First, an interface is a boundary surface that exists between two substances with different properties, and interfaces exist between liquids and solids, liquids and liquids, and liquids and gases.

Surfactants enhance performance by performing functions such as washing, emulsifying, dispersing, wetting, and penetrating at this interface.

Interface = a boundary surface that exists between two substances with different properties
Liquid and solid: cup and coffee, machine and lubricant 
Liquid and liquid: water and oil 
Liquid and gas: seawater and air, soap bubbles

Examples of roles of surfactants
Cleaning ・・・ Removing dirt 
Emulsification ・・・ Dispersion ・・ Making unmixable things easier to mix
Wetting / Penetration ・・・ Makes wetting and soaking easier

-Surfactants have different structures in their molecules with different properties: lipophilic groups (oil-loving parts) and hydrophilic groups (water-loving parts).

-Surfactants are broadly classified into four types according to the structure of the hydrophilic group: nonionic, anionic, cationic, and amphoteric (having both anionic and cationic groups).

It consists of seven short movies for each function. 
0:00　Introduction of surfactants functions　
0:16　Part1　Washability
1:00　Part2　Permeability
2:10　Part3　Dispersion
2:55　Part4　Foaming properties
3:25　Part5　Defoaming properties
3:39　Part6　Smoothness
4:20　Part7　Antibacterial properties

Examples of amphoteric surfactants

Anionic surfactants command a major share of the household detergent market, including soaps, and cationic surfactants are well- known as germicides for disinfection and as finishing agents for synthetic fibers such as nylon. Then, what is a familiar example of an amphoteric surfactant? 

It is an important ingredient in cosmetics, especially shampoo. One of the most popular amphoteric surfactants is cocoamidopropyl betaine, derived from coconut fatty acid and dimethyl aminopropylamine.

Classification of Amphoteric Surfactants

Although only limited kinds of amphoteric surfactants are used practically, many kinds are conceivable. More concretely, as amphoteric surfactants are composed of anion-cation combinations, the theoretical number of amphoteric surfactants that could be synthesized should be at least as large as the number of kinds of anionics multiplied by that of cationics.

In many practical cases, however, either amine salts or quaternary ammonium salts are used as a hydrophilic group with a cationic property. Therefore, it is convenient to classify an amphoteric surfactant by the type of its anionic part.

The classification of amphoteric surfactants by type of anionic portion is summarized below.

However, this table represents experimentally developed amphoteric surfactants only. In practice, most amphoteric surfactants currently on the market are carboxylate type. In this page, therefore, discussion is focused on carboxylate type amphoteric surfactants.

A carboxylate type amphoteric surfactant is one that possesses a carboxyl group as its anionic part. Those possessing an amine salt type cationic part are called amino acid type amphoteric surfactants, and those possessing a quaternary ammonium salt type cationic part are called betaine type amphoteric surfactants (As shown in table above).

A compound with the following composition is produced when one mole of methyl acrylate (CH2 = CHCOOCH3) is added during stirring to one mole of higher alkylamine (C12 to C18) such as lauryl amine that has been melted by heating to 60 to 70 °C.

Fig. Synthesis of methyl lauryl amino propionate (secondary amine)

The methyl lauryl amino propionate thus produced is a secondary amine, although it has a slightly complex structure. Therefore, it yields water-soluble cationic surfactants by neutralization with an acid such as hydrochloric acid.

Fig. Neutralization reaction of methyl lauryl amino propionate (cationic surfactant)

However, by focusing on the ester linkage rather than the amine, it becomes apparent that the carboxyl group can be regenerated by saponification with alkali. In this way, an excellent amino acid type surfactant can be obtained.

Fig. Formation reaction of sodium lauryl amino propionate (amino acid type amphoteric surfactant)

The saponification can be carried out easily by adding one mole of aqueous sodium hydroxide solution, slowly, during stirring, to one mole of methyl lauryl amino propionate, in a beaker heated in a boiling water bath. The resultant sodium lauryl amino propionate is easily soluble in water, yielding a transparent solution. Its aqueous solution foams well, and is fairly alkaline because its molecule contains not only sodium carboxylate, as in the case of soap, but also a free secondary amino group.

In an alkaline solution, as shown above, the amino group of an amino acid type amphoteric surfactant performs a relatively minor function as a hydrophilic group because it does not exist as a salt, and the hydrophilic property of the surfactant is attributable mainly to its carboxylate group. Therefore, amphoteric surfactants of this type exhibit properties similar to those of anionic surfactants in alkaline solution.

Behavior of aqueous amino acid-type amphoteric surfactant solutions upon neutralization with hydrochloric acid

Fig. Behavior of alkaline aqueous amino acid-type amphoteric surfactant solutions upon neutralization with hydrochloric acid

Applications and Synthesis of Sodium Lauryl Amino Propionate and Other Amino Acid Type Amphoteric Surfactants

Sodium lauryl amino propionate has fairly good detergency and is used as a specialty detergent. There are a variety of products in this category with different lengths of alkyl groups and different positions and numbers of amino groups and carboxyl groups. On the whole, they have similar general properties to those shown in the above example, but their applications are diverse.

In addition to the process mentioned above, amphoteric surfactants of alkyl amino propionate type can be synthesized by an alternative process using acrylonitrile, which is more economical.

Fig. Synthesis of sodium stearyl propionate (method using acrylnitrile)

Surfactants with a similar structure but with one less methylene group (-CH2-) between the amino and carboxyl groups can be synthesized easily by reacting a higher alkylamine with an aqueous sodium mono chloroacetate solution.

Some amino acid type amphoteric surfactants with this structure are used as germicides with the feature of less toxicity than cationic products.

Fig. Reaction of lauryl amine with sodium monochloroacetate

Betaine and betaine surfactants

Fig. Formation reaction of lauryl dimethyl betaine

Features of lauryl dimethyl betaine

Lauryl dimethyl betaine dissolves in water transparently and foams well. It has excellent detergency and can be considered a representative betaine type amphoteric surfactant.

The largest difference between betaine type and amino acid type amphoteric surfactants is that betaine type surfactants dissolve in water easily, regardless of whether the betaine type surfactant is acidic, neutral or alkaline in nature. Therefore, in the case of betaine type surfactants, there is almost no danger of precipitation even at the isoelectric point, and there is the added advantage of being usable across the entire pH range.

Dimethyl stearyl betaine, dihydroxyethyl lauryl betaine

Amphoteric surfactants (cocoacid amidopropyl betaine, lauryl imidazolinium betaine) used as shampoo base

Cocoamidopropyl betaine and laurylimidazolinium betaine are widely used as shampoo bases. These amphoteric surfactants are manufactured from fattyamide amine and alkylimidazoline, respectively, through the reactions indicated in the following reaction formula. However, alkylimidazolinium betaine is actually a complex mixture of products resulting from a cleavage of the imidazoline ring. 

Fig. Synthetic route of coconaut fatty acid amidopropyl betaine

Fig. Synthetic route of lauryl imidazolinium betaine

A surfactant consisting of an anionic part and a cationic part in its molecule is generally referred to as an amphoteric surfactant. In this class of surfactants, there are various types such as the carboxylate type and the sulfonate type. The most familiar is the carboxylate type, which is subdivided into the amino acid type and the betaine type.

Amino acid type surfactants tend to precipitate at the isoelectric point, but betaine type products dissolve in water relatively easily even at the isoelectric point. In general, the betaine type is better than the amino acid type.


Among these carboxylate-type amphoteric surfactants, the more commonly used forms can be classified based on the raw materials of their hydrophilic and hydrophobic groups, as shown in the table below.

Consumption of amphoteric surfactants is small in comparison to other surfactants. However, if you encounter difficulties with regard to surfactant application, it may be more rewarding than expected to consider using amphoteric surfactants.

This page has been prepared solely for information purposes.
Sanyo Chemical Industries, Ltd. extends no warranties and makes no representations as to the accuracy or completeness of the information contained herein, and assumes no responsibility regarding the suitability of this information for any intended purposes or for any consequences of using this information.

Any product information in this brochure is without obligation and commitment, and is subject to change at any time without prior notice.

Consequently anyone acting on information contained in this brochure does so entirely at his/her own risk.In particular, final determination of suitability of any material described in this brochure, including patent liability for intended applications, is the sole responsibility of the user. Such materials may present unknown health hazards and should be used with caution. Although certain hazards may be described in this brochure, Sanyo Chemical Industries, Ltd. cannot guarantee that these are the only hazards that exist.

First, an interface is a boundary surface that exists between two substances with different properties, and interfaces exist between liquids and solids, liquids and liquids, and liquids and gases.

Surfactants enhance performance by performing functions such as washing, emulsifying, dispersing, wetting, and penetrating at this interface.

Interface = a boundary surface that exists between two substances with different properties
Liquid and solid: cup and coffee, machine and lubricant 
Liquid and liquid: water and oil 
Liquid and gas: seawater and air, soap bubbles

Examples of roles of surfactants
Cleaning ・・・ Removing dirt 
Emulsification ・・・ Dispersion ・・ Making unmixable things easier to mix
Wetting / Penetration ・・・ Makes wetting and soaking easier

-Surfactants have different structures in their molecules with different properties: lipophilic groups (oil-loving parts) and hydrophilic groups (water-loving parts).

-Surfactants are broadly classified into four types according to the structure of the hydrophilic group: nonionic, anionic, cationic, and amphoteric (having both anionic and cationic groups).

It consists of seven short movies for each function. 
0:00　Introduction of surfactants functions　
0:16　Part1　Washability
1:00　Part2　Permeability
2:10　Part3　Dispersion
2:55　Part4　Foaming properties
3:25　Part5　Defoaming properties
3:39　Part6　Smoothness
4:20　Part7　Antibacterial properties

Hydrophilic Groups of Cationic Surfactants

A sodium ion (Na+) and a potassium ion (K+) are certainly hydrophilic groups with positive charges, but there is no way to combine them with hydrophobic groups. However, among the same inorganic cations, it seems possible to find a way of combining an ammonium ion (NH4+) with hydrophobic groups. For instance, it might be possible to substitute a hydrogen atom of ammonium chloride (NH4+Cl-) with a hydrophobic group such as an alkyl group.

In fact, a hydrogen atom can be substituted with an alkyl group, and furthermore, not only one, but also two, three or four hydrogen atoms can be substituted freely. That is, four kinds of substituted ammonium chlorides, each having a specific name, can be prepared, as shown in the table below.

Synthesis of Cationic Surfactants by Neutralization of Amines

In actual practice they are not manufactured by substitution of hydrogen atoms of ammonium chloride with alkyl groups. Instead, just as ammonium chloride is prepared by neutralization of ammonia with hydrochloric acid, alkylated ammonium chlorides (hydrochloric acid salts of amines) with up to three alkyl groups are manufactured easily by neutralization with hydrochloric acid of appropriate primary amines, secondary amines or tertiary amines, respectively, as shown below.

Thus, higher alkylamines can be converted easily to cationic surfactants by simple neutralization with acids. Accordingly, not only strong inorganic acids such as hydrochloric acid, but also relatively weak lower fatty acids such as formic acid and acetic acid may yield amine salt type cationic surfactants by neutralizing amines with them.

Examples of laurylamine acetate

For example, acetic acid salt of laurylamine is obtained as a result of exothermic neutralization by adding a calculated amount of acetic acid during stirring to laurylamine (C12H25NH2, a white, waxy solid insoluble in water), which has been melted by heating to 60 to 70 °C.

Acetic acid salt of laurylamine thus obtained is an excellent surfactant which is easily soluble in water. 

Fig. Formation reaction of laurylamine acetate

Raw Material Amines for Cationic Surfactants

In this connection, special attention should be paid to the fact that neutralization of higher alkylamines with acids such as higher fatty acids, which are difficult to dissolve in water, results in formation of salts of amines that are insoluble in water.

Then, what kinds of amines can be used as raw materials for the cationic surfactants mentioned above ? To make you familiar with these amines, The table below shows not only higher alkylamines that are convertible into surfactants directly but also lower alkylamines, which are important as intermediates.

Synthesis of quaternary ammonium chlorides with alkylating agents

Incidentally, you may note that mono-, di- or trialkylammonium chloride (hydrochloric acid salt of primary, secondary or tertiary alkylamine) can certainly be prepared by the process mentioned above, but tetraalkylammonium chlorides (quaternary ammonium chlorides) cannot be prepared in the same way In other words, it is impossible to prepare alkylammonium chlorides with four alkyl groups that are linked to the central nitrogen atom by neutralizing of any kind of amine with hydrochloric acid.

