9 relationships between surfactants and dyeing plants

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

Properties that reduce the surface tension of a solvent are called surface active, and substances that have surface activity are called surface active substances.

The surfactant is a surfactant that can be associated with molecules in aqueous solution and form micelles and other associated bodies, and has high surface activity, and also has wetting, emulsifying, foaming, washing and other functions.

Surfactant is a kind of organic compound with special structure and properties, they can significantly change the interfacial tension between two phases or the surface tension of liquid (generally water), with wetting, foaming, emulsification, washing and other properties.

In terms of structure, surfactants have a common feature, that is, their molecules contain two groups of different properties, one end is a long chain non-polar group, soluble in oil and insoluble in water, that is, the so-called hydrophobic group or hydrophobic base, this hydrophobic base is generally a long chain of hydrocarbons, and sometimes for organofluorine, organosilicon, organophosphorus, organotin chain, etc. At the other end are water-soluble groups, that is, hydrophilic groups or hydrophilic groups. The hydrophilic group must have sufficient hydrophilicity to ensure that the entire surfactant is soluble in water and has the necessary solubility. Because surfactants contain hydrophilic and hydrophobic groups, they are soluble in at least one phase of the liquid phase. This both hydrophilic and lipophilic property of surfactants is called amphiphilic.

Surfactants are amphiphilic molecules with both hydrophobic and hydrophilic groups. Hydrophobic groups of surfactants are generally composed of long chain hydrocarbons, such as straight chain alkyl C8 ~ C20, branched alkyl C8 ~ C20, alkyl phenyl (alkyl carbon atomic number of 8 ~ 16) and so on. The difference between hydrophobic groups is mainly in the structure of the hydrocarbon chain, the difference is small, and the types of hydrophilic groups are more, so the properties of surfactants in addition to the size and shape of the hydrophobic groups, mainly related to the hydrophilic groups. The structure change of hydrophilic groups is larger than that of hydrophobic groups, so the classification of surfactants is generally based on the structure of hydrophilic groups. This classification is based on whether the hydrophilic group is ionic, and it is divided into anionic, cationic, non-ionic, zwitterionic and other special types of surfactants.

① Adsorption of surfactants on the interface

The surfactant molecule has an oil - and hydrophilic group and is an amphiphilic molecule. Water is a strong polar liquid, when the surfactant dissolves in water, according to the principle of similar polarity, polarity repulsion, its hydrophilic group and water and soluble in water, the oil-philic group and water repulsion and leave water, the result is that the surfactant molecule (or ion) adsorbed on the two-phase interface, so that the interfacial tension between the two phases is reduced. The more surfactant molecules (or ions) adsorbed on the interface, the greater the reduction in interfacial tension.

② Some properties of adsorption film

The surface pressure of the adsorption film: the surfactant is adsorbed at the gas-liquid interface to form an adsorption film, such as the frictionless floating sheet placed on the interface to push the adsorption mass film along the solution surface, and the film produces a pressure on the floating sheet, which is called the surface pressure.

Surface viscosity: Like surface pressure, surface viscosity is a property exhibited by insoluble molecular films. The white gold ring is suspended by a thin wire, so that its plane contacts the water surface of the sink, rotating the white gold ring, the white gold ring is hindered by the viscosity of the water, the amplitude gradually attenuates, according to which the surface viscosity can be measured, the method is: first on the surface of pure water, the amplitude attenuation is measured, and then the attenuation after the formation of the surface film is determined from the difference between the two.

The surface viscosity is closely related to the firmness of the surface film, because the adsorption film has surface pressure and viscosity, it must be elastic. The greater the surface pressure, the higher the viscosity and the greater the elastic modulus of the adsorbed film. The elastic modulus of surface adsorbed film plays an important role in bubble stabilization.

