Synthetic fibers are widely used in various fields of the national economy because of their high strength, abrasion resistance, acid resistance, alkali resistance, high temperature resistance, light weight, warmth retention, good electrical insulation and resistance to mildew. For civilian use, synthetic fibers can be spun purely, or blended or interwoven with natural fibers or man-made fibers. The clothes made of it are stronger and more durable than cotton, wool and man-made fibers; when used as quilts, winter clothes are lighter and warmer. Nylon has excellent abrasion resistance and has the characteristics of certain natural fibers. For example, acrylic fiber is similar to wool, commonly known as artificial wool; vinylon's water absorption performance is similar to cotton; nylon is specially processed, and its products are similar to silk. In industry, synthetic fibers are commonly used as tire cords, fishing nets, ropes, conveyor belts, industrial fabrics (canvas, filter cloth, etc.), sound insulation, heat insulation, and electrical insulation materials. In medicine, synthetic fibers are often used as medical cloths, surgical sutures, hemostatic cotton, artificial organs, etc. In the construction of national defense, synthetic fibers can be used for parachutes, military uniforms, and military quilts. Some special synthetic fibers are also used for special protective materials in the atomic energy industry, aircraft, rockets and other structural materials. The basic raw material for the production of synthetic fibers comes from petroleum. Benzene, xylene, and propylene, which are by-produced in the reformer of the refinery and hydrocarbon cracking to produce ethylene, are processed into raw materials (commonly referred to as monomers) required for synthetic fibers. The way to make synthetic fibers using petroleum as raw materials can be expressed as follows: There are some special synthetic fibers that do not use petrochemical products as raw materials, but they have low output and are not used in daily life. Synthetic fiber production method The synthetic fiber preparation process includes three basic links: monomer preparation and polymerization, spinning and post-processing. 1. Monomer preparation and polymerization Use petroleum, natural gas, coal, limestone, etc. as raw materials to obtain organic low-molecular compounds such as benzene, ethylene, propylene, phenol, etc. as monomers through fractionation, cracking and separation. Under the action of the catalyst, the polymer formed by polymerization is the material of the synthetic fiber, also known as the fiber-forming polymer. The production of synthetic fibers is first to make monomers into fiber polymers through polymerization. These polymerization principles, production processes and equipment are similar to the production of synthetic resins and synthetic rubbers. The difference is that synthetic fibers need to be spun and post-processed. Only by processing can it become a qualified textile fiber. 2. In spinning, the melt or concentrated solution of the fiber-forming polymer is continuously, quantitatively and uniformly extruded from the capillary pores of the spinneret (or spinneret) with a spinning pump (or metering pump), and The process of becoming a liquid trickle and then solidifying into a nascent fiber in air, water or a specific solidification solution is called 'fiber formingThere are two main types of synthetic fiber spinning methods: melt spinning and solution spinning. Melt spinning is a method in which high polymer is heated and melted into a melt, and then a stream of melt is ejected from a spinneret, and then condensed to form a fiber. The melt spinning speed is high, and the high-speed spinning can reach several kilometers per minute. This method is suitable for those high polymers that can be melted, flowed and not easily decomposed, such as polyester, polypropylene, nylon and so on. Solution spinning is divided into wet spinning and dry spinning. Wet spinning is to prepare high polymer into a spinning solution in a solvent, and then spray a thin stream through a spinneret to solidify into a fiber in a liquid coagulation medium. In dry spinning, the coagulation medium is a gas phase medium, and the thin stream formed by the spinning is heated and evaporated by the solvent, and the polymer is condensed into fibers. The solution spinning speed is low, generally tens of meters per minute. Solution spinning is suitable for polymers that are not heat-resistant, not easy to melt, but can be dissolved in specially formulated solvents, such as acrylic and vinylon. 3. Post-processing The structure of the nascent fiber obtained after spinning and forming is not perfect, and its physical and mechanical properties are poor, such as low strength and poor dimensional stability. It cannot be directly used for textile processing and must undergo a series of post-processing. Post-processing varies with synthetic fiber varieties, spinning methods and product requirements. According to the requirements of the textile industry
, synthetic fibers are divided into two types: filament and short fiber. The so-called filament is a filament with a length of more than one kilometer, and the filament is wound into a group. Short fibers are short fibers of a few centimeters to ten centimeters. The post-treatment process of short fiber is mainly: primary fiber-bundling-drawing-heat setting-crimping-cutting-baling-finished short fiber. The post-treatment process of the filament is mainly: primary fiber-drawing-twisting-double twisting-washing and drying-heat setting-winding-grading-packaging-finished filament. It can be seen from the above that the post-treatment of the nascent fiber mainly includes stretching, heat setting, crimping and false twisting. Stretching can change the internal structure of the nascent fiber, improve the breaking strength and abrasion resistance, and reduce the elongation of the product. Heat setting can adjust the internal intermolecular forces of the polymer caused by the spinning process, and improve the stability of the fiber and other physical-mechanical properties and dyeing properties. Crimping is to improve the processability of synthetic fibers (both wool and cotton fibers are crimped) and overcome the lack of smooth and straight surfaces of synthetic fibers. False twist is to improve the style of textiles, make them bulky and increase elasticity.
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