1. Water repellency of fabric
The water repellency of a fabric refers to the fabric’s ability to push water droplets off its surface. The purpose of water repellent finishing is to prevent water from wetting the fabric. It uses the additional pressure of the fabric capillary to prevent the penetration of liquid water, but still maintains the The breathable and moisture-permeable properties of fabrics. Clothing made of this kind of fabric not only has good waterproof properties, but also can discharge sweat vapor from the body surface quickly, keeping the clothing dry and warm, thus greatly improving the comfort of the clothing. Water-repellent finishing fabrics were first used to produce military uniforms and protective clothing, and are now widely used in the production of sportswear, travel bags, travel clothing, tents, etc. The demand for such fabrics in domestic and international markets is increasing year by year.
2. The fabric is water-repellent and oil-repellent Mechanism
According to the wetting theory, the energy of a liquid to wet a solid surface is expressed by the spreading coefficient S:
S=YS-YL/YSL
From the above formula, the following conclusions can be drawn:
(1) The greater the surface energy YS of a solid, the greater S, and the easier it is for the solid to be wetted by the liquid. On the contrary, if the surface energy YS of the solid is smaller, the smaller the S, the harder it is for the solid to be wetted by the liquid, and the solid has the ability to resist liquids. Wetting ability.
(2) The smaller the surface energy YL of the liquid, the larger S is, and the easier it is for the liquid to wet the solid.
(3) The smaller the interface surface energy YSL between solid and liquid, the larger S is, and the surface energy of water is relatively high, which is 72.6mJ/M2. The surface energy of the water-repellent material must be less than this value. The surface energy of oil is generally 20-40 J/M2. The surface energy of oil-repellent materials must be smaller than this value. Therefore, the wetting ability of oil is much greater than that of water. Therefore, oil-repellent materials must be water-repellent, while general The surface energy of polyester fabric is much greater than the surface energy of water and oil. Therefore, in order to make polyester fabric water- and oil-repellent, a layer of low surface energy material must be coated on the surface. The surface energy of silicone rubber is about 25 mJ/m2, which is an ideal water-repellent material. The surface energy of fluororesin is about 5 mJ/m2, which is an ideal anti-pumping material.
3. Water-repellent and oil-repellent finishing agent
It can be seen from the mechanism of water-repellent and oil-repellent finishing that a layer of material is adsorbed on the surface of polyester fabric to turn the original high-energy surface into a low-energy surface, and a fabric with water-repellent effect can be obtained, and the smaller the surface energy, the better the effect. , the water repellents produced and used at home and abroad mainly include the following types: (1) paraffin-aluminum soaps, (2) pyridine quaternary ammonium salts, (3) hydroxymethyl melamine derivatives, (4) stearic acid Chromium complex, (5) silicone type, (6) fluoroalkyl resin type. The first five types of water-repellent agents have common weaknesses: they are not oil-repellent, not stain-proof, and have poor wash resistance. In recent years, the application of fluorine-containing compounds in water-repellent, oil-repellent, and anti-fouling finishing surfaces of fabrics is developing. The water and oil repellent agent of Deco Nano Business Unit has five levels of water repellency and up to seven levels of oil repellency.
4. Lotus leaf effect on polyester fabric Application in water and oil repellent finishing
In the past 30 years, German scientists have used scanning electron microscopes and atomic force microscopes to observe the microstructure of the leaves of 20,000 plants including lotus leaves, revealed the principle of water-repellent self-cleaning of lotus leaves, and applied for a patent. Based on the Lotus-effect principle, German scientists have successfully developed a water-repellent and self-cleaning building surface coating, which has been on the market since 1999. Tiles with the same performance were also put on the market at the end of 2000. Clothing with lotus leaf effect is also being developed. Since the lotus leaf effect has broad application prospects and high commercial value, the key technologies and principles have been patented and kept strictly confidential.
The secret of the lotus leaf effect lies mainly in its microstructure and nanostructure, not in its chemical composition. Holloway analyzed the surface chemical components of lotus leaves and other plants in 1994. All plants have a skin on their surface that separates the plant from its surroundings. The main component of the epidermis of all plants is soluble oil embedded in the polyester matrix. Therefore, the epidermis of plants has a certain degree of water repellency. After analyzing the surfaces of 20,000 plants, it was found that plants with smooth surfaces have no water-repellent and self-cleaning function, while plants with rough surfaces have a certain water-repellent effect. Among all plants, lotus leaves have It has a strong water-repellent and self-cleaning effect. The contact angle of water on its surface reaches 160.4°. In addition to lotus leaves, taro leaves and kohlrabi leaves also have strong water-repellent and self-cleaning effect. The contact angles of water on their surfaces reach 160.3 and 159.7 respectively. . The contact angles of water on various commonly used fiber surfaces are shown in Table 1 below.
Generally speaking, no fiber has a contact angle of water on its surface greater than 90°, so it can be said that none of the commonly used textile fibers have water-repellent capabilities. Of course, it does not have the ability to repel oil.
By studying the water-repellent self-cleaning principle of the lotus leaf effect, it can be seen that a highly water-repellent self-cleaning fabric must meet the following conditions: (1) First, the fiber surface must have basic water-repellent properties (that is, the contact angle between water and its surface is greater than 90 °). This step can be achieved through nanotechnology, plasma treatment technology and coating padding technology. (For example: using organic peroxides at high temperatures) decompose to form free radicals, triggering silicon-containing or fluorine-containing organic monomers with lower free energy to graft and modify the surface of PET fabrics. (2) Make the fabric have a rough surface. Although the fabric surface itself is very rough, this rough structure is based on fibers as small units, which is much larger than the requirements of nanostructures. The surface roughness of the water-repellent self-cleaning fabric should be the roughness of the fiber surface, and the roughness should reach the nanometer level.
Therefore, by using the principle of bionics and applying the lotus leaf effect principle to the water-repellent and oil-repellent finishing of polyester fabrics, a super water-repellent and breathable textile can be developed.
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