③ Formation of micelles

Dilute solutions of surfactants obey the laws followed by ideal solutions. The adsorption amount of surfactant on the surface of the solution increases with the increase of the concentration of the solution, when the concentration reaches or exceeds a certain value, the adsorption amount does not increase, and these excessive surfactant molecules are chaotic in the solution, or exist in a regular way. Both practice and theory show that they form an association in solution, which is called micelle.

Critical micelle concentration: The lowest concentration at which a surfactant can form micelles in a solution is called the critical micelle concentration.

④cmc values of common surfactants.

HLB is the abbreviation of hydrophile lipophile balance, which indicates the hydrophilic and lipophile balance value of the surfactant, that is, the HLB value of the surfactant. High HLB value indicates strong hydrophilicity and weak lipophilicity. On the contrary, oleophilicity is strong and hydrophilicity is weak.

① The HLB value is specified

The HLB value is a relative value, so when formulating the HLB value, as a standard, the HLB value of paraffin wax without hydrophilic energy is 0, and the HLB value of sodium dodecyl sulfate with strong water solubility is 40. Therefore, the HLB value of the surfactant is generally within the range of 1 to 40. In general, an emulsifier with an HLB of less than 10 is a lipophilic, while an emulsifier with an HLB of more than 10 is a hydrophilic. Therefore, the turning point from lipophilic to hydrophilic is about 10.

Based on the HLB values of surfactants, you can roughly understand their possible uses, as shown in Table 1-3.

Table 1-3 HLB ranges and their application performance

It can be seen from the above table that the HLB value of surfactants suitable for water-in-oil emulsifiers ranges from 3.5 to 6, while that of oil-in-water emulsifiers ranges from 8 to 18.

② Determination of HLB value (omitted).

A system of two insoluble liquids, one consisting of particles (droplets or liquid crystals) dispersed in the other, is called emulsion. Due to the increase of the boundary area between the two liquids, the system is thermodynamically unstable. In order to stabilize the emulsion, the third component, emulsifier, needs to be added to reduce the interfacial energy of the system. Emulsifier belongs to the surfactant, its main function is to milk. The proportion in the emulsion with the presence of droplets is the dispersed phase (or internal phase, discontinuous phase), and the other phase connected into a piece is called the dispersing medium (or external phase, continuous phase).

①Emulsifiers and emulsions

Common emulsion, one phase is water or aqueous solution, the other phase is not miscible with water organic matter, such as grease, wax and so on. The emulsion formed by water and oil can be divided into two types according to its dispersion: the oil is dispersed in water to form an oil-in-water emulsion, which is expressed by O/W (oil/water) : The oil-in-water emulsion is formed in water dispersed oil, and is expressed by W/O (water/oil). In addition, complex water-in-oil W/O/W type and oil-in-water O/W/O type multi-emulsion may be formed.

The emulsifier stabilizes the emulsion by reducing the interfacial tension and forming a single molecular interfacial film.

The emulsifier requirements in the emulsification: a: the emulsifier must be able to adsorb or concentrate on the interface of the two phases, so that the interfacial tension is reduced; b: The emulsifier must give the particles an electric charge, cause electrostatic repulsion between the particles, or form a stable protective film around the particles with a particularly high viscosity. Therefore, the substances used as emulsifiers must have amphiphilic groups in order to emulsify, and surfactants can meet this requirement.

 ②Preparation method of emulsion and factors affecting the stability of emulsion

There are two methods to prepare the emulsion: one is to use the mechanical method to disperse the liquid in a small particle in another liquid, and the industry uses this method to prepare the emulsion; The other is to dissolve the liquid in a molecular state in another liquid, and then allow it to gather properly to form an emulsion.

The stability of the emulsion refers to the ability to resist particle aggregation resulting in phase separation. Emulsions are thermodynamically unstable systems with large free energies. Therefore, the so-called stability of the emulsion actually refers to the time required for the system to reach an equilibrium state, that is, the time required for a liquid in the system to separate.