The table bellow shows typical examples of alkylating agents which are used frequently to manufacture quaternary ammonium salt type cationic surfactants. These alkylating agents yield quaternary ammonium salts through the following reaction examples.

Fig. Formation reaction of quaternary ammonium salts by alkylating agents

In this page, salts of primary, secondary and tertiary amines are called collectively amine salt type cationic surfactants because there are no sharp distinctions among them, as a result of their similar properties. Furthermore, many commercial products contain primary and secondary amines together.

Since products of this type are classified into surfactants, it is no wonder that each of their hydrophobic groups consists predominantly of alkyl groups with carbon numbers from 12 to 18. However, curiously enough, amine salt type cationic surfactants are rarely used for applications that would require surface activity, in the basic sense of the term. Examples will be introduced in the following pages.

Synthetic method for aliphatic higher amines

Higher alkylamines are synthesized by hydrogenating fatty nitriles, which are prepared by heating fatty acids or esters with ammonia.

Fig. Synthetic route of aliphatic amines

Coconut amine containing mainly laurylamine (C12), and hydrogenated tallow amine containing mainly stearylamine (C18), are manufactured commercially by this process from coconut oil and tallow, respectively Low-priced amines such as rosin amine produced from rosin acid are also available.

As previously discussed, these amines are converted to surfactants easily by neutralization with acids such as hydrochloric acid and acetic acid. Relatively speaking, however, only a small amount of salts of higher alkylamines is consumed commercially.

Synthetic method for higher alkylamine ethylene oxide adducts

Water solubility of higher alkylamine ethylene oxide adducts

Examples of applications of higher alkylamine ethylene oxide adducts

The effect of this structure's nonion-cation combination is directly apparent in its properties, and it is used relatively widely for special applications, for example, as a dyeing auxiliary.

Higher alkylamines are fairly expensive, so there is a demand to manufacture cationic surfactants from raw materials that are cheaper. Whatever the approach, there may be no appropriate way to achieve this other than to use something like fatty acid, which is a cheap source of hydrophobic groups. Then, it will be of great practical value to try to synthesize cationic surfactants by reacting fatty acids such as oleic acid and stearic acid with lower alkylamines. In practice, the reaction proceeds very smoothly, and furthermore, it easily yields products with a variety of structures.

In many cases, this series of products is not only inexpensive, but also excellent in performance. Cationic surfactants used as textile softeners generally belong to this series.

Products in this category in particular are among the less expensive cationic surfactants because they can be manufactured easily with cheap raw materials. They also have high performance, and are still used commercially today. Their disadvantage is the easy hydrolysis of the ester linkage that combines the hydrophobic group with the hydrophilic group. Hydrolysis is prevented to some extent when strong acid is used for neutralization of the amine.

Ahcovel A is a typical product among the Ahcovel series of cationic softeners, first developed by Arnold Hoffman Co. of the USA in the 1940s.

Ahcovel A is manufactured by a series of complicated reactions. An intermediate obtained by condensation between stearic acid and aminoethyl- ethanolamine during heating is reacted with urea, and the resultant amine is neutralized by acetic acid. 

Fig. Synthesis route of urea condensed amine salt type cationic surfactant (Ahcobel A)

Close examination of the structural formula of Ahcovel A reveals that it does not contain any amino group. If so, how is neutralization with acetic acid possible? As the above formula appears in a patent owned by that company, this is the formula that has generally been in use. 

Urea condensed amine salt type cationic surfactant applications

This Ahcovel series of products shows excellent performance as textile softeners, and many companies supply equivalents. Other amines such as diethylenetriamine are also used in some cases. Cationic surfactants sold as textile softeners of this kind are supplied generally in the form of a white paste of aqueous emulsion with a concentration of 20% to 40%. When warm water is added during stirring, a dilute emulsion with fine and uniform particles is easily obtained.

When amines such as aminoethylethanolamine and polyethylenepolyamine are reacted with fatty acids at 160 to 180 °C, amines in the form of amide are obtained, as discussed above. When they are reacted at higher temperatures between 200 and 250 °C, amines of a new type called imidazoline derivatives are obtained. Imidazoline derived from oleic acid and aminoethylethanolamine is shown in the following formula, but it is actually not as simple as the compound shown in this formula. Rather, it is a mixture of products resulting from cleavage of an imidazoline ring.

Fig. Example of formation reaction of imidazoline derivatives

Imidazoline type cationic surfactants derived from oleic acid can be used as emulsion breakers. They are also used as intermediates for further reactions to manufacture quaternary ammonium salt type cationic surfactants or amphoteric surfactants.

Onyxan HSB (Refined-Onyx Div., Milmaster Onyx Corp.) is a famous textile softener in this category, and its nature is very similar to that of Ahcovel G. Imidazoline type cationic surfactants derived from lauric acid are used as intermediates to manufacture amphoteric surfactants. 

Quaternary ammonium salt type cationic surfactants are manufactured by means of the reaction between tertiary amines and alkylating agents. Various combinations of the two reactants yield a great variety of products.

These quaternary ammonium salts, which have particularly strong germicidal properties, are produced by alkylating alkyldimethylamine (tertiary amine) with benzyl chloride. Alkyl groups in the vicinity of lauryl (C12) are preferred.

These compounds are also called benzalkonium chlorides, and are produced in fairly large quantities as germicides. They dissolve in water transparently and generate large amounts of foam. They are used widely in hospitals and similar facilities as their germicidal effect is about 500 times stronger than that of phenol. Furthermore, these compounds have no smell and will not irritate the skin.

Fig. Synthesis route of benzylauryl dimethyl ammonium chloride (benzalkonium chloride)

It is possible to manufacture inexpensive quaternary ammonuim salts starting with lower alkylamines and cheap hydrophobic groups. As this result in a wider choice of structures and properties, there has been a lot of development and diversification of this type of surfactant.

Cationic surfactants are divided broadly into two categories, amine salt type and quaternary ammonium salt type. These two types have different properties and manufacturing processes. It is very important to understand the differences between the two types, as summarized in the table bellow.

On mixing cationic and anionic surfactants

Aqueous cationic surfactant solutions are generally acidic in contrast to those of anionic surfactants, which are generally neutral or alkaline. That is, roughly speaking, cationic surfactants ionize into weaker base and stronger acid, and anionic surfactants ionize into weaker acid and stronger base. The table bellow explains the matter to enable better understanding by comparing equivalent inorganic compounds.

The table bellow shows the usual classification of cationic surfactants according to the combination of hydrophobic and hydrophilic raw materials. 

In this page, discussion of cationic surfactants is limited to only nitrogen compounds. In fact, all commercial products of this type are nitrogen compounds. From the scientific point of view, however, some sulfur compounds, such as sulfonium salts, and some phosphorus compounds, such as phosphonium salts, are also regarded as cationic surfactants.

This page has been prepared solely for information purposes.
Sanyo Chemical Industries, Ltd. extends no warranties and makes no representations as to the accuracy or completeness of the information contained herein, and assumes no responsibility regarding the suitability of this information for any intended purposes or for any consequences of using this information.

Any product information in this brochure is without obligation and commitment, and is subject to change at any time without prior notice.

Consequently anyone acting on information contained in this brochure does so entirely at his/her own risk.In particular, final determination of suitability of any material described in this brochure, including patent liability for intended applications, is the sole responsibility of the user. Such materials may present unknown health hazards and should be used with caution. Although certain hazards may be described in this brochure, Sanyo Chemical Industries, Ltd. cannot guarantee that these are the only hazards that exist.

First, an interface is a boundary surface that exists between two substances with different properties, and interfaces exist between liquids and solids, liquids and liquids, and liquids and gases.

Surfactants enhance performance by performing functions such as washing, emulsifying, dispersing, wetting, and penetrating at this interface.

Interface = a boundary surface that exists between two substances with different properties
Liquid and solid: cup and coffee, machine and lubricant 
Liquid and liquid: water and oil 
Liquid and gas: seawater and air, soap bubbles

Examples of roles of surfactants
Cleaning ・・・ Removing dirt 
Emulsification ・・・ Dispersion ・・ Making unmixable things easier to mix
Wetting / Penetration ・・・ Makes wetting and soaking easier

-Surfactants have different structures in their molecules with different properties: lipophilic groups (oil-loving parts) and hydrophilic groups (water-loving parts).

-Surfactants are broadly classified into four types according to the structure of the hydrophilic group: nonionic, anionic, cationic, and amphoteric (having both anionic and cationic groups).

It consists of seven short movies for each function. 
0:00　Introduction of surfactants functions　
0:16　Part1　Washability
1:00　Part2　Permeability
2:10　Part3　Dispersion
2:55　Part4　Foaming properties
3:25　Part5　Defoaming properties
3:39　Part6　Smoothness
4:20　Part7　Antibacterial properties

Anionic surfactants have been used for a long time and are still the second most commonly used surfactants after nonionic surfactants.

The history of surfactants begins with the widespread use of soap, which replaced traditional methods of washing clothes with lye and similar substances. Turkey red oil (sulfated castor oil) followed as a pioneer of synthetic surfactants, and its efficacy was praised for a long time in the dyeing and finishing of textiles industry. Over time, the surfactant industry evolved, with the introduction of salts higher alcohol sulfates, alkanoyl methyl tauride, and alkyl benzene sulfonates, laying the foundation for the modern range of anionic surfactants.

First, anionic surfactants are classified as shown in the table below.

When natural oils and fats are stirred together with an aqueous solution of sodium hydroxide (generally an alkaline solution) while heating, they react (saponification) to form soap (i.e., alkali metal salts of higher fatty acids) and glycerin.

Fig. Saponification reaction of fats and oils

When a concentrated solution of salt is added, the soap precipitates (salting out) and floats to the top, where it is extracted, refined, and marketed. Since sodium hydroxide is the most commonly used alkali, the word "soap" usually refers to sodium soap, but potassium hydroxide is sometimes used specially for cosmetics, etc. In this case, potassium soap is used in a soft state containing glycerin without salting out. Potassium hydroxide is also used for cosmetic purposes.

The raw material oils and fats used include beef tallow, coconut oil, palm oil, rice bran oil, soybean oil, peanut oil, and hydrogenated oil, with coconut oil and palm oil being the most common in terms of volume. Different types of raw material oils and fats contain different types of fatty acids and their ratios, so the performance of the resulting soaps will vary. The following is a comparison of the properties of typical fatty acid soaps.

It is the main ingredient in soap made from coconut oil, and has a relatively short hydrophobic group with a total of 12 carbons. This makes it easily soluble in water and has excellent detergency (when the carbon number is less than 12, water solubility becomes better, but detergency becomes worse).

It is an 18-carbon saturated fatty acid soap that is commonly found in soaps from solid fats and oils such as hydrogenated oil. The long hydrophobic groups and significant hydrophobicity make it difficult to dissolve in water. Even with the hydrophilic carboxyl group (COO- Na+), the sodium salt is not sufficiently hydrophilic for good water solubility.

Sodium oleate is the main ingredient in soap made from olive oil, etc. Most beef tallow soap is also made from sodium oleate.

 Like stearic acid, it has a total of 18 carbons, but its properties are different because of the double bond in the middle of the molecule. Although, the double bond is weak, it has an affinity with hydrophilic groups. For this reason, sodium oleate dissolves well in water and also has excellent detergent properties.

 (Having too strong a hydrophilic group in the middle of the molecule reduces detergency. Castor oil soap, for example, has a hydroxyl group in the middle of the molecule in addition to the double bond, making it soluble in water but not suitable for cleaning.)

Soap solubility/acid effects

Soap is generally less water soluble, so even a slightly higher concentrated solution, it will become viscous and forms gel when left standing. Soap solution is alkaline in nature and loses detergency under neutral conditions, and fatty acids are formed under neutral or acidic environments.

Fig. Reaction of soap and acid

Effect of hard water on soap

In addition, when hard water (water containing high levels of calcium and other salts) is used, water will produce insoluble calcium soap and other substances that will precipitate out, rendering it ineffective.

