1. Fluorinated surfactants
Fluorinated surfactants have many properties that ordinary surfactants do not have or are superior to, such as high surface activity, low dosage, excellent heat resistance and chemical stability, and can significantly improve the wetting, penetration, emulsification and It has excellent water-repellent, oil-repellent and anti-fouling properties and is widely used in fire protection, chemical industry, pesticides, mineral processing, papermaking, leather, textile and other fields. It is one of the important varieties of special surfactants. one.
The high surface activity of fluorocarbon surfactants comes from its extremely low surface energy. Due to the flexibility of the chain, small cohesive energy, and weak interaction with polar molecules, the chain bond energy is large, the polarizability is small, and the bond distance is small. Short, so it has strong heat resistance. The reason why fluorocarbon surfactants are stable is that firstly, the fluorocarbon bond energy is high, and secondly, the molecular skeleton of linear perfluoroalkane is a zigzag carbon chain, surrounded by fluorine atoms. The excess electronegative fluorine atoms form a negative charge protective layer, allowing the fluorine atoms to shield the chain. As a high-efficiency emulsifier, fluorocarbon surfactants have high efficiency compared with ordinary hydrocarbon surfactants, and the dosage is small, which can effectively prevent the gelation and precipitation of particles in aqueous dispersion systems.
In the leather manufacturing and processing process, fluorocarbon surfactants can be used as wetting, dispersing, emulsifying and leveling auxiliaries, which can improve efficiency, reduce operating time, and improve the quality of leather products. As a soaking agent, it can greatly improve the wetting and permeability of dry skin, shorten the soaking time, and facilitate the removal of various impurities on the skin; as a leveling agent, it uses the permeability, dispersion, and retarding properties of fluorocarbon surfactants. It has dye migration properties to achieve the purpose of leveling and assisting dyeing; it is used as a filler to make the leather have excellent waterproof and oil-proof properties while filling. Using fluorine-containing chromium complexes instead of chromium salts as fixatives for waterproofing treatment can form a fluororesin film on the surface of the leather, making the leather moisturizing, breathable, scratch-resistant, and dry-cleaning resistant; as a leveling agent, it has the characteristics of fast leveling and also A more uniform coating film can be obtained, which can effectively cover the damage of leather and improve the wear resistance of leather. As a dyeing auxiliary, oil-soluble fluorocarbon surfactants with hydrocarbon groups can improve the dispersion of pigment coatings and the uniformity of color carriers, prevent pigments from agglomerating, and make colors more vivid. In addition, it can also be used to increase the waterproof performance of the coating and improve the smoothness of the coating.
However, due to its ultra-high stability, fluorine-containing surfactants are almost not decomposed under various environmental physical and chemical conditions, causing high and continuous pollution to the environment. After the European Union completely banned their use in goods, my country’s leather products exports have been greatly affected. Therefore, the development of new environmentally friendly alternative products has received attention. 3M Company developed perfluorobutanesulfonic acid in 2008. Its fluorocarbon chain is short and has no obvious accumulation in the body. It can be eliminated from the body through metabolism, and the degradation products are non-toxic to the environment.
2. Waterproof, oil-proof and anti-fouling finishing agent
Leather is a porous material and is easily wetted by liquids such as water. In the finishing process, hydrophobic and oleophobic organic substances are often sprayed on the leather surface to cover the surface of collagen fibers. The hydrophobic and oleophobic materials replace the collagen fibers in contact with air and liquid to achieve the purpose of making the leather waterproof, oil-proof and anti-fouling. Organic fluorine products are used for leather surface treatment. Since their critical surface tension is very low, when the leather fiber surface is oriented and arranged, the leather surface tension can be reduced to about 20mN/m, which is much lower than the surface tension of water and oil. It gives the leather surface excellent waterproof, oil-proof and anti-fouling properties, maintains good hand feel and excellent breathability and wettability, and does not change the organizational structure of the leather surface.
There are generally three mechanisms for leather waterproofing and oil-proofing: first, after treatment with leather-based materials, the pores of the leather fibers are clogged, making it difficult for water or oil substances to penetrate the cortex to achieve the purpose of waterproofing and oil-proofing; second, After the leather is treated by the processor, the leather material interacts with the leather surface fibers, which greatly reduces the surface tension of the leather fibers, making it difficult for various types of dust such as water or grease to adhere to the surface of the leather fibers, making water or grease dirt appear as beads. The objects slide off the surface of the leather fibers to achieve the purpose of waterproofing and oil-proofing; the third is to treat the leather with a specific leather material to form a dense surface layer on the leather surface fibers to prevent water or oil from further penetrating into the cortex, achieving Waterproof and oilproof purpose. The earliest used organofluorine leather finishing agent is a perfluorocarboxylic acid containing more than six carbon atoms. It forms a chromium salt complex with the trivalent chromium ion in the treatment agent. The trivalent chromium ion is also a leather tanning agent. It forms coordination bonds with amino groups and other groups in the leather collagen fibers, so that the perfluoroalkyl groups are firmly “planted” on the leather surface, forming a hydrophobic, oil-repellent and anti-fouling film on the leather surface, making the leather surface become Soft, plump, elastic, waterproof, oil-proof, stain-proof, mildew-proof, chemical corrosion-proof and other functions.
3M Company of the United States has applied for a patent for a leather waterproof and oil-repellent agent containing fluorocarbon condensation products. The product is composed of hydroxymethylated amine or alkoxylated derivatives, alcohols, amides or fatty acids containing at least 6 carbon atoms and It is formed by the condensation of vinyl monomers containing perfluorocarbon chains. As an ideal waterproof and oil-repellent agent, fluorine-containing waterproof and oil-repellent agents can reduce surface tension and change the surface fibers and internal structure of leather to achieve waterproofing.It has the purpose of “three defenses” of oil and stain resistance, and allows the leather to maintain its natural characteristics.
The performance advantages of fluorine-containing materials in terms of waterproofing, oil resistance and stain resistance are unmatched by other materials. Some authors believe that the development direction of my country’s fluorine-containing leather materials in the next few years will be:
(1) Strengthen research on the compound efficiency of fluorine-containing materials and fluorine-free materials and other fluorine-containing materials with low fluorine content and high performance;
(2) Achieve green production and application of fluorine-containing leather materials by using less or no organic additives;
(3) Develop multifunctional fluorine-containing leather materials so that fluorine-containing materials not only have outstanding three-proof performance, but also have better ancillary properties.
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