Basic Knowledge Of Surfactants Is Indispensable To Textile Knowledge.

1. Surface tension

The contraction force of any unit length on the liquid surface is called surface tension, and the unit is N M-1.

2. Surface active agents and surfactants

The property that can reduce the surface tension of the solvent is called surface activity, and the surface active substance is called surfactant.

Surfactant, which can be associated with molecules in aqueous solution and form micelles and other complexes, has high surface activity, and also has the functions of wetting, emulsifying, foaming, washing and so on. It is called surfactant.

3. Molecular structure characteristics of surfactants

Surfactant is a kind of organic compound with special structure and properties. It can obviously change the interfacial tension between two phases or the surface tension of liquid (generally water), and has the properties of wetting, foaming, emulsifying, washing and so on.

In terms of structure, surfactant has a common feature, that is, its molecules contain two different groups of properties, one end is a long chain non-polar group, which can be dissolved in oil but not insoluble in water, that is, the so-called hydrophobic group or hydrophobic group, which are generally long-chain hydrocarbons, sometimes organic fluorine, organosilicon, organic phosphorus, organic tin chain. The other end is a water-soluble group, that is, a hydrophilic group or a hydrophilic group. The hydrophilic group must have enough hydrophilicity to ensure that the surfactant is soluble in water and has the necessary solubility. Because surfactants contain hydrophilic and hydrophobic groups, they can be dissolved in at least one phase in the liquid phase. The hydrophilic and lipophilic nature of surfactants is called two affinity.

4. Types of surfactants

Surfactant is a two affinity molecule with hydrophobic group and hydrophilic group. The hydrophobic groups of surfactants are generally composed of long chain hydrocarbons, such as linear alkyl C8 to C20, branched alkyl C8 to C20, alkyl phenyl group (alkyl carbon atom number 8~16). The difference of hydrophobic groups is mainly due to the difference in the structure of the hydrocarbon chain, and the difference of the hydrophilic group is more. Therefore, the properties of the surfactant are mainly related to the hydrophilic group in addition to the size and shape of the hydrophobic groups. The structure of hydrophilic groups is larger than that of hydrophobic groups. Therefore, the classification of surfactants is based on the structure of hydrophilic groups. The classification is based on whether the hydrophilic group is ionic type, and can be divided into anionic, cationic, non-ionic, zwitterionic and other special types of surfactants.

5. Characteristics of surfactant aqueous solution

Adsorption of surfactant on the interface

Surfactant molecules are lipophilic and hydrophilic, and are two affinity molecules. Water is a strong polar liquid. When the surfactants are dissolved in water, according to the principle of polarity similarity and polarity exclusion, the hydrophilic group and water phase are dissolved in water, and the lipophilic group repel the water and leave the water. As a result, the surfactant molecules (or ions) adsorb on the two phase interface, resulting in the decrease of the interfacial tension between the two phases. The more adsorption of surfactant molecules (or ions) on the interface, the greater the decrease of interfacial tension.

Some properties of adsorption membrane

The surface pressure of the adsorption membrane: the surface active agent adsorbs on the gas-liquid interface to form an adsorption membrane, such as placing a frictionless movable floating film on the interface, pushing the adsorption film along the solution surface with the floating sheet, and producing a pressure on the floating sheet, which is called surface pressure.

Surface viscosity: like surface pressure, surface viscosity is a property of insoluble molecular membrane. Suspension of a white gold ring with fine metal wire, so that its surface contact with the water surface of the sink, rotate the white gold ring, and the white gold ring is hindered by the viscosity of the water, and the amplitude gradually decays. Based on this, the surface viscosity can be measured. The method is: first, carry out the experiment on the pure water surface, measure the amplitude attenuation, then determine the attenuation after forming the surface film, and obtain the viscosity of the surface film from the difference between the two.

The surface viscosity is closely related to the firmness of the surface film. Because the membrane has surface pressure and viscosity, it must be elastic. The greater the surface pressure and the higher the viscosity, the greater the elastic modulus of the adsorption membrane. The elastic modulus of the surface adsorbed film is of great importance in stabilizing foam.

Formation of micelles

The dilute solution of surfactant obeys the law of ideal solution. The adsorption capacity of surfactants on the surface of solution increases with the increase of solution concentration. When the concentration reaches or exceeds a certain value, the amount of adsorption will no longer increase. Both practice and theory indicate that they form a complex in solution, which is called micelle.