 Therefore, it is difficult to use soap with hard water (those who have experience using soap in hot springs will immediately understand this). In Europe and the U.S., in particular, there are many areas with hard water, making it difficult to use soap, which is why synthetic detergents, which are stable in hard water, were developed early on.

Fig. Reaction of soap and Ca ion

Polyoxyethylene alkyl ether carboxylate is an anionic surfactant that has a nonionic hydrophilic polyethylene glycol chain in addition to the carboxylate, which is a hydrophilic group in soap.

While polyoxyethylene alkyl ether carboxylate is biodegradable and environmentally friendly, it is also more hydrophilic than soap due to its nonionic polyethylene glycol chain. This makes it less irritating to the skin, which is a disadvantage of soap, and it does not produce soap scum, which causes stains on wash basins and other surfaces. Taking advantage of these features, products with a low number of moles of ethylene oxide added (n≤3 in the formula below) are often used in body shampoos, facial cleansers, and hypoallergenic shampoos. They can also be used as detergent base under acidic conditions where soap cannot be used.

Fig. Synthesis route of sodium polyoxyethylene alkyl ether carboxylate

It is a new anionic surfactant that has a hydroxyl group in addition to the carboxylate, the hydrophilic group of soap.

It is mildly acidic to neutral, which is within the pH range of the skin, and produces fine, high-quality foam. It also has moderate detergency, so it does not excessively remove oil from the skin or hair, is hypoallergenic, and is highly biodegradable, making it suitable as a base for body shampoo and hair shampoo.

Fig. Synthetic route to sodium alkyl hydroxy ether carboxylate

Sulfonates are generally represented by R-SO3- Na+ . A similar compound is the sulfate ester salt R-O-SO3- Na+ . Both are obtained by reacting with sulfuric acid, but the reaction to obtain sulfonic acid is sulfonation, while the reaction to obtain sulfate esters is sulfation. Both reactions are important for surfactants in that they introduce hydrophilic groups.

Sulfonates and sulfates are very similar compounds, but they differ in some of their properties, which we know is due to the -O- bond between R (i.e., carbon atom) and S (sulfur atom).

The most important difference is that sulfonates are not hydrolyzed, whereas sulfates are hydrolyzed to their original alcohol and sulfuric acid form when acidified.

Fig. Reaction of sulfates and sulfonates with acids

Therefore, sulfonates can be used in acidic solutions without problems. In addition, sulfonates are often advantageous because they are less susceptible to decomposition than sulfates when heated.

Sulfonate surfactants include alkylbenzenesulfonates, alkanoylmethyltaurides, and dialkylsulfoammonates.

Sulfonation reaction

Sulfonation of aromatic hydrocarbons such as benzene by sulfuric acid or fuming sulfuric acid immediately comes to mind.

Fig. Sulfonation reaction of benzene

Using this reaction, a surfactant can be made by attaching a long alkyl group, such as a dodecyl group (CI2H25-), to benzene and sulfonating it.
In fact, this reaction proceeds smoothly to produce a variety of surfactants, which are collectively called alkylbenzene sulfonates.

Fig. Synthetic route of sodium alkylbenzenesulfonate

In industrial sulfonation, fuming sulfuric acid or anhydrous sulfuric acid, which has a much higher concentration than concentrated sulfuric acid, is used as a sulfonating agent to make the reaction smooth and eliminate the use of extra sulfuric acid. Mass production is carried out in large plants with fully automated controls that use liquid anhydrous sulfuric acid.

Fig. Synthetic route of sodium dodecylbenzenesulfonate

Sodium alkylbenzenesulfonate Applications and Features

Sodium alkylbenzenesulfonate is easily synthesized, so it is industrially manufactured to a high degree of purity. Commercial products for industrial use are supplied as a light yellow paste with an active ingredient of about 60%, as well as a powdered product that is added sodium sulfate and dried in small granules using a spray dryer.

However, it is household synthetic detergents that are consumed in large quantities, and many synthetic powdered detergents for electric washing machines used in your homes have sodium alkyl benzene sulfonate as their main ingredient.

Sodium alkylbenzenesulfonate is much more soluble in water than soap. Its aqueous solution foams well, producing many more fine bubbles than soap, but its low viscosity makes it easier to dissipate. It has excellent penetrating and cleaning power, and often performs better than sulfates, but it is not necessarily superior in every respect, and has its advantages and disadvantages.

There are various methods for producing alkylbenzene, the raw material for sodium alkylbenzenesulfonate. Through many years of research, it is known that the best alkyl group for alkylbenzene is about a dodecyl group (C12H25-). Therefore, as in the aforementioned example, dodecylbenzene is widely used as a raw material for household detergents. However, even a single bite of dodecyl group can make a big difference depending on the presence or absence of branching.

Among surfactants, the following is a brief introduction to the differences among them, since they are produced in large quantities as the main ingredients in household detergents.

 Alkylbenzenes can be divided into two major groups according to the presence or absence of alkyl group branching as follows.

Fig. Synthetic route to branched dodecylbenzene

With the development of petrochemistry, branched alkylbenzenes came to be produced in large quantities at low cost worldwide and became popular as the main ingredient in household washing machine detergents, but their poor biodegradability became a problem and they were replaced by linear alkylbenzenes.

Branched sodium dodecylbenzenesulfonate is abbreviated as ABS (alkylbenzenesulfonate), branched ABS, or hard ABS.

 ABS is originally an abbreviation for alkylbenzenesulfonate, but since branched ABS was in its infancy, it is often used to refer only to branched ABS. As for the type of salt, it is sometimes used to refer to sodium salts, since sodium salts are produced in large quantities.

Fig.Synthetic route to linear alkylbenzenes

Chlorinated paraffins and olefins are mixtures of different chain lengths, so they are not pure dodecylbenzenes but mixtures of alkylbenzenes with carbon numbers around 12.

 These two types of alkylbenzenes, branched and linear, are equally useful as raw materials for sodium alkylbenzenesulfonate. They are almost equally useful in terms of performance, with one major difference. That is biodegradability.

Biodegradability of alkylbenzenesulfonates

Biodegradability refers to whether the soap is easily or easily degraded by microorganisms in sewage or rivers.

 Since soap is made from animal- and plant-derived materials, there is no problem with its biodegradation, since it is quickly decomposed by microorganisms even if it flows into sewage or rivers. However, sodium branched alkylbenzenesulfonate, which was used in large quantities from the 1950s to the 1970s as the main ingredient in electric washing machine detergents, is also resistant to decomposition and foams well even at low concentrations, causing foaming in rivers and sewage treatment plants, which has become a major problem. This has caused foaming in rivers and sewage treatment plants, resulting in a major problem.

 The use of branched sodium alkylbenzenesulfonate was thus considered problematic, and linear sodium alkylbenzenesulfonate, which is more biodegradable, came to dominate the mainstream. Sodium higher alcohol sulfates and higher alcohol EO adducts, which are also biodegradable, have also become important to the problem.

Sodium alkylbenzenesulfonate, introduced in the previous section, is a water-soluble type of alkylbenzenesulfonate that is consumed in large quantities, especially as a cleaning agent. In this section, another type of alkylbenzenesulfonate, the oil-soluble one, is presented.

 Oil-soluble alkylbenzenesulfonates are literally soluble in petroleum and organic solvents.

To make an oil-soluble type, the hydrophobic (lipophilic) alkyl group must be specially enlarged, or a less water-soluble calcium salt must be used instead of a sodium salt.

This type of oil-soluble ABS is widely used as a raw material for dry cleaning detergents (charge soap) and as an emulsifier component for mineral oils such as cutting oils. It is characterized by its oil solubility and strong hydrophilic properties.

Even ordinary ABS, i.e., alkylbenzenesulfonates with alkyl groups of about C12 for detergents, are oil-soluble if they are made less water-soluble, such as calcium salts, instead of sodium salts, and are used as pesticide emulsifier ingredients, for example.

Fig. Synthetic route of calcium dodecylbenzenesulfonate

When α-olefin is reacted with anhydrous sulfuric acid (SO3), α-olefin sulfonate is obtained as a result of a complex reaction. α-olefin sulfonate is used as a raw material for household detergents. α-olefin sulfonate is also abbreviated as AOS (α-olefinsulfonate).

Fig. Synthetic route of α-olefin sulfonate

Among alkanoyl methyltaurides, the most famous product is "IGEPON T," developed by IG in Germany. This is a special type of surfactant made by reacting oleic acid chloride with N-methyl taurine, and is also produced in Japan.

Fig. Synthetic route of oleoylmethyltauride

The amide bond between the hydrophobic and hydrophilic groups is a unique feature of this product. The methyl group attached to the amide group is not an accidental inclusion, but the result of a great deal of research. This product occupies a unique position as a dyeing aid and scouring agent, and is highly valued for its excellent washing texture.

Those in which oleic acid is replaced with palm oil fatty acid are hypoallergenic and are used as detergent ingredients in shampoos. Other known products include those using beef tallow fatty acids, and those in which the methyl group at the amide bond is replaced with a phenyl group.

Among the dialkylsulfoammonates, the most famous is Aerosol OT, which was invented in the United States.

There are many manufacturers in Japan producing products identical to this one. The synthetic method is completely different from the sulfonates described so far. That is, a diester is made from 2-ethylhexanol and maleic anhydride (or fumaric acid), which is heated while stirred with an acidic sodium sulfite solution to insert a sulfonic group into the double bond of the maleic acid (or fumaric acid).

Fig. Sodium di-2-ethylhexyl sulfoammonate

Double bonds such as oleic acid cannot be easily added to acidic sodium sulfite in this way. I won't go into the chemistry, but such reactions are more likely to occur with the double bonds of special compounds such as maleic acid esters.

Sodium alkyl arylsulfoammonate

This sulfation method is used to produce sodium alkyl allyl sulfosulfamate.

 This compound is an asymmetric diester with an alkyl group on one side of the diester and an allyl group with a double bond on the other. This structure makes it a reactive surfactant with copolymerizability with radical polymerizable monomers, etc., and it is used as an emulsifier for soap-free emulsion polymerization.

Fig. Synthetic route to sodium alkyl arylsulfosuccinate

The dialkylsulfoammonate ester salts mentioned earlier are obtained by sulfonation of maleic acid diesters and have one sulfonate in the molecule as a hydrophilic group.

Fig. Dialkyl sulfoammonates

Maleic acid monoesters can be easily obtained from maleic acid by selecting the esterification conditions. Sulfonation of the maleic acid monoester, as in the above reaction, yields alkyl sulfosulfamate disulfonates, each having one sulfonate and one carboxylate. This type of surfactant is hypoallergenic and is used in hair and body shampoos.

Fig. Alkyl sulfoammonate disodium salt

All of these surfactants, like the dialkyl sulfosulphonate ester salts mentioned earlier, have intramolecular ester bonds and are easily hydrolyzed, so they must be used in the neutral to slightly acidic pH range.

Sulfation includes sulfonation and sulfate esterification, and here we discuss sulfate salts obtained by sulfate esterification. Two molecules of sodium hydroxide are required to neutralize one molecule of sulfuric acid, a dibasic acid.

Fig. Neutralization reaction of sulfuric acid (2 equivalents of sodium hydroxide)

If there is only one molecule of sodium hydroxide, the sulfuric acid is only half neutralized to sodium hydrogen sulfate (acidic sodium sulfate). This is also a stable compound.

Fig. Neutralization reaction of sulfuric acid (1 equivalent of sodium hydroxide)

Similarly, when making esters from sulfuric acid and alcohol, monoesters and diesters can be made. Taking methanol as an example, we see the following.

Fig. Esterification reaction of methanol and sulfuric acid

Diesters are insoluble in water, but monoesters are soluble in water. However, if the monoester is dissolved in water, it will gradually hydrolyze to the original methanol and sulfuric acid. To prevent this, neutralize the monoesters with sodium hydroxide to make them stable and neutral in aqueous solution.

Fig. Neutralization reaction of sulfate monoester of methanol

By utilizing the properties of sulfuric acid, a higher alcohol can be used in place of methanol to produce anionic surfactants.

 Furthermore, by using this reaction, most alcohol-like compounds with hydroxyl groups can be converted to sulfates, making it possible to produce a variety of surfactants.

Fig. Synthetic route to higher alcohol sulfates

Sulfation of carbon-carbon double bonds

In addition to alcoholic hydroxyl groups, carbon-carbon double bonds (>C=C<) also react with sulfuric acid to form sulfate monoesters. Therefore, this reaction can also be used to make sulfate ester type surfactants.