When there are fatty alcohols, fatty acids, fatty amines and other polar organic molecules in the interfacial membrane, the membrane strength increases significantly. This is because the emulsifier molecules in the interface adsorption layer interact with polar molecules such as alcohols, acids and amines to form "complexes", which increases the strength of the interface film.

An emulsifier consisting of more than two surfactants is called a mixed emulsifier. The mixed emulsifier is adsorbed on the water/oil interface, and the intermolecular interaction can form a complex. Due to the strong intermolecular interaction, the interfacial tension decreased significantly, the adsorption amount of emulsifier increased significantly, and the density and strength of the formed interfacial film increased.

The charge of liquid bead has obvious influence on the stability of emulsion. A stable emulsion, the beads of which are generally charged. When ionic emulsifiers are used, the emulsifier ions adsorbed on the interface have an oleophilic group inserted into the oil phase, and the hydrophilic group is in the water phase, thus charging the liquid bead. Because the liquid beads of the emulsion carry the same charge, they repel each other and are not easy to coalesce, which increases the stability. It can be seen that the more emulsifier ions adsorbed on the liquid beads, the greater the charge, the greater the ability to prevent the agglomeration of liquid beads, and the more stable the milky liquid system.

The viscosity of dispersing medium has a certain influence on the stability of emulsion. In general, the greater the viscosity of the dispersing medium, the higher the stability of the emulsion. This is because the viscosity of the dispersion medium is large, and the Brownian motion of the liquid beads is strongly hindered, which slows down the collision between the liquid beads and keeps the system stable. Usually soluble in the emulsion of polymer substances can increase the viscosity of the system, so that the stability of the emulsion increased. In addition, the polymer can form a strong interfacial film, making the milky liquid system more stable.

In some cases, the addition of solid powder can stabilize the emulsion. The solid powder is not in water, oil or the interface, depending on the wetting ability of the oil and water to the solid powder, if the solid powder is not completely moistened by water, and can be moistened by oil, it will be retained 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 strengthen the interface film, which is similar to the interface adsorption of emulsifier molecules, so the more closely the solid powder is arranged on the interface, the more stable the emulsion.

After forming micelles in aqueous solution, surfactants have the ability to significantly increase the solubility of insoluble or slightly soluble organic matter, and at this time the solution is transparent, and this effect of micelles is called solubilization. The surfactant that can produce solubilization is called solubilizer, and the organic matter that is solubilized is called solubilized matter.

Foam plays an important role in the washing process. Foam refers to the dispersion system in which the gas is dispersed in liquid or solid, the gas is the dispersing phase, the liquid or solid is the 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) Foam formation

By foam we mean an aggregate of bubbles separated by a film of liquid. Due to the large density difference between the dispersed phase (gas) and the dispersing medium (liquid), and the low viscosity of the liquid, the bubble can always rise quickly to the liquid level.

The process of forming foam is to bring a large amount of gas into the liquid, and the bubbles in the liquid return to the liquid surface quickly, forming a bubble aggregate separated by a small amount of liquid gas

The foam has two remarkable characteristics in morphology: First, the bubble as a dispersed phase is often polyhedral in shape, because at the intersection of the bubble, there is a tendency of liquid film thinning to make the bubble become polyhedron, when the liquid film thinning to a certain extent, it will lead to bubble rupture; The second is that the pure liquid cannot form a stable foam, and the liquid that can form a foam is at least two or more components. The aqueous solution of surfactant is a typical system prone to foam formation, and its ability to foam formation is also related to other properties.

Surfactants with good foaming power are called foaming agents. Although the foaming agent has good foaming ability, the foam formed may not be able to maintain for a long time, that is, its stability may not be good. In order to maintain the stability of the foam, a substance that can increase the stability of the foam is often added to the foaming agent, which is called a foam stabilizer, and the commonly used foam stabilizer is the oxide of lauryl diethanolamine and dodecyl dimethylamine.