Critical micelle concentration: the lowest concentration of surfactant forming micelles in solution is called critical micelle concentration.

(4) the cmc value of common surfactants.

6, hydrophile lipophilic balance value

HLB is the abbreviation of hydrophile lipophile balance, indicating the hydrophile lipophilic balance value of the hydrophilic group and the lipophilic group of the surfactants, that is, the HLB value of the surfactant. The HLB value is large, indicating that the molecule has strong hydrophilicity and low hydrophobicity.

1. The regulation of HLB value

The HLB value is a relative value. Therefore, when the HLB value is formulated, the HLB value of the paraffin without hydrophilicity is 0, while the HLB value of the twelve alkyl sulphate with strong water solubility is 40. Therefore, the HLB value of surfactants is generally within 1~40. Generally speaking, the emulsifier of HLB less than 10 is lipophilic, while the emulsifier of more than 10 is hydrophilic. Therefore, the turning point from lipophilicity to hydrophilicity is about 10.

According to the HLB value of surfactants, we can get a general understanding of its possible uses, as shown in table 1-3.

Table 1-3 HLB range and its application performance

　　 The above table shows that the HLB value of surfactants suitable for oil in water emulsifier is 3.5 to 6, while the HLB value of oil in water emulsifier is 8~18.

(2) determination of HLB value.

7. Emulsification and solubilization

Two insoluble liquids, a system consisting of particles (droplets or liquid crystals) dispersed in another, called emulsion. When the emulsion is formed, the system is thermodynamically unstable due to the increase of the boundary area of the two liquid. In order to stabilize the emulsion, it is necessary to add third components - emulsifier to reduce the interfacial energy of the system. Emulsifier is a surfactant, its main function is to milk. In emulsion, the phase in which droplets exist is called the dispersed phase (or internal phase, discontinuous phase), and the other phase is called a dispersed medium (or outer phase, continuous phase).

Emulsifiers and emulsions

A common emulsion consists of water or aqueous solution, and the other is organic matter miscible with water, such as grease and wax. The emulsion formed by water and oil can be divided into two types according to their dispersing: oil dispersed in water to form oil in water emulsion, expressed in O/W (oil / water): water dispersible oil forms oil in water emulsion, expressed in W/O (water / oil). In addition, complex water in oil and water in W/O/W and oil in oil O/W/O type multicomponent emulsions may also be formed.

Emulsifiers stabilize the emulsion by reducing interfacial tension and forming a single molecular boundary film.

Emulsification requirements for emulsifiers: A: the emulsifier must be able to adsorb or enrich on the two phase interface and reduce the interfacial tension; B: the emulsifier must give the particles charge, make the particles produce electrostatic repulsion, or form a stable, highly viscous protective film around the particles. Therefore, the material used as emulsifier must have two parent groups to emulsify. Surfactant can meet this requirement.

2. Preparation methods of emulsion and factors affecting emulsion stability

There are two ways to prepare emulsions: one is to use mechanical method to disperse liquids in tiny liquid particles in another liquid. In industry, this method is used to prepare emulsion. The other is to dissolve the liquid in molecular liquid in another liquid and then gather it properly to form emulsion.

The stability of emulsion refers to the ability to resist phase separation due to aggregation of particles. The emulsion is thermodynamically unstable and has larger free energy. Therefore, the stability of the emulsion is actually the time required for the system to reach equilibrium state, that is, the time required for separation of a liquid in the system.

The membrane strength increased significantly when polar organic molecules such as aliphatic alcohols, fatty acids and aliphatic amines were found in the interfacial film. This is because the interaction between the emulsifier molecules and the polar molecules such as alcohols, acids and amines forms the "complex" in the interfacial adsorption layer, resulting in the increase of the strength of the interfacial film.

An emulsifier consisting of more than two surfactants is called a mixed emulsifier. The mixed emulsifier adsorbed on the water / oil interface and interacted with each other to form a complex. Because of the strong interaction between molecules, the interfacial tension decreased significantly. The amount of emulsifier adsorbed on the interface increased significantly, and the density of the interfacial film increased and the strength increased.