Fig. Sulfate esterification and neutralization of carbon-carbon double bonds

The relationship between the number of carbons (chain length) of the alkyl group of the raw material alcohol and the water solubility or detergency of its sulfate ester salt is similar to that of soap. Sodium lauryl alcohol sulfate, which has a short chain length (C12), is relatively hydrophobic and soluble in water even at low temperatures and has good detergency. Sodium stearyl alcohol sulfate, which has a long chain length (C18), is not soluble in water, and its water solubility and detergency are not high unless the water is hot, making it difficult to use alone.

Sodium cetyl alcohol sulfate, which has a medium chain length (C16), is between lauryl and stearyl and is somewhat similar to stearyl. Sodium oleyl alcohol sulfate, however, has a weakly hydrophilic double bond in the middle of its molecule, which gives it superior water solubility and detergency, even though the carbon number is 18. This double bond action is exactly the same as in the case of soap, and it is present throughout the entire surfactant.

Calculation of bound sulfuric acid content

The amount of bound sulfate is a numerical value that indicates how much sulfate is bound to the higher alcohol (in this case, lauryl alcohol) as SO3 in the product. We have often mentioned that water solubility changes depending on whether the hydrophobic group per hydrophilic group is long or short. Therefore, the expression of the amount of bound sulfuric acid is the opposite of the hydrophobic group lengths described so far, but the concept is the same.

Thus, for this product,
Molecular weight of C12H25OSO3-Na+ = 288.4
Molecular weight of SO3 = 80.1, and content of main component = 90.0%, then

The amount of bound sulfuric acid (%, per product) = 80.1/288.4 × 100 × 0.900 = 25.0.

 In practice, the amount of combined sulfuric acid (%) is measured and the main component content (%) is obtained by inverse calculation of the above formula. The measurement method is omitted.

Total Fat Calculation

Total fat content is a number that indicates what percentage of oil is contained in the product.
Thus, for this product, if the molecular weight of C12H25OH = 186.3,

 Fatty derived from main ingredients (%) = 186.3/288.4 × 100 × 0.900 = 58.1
 Fat derived from unreacted material (%) = 4.0
 Total fat (%, per product) = 58.1 + 4.0 = 62.1

i) Sodium cetyl alcohol sulfate content (% of main ingredient)

Substituting 40.0% total fat content into the formula Bound Sulfate Content/Total Fat Content × 100 = 28.0 (%), we obtain Bound Sulfate Content = 11.2%.

 Substituting the molecular weight (344.5) of sodium cetyl alcohol sulfate (C16H33OSO3- Na+ , hereafter referred to as "main ingredient") into the formula below, the content of main ingredient is calculated to be 48.2%.

Amount of bound sulfate (%) = Molecular weight of SO3 (80.1) / Molecular weight of sulfate ester salt x Sulfate ester salt content (%)

ii) Reaction rate of cetyl alcohol

Substituting the molecular weight of cetyl alcohol (242.4), the content of the main ingredient (48.2%) and the molecular weight of the main ingredient (344.5) into the formula below, the fat content derived from the main ingredient is calculated to be 33.9%.

Fatty matter derived from main ingredient (%)
= molecular weight of cetyl alcohol/molecular weight of main ingredient × content of main ingredient (%)
= 242.4/344.5 × 48.2 = 33.9

 From these values, the reaction rate of cetyl alcohol and also the unreacted fatty (unreacted cetyl alcohol) content can be calculated.

Reaction rate (%)
= fat derived from main ingredient (%) / total fat (%) × 100
= 33.9/40.0 × 100 = 84.8

 Fat derived from unreacted material (unreacted cetyl alcohol, %) = total fat (%) - fat derived from main ingredient (%) = 40.0-33.9 = 6.1

 This means that 6.1% of unreacted cetyl alcohol remains.

As described above, the content of main ingredients and unreacted materials can be determined from the total fat content and the amount of bound sulfate/total fat content, so it is important to handle surfactants with these values in mind. Now, the bound sulfate content/total fat content of pure sulfate is as shown in the table below.

As can be seen in the table, the longer the hydrophobic group, the less hydrophilic the theoretical value of bound sulfate/total fat (%) becomes. However, the theoretical values for stearyl alcohol and oleyl alcohol are almost the same, but the actual water solubility is significantly different. This is because the weak hydrophilicity due to the double bond has nothing to do with the theoretical value, and even if the theoretical value is almost the same, oleyl is more soluble in water because of the double bond.

 Therefore, hydrophilicity and hydrophobicity, such as double bonds and ester bonds, which have little to do with the amount of bound sulfuric acid, hardly appear as numbers in this method. In general, the hydrophilicity of the sulfate ester salt can be quickly estimated by knowing the amount of bound sulfate as well as the type of alcohol or fat used as the raw material.

The values shown in this table are those when all the higher alcohols in the raw material are sulfated. In industrial terms, it is difficult to achieve 100% reaction, and the product is not manufactured except in special cases. As calculated earlier, usually 80% or 90% of the theoretical value is produced. However, since not all reacted products have better performance, the reaction rate is researched and manufactured according to the purpose of each product. For this reason, even if the same sodium sulfate ester of higher alcohols is used, each company's product has various characteristics, and they are by no means identical.

In the table above, the theoretical value of the amount of bound sulfate/total fat (%) of oleyl alcohol is stated as 29.8%, but this is when only its hydroxyl group reacts, and in reality the true theoretical value is about 29.8 x 2 = 59.6%, since the double bond in the molecule also becomes sulfate. In reality, however, products with such high levels of combined sulfates are not manufactured. In many products, only the hydroxyl group is sulfated, only the double bond is sulfated, and in some cases, both groups are sulfated.

Therefore, for oleyl alcohol sulfated products, the theoretical value of bound sulfate/total fat (%) can be 29.8% or higher, which can be interpreted as a high ratio of both double bonds and hydroxyl groups being sulfated. However, those that react with both have good water solubility, but not much detergency.

 These higher alcohol sulfates are superior to soap in both solubility and detergency, and have various advantages, such as being neutral in aqueous solution and not damaging wool, etc. Moreover, they do not precipitate like soap when used in hard water, so they are widely used in both industrial and household applications. However, this type of soap also has its drawbacks: when the aqueous solution becomes highly acidic, it is hydrolyzed back to its original form of higher alcohol, and it also decomposes easily when exposed to high temperatures.

Higher alcohol EO adduct sulfates are similar to the higher alcohol sulfates described in the previous section.
In other words, ethylene oxide is added to higher alcohols, which are then converted to sulfates.

Fig. Sodium Lauryl Alcohol EO Adduct Sulfate

Higher alcohol EO adducts are called higher alkyl polyethylene glycol ethers, or higher alkyl ethers for short, so higher alcohol EO adduct sulfates are sometimes called higher alkyl ether sulfates.

The above formula describes the most commonly used sodium lauryl alcohol EO adduct sulfate. The number of moles of ethylene oxide added (n) is usually between 2 and 4.

Properties and Applications of Lauryl Alcohol EO Adduct Sulfates

What is the difference between lauryl alcohol sulfate and lauryl alcohol EO adduct sulfate? When polyethylene glycol chains are added, water solubility is improved and foaming characteristics in hard water are enhanced.

 Therefore, higher alcohol EO adduct sulfates are widely used as base agents for shampoos.

 Higher alcohol sulfates are known to cause skin irritation. Higher alcohol EO adduct sulfates have a distribution in the number of moles of EO adduct, and include a small amount of higher alcohol sulfates to which ethylene oxide is not added. In recent years, it has become possible to synthesize higher alcohol EO adducts with fewer unreacted alcohols by adding ethylene oxide to alcohols using a special catalyst, and commercially available low-irritant higher alcohol EO adduct sulfates with reduced higher alcohol sulfate content. In this field, too, the advancement of synthetic alcohols has been promoted.

 In this field as well, synthetic alcohols have made great inroads, and oxo alcohol and Zieger alcohol are widely used in shampoos and other products, as are natural lauryl alcohols.

EO adduct sulfates of secondary alcohols

Secondary alcohols (secondary alcohols), which are synthetic alcohols obtained by air oxidation of paraffin, are also used in liquid detergents as higher alcohol EO adduct sulfates. Due to the convenience of synthesis, these secondary alcohols are commercially available as 3-mole ethylene oxide adducts with C11~C15 alkyl group carbons under trade names such as Tergitol and Softanol.

In the previous section, we explained that the hydroxyl groups and double bonds of higher alcohols react with sulfuric acid to form sulfate esters, which are surfactants. Now, what about fatty acids that also have hydroxyl groups and double bonds, or esters of such fatty acids?

As expected, sulfation produces sulfate ester type anionic surfactants. Typical fatty acids and their esters used in sulfation are listed in the table below.

In addition, since the names of many fats and oils will appear in the future, a composition table of each fat and oil is included in the table below to help you understand what fatty acid glycerides each oil is.

When the esters of unsaturated fatty acids shown in the table above are actually sulfated, they have properties very different from those of higher alcohol sulfates. This is because the sulfate groups, which are hydrophilic groups, are attached near the center of the molecule. In this case, it is unlikely that the sulfated products will have the strong detergent power of the higher alcohol sulfates. In fact, most of these sulfated products are used for special textile industry applications other than detergents.

 The following is a brief introduction to the different types of hydrophobic group materials.

Sulfated fatty acids

It is a sulfated product of unsaturated fatty acid as it is, and its properties are similar to those of fatty acid ester sulfides.

We have already mentioned in the previous section that higher alcohols and fats are compounds with hydroxyl groups and double bonds that can be sulfated. These are all obtained from plants and animals. So, can anything like that be obtained from petroleum itself? If we select double-bonded hydrocarbons (olefins) with chain lengths from C12 to C18, we should be able to synthesize good sulfate surfactants. These are collectively called sulfated olefins.

This type of detergent has long been produced mainly in Europe, with Shell's "Teepol" being the most famous. This detergent is made by sulfating C12~C18 alpha-olefins (olefins with a double bond at the end of the molecule) made by breaking down paraffin wax at high temperatures.

As seen in the following equation, sulfuric acid is not attached to the end of the olefin molecule, but to the carbon next to it. α-olefin is not easily sulfated in its entirety at once, so unreacted material is recovered to produce a product with high bound sulfate content.

Fig. Synthetic route to sulfated olefins

Teepol dissolves well in water and can be made into a thick solution, and is used as a raw material for liquid detergents. Sulfonation of α-olefin with anhydrous sulfuric acid also produces α-olefin sulfonates in the sulfonate form rather than the sulfate ester form.

Phosphate-type anionic surfactants are mainly used as antistatic agents or emulsifiers for synthetic fibers. Phosphate ester salts of higher alcohols are widely used.

Fig. Synthesis of phosphate salts (phosphorylation with anhydrous phosphoric acid)

The most widely used phosphate ester type surfactants are the phosphate ester salts of higher alcohol EO adducts. This type has good water solubility due to its polyethylene glycol chain, and its antistatic performance is generally superior to that of higher alcohol phosphate salts.

Sodium salt or amine salt forms are used, each with its own unique twist. The triester type in particular is not an anionic surfactant but a nonionic surfactant. They are used for special applications where anionic surfactants are not allowed.

Fig. Phosphate

Synthesis of triesters is often done by reaction with phosphorus oxychloride.

Fig. Synthetic route of phosphate triester

Generally speaking, phosphate surfactants are rarely used alone, but are more often used as ingredients in formulations.

The above is a rough description of the important anionic surfactants. These are classified by the combination of hydrophobic and hydrophilic groups as shown in the table below.

All but soap have good hard water resistance. Sulfates are relatively stable in alkaline water, but are easily decomposed in acidic water. In addition, those with ester bonds such as -COOCH2- in the molecule are easily decomposed by alkali or acid. We hope you fully understand these points, and we hope this table will help you organize your knowledge so far.

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Sanyo Chemical Industries, Ltd. extends no warranties and makes no representations as to the accuracy or completeness of the information contained herein, and assumes no responsibility regarding the suitability of this information for any intended purposes or for any consequences of using this information.

Any product information in this brochure is without obligation and commitment, and is subject to change at any time without prior notice.