(2) Foam stability

Foam is a thermodynamically unstable system, and the final tendency is that the total surface area of the liquid in the system decreases and the free energy decreases after the bubble bursting. The defoaming process is the process of the liquid film separating the gas from the thick to the thin until the rupture. Therefore, the stability of the foam is mainly determined by the speed of liquid discharge and the strength of the liquid film. The influencing factors are as follows.

(3) Foam breaking

The basic principle of destroying the foam is to change the conditions of the foam or eliminate the stability of the foam, so there are two kinds of physical and chemical defoaming methods.

Physical defoaming is to change the conditions of foam generation while maintaining the chemical composition of the foam solution, such as external disturbance, temperature or pressure change and ultrasonic treatment are effective physical methods to eliminate foam.

Chemical defoaming method is to add some substances to interact with the foaming agent to reduce the strength of the liquid film in the foam and then reduce the stability of the foam to achieve the purpose of defoaming, such substances are called defoaming agents. Most of the antifoaming agents are surfactants. Therefore, according to the mechanism of defoaming, the defoaming agent should have a strong ability to reduce the surface tension, and it is easy to adsorb on the surface, and the interaction between surface adsorbed molecules is weak, and the arrangement structure of adsorbed molecules is loose.

There are many kinds of defoamer, but basically they are non-ionic surfactants. Nonionic surfactants have anti-foam properties near or above their turbidity points and are commonly used as defoamer. Alcohols, especially branching alcohols, fatty acids and fatty acid esters, polyamides, phosphate esters, silicone oils, etc., are also commonly used as excellent defoamer.

(4) Foam and washing

There is no direct relationship between foam and washing effect, and the amount of foam does not mean the quality of washing effect. For example, non-ionic surfactants have far less foaming properties than soap, but their detergency is much better than soap.

In some cases, foam can be helpful in removing dirt. For example, when the family washes the tableware, the foam of the washing liquid can take away the oil droplets that are washed down; When scrubbing the carpet, the foam helps to remove solid dirt such as dust and powder. In addition, the foam can sometimes be used as a sign of whether the washing liquid is effective, because the fatty oil has an inhibitory effect on the foam of the washing liquid, when the oil is too much and the washing dose is small, there will be no foam generation, or the original foam will disappear. Foam can sometimes be used as an indicator of whether the rinse is clean, because the amount of foam in the rinse solution is often reduced with the reduction of the detergent content, so the amount of foam can be evaluated to evaluate the degree of rinsing.

In a broad sense, washing is the process of removing unwanted components from the object being washed and achieving some purpose. Washing usually refers to the process of removing dirt from the surface of the carrier. During washing, the interaction between dirt and carrier is weakened or eliminated through the action of some chemicals (such as detergent, etc.), so that the combination of dirt and carrier is transformed into the combination of dirt and detergent, and finally the dirt and carrier are separated, because the object to be washed and the dirt to be removed is diverse, so washing is a very complex process. The basic process of washing can be represented by the following simple relationship

    Carrier • Dirt + detergent = carrier + dirt • detergent

The washing process can usually be divided into two stages: first, under the action of detergent, the dirt is separated from its carrier; Second, the detached dirt 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 re-precipitate from the medium to the wash. Therefore, in addition to the ability to make dirt out of the carrier, an excellent detergent should also have a better ability to disperse and suspend dirt and prevent dirt redeposition.

(1) Types of dirt

Even if it is the same item, if the use environment is different, the type, composition and amount of dirt will be different. Oil body dirt is mainly some mobile, vegetable oil and mineral oil (such as crude oil, fuel oil, coal tar, etc.), solid dirt is mainly smoke, gray soil, rust, carbon black and so on. As far as the dirt of clothes is concerned, there is dirt from the human body, such as sweat, sebum, blood, etc.; Dirt from food, such as fruit stains, edible oil stains, condiment stains, starch, etc.; Dirt from cosmetics, such as lipstick, nail polish, etc. Dirt from the atmosphere, such as smoke, dust, mud, etc.; Others such as ink, tea, paint and so on. It can be said that there are many kinds and varieties.