The charge of liquid bead has obvious effect on the stability of emulsion. A stable emulsion is generally charged with liquid beads. When an ionic emulsifier is used, the emulsifier adsorbed on the interface is attached to the oil phase by its lipophilic group, and the hydrophilic base is in the aqueous phase, thereby causing the liquid beads to be charged. Because the liquid beads of the emulsion have the same charge, they repel each other and are not easy to coalescence, so that the stability is increased. It can be seen that the more ions adsorbed on the liquid beads, the greater the charged capacity, and the greater the ability to prevent liquid beads from coalescence. The more stable the emulsion system is.

The viscosity of emulsion dispersion medium has certain effect on the stability of emulsion. Generally, the greater the viscosity of the dispersed medium is, the higher the stability of the emulsion is. This is because the viscosity of the dispersion medium is large, which hinders the Brown movement of the liquid beads, slows the collision between the beads and keeps the system stable. Generally, polymer materials which can be dissolved in emulsion can increase the viscosity of the system and increase the stability of the emulsion. In addition, polymer can also form a strong interfacial film to make emulsion system more stable.

In some cases, the addition of solid powder does not stabilize the emulsion. Solid powder is not in water, oil or interface. It depends on the wetting ability of oil and water to solid powder. If solid powder is not completely wetted by water, and can be wetted by oil, it will remain on the water oil interface.

The reason why the solid powder does not stabilize the emulsion is that the powder gathered at the interface does not enhance the interfacial film, which is similar to that of the interfacial adsorption emulsifier molecule. Therefore, the solid particles are arranged more tightly on the interface, and the emulsion is more stable.

The formation of micelles in aqueous solutions has the ability to increase solubility of insoluble or slightly soluble organic compounds, and the solution is transparent at this time, and micelles are called solubilization. The solubilizing agent that can produce solubilization is called solubilizing agent, and the solubilized organic matter is called solubilized substance.

8, bubble

Foam plays an important role in the washing process. Foam refers to the dispersing system of gas dispersed in liquid or solid. The gas is dispersed phase, liquid or solid as dispersing medium, the former is called liquid foam, and the latter is called solid foam, such as foam plastic, foam glass, foam cement, etc.

(1) formation of bubbles

The foam we refer to here refers to the aggregates of bubbles separated by liquid membranes. Because of the large difference in density between dispersed phase (gas) and dispersed medium (liquid) and the low viscosity of the liquid, the bubble can always rise rapidly to the liquid level.

The process of forming a bubble is to bring a large amount of gas into the liquid, and the bubbles in the liquid will soon return to the liquid surface, forming a bubble cluster separated by a small amount of liquid gas.

Foam has two distinct characteristics in morphology: one is that the bubble as a dispersed phase is usually polyhedron. This is because at the intersection of bubbles, a thin film tends to make the bubbles become polyhedra. When the liquid film thins to a certain extent, the bubbles break up. Secondly, pure liquid can not form stable foam, and can form a foam liquid, at least more than two components. The aqueous solution of surfactant is a typical foam prone system, and its ability to generate foam is also related to other properties.

Surfactant with good foaming power is called foaming agent. Although foaming agent has good foam capacity, the foam formed may not be able to maintain a longer time, that is, its stability is not necessarily good. In order to maintain the stability of foam, the foam stabilizer is added to the foaming agent. This substance is called foam stabilizer. The commonly used stabilizer is lauryl two ethanolamine and twelve alkyl two methyl amine oxide.

(2) foam stability

Foam is a thermodynamically unstable system. The final trend is that the total surface area of the system decreases and the free energy decreases after the bubble breaking. The defoaming process is the process of separating the thin film of gas from thinning until it breaks. Therefore, the stability of foam is mainly determined by the speed of liquid drainage and the strength of liquid film. The influencing factors are as follows.

Surface tension

From the point of view of energy, low surface tension is beneficial to the formation of foam, but it can not guarantee bubble stability. The surface tension is low, the pressure difference is small, the drainage speed is slower, the liquid film thinning is slower, which is conducive to the stability of the foam.

Surface viscosity

The key factor determining the stability of foam is the strength of liquid film. The strength of liquid film is mainly determined by the firmness of the surface adsorption film, and the surface viscosity is taken as its measurement. Experiments show that the foam formed by the solution with larger surface viscosity has a longer life. This is because the interaction between molecules on the surface leads to the increase of membrane strength, thereby enhancing the life of the foam.

