates
Common types of such surfactants include sodium fatty alcohol polyoxyethylene ether sulfate and sodium dodecyl sulfate.
Sodium fatty alcohol polyoxyethylene ether sulfate, also known as AES or alcohol ether sulfate, is easily soluble in water. When the active substance content reaches 70%, it appears as pale yellow viscous translucent liquid, and its stability is inferior to that of common sulfonates. It undergoes rapid hydrolysis when the pH value is below 4, yet boasts excellent hydrolysis stability in alkaline environments. After being stored for three days at 30°C under pH 2, pH 4 and pH 10 conditions, its hydrolysis rates are 100%, 50% and 0 respectively. It features low irritation with an irritation index of 2.3 for its 10% aqueous solution, a biodegradation rate of over 90%, and an LD50 value of 1800 mg/kg.
Sodium dodecyl sulfate, referred to as AS, K12, sodium cocoalkyl sulfate, sodium lauryl sulfate or foaming agent, is soluble in water with a water solubility of approximately 15 at 25°C, which is lower than that of AES. It is insensitive to alkalis and hard water, but its stability under acidic conditions is weaker than common sulfonates and close to that of AES. The long-term heating temperature should not exceed 95°C. It has moderate irritation among surfactants; its 10% solution has an irritation index of 3.3, higher than AES and lower than LAS, with an LD50 value of 1300 mg/kg.
AES is widely applied in shampoo, body wash, dishwashing liquid and laundry liquid detergent. In practical application, the pH value should be raised to neutral or weakly alkaline as much as possible if relevant pH quality standards permit. When AES has to be used under low pH conditions such as in shampoo, its ethanolamine salt form is generally adopted. AES possesses better water solubility than AS and can be formulated into transparent aqueous solutions in any proportion at room temperature. Compared with LAS, AES enjoys wider application in liquid detergents and superior compatibility, capable of being compounded with numerous surfactants in binary or multiple combinations to form transparent aqueous solutions. Among synthetic surfactants, AES ranks the third in output with a lower price than AS; the price of 70% AES was 8500 yuan per ton in 2002. Its prominent advantages include low irritation, favorable water solubility, excellent compatibility and remarkable effect in preventing dry and rough skin. Its main drawback lies in poor stability in acidic media, which requires the pH value to be kept far above 4, and its detergency is weaker than that of LAS and AS.
When applying AS in liquid detergents, the pH environment must be controlled to avoid excessive acidity. Its ethanolamine salts or ammonium salts are necessary for its application in shampoo and body wash. The adoption of its ethanolamine salts can not only enhance acid resistance stability but also reduce irritation, and the irritation index of its 10% triethanolamine salt solution is 3.0. AS is rarely used in dishwashing liquid and seldom serves as the primary surfactant with low dosage in formulas, mainly because it is unfavorable for cutting product costs and such products barely have requirements for foaming performance. Ranking fifth in the output of synthetic surfactants, AS is priced relatively high, and its powder form was priced at 15000 yuan per ton in 2002. Aside from outstanding foaming capacity and strong detergency, AS is inferior to AES in most service performances, such as slightly poorer acid resistance stability and relatively higher irritation (only lower than LAS), and it also has the highest price among conventional anionic surfactants.
The main types of non-ionic surfactants include alkylolamide (FFA), fatty alcohol polyoxyethylene ether (AE), and alkylphenol polyoxyethylene ether (APE or OP). Non-ionic surfactants possess excellent properties such as solubilization, detergency, antistatic performance, low irritation and lime soap dispersing capacity. They have a wider applicable pH range than common ionic surfactants, and are superior to ordinary anionic surfactants in most properties except detergency and foaming ability. Experiments prove that adding a small amount of non-ionic surfactants into ionic surfactant systems can enhance the overall surface activity when compared under the same active substance content.
Alkylolamides are high-performance, widely used and frequently applied non-ionic surfactants, which are commonly adopted in various liquid detergents. The mainstream specifications of alkylolamides used in liquid detergents are 2:1 amide and 1.5:1 amide, and 1:1 amide is also available for use. These three specifications differ greatly in water solubility and thickening property. Generally speaking, 1.5:1 amide has moderate comprehensive performance and is widely used in dishwashing liquid. Normally, 1:1 amide can be easily dissolved only when compounded with other water-soluble surfactants. Alkylolamides are more suitable for alkaline detergents and can also be used in weakly acidic detergents.
Among all non-ionic surfactants, alkylolamides are the most cost-effective, with a price of 7,800 yuan per ton in 2002. They are more frequently used in liquid detergents than fatty alcohol polyoxyethylene ethers, and are also the primary non-ionic surfactants applied in shampoo. The main reasons are as follows: FFA has more comprehensive and superior functions than AE; FFA is cheaper in price; FFA features better solubility; and FFA has stronger foaming performance compared with AE.
Amphoteric surfactants are surfactants that possess both anionic and cationic hydrophilic groups. Accordingly, they exhibit cationic properties in acidic solutions, anionic properties in alkaline solutions, and properties similar to non-ionic surfactants in neutral solutions.
Amphoteric surfactants are easily soluble in water, concentrated acid and alkali solutions, and even concentrated inorganic salt solutions. They feature excellent hard water resistance, low skin irritation, favorable fabric softening performance, outstanding antistatic property and good bactericidal effect, and boast great compatibility with various types of surfactants.
Such products can be used within a wide pH range. In view of their ionic states under different acid-base environments, they deliver better performance under acidic and neutral conditions than under alkaline conditions. Generally speaking, amphoteric surfactants are more expensive than non-ionic surfactants.
Common important varieties of amphoteric surfactants include dodecyldimethylbetaine and carboxylate-type imidazoline. Compared with anionic surfactants, non-ionic surfactants have more comprehensive properties with fewer drawbacks, only inferior in detergency and foaming capacity. When compared with non-ionic surfactants, amphoteric surfactants are superior in certain properties and comparable in others.
Amphoteric surfactants have stronger foaming power than ordinary non-ionic surfactants (while AE surfactants have poor foaming capacity), superior bactericidal activity relative to non-ionic and anionic surfactants, and better conditioning effects. For this reason, in liquid detergents, amphoteric surfactants are mainly applied in shampoo, followed by skin cleansing products such as body wash.
Common types of cationic surfactants include Cetyl Dimethyl Ammonium Chloride (1631), Octadecyl Trimethyl Ammonium Chloride (1831), Cationic Guar Gum (C-14S), cationic panthenol, cationic silicone oil, Dodecyldimethylamine Oxide (OB-2) and so on.
In liquid detergents, cationic surfactants serve as auxiliary surfactants and conditioning ingredients with low dosage in formulas. They are generally applied in high-end products, most commonly in shampoos. Cationic surfactants cannot be directly compounded with anionic surfactants. Although combinations of cationic and anionic surfactants may achieve ideal effects, they carry a high risk of sedimentation and crystallization.
A wide variety of cationic surfactants are used in shampoos with scattered application frequencies, meaning no single or two types are predominantly adopted, and they are often formulated into finished conditioning products. Cationic surfactants account for a small proportion in the total output of surfactants and are usually more expensive than other categories.
Compared with other types of surfactants, cationic surfactants possess the most prominent conditioning effect and the strongest bactericidal activity. Despite their drawbacks such as poor detergency, weak foaming capacity, inferior compatibility, high irritation and high cost, they are irreplaceable by other surfactants as conditioning components in high-end liquid detergents and shampoos. It is noteworthy that cationic surfactants can only be used as conditioning ingredients or bactericides.
Post time: May-21-2026