A variety of dirt can usually be divided into solid dirt, liquid dirt and special dirt three categories.

①Solid dirt Common solid dirt are ash, mud, earth, rust and carbon black particles. Most of these particles are charged on the surface, and most are negatively charged, which is easy to adsorb on fiber items. General solid dirt is difficult to dissolve in water, but it can be dispersed and suspended by detergent solution. Solid dirt with small particles is more difficult to remove.

②Liquid fouling Liquid fouling is mostly oil-soluble, including plant oils, fatty acids, fatty alcohols, mineral oils and their oxides. Among them, animal and plant oil and fatty acids can saponify with alkali, while fatty alcohol and mineral oil are not saponified by alkali, but can dissolve in alcohol, ether and hydrocarbon organic solvents, and are emulsified and dispersed by detergent aqueous solution. Oil-soluble liquid dirt generally has a strong force with fiber items, and the adsorption on the fiber is more firm.

③Special dirt Special dirt include protein, starch, blood, human secretions such as sweat, sebum, urine and juice, tea juice and so on. Most of these dirt can be strongly adsorbed on fiber items through chemical action. So it is more difficult to wash.

All kinds of dirt rarely exist alone, often mixed together, together adsorbed on the item. Dirt sometimes oxidizes, decomposes or corrupts under the influence of the outside world, resulting in new dirt.

(2) Adhesion of dirt

The reason why clothes, hands, etc. can be stained with dirt is because there is some interaction between the object and the dirt. There are many kinds of adhesion of dirt on objects, but there are only two kinds of physical adhesion and chemical adhesion.

① Soot, dust, sand, carbon black and other adhesive physical adhesion on the clothing. In general, through this adhesion of dirt, the effect between the dirt and the contaminated object is relatively weak, and the removal of dirt is relatively easy. According to the different forces, the physical adhesion of dirt can be divided into mechanical adhesion and electrostatic adhesion.

A: Mechanical adhesion This type of adhesion mainly refers to the adhesion of some solid dirt (such as dust, sediment). Mechanical adhesion is a relatively weak adhesion method of dirt, and the dirt can be almost removed by simple mechanical methods, but when the particle of the dirt is relatively small (<0.1um), it is more difficult to remove.

B: Electrostatic adhesion Electrostatic adhesion is mainly manifested in the action of charged dirt particles on oppositely charged objects. Most fibrous items are negatively charged in water and are easily adhered to by some positively charged dirt, such as lime. Although some dirt has a negative charge, such as carbon black particles in aqueous solution, it can be attached to the fiber through the ion bridge formed by positive ions in water (such as Ca2+, Mg2+, etc.) (ions between multiple charges of opposite sex, acting together with them, acting like a bridge).

The electrostatic action is stronger than the simple mechanical action, so the dirt removal is relatively difficult.

② Chemical adhesion

Chemical adhesion refers to the phenomenon of dirt acting on objects through chemical bonds or hydrogen bonds. Such as polar solid dirt, protein, rust and other adhesion on fiber items, fiber contains carboxyl, hydroxyl, amide and other groups, these groups and oily dirt fatty acids, fatty alcohols are easy to form hydrogen bonds. The chemical forces are generally strong, so the dirt binds more firmly to the object. This kind of dirt is difficult to remove with the usual method, and special methods are needed to deal with it.

The firmness of the adhesion of dirt is related to the nature of the dirt itself and the nature of the adhesive. General particles are easy to adhere to fibrous articles. The smaller the solid dirt particles, the stronger the adhesion. Polar dirt on the surface of hydrophilic objects such as cotton, glass, etc. adheres more firmly than non-polar dirt. The adhesion strength of non-polar dirt is larger than that of polar dirt such as polar fat, dust, clay, etc., and it is not easy to remove and clean.

(3)Fouling removal mechanism

The purpose of washing is to remove dirt. In a medium of a certain temperature (mainly water as the medium). The use of detergent produced by a variety of physical and chemical effects, weaken or eliminate the dirt and the role of the washed items, under the action of a certain mechanical force (such as hand rubbing, washing machine agitation, water impact), so that dirt and the washed items from the purpose of decontamination.