Solution viscosity

When the viscosity of the liquid increases, the liquid in the liquid film is not easy to discharge, and the thickness of the liquid film becomes thinner. It slows down the time of the breakup of the liquid film and increases the stability of the foam.

Fourth, the role of surface tension in "restoration".

The surfactant adsorbed on the surface of the liquid membrane has the ability to resist the expansion or contraction of the surface of the liquid membrane. We call this capability a repair function. This is because there is a liquid membrane adsorbed on the surface by surfactant. The surface area of the liquid film will be expanded to reduce the concentration of the surface adsorption molecules and increase the surface tension. Further expansion of the surface will require greater efforts. Conversely, surface area shrinkage will increase the concentration of surface adsorption molecules, that is, reducing surface tension, which is not conducive to further shrinkage.

Diffusion of gas through liquid membrane

Due to the presence of capillary pressure, the pressure of foam bubbles is higher than that of bullae, which causes the gas in the vesicles to diffuse through the liquid membrane to the low pressure bullae, resulting in smaller vesicles, larger bubbles and eventually bubble rupture. If the surfactant is added, foaming can make the foam even and dense, and it is not easy to defoaming. Because the surfactant is tightly arranged on the liquid membrane, the air permeability is difficult, and the foam is more stable.

Surface charge effects

If the foam liquid film has the same symbol charge, the two surfaces of the liquid membrane will repel each other, preventing the liquid film from thinning or even damaging. Ionic surfactant can play a stabilizing role.

In summary, the strength of liquid film is the key factor to determine the stability of foam. As a surfactant for foaming agents and foamers, the tightness and firmness of the molecules on their surfaces are the most important factors. When the surface adsorption molecules interact strongly, the adsorbent molecules have a tight array structure, which not only makes the surface film itself have higher strength, but also makes the solution of the adjacent surface film difficult to flow because of the high surface viscosity. The liquid membrane is relatively difficult to discharge liquid, and the thickness of the liquid film is easy to maintain. In addition, the tight surface molecules can also reduce the permeability of gas molecules and increase the stability of foam.

(3) bubble damage

The basic principle of destroying bubbles is to change the conditions for producing bubbles or eliminate the stabilizing factors of bubbles. Therefore, there are two ways of defoaming, physical and chemical.

Physical defoaming is to change the conditions of foam production when the chemical composition of the foam solution remains unchanged, such as external force disturbance, temperature or pressure changes and ultrasonic treatment are effective physical methods to eliminate foam.

The chemical defoaming method is the addition of some substances and foaming agents to reduce the strength of the liquid film in the foam, thereby reducing the stability of the foam to achieve the purpose of defoaming. This substance is called defoamer. Defoaming agents are mostly surfactants. Therefore, according to the mechanism of defoaming, defoamer should have strong ability to reduce surface tension, easy to adsorb on the surface, and the adsorption of molecules on the surface is weak, and the adsorption molecules have a loose structure.

There are many kinds of defoamer, but basically they are non-ionic surfactants. Nonionic surfactants have antifoaming properties near their cloud point or above cloud point. They are commonly used as defoamer. Alcohols, especially branched alcohols, fatty acids and fatty acids, polyamides, phosphate and silicone oil, are also commonly used good defoamer.

(4) foam and washing

There is no direct relationship between foam and washing effect. The amount of foam does not mean the quality of washing. For example, the foaming performance of nonionic surfactants is far less than that of soap, but its detergency is much better than that of soap.

In some cases, foaming is helpful in removing dirt. For example, when the household washing dishes, the foam of the washing liquid can take away the washed oil drops. When cleaning the carpet, the foam helps to take away the dirt and other solid dirt. In addition, the foam can sometimes be a sign of the effectiveness of the washing liquid, because fatty oil has an inhibitory effect on the foam of the washing liquid. When there is too much oil and a small amount of detergent, there will be no foam formation or the original foam will disappear. Foam can also be used as an indicator of rinsing cleanliness, because the amount of foam in rinsing fluid often decreases with the decrease of detergent content, so the amount of foam can be used to evaluate the degree of rinsing.

