A Brief Introduction to ''Industrial Seasoning'': Surfactants

Industrial seasonings are also called surfactants. Surfactants are a type of substance that, when added in small amounts, can greatly reduce the surface tension of the solvent (usually water) and change the interface state of the system; when it reaches a certain concentration, it associates into micelles in the solution. This produces wetting or dewetting, emulsification and demulsification, foaming or defoaming, solubilization, washing and other effects to meet the requirements of practical applications. Seasonings, as a flavor substance, are ubiquitous in our diet. In industrial production, surfactants are substances very similar to seasonings. They do not need to be used in large amounts, but they can work very magically. This type of substance is commonly

known as surfactants.

Surfactant Introduction

Surfactants have an amphiphilic molecular structure: one end is a hydrophilic group, referred to as a hydrophilic group, also known as an oleophobic group or an oleophobic group, which enables the surfactant to dissolve in water in the form of a monomer. The hydrophilic group is often a polar group, which can be a carboxyl group (-COOH), a sulfonic acid group (-SO3H), an amino group (-NH2) or an amine group and its salts. Hydroxyl (-OH), amide group, ether bond (-O-), etc. can also be used as polar hydrophilic groups; the other end is a hydrophobic group, referred to as a lipophilic group, also known as a hydrophobic group or a hydrophobic group. The hydrophobic group is usually a non-polar hydrocarbon chain, such as a hydrophobic alkyl chain R- (alkyl), Ar- (aryl), etc.

Surfactants are divided into ionic surfactants (including cationic surfactants and anionic surfactants), nonionic surfactants, amphoteric surfactants, compound surfactants, and other surfactants. In a surfactant solution, when the concentration of the surfactant reaches a certain value, the surfactant molecules will form various ordered combinations called micelles. Micellization or the formation of micelles is a very important basic property of surfactant solutions, and some important interfacial phenomena are related to the formation of micelles. The concentration at which surfactants form micelles in a solution is called the critical micelle concentration (CMC). Micelles are not fixed spheres, but extremely irregular and dynamically changing shapes. Under certain conditions, surfactants can also appear in the state of reverse micelles.

Main factors affecting critical micelle concentration

Structure of surfactants;

Additive addition and type;

Effect of temperature;

Interaction between surfactants and proteins

Proteins contain non-polar, polar and charged groups, and many amphiphilic molecules can interact with proteins in various ways. Surfactants can form ordered molecular assemblies with different structures under different conditions, such as micelles, reverse micelles, etc., and their interactions with proteins are also different. There are mainly electrostatic and hydrophobic interactions between protein-surfactant (P-S). The interaction between ionic surfactants and proteins is mainly the electrostatic interaction of polar groups and the hydrophobic interaction of hydrophobic hydrocarbon chains, which bind to the polar and hydrophobic parts of proteins respectively to form a P-S complex. Non-ionic surfactants mainly interact with proteins through hydrophobic forces, and the interaction between their hydrophobic chains and the hydrophobic groups of proteins can have a certain impact on the structure and function of both surfactants and proteins. Therefore, the type, concentration and system environment of surfactants determine whether the surfactant stabilizes or destabilizes the protein, aggregates or disperses it.

Surfactant HLB value

For surfactants to exhibit unique interfacial activity, there must be a certain balance between the hydrophobic group and the hydrophilic group. HLB (Hydrophile-Lipophile Balance) is the hydrophilic-lipophilic balance value of surfactants, and is an indicator to measure the hydrophilic and hydrophobic properties of surfactants. The HLB value is a relative value (between 0 and 40), such as paraffin HLB value = 0 (no hydrophilic group), polyoxyethylene is 20, and SDS with strong hydrophilicity has an HLB value of 40. The HLB value can be used as a reference for selecting surfactants. The larger the HLB value, the better the hydrophilicity of the surfactant; the smaller the HLB value, the worse the hydrophilicity of the surfactant.

Surfactant Main function

Emulsification

Due to the high surface tension of oil in water, when oil is dropped into water and stirred vigorously, the oil is crushed into fine beads and mixed into an emulsion, but the stirring stops and the layers are separated again. If a surfactant is added and stirred vigorously, it is not easy to separate for a long time after stopping. This is the emulsification effect. The reason is that the hydrophobicity of the oil is surrounded by the hydrophilic groups of the surfactant, forming a directional attraction, which reduces the work required for the oil to disperse in water and makes the oil well emulsified.

Wetting effect

The surface of the parts often adheres to a layer of wax, grease or scaly substances, which are hydrophobic. Due to the contamination of these substances, the surface of the parts is not easily wetted by water. When a surfactant is added to the aqueous solution, the water droplets on the parts are easily dispersed, which greatly reduces the surface tension of the parts and achieves the purpose of wetting.

Solubilization effect

Oil substances can only be "dissolved" after adding surfactants, but this dissolution can only occur when the concentration of the surfactant reaches the critical concentration of the colloid. The solubility is determined by the solubilization object and properties. In terms of solubilization, long hydrophobic hydrocarbon chains are stronger than short hydrocarbon chains, saturated hydrocarbon chains are stronger than unsaturated hydrocarbon chains, and non-ionic surfactants generally have a more significant solubilization effect.