① Removal mechanism of liquid dirt

A: Wet liquid dirt is mostly oily dirt. Oil can moisten most of the fiber items, more or less spread on the surface of the fiber material into an oil film. The first step of washing is to wet the surface with the washing liquid. For ease of illustration, the surface of the fiber can be regarded as a smooth solid surface.

B: The second step of the washing action is the removal of oil, and the removal of liquid dirt is achieved in a crinkling way. Liquid dirt originally exists on the surface in the form of spread oil film, in the washing liquid on the solid surface (that is, the fiber surface) preferential wetting action, gradually rolled into oil beads, replaced by the washing liquid, and finally left the surface under the action of a certain external force.

② Removal mechanism of solid dirt

The removal of liquid dirt is mainly through the preferential wetting of the dirt carrier by washing liquid, while the removal mechanism of solid dirt is different. In the washing process, the main thing is the wetting of the dirt particle and its carrier surface by washing liquid. Due to the adsorption of surfactants on the surface of solid dirt and its carrier, the interaction between dirt and surface is reduced, and the adhesion strength of dirt particles on the surface is reduced, so dirt particles are easily removed from the carrier surface.

Not only that, the adsorption of surfactants, especially ionic surfactants, on the surface of solid dirt and its carrier may increase the surface potential of solid dirt and its carrier surface, which is more conducive to the removal of dirt. The surface of a solid or general fiber is usually negatively charged in the water medium, so a diffused double electric layer can be formed on the dirt particle or solid surface. Because the same charges repel each other, the adhesion strength of dirt particles in water on the solid surface will be weakened. When the anionic surfactant is added, because the anionic surfactant can increase the negative surface potential of the dirt particle and the solid surface at the same time, the repulsive force between them is enhanced, so the adhesion strength of the particle is reduced, and the dirt is easier to remove.

Non-ionic surfactants can produce adsorption on the general charged solid surface, although they can not significantly change the interface potential, but the adsorbed non-ionic surfactants often form a certain thickness of adsorption layer on the surface, helping to prevent dirt redeposition.

For cationic surfactants, their adsorption can reduce or eliminate the negative surface potential of the dirt particle and its carrier surface, which reduces the repulsion between the dirt and the surface, so it is not conducive to the removal of dirt. In addition, after the adsorption of cationic surfactants on the solid surface, the solid surface often becomes hydrophobic, which is not conducive to the wetting of the surface, which is not conducive to washing.

③ Special dirt removal

Protein, starch, human secretions, fruit juice, tea juice and other such dirt is difficult to remove with ordinary surfactants, and special treatment methods are required.

Protein dirt such as cream, eggs, blood, milk, and skin excrement is easy to coagulate and denature on the fiber, and the adhesion is more firm. For protein dirt, protease can be used to remove it. The proteases break down the proteins in the dirt into water-soluble amino acids or oligopeptides.

Starch dirt mainly comes from food, others such as gravy, paste, etc. Amylase has a catalytic effect on the hydrolysis of starch dirt, so that starch can be decomposed into sugars.

Lipase can catalyze the decomposition of some trifatty acid triglyceride dirt that is difficult to be removed by normal methods, such as sebum secreted by the human body, edible oil, etc., so that trifatty acid triglyceride can be decomposed into soluble glycerol and fatty acids.

Some colored stains from juice, tea juice, ink, lipstick, etc., are often difficult to clean thoroughly even after repeated washing. Such stains can be removed by oxidizing agents or reducing agents such as bleach powder to destroy the structure of color groups or color auxogroups and degrade them into smaller water-soluble components.