9. Washing process

Broadly speaking, washing is the process of removing unnecessary ingredients and achieving some purpose from the object being washed. Washing in general sense refers to the process of removing dirt from the surface of the carrier. During washing, through the action of some chemicals (such as detergents), the interaction between dirt and carrier can be weakened or eliminated, and the combination of fouling and carriers can be changed into a combination of dirt and detergent. Eventually, dirt and carriers can be separated. Because washing objects and dirt to be removed are various, washing is a very complicated process. The basic process of washing can be expressed as follows.

Carrier + dirt + detergent = carrier + dirt - detergent.

The washing process can usually be divided into two stages: one is the separation of dirt from its carrier under the action of detergent; the two is that the dirt separated is dispersed and suspended in the medium. The washing process is a reversible process, and the dirt dispersed and suspended in the medium may also be re precipitated from the medium to the washed object. Therefore, in addition to having the ability to remove dirt from the carrier, a good detergent should also have better dispersion and suspended fouling, and prevent dirt from re depositing.

(1) types of dirt

Even if the same thing is used, if the environment is different, the type, composition and quantity of the dirt will be different. The oil dirt is mainly some animal and vegetable oils and mineral oils (such as crude oil, fuel oil, coal tar, etc.). The solid fouling is mainly dust, ash, rust, carbon black and so on. As for the dirt of clothes, there are dirt from human body, such as sweat, sebum, blood and so on. Dirt from food, such as fruit stains, edible oil stains, seasoning stains, starch, etc., has dirt from cosmetics, such as lipstick, nail polish and so on. Dirt from the atmosphere, such as smoke, dust, dirt, etc., and other ink, tea, paint and so on. It can be said that there are many kinds.

All kinds of dirt can be divided into three categories: solid dirt, liquid dirt and special dirt.

(1) solid fouling commonly occurs in solid dirt, such as ash, mud, soil, rust and carbon black. Most of these particles are electrically charged, and most of them are negatively charged and easily adsorbed on fiber objects. Generally, solid fouling is difficult to dissolve in water, but it can be dispersed and suspended by detergent solution. It is more difficult to remove solid particles with smaller particle size.

Liquid dirt is mostly oil soluble, including mobile vegetable oil, fatty acid, fatty alcohol, mineral oil and its oxide. Animal and vegetable oils and fatty acids can saponification with alkali, while fatty alcohols and mineral oils are not saponified by alkali, but can be dissolved in alcohols, ethers and hydrocarbon organic solvents, and are emulsified and dispersed by detergent aqueous solutions. Oil soluble liquid fouling generally has strong force with fiber objects and is firmly adsorbed on fibers.

Special dirt, special dirt, such as protein, starch, blood, human secretion, such as sweat, sebum, urine, juice, tea juice, etc. Most of these dirt can be adsorbed on fiber objects by chemical action. So washing is difficult.

All kinds of dirt rarely exist alone. They are often mixed together and adsorbed together on objects. Dirt sometimes oxidize, decompose or corrupt under the influence of the outside, resulting in new fouling.

(2) adhesion of dirt.

Clothes, hands and so on can be stained with dirt because there is some interaction between objects and dirt. There are many kinds of adhesion of dirt on objects, but there are two kinds of physical adhesion and chemical adhesion.

(1) soot, dust, sediment, carbon black and other physical adhesion on clothing. Generally speaking, the adhesion between the dirt and the contaminated object is relatively weak, and the removal of dirt is relatively easy. Depending on the force, the physical adhesion of dirt can be divided into mechanical adhesion and electrostatic adhesion.

A: mechanical adhesion to this kind of adhesion mainly refers to the adhesion of some solid dirt (such as dust and silt). Mechanical adhesion is a relatively weak form of adhesion. It can remove dirt almost by mechanical means. However, when the particle size of dirt is relatively small (< 0.1um), it is difficult to remove it.

B: the electrostatic force adhesion is mainly manifested by the role of charged dirt particles on oppositely charged objects. Most fibrous substances are negatively charged in water and are easily adhered to some positively charged dirt such as lime. Some dirt, though negatively charged, such as carbon black particles in aqueous solution, can be attached to fibers by ion bridges formed by positive ions (such as Ca2+, Mg2+, etc.) in water.

Electrostatic action is stronger than simple mechanical action, so dirt removal is more difficult.

