Among the many functional varieties, elastic fiber, as a "sunrise industry", can give the human body a good sense of contact, and plays an irreplaceable role in the wearing comfort and fluffy warmth of clothing, so it occupies a stable position in the textile industry in China and even the world, and giving textile fabrics a certain elasticity has become an inevitable development trend of taking textiles.
1. Diene elastic fiber (rubber yarn)
Diene elastic fibers are commonly known as rubber filaments or elastic filaments, and the elongation is generally between 100%~300%. The main chemical component is sulfide polyisoprene, which has good chemical and physical properties such as high temperature resistance, acid and alkali resistance, and wear resistance, and is widely used in knitting industries such as socks and ribbed cuffs. Rubber yarn is an early elastic fiber, and because it is mainly made into coarse yarns, it has a limited range of use in woven fabrics.
2. Polyurethane fiber (spandex)
Polyurethane elastane refers to a fiber made of a block copolymer with polyurethane as the main component, which is referred to as spandex in China, and the original trade name in the United States was Spandex, and later changed its name to Lycra Lycra, Elastane in Europe, Neolon in Japan, and Dorlastan in Germany. Its elasticity comes from its molecular structure, which consists of a network of block copolymers consisting of so-called "soft" and "hard" segments. With the different block copolymers and different spinning processes, the elasticity and dyeing and finishing properties of this fiber are also different after forming a different "segment" network structure.
Spandex spinning methods include dry spinning, wet spinning, chemical reaction spinning, and melt spinning. Dry spinning technology is the most common method of spandex industrial production at present, which has the advantages of fast spinning speed (1000 m/min), small spinning denter, good product quality and small production workshop area, but at the same time there are serious environmental pollution and high cost and other shortcomings. On the contrary, melt spinning technology, without the use of solvents and coagulants, without the problem of waste water and waste liquid treatment, has low production cost, has great development potential, and is one of the hot spots of current research.
Spandex is the earliest and most widely used variety of elastic fiber, and the most mature production technology.
3. Polyether ester elastane
Polyether ester elastane is an elastane fiber made from polyester and polyether copolymers through melt spinning, and was first produced by Teijin Corporation in Japan in 1990. Polyether ester elastane fibers are structurally similar to polyurethane elastane fibers and also have a "segmental" structural characteristic. The "soft" chain segment is mainly polyether segment, which has good flexibility, long chain, and easy elongation and deformation; The "hard" segment is the polyester segment, which is relatively stiff and easy to crystallize, and the chain is shorter, which acts as a node when the fiber is deformed by force, imparts elastic recovery properties, and determines the strength and heat resistance of the fiber.
Polyether ester elastane fiber not only has high strength, but also good elasticity, at 50% elongation, the elasticity of medium strength elastane fiber has been equivalent to spandex, and the melting point is also higher, blended with PET fiber, can be dyed at 120~130 °C, so polyester fiber can also be processed into elastic textiles. In addition, they have excellent lightfastness, chlorine bleaching resistance, acid and alkali resistance, etc., which are better than ordinary spandex. Due to its good acid and alkali resistance, the fabric composed of it and polyester can also be processed with alkali reduction to improve the drape of the fabric.
This fiber also has the advantages of cheap raw materials, easy production and processing, and is a more promising type of fiber.
4. Polyolefin elastane fiber (DOW XLA fiber)
Polyolefin elastane fibers are made from polyolefin thermoplastic elastomers that are melt-spun. XLA, introduced by DOW Chemical in 2002, was the first commercially available polyolefin elastane fiber produced by melt-spinning ethylene-octene copolymer (POE) catalyzed by a metallocene catalyst for in-situ polymerization. It has good elasticity, 500% elongation at break, high temperature resistance of 220°C, resistance to chlorine bleaching and strong acid and alkali treatment, and strong resistance to ultraviolet degradation. Its production process is simpler, the price of raw materials is lower than spandex, and the production process is almost non-polluting and easy to recycle.
Polyolefin elastane fibers have been widely used in recent years due to their excellent properties.
5. Composite elastic fiber (T400 fiber)
CONTEX (ST 100 composite elastane, collectively known as T400 elastane in the market) is a new two-component composite elastic fiber made of DuPont Sorona as the main raw material and ordinary PET through advanced composite spinning process; With natural permanent spiral crimp and excellent bulkiness, elasticity, elastic recovery rate, color fastness and particularly soft feel, it can be woven alone, or interwoven with cotton, viscose, polyester, nylon, etc., to form a variety of types of styles. It not only solves many problems such as traditional spandex yarn is not easy to dye, excess elasticity, complex weaving, unstable fabric size, and easy aging during use, but also can be directly woven on air-jet, water-spray, and arrow looms, and does not have to be woven on the machine after being made into covered yarn like spandex, which reduces the cost of yarn and improves the quality uniformity of products.
6. Hard elastic fiber
The above-mentioned elastic fibers are soft elastic fibers, which undergo greater deformation and recovery under lower stress. From a thermodynamic point of view, elasticity comes from the degree of freedom (or chaos) of the molecular chain, that is, the change in the entropy of the system, so the crystallinity of the above fibers is low. However, some fibers prepared under special processing conditions, such as polypropylene (PP), polyethylene (PE) and other fibers, although they are not easy to deform under low stress (because they have a higher modulus), but also have good elasticity under higher stress, especially at lower temperatures, so this kind of fiber is called hard elastic fiber.
The deformation and recovery of hard elastic fibers are significantly different from those of elastic fibers. For example, the modulus and strength of the hard elastic PP fiber are much lower than that of the second stretch immediately after the tensile recovery, but if it is placed for a period of time after removing the stress, or if the temperature is raised to make it fully relaxed and then the second stretch is carried out, the deformation recovery is basically close to the curve of the first time. This is due to the fact that when the hard elastic fiber is stretched and recovered, not only the tensile and retracted deformation of the long chain segment of the condensed molecule of the above-mentioned soft elastic fiber occurs, but also some changes in the microporous structure during the stretching process, and their wafer network structure also changes. Only after these structural changes are gradually restored can they return to their original state, so they deform and recover under higher pressure, which is called hard elastic fiber.
At present, hard elastic fibers are not used much in textiles, but because their elastic characteristics are different from soft elastic fibers, some special textiles can be developed.