(4) Dry cleaning decontamination mechanism

The above is actually for the washing effect of water as the medium. In fact, due to the different types and structures of clothes, some clothes are not convenient or easy to wash clean, and some clothes are even deformed after washing, fading, etc., for example: most natural fibers absorb water easily expand, and dry and easy to shrink, so they will be deformed after washing; Wool products washed by water also often appear shrinkage phenomenon, some wool products are easy to pilling, color out of shape after washing; Some silk after washing with water feel poor, lose luster and so on. These garments are often decontaminated by dry cleaning. The so-called dry cleaning generally refers to the way of washing in organic solvents, especially in non-polar solvents.

Dry cleaning is a gentler way of washing than washing. Because dry cleaning does not require too much mechanical action, it will not cause damage, wrinkles and deformation of clothing, and dry cleaning agents are not like water, which rarely produce expansion and contraction. As long as the technology is properly handled, it can make the clothes dry clean to achieve no deformation, no fading and extend the service life and other excellent results.

From the point of view of dry cleaning, there are roughly three kinds of dirt.

Oil-soluble dirt Oil soluble dirt includes a variety of oils and greases, is liquid or greasy, soluble in dry cleaning solvents.

Water soluble dirt Soluble dirt can be dissolved in aqueous solution, but not soluble in dry cleaning agent, is adsorbed on the clothing in aqueous solution, water volatilization after precipitation granular solid, such as inorganic salt, starch, protein and so on.

Oil-water insoluble dirt oil-water insoluble dirt is neither soluble in water, nor soluble in dry cleaning solvents, such as carbon black, various metal silicates and oxides.

Due to the different nature of various dirt, there are different ways to remove dirt in the dry cleaning process. Oil-soluble dirt, such as plant oil, mineral oil and grease, is easily soluble in organic solvents and is easier to remove in dry cleaning. The excellent solubility of dry cleaning solvents to oil and grease is essentially due to the intermolecular van der Waals forces.

For the removal of water-soluble dirt such as inorganic salt, sugar, protein, sweat, etc., it is also necessary to add an appropriate amount of water to the dry cleaning agent, otherwise it is difficult to remove water-soluble dirt from the clothing. However, water is difficult to dissolve in the dry cleaning agent, so in order to increase the amount of water, it is also necessary to add surfactants. The water in the dry cleaning agent can hydrate the surface of dirt and clothing, so that it is easy to interact with the polar groups of surfactants, which is conducive to the adsorption of surfactants on the surface. In addition, when surfactants form micelles, water-soluble dirt and water can be added to the micelles. In addition to increasing the content of water in dry cleaning solvents, surfactants can also play a role in preventing dirt redeposition to enhance the decontamination effect.

The presence of a small amount of water is necessary to remove water-soluble dirt, but excessive water will cause some clothing deformation, wrinkling, etc., so the content of water in the dry cleaning agent must be moderate.

Solid particles of dirt that are neither water soluble nor oil soluble, such as ash, mud, soil and carbon black, are generally adsorbed by electrostatic force or bonded to oil. In dry cleaning, the flow and impact of the solvent can make the dirt adsorbed by electrostatic force fall off, and the dry cleaning agent can dissolve the oil, so that the solid particles combined with the oil and attached to the clothing fall off in the dry cleaning agent, a small amount of water and surfactants in the dry cleaning agent, the solid dirt particles that fall off can be stably suspended and dispersed to prevent it from being redeposited on the clothing.

(5) Factors affecting washing effect

The directional adsorption of surfactants at the interface and the reduction of surface (interfacial) tension are the main factors in the removal of liquid or solid dirt. However, the washing process is more complex, even if the washing effect of the same detergent is also affected by many other factors. These factors include the concentration of the detergent, the temperature, the nature of the dirt, the type of fiber, the structure of the fabric and so on.

① The concentration of surfactant

The micelles of surfactants in the solution play an important role in the washing process. When the concentration reaches the critical micelle concentration (cmc), the washing effect increases sharply. Therefore, the concentration of detergent in the solvent should be higher than the cmc value, in order to have a good washing effect. However, when the concentration of the surfactant is higher than the cmc value, the washing effect is not obvious, and it is unnecessary to increase the concentration of the surfactant too much.

