Surfactants, also known as surfactants, are substances that significantly reduce the surface tension of a target solution, either between two liquids or between a liquid and a solid. Surfactants are generally organic amphiphilic molecules with hydrophilic and hydrophobic groups, usually amphiphilic organic compounds containing a hydrophobic group ‘tail’ and a hydrophilic group ‘head’. There are many types of surfactants, and different surfactants have different roles. Generally speaking, surfactants have the functions of wetting, penetrating, emulsifying, dispersing, solubilising, foaming, defoaming, washing, levelling, softening, sterilising, eliminating static electricity and so on.
Textile industry in the spinning, spinning, weaving, printing and dyeing to the finished product of the various processing procedures, according to the performance of various fibres need to use different auxiliary chemical additives, in order to improve the quality of textiles, improve the processing effect, improve productivity, simplify the process, reduce production costs and give the textile a variety of excellent application performance, this auxiliary chemicals are commonly known as the textile dyeing and finishing additives. Textile auxiliaries as a chemical used in textile production and processing, in addition to a part of the functional auxiliaries, about 80 per cent of the textile dyeing and printing auxiliaries are a variety of surfactants as raw materials, processing and compounding or as an auxiliary agent materials.
wettability
Water or aqueous solutions are particularly common fluids that displace gases, so wetting usually refers to the phenomenon of spreading of water or liquid on a solid surface. The contact angle θ > 90° of a liquid on a solid surface is usually considered non-wetting, while θ < 90° is considered wetting, and the smaller the contact angle θ, the better the wetting properties.
Printing and dyeing process in the vast majority of aqueous solution, due to the water has a large surface tension, so that the aqueous solution can not quickly and well on the fibre wetting, penetration, is not conducive to the printing and dyeing process. In order to make the water can automatically wetting of solids, need to add surfactants in water, change the interfacial tension of the system. Adding surfactant to water not only reduces the surface tension of water, but also reduces the interfacial tension between water and solids, so that water can wet itself on the solids, so the presence of surfactant can promote the wetting of the liquid surface at the same time, but also promote the penetration of the fabric to the interior, so the textile dyeing and finishing industry in the actual application of surfactants with wetting and penetration is often referred to as wetting penetrant or penetrating agent for short.
Wetting agent and penetrating agent can promote the wetting and penetration of water on fibre and fabric, and can also enhance the wetting and dispersing ability of dyes and pigments which are difficult to dissolve in water in the colour paste, so they are the most widely used textile auxiliaries. It is the most widely used textile auxiliaries. Some anionic surfactants and non-ionic surfactants are mainly suitable for wetting and penetrating agents.
Emulsification and dispersion
emulsification
Emulsification is the process of dispersing one of the two immiscible liquids in tiny droplets uniformly in another liquid to form a stable dispersion system, which is called emulsion or emulsion. A variety of auxiliaries and finishing agents used in dyeing and printing processes are emulsions, which are usually aqueous emulsions made by emulsifying functional compounds in water.
One phase that is dispersed in the emulsion is called the dispersed phase or inner phase, and the other phase is called the dispersing medium or outer phase.
dispersion
The main role of the dispersant is to disperse the emulsion dispersion or insoluble in liquid solid material with very small particles uniformly dispersed in the liquid to form a In printing and dyeing processing, disperse dye ink and paint ink, are typical suspension system, containing a large number of insoluble solid particles (such as dyes, pigments), the stability of these systems directly affects the colour fastness, uniformity and printing and dyeing effect of the product. The dispersing and emulsifying effects are relatively similar, and the surfactants used are almost the same, so they are often called emulsifying dispersants in practical applications.
Dispersing principle of dispersants: Surfactants adsorb on the surface of the pigment and reduce the interfacial energy, making the surface of the particles easier to wet in water or other solvents. The dispersant has a chemical structure that has an affinity for both solid particles and liquids and has functional groups that adsorb to the particle surface. This adsorption results in the particle surface being covered with an adsorbed layer of dispersant, which increases the electrostatic repulsion or spatial site resistance between particles, allowing dispersions with good long-term stability to be obtained.
solubilisation
The phenomenon in which a substance that is completely insoluble or slightly soluble in a solvent is solubilised by the addition of a surfactant is called solubilisation. The solubilised substance is called solubilising solute, and the surfactant playing this role is called solubilising agent. Solubilisation is related to the formation of micelles, and the solubilised system forms a transparent, thermodynamically stable solution system.
Solubilisation is fundamentally different from emulsification and dispersion. Emulsification and dispersion form a thermodynamically unstable system, while solubilisation forms a thermodynamically stable system. Solubilisation can be applied to many aspects, such as: in the cosmetic industry, the use of solubilisation to produce make-up and water-soluble hair cream; in the polymer materials industry, polymer emulsion polymerisation; in the printing and dyeing industry, mainly used in the washing and dyeing process. In the washing process, the solubilising agent plays the role of removing oil and dirt. Commonly used solubilisers are short-chain alkylbenzene sulphonates, such as the sulphonates of toluene, xylene and p-isopropylbenzene.