The stain-repellent and stain-removing mechanism of fabrics
1. Contamination repellency mechanism of fabrics
The higher the surface energy of the fabric, the greater the surface tension, and the easier it is for the fabric to be wetted, that is, the easier it is for the fabric to be stained by oil. Generally, the surface tension of textile fiber fabrics is greater than that of water and oil, so it is easy to be stained. To make a fabric water- and oil-repellent, the critical surface tension of the fabric must be lower than the surface tension of water or oil. That is, by reducing the surface tension of the fiber fabric, the stain resistance of the fabric can be improved to a certain extent.
Solid dirt is usually deposited at irregularities and intersections on the fabric surface, and its interaction with fibers is mainly mechanical adsorption. Greasey dirt is mainly combined with the fabric surface through mechanical adsorption and chemical forces (van der Waals forces and adhesion forces). Therefore, the surface energy of the fiber can be reduced by reducing or eliminating electrostatic attraction (such as antistatic finishing), reducing intermolecular forces (such as hydrophilization treatment), reducing the contact area between fiber and dirt (such as surface smoothing), etc. Reduce the adsorption force of dirt and weaken the adhesion of dirt, thereby improving the contamination of dirt.
2. Anti-fouling finishing
The finishing that makes textiles antifouling is called antifouling finishing. Fabric anti-fouling finishing technologies mainly include water- and oil-repellent finishing, anti-fouling and dust-proof finishing, and easy-to-contaminate finishing. According to different fabric raw materials and different purposes of use, appropriate finishing methods and finishing agents can be selected.
3. The easy stain removal mechanism of fabrics
Textiles become stained over time. Once an ideal textile is stained, the dirt should be easily washed away under normal washing conditions. At the same time, the fabric will not absorb the dirt in the washing liquid and become stained again. This property of textiles is called easy stain removal.
The removal of dirt adsorbed on the fabric from the fabric, in addition to factors related to washing, also depends on the surface properties of the fabric. When dirt adheres to the surface of the fabric and the bonding force is strong, the contact angle of the dirt is between 0 and 90°; when the contact angle is greater than 90° and gradually increases, the bonding force gradually decreases. When the contact angle reaches 180 °, the dirt can be separated from the fabric. In fact, decontamination means gradually increasing the contact angle to 180°, and the dirt (liquid dirt) “rolls up” and breaks away from the fabric. Introducing hydrophilic groups on the surface of non-polar fibers (such as synthetic fibers) or using hydrophilic polymers to clean the fiber surface can improve the fiber’s ease of stain removal and reduce the electrostatic force of the fiber accordingly, thereby reducing particulate pollution. of contamination. In addition to considering decontamination from the perspective of surface energy, kinetic effects must also be taken into consideration. Shortening the initial stage of cleaning and reducing the contamination content on the fabric in the post-cleaning stage is also the purpose of easy decontamination finishing.
Easy decontamination finishing actually promotes the diffusion of water into the interior of the fiber and the oil stain-fiber interface. Because it promotes the hydration of the interface, it is easy to separate the oil stain from the fiber. The easier water spreads, the easier it is for oil to fall off. The diffusion of water depends on the swelling ability of the easy detergent, and the swelling ability comes from its chemical properties, hydrophilicity, cross-linking degree and washing temperature. Of course, after water enters, a certain amount of mechanical force is required to make the oil stains “bead” away. In general, as long as the hydrophilicity of the fiber is increased, the penetration of water can be accelerated, which is beneficial to decontamination.
There are two main factors that affect the easy decontamination. One is the hydrophilicity of the fibers that make up the fabric. Fibers with good hydrophilicity have good decontamination properties. The second is the polarity of the finishing agent on the fabric after chemical treatment. If the highly polar finishing agent that can form hydrogen bonds with water adheres to the surface of the hydrophobic fiber, the dirt will be easier to remove during washing.
Easy decontamination finishing is mainly solved from two aspects. One is to improve the hydrophilic properties of the fiber, and the other is to improve the oil-repellent property of the fiber in the air, that is, to improve the surface properties of the fabric through chemical finishing and reduce its surface tension in the air. , thus making the fabric dry and oil-proof; during washing, the hydrophilic segments in the easy-to-decontaminate finishing agent will be oriented and arranged on the surface of the fabric, making it hydrophilic and decontaminating and preventing re-contamination.
4. The relationship between stain resistance and easy stain removal
Anti-fouling requires a reduction in surface tension, while easy decontamination requires increased hydrophilicity. It seems that anti-fouling and easy decontamination cannot have both. However, in the past decade or so, with the development of the chemical additive industry, compounds containing fluorine segments and polyoxyethylene segments have been produced, causing the oxyethylene segments to form a spiral shape in the dry state, while the fluorine segments spread on the fiber. The surface, therefore, exhibits the surface characteristics of organic fluorine, the surface tension is greatly reduced, and the oil and stain repellency is improved. However, when it is in a wet state or immersed in water, the hydration of the oxyethylene chain segments causes it to spread on the surface of the fiber, showing the appearance of oxygen. The surface characteristics of ethylene increase its hydrophilicity, which is beneficial to the diffusion and penetration of water, especially the penetration into the interior of the fiber, which improves easy decontamination. Therefore, fabrics processed with this finishing agent have both stain repellency and easy stain removal.
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