Consequently anyone acting on information contained in this brochure does so entirely at his/her own risk.In particular, final determination of suitability of any material described in this brochure, including patent liability for intended applications, is the sole responsibility of the user. Such materials may present unknown health hazards and should be used with caution. Although certain hazards may be described in this brochure, Sanyo Chemical Industries, Ltd. cannot guarantee that these are the only hazards that exist.

First, an interface is a boundary surface that exists between two substances with different properties, and interfaces exist between liquids and solids, liquids and liquids, and liquids and gases.

Surfactants enhance performance by performing functions such as washing, emulsifying, dispersing, wetting, and penetrating at this interface.

Interface = a boundary surface that exists between two substances with different properties
Liquid and solid: cup and coffee, machine and lubricant 
Liquid and liquid: water and oil 
Liquid and gas: seawater and air, soap bubbles

Examples of roles of surfactants
Cleaning ・・・ Removing dirt 
Emulsification ・・・ Dispersion ・・ Making unmixable things easier to mix
Wetting / Penetration ・・・ Makes wetting and soaking easier

-Surfactants have different structures in their molecules with different properties: lipophilic groups (oil-loving parts) and hydrophilic groups (water-loving parts).

-Surfactants are broadly classified into four types according to the structure of the hydrophilic group: nonionic, anionic, cationic, and amphoteric (having both anionic and cationic groups).

It consists of seven short movies for each function. 
0:00　Introduction of surfactants functions　
0:16　Part1　Washability
1:00　Part2　Permeability
2:10　Part3　Dispersion
2:55　Part4　Foaming properties
3:25　Part5　Defoaming properties
3:39　Part6　Smoothness
4:20　Part7　Antibacterial properties

Nonionic surfactants are used in the largest quantities among surfactants, and their raw materials, such as ethylene oxide, are stably supplied in large quantities.

Nonionic surfactants are surfactants that have hydroxyl groups (-OH) or ether bonds (-O-) as hydrophilic groups that do not dissociate into ions in water.

 However, since hydroxyl groups and ether bonds do not dissociate into ions in water, their hydrophilicity is quite weak, so they alone do not have the power to dissolve large hydrophobic groups in water. Therefore, several of these groups come together in one molecule to exhibit good hydrophilicity. This is very different from anionic and cationic surfactants, where only one hydrophilic group is sufficient to exhibit hydrophilicity.

Nonionic surfactants can be classified by the type of hydrophilic group into polyethylene glycol type and polyhydric alcohol type.
Polyethylene glycol-type nonionic surfactants are nonionic surfactants made by adding ethylene oxide as a hydrophilic group to a hydrophobic raw material.

Fig. Example of polyethylene glycol-type nonionic surfactant

Polyhydric alcohol-type nonionic surfactants are nonionic surfactants in which a hydrophobic group such as a higher fatty acid is bonded to a polyhydric alcohol such as glycerol, pentaerythritol, sorbitol, etc. The hydrophobic group has multiple hydroxyl groups bonded to it, which gives it hydrophilic properties.

Fig. Example of polyhydric alcohol-type nonionic surfactant

A more detailed classification of polyethylene glycol-type nonionic surfactants is made according to the type of hydrophobic group, whereas in the case of polyhydric alcohol-type nonionic surfactants, it is made according to the type of polyhydric alcohol, the hydrophilic group. This classification is shown in the table below.

Polyethylene glycol-type nonionic surfactants are surfactants made by adding ethylene oxide (EO: ethylene oxide) to hydrophobic raw materials containing reactive hydrogen atoms.

 Reactive hydrogen atoms are specifically hydrogen atoms such as hydroxyl group (-OH), carboxyl group (-COOH), amino group (-NH2), or amide group (-CONH2). Hydrophobic groups bonded to the above atomic groups can react with ethylene oxide to form polyethylene glycol-type nonionic surfactants. For example, a higher alcohol with a hydroxyl group reacts to an EO adduct as follows

Fig. Reaction of higher alcohols with ethylene oxide

The following hydrophobic raw materials with reactive hydrogen atoms are currently used in relatively large quantities. Among these, higher alcohols are particularly important. However, alkylphenols are no longer used since it was found that they have endocrine disrupting effects.

The effect of a surfactant is originally derived from the balance between the opposing properties of the hydrophobic and hydrophilic groups, and the cloud point, which indicates the degree of this balance, is the most important value that determines the properties of polyethylene glycol-type nonionic surfactants.

In fact, quality control of this type of surfactant and guidelines for its use are based on the measurement of the cloud point. For example, it is generally accepted that a surfactant with a cloud point near the operating temperature has excellent permeability. However, the presence of salts or alkalis such as sodium hydroxide causes the cloud point to drop dramatically, so in such cases, it is necessary to measure the cloud point under operating conditions to make a judgment.

Nonionic surfactants are obtained by adding ethylene oxide to the phenolic hydroxyl group of alkyl phenols or the alcoholic hydroxyl group of higher alcohols. These are also called polyethylene glycol ether type nonionic surfactants because the hydrophobic and hydrophilic groups are linked by an ether bond (-O-). This type of surfactant is rarely degraded by acids or alkalis.

The majority of polyethylene glycol-type nonionic surfactants currently on the market are made by adding ethylene oxide to higher alcohols. Higher alcohols, which are used as raw materials for hydrophobic groups, can be broadly classified into two types: natural alcohols obtained from animal and vegetable oils and waxes, and synthetic alcohols made from petroleum.
Higher alcohols are often used as mixtures of various carbon numbers.

Natural alcohols have been replaced by synthetic alcohols for some time due to their generally high price volatility, but their use is now increasing due to environmental concerns and other factors. Generally speaking, C12~C14 alcohols are more suitable as surfactant raw materials than C16~C18.

Typical example of saturated natural alcohol: Coconut oil-reduced alcohol

The most typical saturated natural alcohol is palm oil-reduced alcohol (C12~C14), which is obtained by esterifying palm oil with methanol and reducing the resulting methyl palm oil fatty acid.

Typical examples of unsaturated natural alcohols: palm oil alcohol, olive oil alcohol

Unsaturated alcohols include palm oil alcohol and olive oil alcohol, which are obtained in a similar fashion from palm oil and olive oil, respectively. Both are mixtures of oleyl alcohol (CI8 double bond 1) and cetyl alcohol (C16), among others.

About Natural Alcohols of Animal Origin

Beef fat reducing alcohol (C16~C18) obtained by hydrogenating methyl bovine fatty acid and macko alcohol (C16-C18 double bond 1) obtained by hydrogenating macko whale oil were also used, but are rarely used anymore due to the avoidance of using animal materials and the protection of whale resources. However, it is rarely used anymore due to the avoidance of using animal materials and the protection of whale resources.

Synthetic alcohols include Ziegler alcohol, which has the same composition as natural alcohols, oxo alcohol, which contains a methyl-branched component, and secondary alcohol, which has a hydroxyl group in the middle of the molecule. All are widely used because they are inexpensive and in stable supply.

Secondary alcohol

It is made by air oxidation of paraffin. It has hydroxyl groups randomly attached to the ends of the carbon chain (linear secondary alcohol). It is usually sold as a 3-mol ethylene oxide adduct. This is because ethylene oxide does not uniformly add under normal reaction conditions without the addition of ethylene oxide.

A comparison of polyethylene glycol ether type nonionic surfactants (higher alcohol EO adducts and alkylphenol EO adducts) with anionic surfactants is shown in the table below.

Ethylene oxide can also be added to fatty acids with an alkali catalyst. This type of product is sometimes called a polyethylene glycol ester-type nonionic surfactant because, as the reaction formula shows, the hydrophobic and hydrophilic groups are linked by an ester bond (-COO-).

Fig. EO adducts of fatty acids

Since ester bonds are susceptible to hydrolysis, this type of product may decompose into soap when used in strongly alkaline baths. This type of soap is also produced by addition of ethylene oxide as described above, but can also be easily produced by direct esterification of fatty acids with polyethylene glycol.

Polyoxyethylene fatty acid esters are generally inferior to higher alcohols or alkylphenol EO adducts in terms of penetration and detergency. Therefore, they are mainly used as emulsion dispersants, textile oils (for spinning and finishing), or dyeing auxiliaries.

Fig. Polyethylene glycol laurate

Ethylene oxide can be added also to higher alkylamines or fatty acid amides in the presence of alkaline catalyst.

Higher alkyl amine ethylene oxide adduct

Higher alkyl amines react particularly easily with ethylene oxide, so the reaction can be carried out without a catalyst. In such cases, the polyethylene glycol chain grows after the complete addition of two moles of ethylene oxide to the nitrogen atom first. This type of product has properties intermediate between those of nonionic and cationic surfactants and is used as a dyeing aid.

Fig. Higher alkyl amine ethylene oxide adduct

Fatty acid amide ethylene oxide adduct

Fatty acid amides are relatively unreactive with ethylene oxide and usually react as in the following equation, but in reality they are a complex mixture of reactants. In the usual synthesis process, exchange reactions occur during the reaction and the ester and amide bonds are interchanged, resulting in the formation of some of the following compounds, which are nonionic surfactants with somewhat cationic properties. This type of surfactant is used for special applications and is used in relatively small quantities.

Fig. Fatty acid amide ethylene oxide adduct

Pluronic type nonionic surfactant

Nonionic surfactants made by adding ethylene oxide to polypropylene glycol were first marketed by the Wyandotte Company in the United States under the trade name "Pluronic" and are therefore called Pluronic-type nonionic surfactants. and are therefore referred to as pluronic nonionic surfactants.

Pluronic-type nonionic surfactants have an unusual shape with hydrophilic groups at both ends with hydrophobic groups in between, as shown in the following formula. Since this type of surfactant has a molecular weight of several thousand, it is much higher in molecular weight than ordinary surfactants (molecular weight of several hundred), so it is sometimes classified as a polymer type surfactant.

Pluronic-type nonionic surfactants are not very promising as penetrating agents due to their molecular weight or molecular shape, but they are used in special applications due to their recognized characteristics as special low-foaming detergents, emulsifying dispersants, viscose additives, and the like.

Fig. Structure of Pluronic Nonionic Surfactant

What is a polyhydric alcohol?

Polyhydric alcohols are organic compounds with many alcoholic hydroxyl groups per molecule, such as glycerin, pentaerythritol, and sorbitol.

Fig. Example of polyhydric alcohol

Nonionic surfactants with hydrophobic groups attached to amino alcohols (e.g., diethanolamine) having -NH2 or >NH groups in addition to -OH groups or to saccharides (e.g., glucose) having 1CHO groups are similar to the polyhydric alcohol type. Therefore, they are collectively referred to as polyhydric alcohol-type nonionic surfactants in this section.

The main hydrophilic group materials of polyhydric alcohol-type nonionic surfactants are listed in the table below. Of these, glycerin, pentaerythritol, sorbitan, and diethanolamine are particularly important. Fatty acids are the most commonly used hydrophobic raw materials.

 As shown in the table below, many polyhydric alcohol-type nonionic surfactants are not soluble in water, and most are only hydrophilic enough to be emulsified and dispersed in water. Therefore, they are rarely used as detergents or penetrating agents.

The appearance of polyhydric alcohol esters is similar to that of fats, oils, or fatty acids, and they are light yellow solids. Both glycerol esters and pentaerythritol esters are widely used as emulsifiers or raw materials for textile oils (spinning oil or softener), but there are differences in their detailed properties.

Fatty acid esters of glycerin

Glycerol monolaurate or glycerol monostearate is widely used as an emulsifier in food and cosmetics because of its high safety, and especially the technology to produce high-purity products has been developed. They are also used as oils for textiles, but their characteristics as fabric softeners are limited to relatively specialized applications.

Fig. Glycerol monolaurate

Fatty acid esters of pentaerythritol

Pentaerythritol stearate, for example, is also used as an emulsifier, and is widely used as a base for textile oil formulations due to its excellent softening properties for human silk, staple fibers, and cotton.

Fig. Example of Pentaerythritol Fatty Acid Esters

Fatty acid esters of sorbitol

Sorbitol is a sweet-tasting polyhydric alcohol produced by reducing glucose with hydrogen and has six hydroxyl groups.
Since sorbitol has no aldehyde groups in its molecule, it is more stable to heat and oxygen than glucose, and there is no risk of decomposition or coloration when reacting with fatty acids.
Sorbitol esters are suitable for textile softeners, but do not work well as general W/O emulsifiers.