Chemical adhesion

Chemical adhesion refers to the phenomenon of dirt acting on a substance through chemical bonds or hydrogen bonds. Such as polar solid fouling, protein, rust and so on the adhesion of fiber objects, fiber contains carboxyl, hydroxyl, amide and other groups, these groups and oil dirt fatty acids, fatty alcohols easy to form hydrogen bonds. Chemical force is generally strong, so dirt on the object is firmly combined. This kind of dirt is difficult to remove in the usual way and needs special treatment.

The firmness of dirt adhesion is related to the nature of the dirt itself and the nature of the adhesive. General particles tend to adhere to fibrous substances. The smaller the solid particle size is, the stronger adhesion is. The polar dirt on the surface of hydrophilic objects such as cotton and glass should be more firm than non polar dirt. The adhesion strength of non-polar dirt is greater than polar dirt such as polar fat, dust, clay, and so on, and it is not easy to remove and clean.

(3) mechanism of fouling removal

The purpose of washing is to remove dirt. In a certain temperature medium (mainly water as a medium). By using various physical and chemical actions produced by detergents, we can weaken or eliminate the action of dirt and washing objects. Under certain mechanical forces (such as hand rubbing, washing machine agitation, water impact), dirt and washing products are separated from each other so as to achieve the purpose of decontamination.

Removal mechanism of liquid fouling

A: wetting liquid dirt is mostly oily dirt. Oil pollution can moisten most of the fiber items and spread to a layer of oil film on the surface of fiber material. The first step of washing is to moisten the surface with washing liquid. In order to explain the convenience, the surface of the fiber can be regarded as a smooth solid surface.

B: the separation of oil pollution - the second step of scrubbing mechanism is the removal of oil. The removal of liquid fouling is achieved in a way of curling. The liquid fouling is formed on the surface in the form of a spreading oil film, and is gradually curled into oil beads on the solid surface (i.e., the surface of the fiber) under the preferential wetting effect of the washing liquid. The liquid is replaced by the washing liquid, and finally leaves the surface under certain external forces.

Removal mechanism of solid fouling

The removal of liquid fouling is mainly through the priority wetting of scrubbing liquid to fouling carriers, and the removal mechanism of solid fouling is different. During washing process, the washing liquid mainly deals with wetting of dirt particles and their carrier surfaces. Because of the adsorption of surfactants on the surface of solid fouling and its carrier, the interaction between dirt and the surface is reduced, and the adhesion strength of dirt particles on the surface is reduced. Therefore, dirt particles are easily removed from the surface of the carrier.

Moreover, the adsorption of surfactants, especially ionic surfactants on the surface of solid fouling and their carriers, may increase the surface potential of solid fouling and its carriers, and is more conducive to the removal of fouling. The surface of solid or general fibers is usually negatively charged in water medium, so diffusion double layer can be formed on the surface of dirt or solid. Because isotropic charges repel each other, the adhesion strength of dirt particles on the solid surface will be weakened. When anionic surfactants are added, because the anionic surfactants can simultaneously enhance the negative surface potential of the fouling particles and the solid surface, the repulsive force between them will be enhanced. Therefore, the adhesion strength of the particles will be reduced and the dirt will be removed easily.

Nonionic surfactants can adsorb on the surface of a generally charged solid surface. Although the interfacial potential can not be significantly changed, the adsorbed non-ionic surfactant often forms a certain thickness of adsorbed layer on the surface, which helps to prevent fouling from re depositing.

For cationic surfactants, because of their adsorption, the negative surface potential of the fouling particles and their carriers will be reduced or eliminated, which will reduce the repulsion between the fouling and the surface. Therefore, it is not conducive to the removal of fouling. Moreover, when the cationic surfactant is adsorbed on the solid surface, the surface of the solid will become hydrophobic, which is not conducive to the wetting of the surface, and is also not conducive to washing.

Removal of special dirt

Such dirt as protein, starch, human secretion, juice and tea juice are difficult to be removed by ordinary surfactants, and special treatment methods are needed.

Protein stains, such as cream, eggs, blood, milk, skin excrement and so on, are easily coagulated and denatured on fiber, and adhesion is firm. For protein fouling, protease can be used to remove it. Protease can decompose the protein in the fouling into water-soluble amino acids or oligopeptides.