When using solubilization to remove oil, even if the concentration is above cmc value, the solubilization effect still increases with the increase of surfactant concentration. At this time, it is appropriate to use detergent locally, for example, there is more dirt at the cuff and collar of the clothes, and a layer of detergent can be applied first when washing to improve the solubilization effect of the surfactant on the oil.

② Temperature has a very important effect on decontamination. In general, increasing the temperature is conducive to the removal of dirt, but sometimes the temperature is too high will cause adverse factors.

The increase of temperature is conducive to the diffusion of dirt, the solid oil scale is easy to be emulsified when the temperature is higher than its melting point, and the fiber also increases the swelling degree due to the increase of temperature. These factors are conducive to the removal of dirt. However, for tight fabrics, the micro-gap between fibers is reduced after fiber expansion, which is unfavorable to the removal of dirt.

Temperature changes also affect the solubility of surfactants, cmc value, micelle size, etc., thus affecting the washing effect. When the temperature of the long carbon chain surfactant is low, the solubility is small, and sometimes the solubility is even lower than the cmc value, at this time, the washing temperature should be appropriately increased. The influence of temperature on the cmc value and micelle size is different for ionic and non-ionic surfactants. For ionic surfactants, the increase of temperature can generally increase the cmc value and decrease the micelle size, which means that the surfactant concentration should be increased in the washing solution. For non-ionic surfactants, the cmc value decreases with the increase of temperature, while the micelle amount increases significantly. It can be seen that the appropriate increase of temperature is conducive to the surface activity of non-ionic surfactants. But the temperature should not exceed its turbidity point.

In short, the most suitable washing temperature is related to the formula of the detergent and the object to be washed. Some detergents have a good washing effect at room temperature, and some detergents have a lot of difference in decontamination effect between cold washing and hot washing.

③ Foam

People are used to confusing the foaming ability with the washing effect, and think that the detergent with strong foaming power has a good washing effect. The results show that the washing effect is not directly related to the amount of foam. For example, washing with low-foam detergent, the washing effect is not worse than that of high-foam detergent.

Although the foam is not directly related to washing, in some cases, the foam can help remove dirt, for example, when washing dishes by hand, the foam of the washing liquid can carry away the oil droplets. When scrubbing the carpet, the foam can also take away solid dirt particles such as dust, and the dust in the carpet dirt accounts for a large proportion, so the carpet cleaning agent should have a certain foaming ability.

Foaming power is also important for shampoos, and the fine foam produced by the liquid during shampoos or baths makes people feel lubricating and comfortable.

(4) The variety of fibers and the physical characteristics of textiles

In addition to the chemical structure of the fiber affecting the adhesion and removal of dirt, the appearance of the fiber and the organizational structure of the yarn and fabric have an impact on the ease of dirt removal.

The scales of wool fibers and the curved flat ribbon structure of cotton fibers accumulate dirt more easily than smooth fibers. For example, carbon black on cellulose film (sticky film) is easy to remove, while carbon black on cotton fabric is difficult to eluate. For example, polyester short fiber fabric is easier to accumulate oil than long fiber fabric, and the oil on short fiber fabric is also harder to remove than the oil on long fiber fabric.

Tightly twisted yarn and tight fabric, because the micro-gap between the fibers is small, can resist the invasion of dirt, but also can prevent the washing liquid to remove the internal dirt, so the tight fabric is good at the beginning of the stain resistance, but once contaminated washing is more difficult.

⑤ The hardness of water

The concentration of metal ions such as Ca2+ and Mg2+ in water has a 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 surfactant concentration is higher, the decontamination effect is still much worse than in distillation. In order to make the surfactant play the best washing effect, the concentration of Ca2+ ion in water should be reduced to 1×10-6mol/L(CaCO3 should be reduced to 0.1mg/L). This requires the addition of various water softeners to the detergent.