Fig. Example of fatty acid esters of sorbitol

Dehydration-condensation reaction of sorbitol

Sorbitol, when treated under appropriate conditions (e.g., acidic and heated), becomes sorbitan, which is dehydrated one molecule of water, followed by sorbide, through further dehydration of another one molecule of water.

Fig. Dehydration-condensation reaction of sorbitol

Sorbitan is a polyhydric alcohol with four hydroxyl groups, but various isomers are formed depending on the position of the hydroxyl group that reacts when sorbitol is dehydrated. Therefore, what is commonly called sorbitan is a mixture of various sorbitans, not a compound with a single composition. Sorbitan is further dehydrated and has only two hydroxyl groups. In fact, when sorbitol is dehydrated, the reactions shown above occur in a complex manner to produce a mixture of many compounds. Therefore, these sorbitol dehydration products are sometimes collectively called anhydrosorbitols.

Synthesis of sorbitan esters

When the esterification reaction of sorbitol is carried out at 230-250°C, intramolecular dehydration (sorbitanation) of sorbitol also occurs at the same time. If the reaction is stopped after an appropriate time, monopalmitate esters of sorbitan can be obtained in one step.

 If the reaction is further continued to proceed with intramolecular dehydration, a product consisting mainly of the sorbitan ester can be obtained.

Fig. Example of synthesis of sorbitan ester

Sorbitan Ester Performance and Applications

Sorbitan esters have excellent performance as emulsifiers and textile oils.
Sorbitan ester-type nonionic surfactants are so well known that they are called "spun-type nonionic surfactants" since they were first marketed by Atlas Corporation in the United States under the trade name "Span" (Span) in various varieties.
These sorbitan esters are mainly used as emulsifiers, but since they themselves are almost insoluble in water, they are rarely used alone.

Ethylene oxide adduct of fatty acid esters of sorbitan

A variety of water-soluble emulsifiers are used in sorbitan esters, including a nonionic surfactant with the trade name Tween, which is made by adding ethylene oxide to sorbitan esters.

Fig. Ethylene oxide adducts of fatty acid esters of sorbitan

Fatty acid esters of polyhydric alcohols and sugars are susceptible to hydrolysis. Instead of these esters, those linked by amide bonds are surfactants that are also resistant to hydrolysis. Many polyhydric alcohol-type nonionic surfactants with amide bonds have been synthesized by combining fatty acids with compounds that have amino and hydroxyl groups.

Fig. Fatty acid alkanolamides

Fatty acid esters of polyhydric alcohols and sugars are susceptible to hydrolysis. Instead of these esters, those linked by amide bonds are surfactants that are also resistant to hydrolysis. Many polyhydric alcohol-type nonionic surfactants with amide bonds have been synthesized by combining fatty acids with compounds that have amino and hydroxyl groups.

The most prominent of these polyhydric nonionic surfactants with amide bonds is fatty acid alkanolamide, which is synthesized by the condensation of alkanolamine and fatty acids.

1:2 type fatty acid alkanolamide

Fatty acid alkanolamides were first marketed by the U.S.-based Ninol Corporation and were therefore also called "Ninol-type detergents. This is the product of dehydration-condensation of 1 mole of lauric acid or palm oil fatty acid with 2 moles of diethanolamine.

Although this formula may seem to leave an extra mole of diethanolamine, the extra diethanolamine is actually loosely bound to the produced lauric acid diethanolamide, making the resulting fatty acid alkanolamide very water soluble.

 It is also called 1:2 fatty acid diethanolamide because it is produced at a ratio of 2 moles of diethanolamine to 1 mole of fatty acid.

Fig. 1:2 fatty acid alkanolamide (Ninol detergent)

1:1 type fatty acid alkanolamide

The detergency-enhancing and foam-stabilizing effects of 1:2 fatty acid alkanolamides described above are caused by their main component, the fatty acid alkanolamide, and have little to do with the second mole of diethanolamine. Therefore, when added as a foam stabilizer to a highly water-soluble detergent, such as sodium dodecylbenzenesulfonate, the extra diethanolamine is unnecessary, as it is added simply to provide water solubility.

From this perspective, 1:1 type fatty acid diethanolamides without the second mole of diethanolamine were produced for compounding. Lauric acid or coconut oil fatty acid is still used as the fatty acid, but it is usually made into a methyl ester to facilitate the reaction.

This one is widely used as a base for detergent formulations because of its high purity and economic efficiency. A 1:1 type alkanolamide is also made from monoethanolamine and monoisopropanolamine and used for similar purposes.

Fig. 1:1 Fatty Acid Diethanolamide

Two very different types of nonionic surfactants with very different properties

Many polyethylene glycol-type nonionic surfactants are well soluble in water and are mainly used as detergents, dyeing aids, and emulsifiers,

Many polyhydric alcohol-type nonionic surfactants are insoluble in water and are mainly used as fabric softeners and emulsifiers. Nonionic surfactants are classified by hydrophobic and hydrophilic group materials as shown in the table below.

Of the raw materials shown in this table, ethylene oxide is produced inexpensively due to the development of petrochemistry. In addition to those derived from natural products, a wide variety of synthetic higher alcohols have also appeared on the market.

Furthermore, considering the excellent performance and versatility of polyethylene glycol-type nonionic surfactants, this type of product is likely to become increasingly important in the future.

In addition to those listed in the table above, there are also higher alkyl mercaptans (R-SH) as hydrophobic group materials and dipentaerythritol and polyglycene as hydrophilic group materials, but these are omitted in this section.

Reference: "Introduction to Surfactants" by Takehiko Fujimoto, Sanyo Kasei Kogyo (2014)

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First, an interface is a boundary surface that exists between two substances with different properties, and interfaces exist between liquids and solids, liquids and liquids, and liquids and gases.

Surfactants enhance performance by performing functions such as washing, emulsifying, dispersing, wetting, and penetrating at this interface.

Interface = a boundary surface that exists between two substances with different properties
Liquid and solid: cup and coffee, machine and lubricant 
Liquid and liquid: water and oil 
Liquid and gas: seawater and air, soap bubbles

Examples of roles of surfactants
Cleaning ・・・ Removing dirt 
Emulsification ・・・ Dispersion ・・ Making unmixable things easier to mix
Wetting / Penetration ・・・ Makes wetting and soaking easier

-Surfactants have different structures in their molecules with different properties: lipophilic groups (oil-fitting parts) and hydrophilic groups (water-fitting parts).

-Surfactants are broadly classified into four types according to the structure of the hydrophilic group: nonionic, anionic, cationic, and amphoteric (having both anionic and cationic groups).

Agents that perform dispersing functions are called dispersing agents. For example, they break up solid particles one by one and disperse them uniformly in a dispersing medium, and they also prevent the dispersed particles from re-agglomerating and maintaining a stable dispersed state.

Fig. How dispersants work

Adsorption and dispersion stabilizing action of dispersants on particles

Dispersants have a chemical structure that has an affinity for both solid particles and liquids, and have functional groups that adsorb to the particle surfaces.

This adsorption results in the particle surfaces being covered with an adsorbed layer of charged dispersant, increasing the electrostatic repulsive force between particles and stabilizing their dispersion.

 For example, as shown in the figure below, when a surfactant with an ionic group of opposite sign to the charge of a particle (A) dispersed in water is added, the particle becomes hydrophobic (lipophilic) because the hydrophilic part faces the particle and the opposite side becomes lipophilic, forming an adsorption layer as shown in (B). When various surfactants are added, adsorption occurs with the lipophilic part on the adsorption layer and the hydrophilic group on the outside, as shown in (C), (D), and (E), and the entire particle becomes hydrophilic, making it easier to wet in water and at the same time increasing electrostatic repulsion and stabilizing dispersion.

In the case of polymer-type dispersants, in addition to this electrostatic repulsion, the repulsive force due to steric hindrance of the polymer chain is added, which further improves dispersibility.

Fig. Adsorption of surfactant on charged particles

Dispersants can be divided into three types: (1) polymer-type dispersants, (2) surfactant-type dispersants, and (3) inorganic-type dispersants (such as polyphosphoric acid).

 The characteristics of each dispersant are summarized in the table below.

Fig. Dispersant Action Mechanism Model

A wide variety of dispersants are used in various fields, depending on the nature of the particles to be dispersed (hydrophilic or hydrophobic surface) and the type of dispersant (dispersed in water or oil).

Important point when water is the dispersant

-Select a dispersant that is soluble in water and easily adsorbed on the particles to be dispersed.

-The finer the particle diameter, the more cohesive and difficult dispersion becomes, so it is better to use a wetting surfactant that reduces interfacial energy.

-When the particle concentration is high, a high molecular weight type is effective as it is expected to have repulsive force due to steric hindrance.

Sedimentation is a phenomenon that plays a major role in the stability of solid-liquid dispersion systems. The sedimentation velocity of particles, v, is discussed by the following equation called "Stokes' law. The following equation shows that the sedimentation velocity of particles decreases with decreasing particle size, decreasing density difference between particles and dispersant, and increasing viscosity of dispersant.

v＝2r2 (ρーρp)g／9η

r: radius of particle,
ρ: density of particle,
ρp: density of dispersant,
η: viscosity of dispersant,
g: gravitational constant

Two forces generally act on particles dispersed in a liquid.

-Electrostatic repulsive force based on the charge on the particle surface
-Van der Waals force  (cohesive force)

Whether particles disperse or agglomerate depends on the combination of these two forces. If the surface charge is high and the repulsive force is high, the dispersion is stable. On the other hand, if the cohesive force is high, the particles agglomerate, and the difference in specific gravity between the particles and the dispersant causes them to settle and separate.

HLB (Hydrophile-Lipophile Balance) is a useful method for selecting dispersants.

This is a numerical value that expresses the degree of hydrophilicity/lipophilicity of a surfactant, and the affinity between the dispersant and the dispersed material is viewed from the balance of hydrophilicity and lipophilicity (hydrophobicity). In other words, if a dispersant is used that is close to the HLB of the dispersed material, dispersibility will be better in many cases.

An example of HLB is shown in the table below: the lower the HLB, the more lipophilic (hydrophobic) the dispersant is, and the higher the HLB, the more hydrophilic the dispersant is.

Polymer-type dispersants are able to stably disperse pigments and other substances by the protective colloidal effect and electric charge of polymers adsorbed on the surface of pigment particles.

When selecting a polymeric dispersant, attention should be paid to its molecular weight in addition to its chemical structure.If the molecular weight exceeds several hundred thousand, agglomeration is likely to occur. Molecular weight distribution is also known to affect the dispersion effect.

Paint Classification

Paints can be broadly classified into aqueous paints (water-based paints) and non-aqueous paints, which can be classified into inorganic pigmented and organic pigmented types, respectively.

 Non-waterborne paints are generally used for automobiles, construction, ships, machinery, woodworking, etc. Non-waterborne paints are generally used in fields where water resistance and gloss are required.

 Waterborne paints are composed mainly of resin emulsions and inorganic pigments. In the dispersion process, dispersing agents, thickeners to help the dispersing agents work, anti-sagging agents, and antifoaming agents are added, and in the formulation process, additives such as antiseptic agents and antifoaming agents are added. Inorganic pigments consist of an agglomerate (secondary particles) of several to several dozen fine particles ranging from 0.01 to several microns in diameter.

 In the dispersion process, the inorganic pigment agglomerates are dispersed into fine particles (primary particles), which are then mixed to produce the paint. The vivid colors of paints are due to the dispersion of pigment particles as microparticles.

What would happen if dispersants were not added in the paint manufacturing process?

First, the dispersion of pigments by the machine becomes less efficient, requiring a longer time for dispersion and placing a greater load on the machine.

Second, the color of the paint becomes dull because the dispersed particles re-agglomerate. Also, due to the precipitation of agglomerated particles, the paint can separate.

To prevent these problems, paint dispersants are used.

Inorganic pigments with high hydrophilic properties, such as calcium carbonate, titanium dioxide, and clay, are used in waterborne paints. To disperse these pigments in water, dispersants with a structure that easily blends with hydrophilic surfaces, especially polymer-type dispersants, are effective.