Starch fouling mainly comes from food, others such as gravy and paste. Amylase can catalyze the hydrolysis of starch dirt and break starch into sugars.

Lipase catalyzes the decomposition of three fatty acids, glycerides, which are difficult to remove by ordinary methods, such as sebum and edible oils, which make the three fatty acids glycerides break down into soluble glycerides and fatty acids.

Some stains, such as juice, tea juice, ink, lipstick and so on, are often difficult to wash thoroughly even after repeated washing. Such stains can be oxidated or reduced by oxidizing agents or reducing agents such as bleaching powder, which destroy the structure of chromophore or chromophore group and degrade it into smaller water-soluble components.

(4) decontamination mechanism of dry cleaning

The above is actually aimed at washing with water as the medium. In fact, because of the different types and structures of clothing, some clothes are not easy to wash or wash easily after washing. Some clothes are washed and even deformed and fade. For example, most natural fibers absorb water easily and then shrink easily after drying, so they will be deformed after washing. The wool products washed by water often shrink. Some wool fabrics are easy to pilling and color out after washing with water. Some silk washes with poor feeling and luster. These clothes are often cleaned by dry cleaning. Dry cleaning is generally referred to as washing in organic solvents, especially in non-polar solvents.

Dry cleaning is a relatively mild way of washing with respect to water washing. Because dry cleaning does not require too much mechanical action, it does not cause damage, wrinkle or deformation to the clothes. At the same time, dry cleaners do not produce expansion and shrinkage as water does. As long as the technology is properly handled, it can make the clothes dry cleaned without deformation, fading and prolonging the service life.

In terms of dry cleaning, there are basically three kinds of dirt.

1. The soluble dirt of oil soluble oil includes all kinds of oils and fats. It is liquid or greasy and can be dissolved in dry cleaning solvents.

Water soluble dirt can be dissolved in aqueous solution, but it is insoluble in dry cleaning agent. It is adsorbed on clothes by aqueous solution. After water volatilization, granular solids are precipitated, such as inorganic salts, starch and protein.

Oil and water insoluble dirt, oil and water insoluble dirt are neither soluble in water nor insoluble in dry cleaning solvents, such as carbon black, silicate and oxides of various metals, etc.

Because of the different nature of dirt, there are different ways of removing dirt in the process of dry cleaning. Oil soluble dirt, such as mobile vegetable oil, mineral oil and grease, is easy to dissolve in organic solvents and is easier to remove in dry cleaning. The excellent solvability of dry cleaning solvents to oil and grease essentially comes from the intermolecular Fan Dehua force.

For the removal of water-soluble dirt, such as inorganic salts, carbohydrates, protein and sweat, it is necessary to add proper amount of water to the dry cleaning agent, otherwise the water soluble dirt can not be removed from the clothes. However, water is more difficult to dissolve in dry cleaners, so to increase the amount of water, it is necessary to add surfactants. The presence of water in the dry cleaning agent can hydrate the surface of dirt and clothing, thus easily interact with the polar groups of surfactants, and facilitate the adsorption of surfactants on the surface. In addition, when the surfactants form micelles, water-soluble fouling and water can be solubilized into micelles. Surfactant can not only increase the content of water in dry cleaning solvents, but also prevent dirt from re depositing, so as to enhance the decontamination effect.

A small amount of water is necessary to remove water-soluble dirt, but excessive water can cause some clothes to be deformed and wrinkled. Therefore, the content of water in dry lotion must be moderate.

Neither the water soluble nor the oil soluble dirt, such as ash, mud, soil and carbon black, is usually adhered to the clothing by electrostatic adsorption or oil contamination. In dry cleaning, the flow and impact of solvents can remove the dirt that is adsorbed by electrostatic forces. The dry cleaning agent can dissolve the oil pollution, so that the solid particles that are attached to the clothes and the solid particles that are attached to the clothes will fall off in the dry cleaning agent. A small amount of water and surfactant in the dry cleaning agent will make the solid particles that fall off can be suspended and dispersed in a stable way so as to prevent them from depositing on the clothes again.

(5) factors affecting washing effect

The directional adsorption of surfactant on the interface and the decrease of surface (interfacial) tension are the main factors for the removal of liquid or solid fouling. But the washing process is more complicated, even though the washing effect of the same type of detergent is also affected by many other factors. These factors include the concentration of detergent, temperature, the nature of fouling, the type of fiber, and the fabric structure.