Dispersion effect

Solid particles such as dust and dirt particles are easy to gather together and settle in water. The molecules of surfactants can divide solid particle aggregates into fine particles, disperse them and suspend them in the solution, and play a role in promoting the uniform dispersion of solid particles.

Foaming effect

The formation of foam is mainly due to the directional adsorption of surfactants, which is caused by the reduction of surface tension between the gas and liquid phases. Generally, low-molecular surfactants are easy to foam, while high-molecular surfactants have less foam. Myristic acid yellow has higher foaming properties, and sodium stearate has the worst foaming properties. Anionic surfactants have better foaming properties and foam stability than non-ionic surfactants, such as sodium alkylbenzene sulfonate, which has strong foaming properties. Commonly used foam stabilizers include fatty alcohol amides, carboxymethyl cellulose, etc., and foam inhibitors include fatty acids, fatty acid esters, polyethers, etc. and other non-ionic surfactants.

Surfactant classification

Surfactants can be divided into anionic surfactants, nonionic surfactants, zwitterionic surfactants, and cationic surfactants according to their molecular structure characteristics.

Anionic surfactants

Sulfonates

Common surfactants of this type include linear sodium alkylbenzene sulfonate and α-olefin sodium sulfonate.

Linear sodium alkylbenzene sulfonate, also known as LAS or ABS, is a white or light yellow powder or flaky solid. It has good solubility in compound surfactant systems and is relatively stable to alkali, dilute acid, and hard water. It is commonly used in detergents (dishwashing liquid detergents) and liquid laundry detergents, but is generally not used in shampoos and rarely in shower liquids. Its usage in detergents can account for about half of the total amount of surfactants, and its actual adjustment range in liquid laundry detergents is relatively wide. The more typical compound system used in detergents is the ternary system "LAS (linear sodium alkylbenzene sulfonate)-AES (sodium alcohol ether sulfate)-FFA (alkyl alcohol amide)". The outstanding advantages of linear sodium alkylbenzene sulfonate are good stability, strong detergency, minimal environmental damage, good biodegradability into harmless substances, and low price. The outstanding disadvantage is high irritation.

Sodium α-olefin sulfonate, also known as AOS, is very soluble in water and has good stability in a wide range of pH values. Among the sulfonate varieties, it has better performance. The outstanding advantages are good stability, good water solubility, good compatibility, low irritation, and ideal microbial degradation. It is one of the main surfactants commonly used in shampoos and shower gels. Its disadvantage is that it is expensive.

Sulfate

Common surfactants of this type include sodium fatty alcohol polyoxyethylene ether sulfate and sodium dodecyl sulfate.

Sodium fatty alcohol polyoxyethylene ether sulfate is also known as AES and sodium alcohol ether sulfate. It is easily soluble in water and can be used in shampoos, shower gels, dishwashing liquid detergents (dishwashing liquids), and liquid laundry detergents. It has better water solubility than sodium dodecyl sulfate and can be made into transparent aqueous solution of any proportion at room temperature. It is more widely used in liquid detergents than linear sodium alkylbenzene sulfonate and has better compatibility; it can be compounded with many surfactants in binary or multi-component form into transparent aqueous solution. Its outstanding advantages are low irritation, good water solubility, good compatibility, and good performance in preventing skin dryness and roughness. Its disadvantages are slightly poor stability in acidic medium and inferior detergency to linear sodium alkylbenzene sulfonate and sodium dodecyl sulfate.

Sodium dodecyl sulfate is also known as AS, K 12, sodium coconut sulfate, sodium lauryl sulfate foaming agent. It is insensitive to alkali and hard water. Its stability under acidic conditions is inferior to that of general sulfonates, close to sodium fatty alcohol polyoxyethylene ether sulfate, easy to degrade, and has minimal harm to the environment. When used in liquid detergents, the acidity cannot be too high; using its ethanolamine salt or ammonium salt in shampoo and shower gel can not only increase acid resistance and stability, but also help reduce irritation. Except for good foaming and strong detergency, its other performances are not as good as those of sodium alcohol ether sulfate. Its price is generally higher than that of common anionic surfactants.

Cationic surfactants

Compared with various types of surfactants, cationic surfactants have the most prominent regulating effect and the strongest bactericidal effect, despite the disadvantages of poor detergency, poor foaming, poor compatibility, high irritation, and high price. Cationic surfactants are not directly compatible with anionic surfactants and can only be used as conditioning agent components or bactericides. Cationic surfactants are generally used in higher-end products as auxiliary surfactants (conditioning agent components with a small amount of formula) in liquid detergents, mainly in shampoos. As a regulating agent component, it cannot be replaced by other types of surfactants in high-end liquid detergents and shampoos.

Common cationic surfactant varieties include hexadecyl dimethyl ammonium chloride (1631), octadecyl trimethyl ammonium chloride (1831), cationic guar gum (C-14 S), cationic panthenol, cationic silicone oil, dodecyl dimethyl amine oxide (OB-2), etc.