Typical examples of inorganic dispersants for waterborne coatings

-Sodium polyacrylate (low foaming and excellent dispersibility of many pigments)
-Copolymer of diisobutylene and maleic acid (good compatibility with resin emulsions and excellent anti-sagging property of paints)
-Condensed naphthalene sulfonic acid

These dispersants are sometimes used in combination with low-foaming nonionic surfactants that have excellent wetting properties.
For pigments with surfaces that are relatively difficult to wet, such as talc, poly(styrenesulfonic acid)-type polymers, which have both low polarity and water-soluble portions in their molecular chains, provide good dispersing effects.

In the case of non-aqueous paints, dispersants are less frequently used because the resin component of the paint acts as a dispersing agent, or because the pigments are modified on the surface to facilitate dispersion.

However, since paint itself is a complex system consisting of many components, alkylene polyamine surfactants and metal soaps are used as a type of dispersant to achieve other functions, such as thickening, anti-sagging, color separation, and leveling.

It is difficult to describe the relationship between the composition of dispersants and their effects in a few words, but basically, the adsorption of dispersants on the surface of pigment particles determines the performance of various paints. The table below summarizes the effects of pigment dispersants by process.

Printed matter covers a wide range of materials, including paper, metals, textiles, ceramics, and plastics. Each of these is printed in a wide variety of ways, using printing inks and printing methods that suit the purpose and application of the printed material.

Printing methods can be broadly classified into four types according to plate type: letterpress, intaglio, planographic, and digital duplicating (see figure below). The table below shows the main types of printing methods.

Fig. Types of illustrations (Reference: Zenzo Seki, "Printing Guide," p. 9, Seibundo Shinkosha (1971))

The basic composition of printing inks consists of (1) pigments, (2) carriers that transfer and adhere the pigments to the substrate, and (3) auxiliaries that assist the functions of the carriers, of which dispersants are one type. The table below shows the raw materials that make up printing inks.

Required viscosity of printing inks

Printing inks require pigments to be dispersed to a low viscosity to facilitate printing. The required viscosity varies depending on the printing method.

-In the case of gravure ink: A low viscosity liquid of 1 Pa･s or less is required to make it easier for the ink to penetrate into the screen cells of the plate.

-In the case of flat plate ink: A slightly higher viscosity liquid of 1 Pa･s to 100 Pa･s is required because the ink is transferred between many rollers.

 In addition, printing suitability is affected by differences due to post-processing methods and printing machines, and must be optimized under these conditions. Therefore, it is necessary to select and formulate pigments, carriers, and auxiliaries to adjust and optimize their viscosity and wettability according to each printing method.

In recent years, offset printing has been improving image reproducibility and increasing speed, and has also come to be able to produce low-cost, high-quality printed materials in a short time with simple operations. Offset inks are printed with the thinnest film thickness of all inks, so the inks must be able to use pigments with strong coloring power in high concentration.

Principle of Offset Printing

Offset printing uses a flat printing plate with no irregularities and is composed of a hydrophilic drawing area and a hydrophilic non-printing area.

 First, a fountain solution is supplied to the plate surface, covering the hydrophilic non-graphic areas with a film of fountain solution. Next, oil-based ink is supplied.

 At this time, the ink is repelled by the fountain solution film on the non-graphic area, and ink does not adhere to the non-graphic area, but only to the lipophilic area, thus reproducing the image

Offset Ink Requirements

In offset printing, optimization of ink and fountain solution is an important point to ensure that the thickness of the fountain solution is appropriate, that there is no adhesion of the fountain solution to the ink surface, and that the ink does not leach into the fountain solution.

 In offset inks, dispersants are rarely used. In many cases, resin components (binders) are used as dispersants or pigments are surface-treated to improve dispersion. In offset printing, pigment dispersion is achieved by wetting the pigment with the appropriate polarity of the resin, blending it in large quantities, and stabilizing the dispersion through the steric hindrance of polymers.

Main resins used for binders

-Modified alkyd resin (high polarity)
-Rosin-modified phenolic resin (excellent drying and emulsification properties)

Gravure printing is one type of intaglio printing, used for publications such as magazines and posters, food packaging, and construction materials such as wallpaper and decorative laminates, and produces crisp colors and heavy printed materials. Since low-boiling-point solvents are used in the ink, it is characterized by its quick-drying properties, and is used not only for paper, but also in a wide range of fields, including plastics, metals, and composite sheets.

Principles of Gravure Printing

(1) A plate cylinder made by burning, corroding, or engraving a photograph or other image on a copper-plated cylinder is rotated while immersed in an ink pan.
(2) When the ink is pumped out and scraped off with a doctor blade, ink remains in the indentations of the strokes.
(3)This ink is transferred to the substrate with the help of the pressure cylinder to reproduce the image.

Gravure Ink Requirements

In gravure printing, ink is not transferred to the substrate by printing pressure alone, as in offset printing, but is strongly absorbed by the capillary action between the plate cylinder and the substrate. Therefore, the degree of adhesion to the plate cylinder and the smoothness and flexibility of the substrate are key points for ink transfer.

 In this case, surfactants are often used as auxiliaries to improve pigment dispersion. In other words, surfactants adsorb onto the pigment surface and lower the interfacial energy, making the pigment surface easier to wet with organic solvents. In particular, since many organic pigments are not wettable, it is better to use a surfactant rich in wettability in combination with a surfactant to obtain good dispersion.

Surfactants suitable for gravure inks

-Fatty acid esters of polyhydric alcohols
-Polyoxyethylene-polyoxypropylene block polymers, etc.

Paper is used for a wide variety of purposes, including newsprint, tissue paper, and copy paper, making it an indispensable part of daily life. This section focuses on coated paper, which is particularly familiar with dispersion.

When paper is viewed under a microscope, the fibers overlap to form an uneven surface. Coated paper, also called coated paper, is made by coating the surface of paper with paint. The surface is covered with the coating to give it a beautiful surface. Coated paper is used for color printed flyers, posters, book covers, and photo magazines.

Coated paper has developed rapidly in recent years along with the development of printing technology, and in order to obtain a more beautiful printed product, a paper with a smoother surface and better ink transferability is being sought.

Coated papers are classified according to the amount of coating applied to the paper as shown in the table below.

Coated paper used as printing paper is made by applying a pigment dispersion called a coating color to the surface of the paper, and the pigment dispersion can be considered a kind of paint. Clay and calcium carbonate are mainly used as pigments, and titanium dioxide and satin white are also used.

Coating solution manufacturing procedure

(1) Add a predetermined amount of pigment to water in which an appropriate amount of dispersant has been dissolved in advance, while stirring with a dispersing machine.
(2) Add a water-soluble binder such as starch and synthetic latex such as SB latex while continuing stirring.
(3) Add a waterproofing agent, lubricant, antifoaming agent, preservative, etc.

 The resulting coating solution is filtered and sent to the coating station, where it is applied to the paper, the surface is smoothed, dried, and finished with a surface finishing machine called a super calender.

Dispersants for coating liquids

As dispersing agents, natural polymers such as casein and gum arabic, and complex phosphates such as sodium hexametaphosphate have been used in the past, although this is influenced by the type of pigment. Currently, polycarboxylic acid polymers (e.g., polyacrylates) are most commonly used for their dispersing effect.

 These polymers are adaptable to various dispersant needs by changing the average molecular weight, type of neutralizing salt, and copolymerization ratio with other monomers. A recent trend is the shift to high-speed coating from the viewpoint of productivity improvement. In order to further increase the concentration of coating solution, there is a growing demand for dispersants that can reduce viscosity, and development of such dispersants is ongoing.

 In many cases, pigments used in coating solution are fed into a pigment slurry with a dispersing agent in advance. In this case, as in the case of coating liquids, there is a growing demand for dispersants that can further increase the concentration of pigment slurry and reduce its viscosity in order to enable high speed coating.

The types of makeup cosmetics and their raw materials are shown in the table below.

 First, the key to manufacturing cosmetics is to disperse these pigments finely into primary particles and uniformly disperse them in a dispersing medium. If agglomeration occurs, colors may become dull or uneven. Next, stability over time is important. Poor stability may cause color separation, pigment sedimentation, or gelation. For this reason, the following points should be considered

Dispersion considerations for cosmetics manufacturing

(1) Before or during the formulation of cosmetics, reduce the particle size of pigments and achieve a sharp particle size distribution.

(2)Select a dispersant that is close to the specific gravity of the pigment. (At this time, you can also add polymers or swollen viscosity substances to increase the viscosity of the dispersant.) 

(3) Use ionic surfactants to create an adsorption layer on the pigment surface to increase the surface potential and repulsion force.

(4) Use a surfactant that improves the wettability of pigments with dispersants in combination with an ionic surfactant.

(5) Adsorb polymers such as cellulose derivatives onto the pigment to create a protective colloidal layer.

Typical cosmetics in which pigments are dispersed in aqueous systems include water oshiroi and eyeliner. Nonionic surfactants, especially ester surfactants, are effective dispersants.

Lipstick, oil-based foundations, eyebrow pencils, and nail enamel are examples of cosmetics in which pigments are dispersed in a non-aqueous system. Lipsticks, for example, are often dispersed in a molten state by applying heat, placed in a mold, and allowed to cool and harden. The key is to make the pigment surface hydrophobic and close to the polarity of the solvent. By using a surfactant of the opposite ion to the colloidal particles of the pigment as a dispersing agent, a monolayer is formed on the pigment surface, making the pigment lipophilic (hydrophobic).

Anionic surfactants and sulfosuccinate types are good dispersants. Other methods to stabilize dispersion include the use of natural waxes and surface treatment of pigments to change their hydrophilicity from hydrophilic to hydrophobic.

Concrete is a material consisting of fillers such as sand and gravel bound together by a type of inorganic adhesive called cement.

 Cement, which plays an important role in the composition of concrete, is made by firing limestone, clay, or gypsum at approximately 1,500°C. The resulting cement reacts with water and hardens. The resulting cement reacts with water and hardens, acting as an adhesive to hold together the sand and gravel that are mixed in at the same time to form concrete. The composition of a typical Portland cement and its reaction products with water are shown in the table below.

Role of cement dispersant (water reducer)

The strength of concrete tends to decrease as the amount of water is increased. However, as the amount of water is reduced, the fluidity of the concrete deteriorates and workability worsens. The theoretical amount of water required for cement to hydrate and solidify is usually 20-25% of the cement mass. On the other hand, to mix concrete to a workable level, 40-60% of water is required relative to the mass of the cement.

This is where dispersants (water-reducing agents) come in: they are added to cemento water-mixture systems to improve the dispersion of cemento particles in water, give fluidity even with small amounts of water, and contribute to improved workability and concrete strength.

 In some cases, it takes several hours or more after the concrete mixture is mixed at the plant before it is used at the construction site. In such cases, the viscosity of the concrete slurry increases over time, making it difficult to handle and, in extreme cases, impossible to work with. This can be a major problem especially in cities with poor road conditions and heavy traffic congestion.

 Again, a dispersing agent (fluidizing agent) that can maintain the initial fluidity is needed. The role of cement dispersants in the manufacture and use of ready-mixed concrete is shown in the table below.

Dispersing agents for cement can be classified into two categories according to their intended use: water reducers and fluidizing agents. In order to create strong concrete structures, the amount of water used for mixing must be reduced as much as possible. Therefore, water reducers, which are dispersants for cement, are used in ready-mixed concrete production plants and concrete product manufacturing plants.

Superplasticizer

Concrete products (poles, piles, hume pipes), concrete blocks for seawalls, and sleepers require even higher concrete strength than general-purpose concrete construction. When used in these applications, air bubbles must be removed to further increase the density or further reduce the amount of water. In this case, a dispersant that is more effective in reducing water and removing air bubbles must be used. This water reducer is specifically called a high-performance water reducer.

AE water reducer

AE (Air Entraining), also known as air entraining, is a property of ready-mixed concrete that allows air bubbles to be trapped within the concrete. When water left inside a concrete structure freezes and thaws during the winter and this process is repeated, the concrete cracks and its strength is significantly reduced. However, adding air bubbles to ready-mixed concrete has the effect of preventing this from happening.

Lignin sulfonic acid type

The oldest dispersant in use, it is made by denaturing lignin sulfonic acid, which is generated in the sulfite pulp manufacturing process. Although it is not very effective in reducing the amount of water added, it is often used as an AE reducer in the construction of general concrete structures because it is inexpensive and has AE properties as well. 