Concentration of surfactant

Micelles of surfactant in solution play an important role in washing process. When the concentration reached critical micelle concentration (CMC), the washing effect increased sharply. Therefore, the concentration of detergents in solvents should be higher than cmc value, so that good washing effect can be achieved. However, when the concentration of surfactants is higher than CMC, the effect of washing is not obvious. It is unnecessary to increase the concentration of surfactants too much.

With the increase of surfactant concentration, the solubilization increased with increasing concentration of CMC. At this point, it is advisable to use detergent locally. For example, there are more dirt on the cuffs and collar of clothes. When washing, we can first apply a layer of detergent to improve the solubilization effect of surfactants on oil.

Temperature has an important effect on detergency. Generally speaking, raising temperature is good for removing dirt, but sometimes the temperature is too high.

The increase of temperature is conducive to the diffusion of fouling. Solid oil stain is easy to emulsify at higher temperature than melting point, and the fiber also increases the degree of expansion due to the increase of temperature. All these factors are conducive to the removal of dirt. But for compact fabrics, the micro gap between fibers is reduced, which is unfavorable to the removal of dirt.

Temperature changes also affect the solubility, CMC and micelle size of surfactants, thus affecting the washing effect. When the surface temperature of the long carbon chain is low, the solubility is small, sometimes the solubility is even lower than the cmc value. At this time, the washing temperature should be increased appropriately. The effect of temperature on the CMC and micelle size is different for ionic and non-ionic surfactants. For ionic surfactants, the increase of CMC generally increases with the increase of temperature, while the micelle content decreases. This means that the concentration of surfactants should be increased in the washing solution. For non-ionic surfactants, the increase in temperature leads to a decrease in CMC and a significant increase in micelle content. It is suggested that increasing the temperature will help non-ionic surfactants exert their surface activities. But the temperature should not exceed its cloud point.

In short, the most suitable washing temperature is related to the formula of detergent and the object of washing. Some detergents have good washing effect at room temperature, while some detergents are quite different from cold washing and hot washing.

Foam

It is customary to confuse foaming power with washing effect. It is believed that the detergent with strong foaming power has good washing effect. The results show that washing effect is not directly related to the number of bubbles. For example, washing with low foaming detergents is not as effective as high foaming detergents.

Although foam is not directly related to washing, foam can help remove dirt on certain occasions. For example, when washing dishes with hands, the foam of washing liquid can carry away the washed oil drops. When cleaning the carpet, the foam can also take away the solid dirt particles such as dust. The dust in the carpet dirt takes up a large proportion, so the carpet cleaning agent should have a certain foaming ability.

Foaming power is also important for shampoo. When the shampoo or bathing is done, the liquid foam will make people feel comfortable and comfortable.

4. Fiber varieties and physical properties of textiles

In addition to the chemical structure of fibers affecting the adhesion and removal of dirt, the appearance of fibers and the structure of yarns and fabrics affect the removal of dirt.

The flattened banded structure of wool fibers and cotton fibers is easier to accumulate dirt than smooth fibers. For example, carbon black on cellulose membrane is easy to remove, and carbon black on cotton fabric is difficult to elute. For example, polyester staple fabric is easier to accumulate oil stains than long fiber fabrics, and oil on staple fabric is also harder to remove than oil on long fiber fabrics.

Tightly twisted yarns and tightly knitted fabrics, because of the small gap between fibers, can resist fouling invasion, but they also prevent the washing liquid from removing internal dirt. Therefore, the fabric has good antifouling properties at the beginning, but it is also difficult to stain and wash.

Hardness of water

The concentration of metal ions such as Ca2+ and Mg2+ in the water has great influence on the washing effect. Especially, the solubility of calcium and magnesium salts formed by Ca2+ and Mg2+ ions in anionic surfactants is poor, which will reduce its decontamination ability. In hard water, even if the concentration of surfactants is high, the detergency effect is still much worse than that in distillation. For the best washing effect of surfactants, the concentration of Ca2+ ions in water should be reduced to 1 x 10-6mol/L (CaCO3 to 0.1mg/L). This requires adding various softeners to detergents.