Zwitterionic surfactants

Amphoteric surfactants refer to surfactants with both anionic and cationic hydrophilic groups. Therefore, this type of surfactant is cationic in acidic solutions, anionic in alkaline solutions, and has non-ionic properties in neutral solutions. Amphoteric surfactants are easily soluble in water, soluble in relatively concentrated acid and alkaline solutions, and can even be dissolved in concentrated solutions of inorganic salts. They have good hard water resistance, low skin irritation, good fabric softness, good antistatic properties, good bactericidal effects, and good compatibility with various surfactants. Important amphoteric surfactant varieties include dodecyl dimethyl betaine, carboxylate imidazoline, etc.

Nonionic surfactants

Nonionic surfactants have good solubilization, washing, antistatic, low irritation, calcium soap dispersion and other properties; the applicable pH range is wider than that of general ionic surfactants; except for the detergency and foaming properties, other properties are often better than those of general anionic surfactants. Adding a small amount of nonionic surfactants to ionic surfactants can increase the surface activity of the system (comparison between the same active matter content). The main varieties are alkyl alcohol amide (FFA), fatty alcohol polyoxyethylene ether (AE), alkylphenol polyoxyethylene ether (APE or OP).

Alkyl alcohol amide (FFA) is a kind of non-ionic surfactant with superior performance, wide application and high frequency of use. It is commonly used in various liquid detergents. It is often used in liquid detergents with amides, and the ratio is generally "2:1" and "1.5:1" (alkyl alcohol amide: amide). Alkyl alcohol amide can be used in general slightly acidic and alkaline detergents, and is the cheapest variety among non-ionic surfactants.

Surfactant Application

With the development of science and technology, especially the progress of the chemical industry and the penetration of related disciplines, the role and application of surfactants have become more extensive and in-depth. From the mining of minerals and the development of energy to the role of cells and the effect of enzymes, surfactants can be found. Today, the application of surfactants is no longer limited to detergents, detergents, toothpaste detergents, cosmetics emulsifiers and other daily chemical industries, but has spread to other production fields such as petrochemicals, energy development, and pharmaceutical industries.

Oil extraction

In oil extraction, the use of a dilute solution of surfactants with water, or a concentrated solution of surfactants mixed with oil and water, can increase the crude oil extraction rate by 15% to 20%. Since surfactants have the ability to reduce the viscosity of the solution, they are used during drilling to reduce the viscosity of crude oil and reduce or prevent the occurrence of drill jams. They can also make old wells that no longer spray oil spray again.

Energy development

Surfactants can also contribute to energy development. Nowadays, with the rise in world oil prices and the shortage of oil sources, the development of oil-coal mixed fuels is of far-reaching significance. That is, adding surfactants to the process can produce a new type of fuel with high flow properties, which can replace gasoline as a power source. In addition, adding surfactants that play an emulsifying role to gasoline, diesel and heavy oil can not only save oil sources, but also improve thermal effects and reduce pollution to the environment. Therefore, surfactants have far-reaching significance for energy development.

Textile industry

The application of surfactants in the textile industry has a long history. Compared with natural fibers, synthetic fibers are rough, not fluffy enough, prone to electrostatic adsorption of dust, and have poor hygroscopicity and feel. If treated with special surfactants, the above defects of synthetic fibers can be greatly improved. In addition, surfactants are also softeners, antistatic agents, wetting penetrants, and emulsifiers in the textile printing and dyeing industry. It can be seen that the application of surfactants in the textile printing and dyeing industry is very extensive.

Metal cleaning

In metal cleaning, traditional solvents are organic solvents such as gasoline, kerosene, and carbon tetrachloride. According to relevant statistics, the annual amount of gasoline used to clean metal parts in the country is as high as 500,000 tons. The water-based metal cleaning agent prepared with surfactants can save energy. It is estimated that one ton of metal cleaning agent can replace 20 tons of gasoline, and 1 ton of petroleum raw materials can be made into 4 tons of metal cleaning agent. It can be seen that surfactants have far-reaching significance for energy saving. In addition, surfactant metal cleaning agents are also non-toxic, non-flammable, non-polluting, and ensure the safety of workers. This type of metal cleaning agent has been promoted and applied to the cleaning of different types of metal parts such as aerospace engines, aircraft, and bearings.

Food industry

In the food industry, surfactants are multifunctional additives for making food. Surfactants for food have excellent emulsification, wetting, anti-sticking, preservation and flocculation effects. Due to the special effects of this type of additive, pastries can be crispy, foaming foods can be foamed, bread can be soft, and the raw materials of products such as margarine, mayonnaise, and ice cream can be evenly dispersed and emulsified, which has a unique effect on improving the production process of products and the intrinsic quality of products.

Agriculture

Pesticides are emulsions. Due to the surface tension of the liquid, it is difficult to spread when sprayed on the leaves of plants. If surfactants are added to the pesticide solution, the surfactant can reduce the surface tension of the liquid, that is, the emulsion loses its surface activity, and the pesticide emulsion will be easily spread on the leaves, so that its insecticidal effect will be better.