Naphthalene sulfonate, melamine sulfonate

These water reducers are used as high performance water reducers because they have a greater water reduction effect than lignin sulfonate reducers. They are also used as fluidizing agents because they improve the fluidity of concrete when added in small quantities. Melamine sulfonate is used especially for structures where aesthetics are important, as it gives the finished product a beautiful surface.

Polycarboxylic acid type

Compared to the above water reducers, the effect of water reduction is not so great, but it is characterized by its ability to control the increase in concrete paste viscosity for a relatively long period of time. Therefore, it is best suited as a fluidizing agent, and is often used in combination with other water reducers or high-performance water reducers.

In general, polymers are more advantageous as dispersants than low-molecular surfactants, but there is an optimum molecular weight; for example, naphthalenesulfonic acids have a molecular weight of 2,000 to 3,000, and polycarboxylic acids have a molecular weight of 5,000 to 10,000.

If the molecular weight becomes too large, the molecules adsorbed on the cement surface form long dangling chains, which entangle with each other, increasing the dispersion viscosity and deteriorating flowability. Also, when the molecular weight becomes extremely large, the agglomeration effect takes precedence over dispersion.

Dispersant for agrochemical granules

Although the amount of dispersant used is as small as 1-3%, it plays an important role in the disintegration and spreading of the granules.

-Polyacrylic acid type polymers such as sodium polyacrylate have the best dispersing performance among them.
-Sodium lignin sulfonate is inexpensive and is often used when dispersibility is not so important.
-Formalin condensates of sodium naphthalenesulfonate have the advantage of not being affected by the hardness or pH of the water.

Granular agents manufactured in this way are generally applied at a rate of several kilograms per 1,000 meters2 of paddy field. Recently, 1 kg granules, which contain about three times as much active ingredient as the 3 kg granules and have a slightly larger particle diameter, are becoming the mainstream.

The role of dispersants for agrochemical granules is mainly to disperse the inorganic carrier with the agrochemical API adsorbed in water. In the past, low molecular weight anionic surfactants such as sodium alkylbenzenesulfonate were used as dispersants, but in recent years, water-soluble polymers such as sodium polyacrylate have become the mainstream. The reason for this is said to be that they bind strongly to the carrier and form a stable protective colloid, thereby improving dispersibility.

The figure below shows the dispersion of granules made with water-soluble polymers in water.

Fig. State of pesticide granules in water

The difference between dyeing with pigments and dyeing with dyes is that pigments are adhered to the fiber surface with binders in the form of primary or secondary particles to produce color, whereas dyes diffuse at the molecular level into the amorphous part of the high molecular chain that constitutes the fiber and react with or fix to the fiber to produce color.

Fibers composed of cellulose such as cotton and rayon have hydroxyl groups, while nylon and wool have amino groups and other functional groups that are hydrophilic and easy to react with, and can be dyed with water-soluble dyes that react with these functional groups. However, for fibers that are strongly lipophilic (hydrophobic) and do not have functional groups, such as polyester fibers, dyeing is performed using disperse dyes that are insoluble in water. Therefore, a dispersing agent is required to disperse the dye uniformly in water.

 Commercially available disperse dyes contain about half of ionic dispersants in addition to dyes. When polyester fibers are dyed by the dip-dyeing method (a method of dyeing a single color with a water-dispersion system of dyes), a disperse dye dispersion solution is often circulated. At this time, dye particles must be stably dispersed in a temperature range from room temperature to 120~130°C. If the dispersion stability is poor, uneven dyeing or dull colors may occur, and therefore, the choice of dispersing agent is important.

On the combination of dispersants

In general, there are few dispersants that exhibit good dispersibility from room temperature to the high temperature (120-130°C) range, and they are often used in combination.

 For example, formalin condensate of sodium naphthalenesulfonate (NSF) shows excellent dispersibility near room temperature, but tends to decrease dispersibility at temperatures above 50°C. NSF has no functional group in its molecule that interacts with dyes and simply provides dispersibility by physical adsorption. and dispersibility decreases above 50°C. On the other hand, metacresol sulfone has a tendency to decrease dispersibility above 50°C.

 On the other hand, CSF, a formalin condensed product of sodium metacresol sulfonate, has a phenolic hydroxyl group and thus adsorbs functional groups such as -NH2 (amino group), >C=O (ketone), and -COOH (carboxyl group) on the dye surface through ionic interaction and shows excellent dispersibility at high temperature. Therefore, the combined system of NSF and CSF provides stable dispersibility from low to high temperatures.

However, dispersion of dyes is often insufficient with these dispersants alone, and surfactants are often used in combination.
-Function of non-ionic surfactant: Eliminates unevenness of dyeing color and makes dyeing uniform.
-Function of anionic surfactant: To improve dye dispersion

Dispersing and equalizing agent for polyester dyeing

In practice, dispersion equalizing agents for polyester dyeing, which are a well-balanced combination of these various surfactants, are generally used. In recent years, liquid flow dyeing machines, in which dyeing solution is sprayed from a jet nozzle and moves through the dyed cloth in contact with the cloth, have become widely used for dyeing polyester fibers. In addition to improving the dispersibility of disperse dye, foaming is often a problem, requiring a dispersing agent with low foaming characteristics.

Dyeing method for polyester

There are three industrial dyeing methods for polyester fibers:
(1) high-temperature, high-pressure dyeing, (2) carrier dyeing, and (3) thermosol dyeing.

In all cases, as shown in the figure below, polyester is dyed by loosening the molecular chains of the polyester (making the crystal structure loose). 

(1) High-temperature, high-pressure staining method

This method is based on the fact that molecular motion becomes more active as temperature is raised. The dyeing temperature is set to 120-130°C to loosen the crystalline structure of the fiber and increase the gap between the fibers, allowing dye molecules to enter the fiber.

(2) Carrier staining method

This method uses a chemical called "carrier" to expand the gaps in the amorphous region of the fiber, even at dyeing temperatures of 100°C, to make it easier for the dye to penetrate. 

(3)Thermosol staining method

After being padded with a dye dispersion mixed with a small amount of glue, the dye is dried and placed evenly on the surface of the fabric, which is then heated to 180 to 200°C for 30 to 60 seconds to instantaneously sublimate the dye and feed it into the fabric.

Fig. Dyeing model for polyester fiber

The dyeing process of disperse dyes is shown in the figure below. When a disperse dye is combined with a surfactant, the state of the disperse dye in aqueous solution changes as shown in the figure below.

 When the temperature is raised in this state, the slightly dissolved dye enters the amorphous region of the polyester fiber, the gap of which is widened by the water, and the dyebath is devoid of the dissolved dye. At this stage, there is only a trace of color on the fiber.

 Next, the dye equivalent to the solubility in the bath solution (about 5 to 10 mg per 1 L) dissolves out of the dispersed dye area as shown in the figure below. The dissolved dye then re-enters the amorphous part and is dyed. This process is repeated, and dyeing of the disperse dye proceeds.

Fig. Schematic diagram with dispersed dye

Internal coloring: Dye or pigment is kneaded into the plastic at the raw material or molding stage to achieve uniform coloring all the way to the inside.

Surface coloring: Coloring the surface by painting, printing, etc.

In general, the term "plastic coloring" often refers to internal coloring.

Pigments do not melt when heated, nor do they dissolve in common organic solvents. In addition, they are often incompatible with the properties and composition of plastics because they are very different. Therefore, it is difficult to mix pigments into plastics without re-agglomerating them as they are. Dispersants called plastic coloring aids solve this problem.

 The following methods are available for coloring plastics

Dry-color process

This method adds pigments to resins as a fine powder whose surface is treated with plastic coloring aids such as surfactants or metallic soap to make it easily blend with the mating resin. Although it is used for most thermoplastic resins, it has disadvantages such as severe scattering contamination due to its dry powder nature and different coloring properties depending on the blending conditions with the raw resin.

Liquid color, paste color

In this method, pigments are dispersed finely and concentrated in plasticizers and solvents in advance, together with plastic coloring aids, and added to the resin as a dispersion. The coloring state is unstable, and the pigments may agglomerate or settle due to volatilization of the plasticizer or solvent after long-term storage.

Master batch

In this method, a master batch is made by using a resin to be pigmented or a resin that is compatible with the pigment and dispersing the pigment in high concentration together with plastic coloring aids, which are then added to the resin. This method has become popular in recent years and has no adverse effects on physical properties or contamination, and the pigments are well dispersed. On the other hand, it requires a resin for the dispersant that can blend well with the other resin.

A typical flow sheet using plastic colorants is shown in the figure below.

Fig. Typical production flow using plastic colorants

As mentioned above, masterbatches are colorants in which pigments are dispersed in resin at high concentration, and are available in pellet, plate, and flake forms. Pigment content is typically 30-70%.

 The amount of pigment required in a final plastic product, for example polyolefin, is generally around 0.5% by mass (vs. resin). Therefore, the master batch should be mixed with 60 to 140 times as much resin. Since the same type of resin as that to be used for coloring is generally used, there are no problems in terms of physical properties, and the dispersion is excellent.

 In particular, if the dilution ratio of the masterbatch to the natural resin (original resin to be colored) is too large (small amount added), uneven coloration is likely to occur.

Synthetic wax-based plastic coloring aids  

For a long time, rolaffin wax, obtained by refining petroleum, has been used as a typical plastic coloring aid, but in recent years there has been a shift to synthetic wax systems, which offer superior pigment dispersibility.

-Synthetic waxes such as polyethylene wax and polypropylene wax
Used to color polyolefins such as polyethylene and polypropylene, and polyvinyl chloride

-Low molecular weight polystyrene
Used for coloring styrene-based resins such as polystyrene and ABS resins

-Modified olefin oligomer
Used to color polyethylene and polypropylene. 

The primary particles of pigments are several microns in size, but when they are actually used, they are sometimes agglomerated to several tens of microns due to static electricity and other factors. When a master batch is made from these pigments, the pigments are again primary particles or in a state similar to this.

 When this is mixed with a natural resin, the pigments that have become fine particles are transferred into the mating resin along with plastic coloring aids, resulting in a uniform dispersion. The figure below shows how a masterbatch is used to color a resin.

Plastic coloring aids have lower melt viscosity and higher affinity for pigments, which is the reason why pigments are dispersed more uniformly in plastic coloring aids than in natural resins.

Fig. Coloring of resins using masterbatches with plastic coloring aids

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Sanyo Chemical Industries, Ltd. extends no warranties and makes no representations as to the accuracy or completeness of the information contained herein, and assumes no responsibility regarding the suitability of this information for any intended purposes or for any consequences of using this information.

Any product information in this brochure is without obligation and commitment, and is subject to change at any time without prior notice.

Consequently anyone acting on information contained in this brochure does so entirely at his/her own risk.In particular, final determination of suitability of any material described in this brochure, including patent liability for intended applications, is the sole responsibility of the user. Such materials may present unknown health hazards and should be used with caution. Although certain hazards may be described in this brochure, Sanyo Chemical Industries, Ltd. cannot guarantee that these are the only hazards that exist.

First, an interface is a boundary surface that exists between two substances with different properties, and interfaces exist between liquids and solids, liquids and liquids, and liquids and gases.

Surfactants enhance performance by performing functions such as washing, emulsifying, dispersing, wetting, and penetrating at this interface.

Interface = a boundary surface that exists between two substances with different properties
Liquid and solid: cup and coffee, machine and lubricant 
Liquid and liquid: water and oil 
Liquid and gas: seawater and air, soap bubbles

Examples of roles of surfactants
Cleaning ・・・ Removing dirt 
Emulsification ・・・ Dispersion ・・ Making unmixable things easier to mix
Wetting / Penetration ・・・ Makes wetting and soaking easier

-Surfactants have different structures in their molecules with different properties: lipophilic groups (oil-fitting parts) and hydrophilic groups (water-fitting parts).

-Surfactants are broadly classified into four types according to the structure of the hydrophilic group: nonionic, anionic, cationic, and amphoteric (having both anionic and cationic groups).

It consists of seven short movies for each function. 
0:00　Introduction of surfactants functions　
0:16　Part1　Washability
1:00　Part2　Permeability
2:10　Part3　Dispersion
2:55　Part4　Foaming properties
3:25　Part5　Defoaming properties
3:39　Part6　Smoothness
4:20　Part7　Antibacterial properties