Elastane fiber refers to a tow with high extensibility and high resilience. The most classic definition is given by the American Society for Testing and Materials (ASTM): "At room temperature, the material is repeatedly stretched to at least twice its original length, and after the tension is released, it can quickly return to the original length". Fibers, while for polyurethane materials, refer to fibers that can quickly recover their original length after releasing the tension force after being stretched to 3 times their original length. In addition, depending on the country and region, there are other definitions.

Among the many functional varieties, elastic fiber, as a "sunrise industry", plays an irreplaceable role in clothing comfort, fluffy warmth, etc., because it can give the human body a good sense of contact, so it is widely used in the textile industry in China and even the world. It occupies a solid position in textiles, and giving textile fabrics a certain elasticity has become an inevitable development trend of clothing textiles.

1. Diene elastic fiber (rubber yarn)

Diene elastic fibers are commonly known as rubber threads or elastic threads, and the elongation is generally between 100% and 300%. The main chemical component is vulcanized polyisoprene, which has good chemical and physical properties such as high temperature resistance, acid and alkali resistance, wear resistance, etc. It is widely used in knitting industries such as socks and rib cuffs. Rubber yarn is an elastic fiber used in the early days. Since it is mainly made into coarse yarn, its use in woven fabrics is very limited.

2. Polyurethane fiber (spandex)

Polyurethane elastic fiber refers to a fiber made of a block copolymer with polyurethane as the main component, which is referred to as spandex in my country. The name is Neolon, and the German name is Dorlastan. Its elasticity comes from the block copolymer network structure in which its molecular structure consists of so-called "soft" and "hard" segments. With different block copolymers and different spinning processes, the fibers have different elasticity and dyeing and finishing properties after forming different "segment" network structures.

The spinning methods of spandex 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. It has the advantages of fast spinning speed (1000 m/min), small spinning fineness, good product quality and small production workshop area, but at the same time there is serious environmental pollution. and high cost. On the contrary, melt spinning technology does not use solvents, coagulants, and has no waste water treatment problems, low production costs, and great development potential, which is one of the current research hotspots.

Spandex is the earliest developed and most widely used elastic fiber with the most mature production technology.

3. Polyetherester elastic fiber

Polyetherester elastic fiber is an elastic fiber obtained by melt spinning of polyester and polyether copolymer, which was first produced by Teijin Corporation in 1990. Polyetherester elastic fibers are similar in structure to polyurethane elastic fibers and also have "segment" structural characteristics. The "soft" segment is mainly a polyether segment, which has good flexibility and long chain, and is easy to elongate and deform; the "hard" segment is a polyester segment, which is relatively stiff, easy to crystallize, and has a short chain. It acts as a node when it is deformed by force, endows it with elastic recovery properties, and determines the strength and heat resistance of the fiber.

Polyetherester elastic fiber not only has high strength, but also has good elasticity. When the elongation is 50%, the elasticity of medium-strength elastic fiber is equivalent to that of spandex, and the melting point is also higher. Dyed, so polyester fibers can also be processed into elastic textiles. In addition, they have excellent light resistance, chlorine bleach resistance, acid and alkali resistance, etc. are better than ordinary spandex. Due to its good acid and alkali resistance, the fabric composed of it and polyester can also undergo alkali reduction processing to improve the drape of the fabric.

This kind of fiber also has the advantages of cheap raw materials, easy production and processing, and is a kind of relatively promising fiber.

4. Polyolefin elastic fiber (DOW XLA fiber)

Polyolefin elastic fibers are produced by melt spinning of polyolefin thermoplastic elastomers. XLA, launched by DOW Chemical in the United States in 2002, is the first commercialized polyolefin elastic fiber, which is obtained by melt spinning of ethylene-octene copolymer (POE) catalyzed by metallocene catalyst in situ polymerization. . It has good elasticity, 500% elongation at break, high temperature resistance of 220 ° C, chlorine bleaching resistance and strong acid and alkali treatment, and strong resistance to ultraviolet degradation. Its production process is relatively simple, the price of raw materials is lower than that of spandex, and at the same time, there is almost no pollution in the production process and it is easy to recycle.

Due to the excellent properties of polyolefin elastic fibers, they have been widely used in recent years.

5. Composite elastic fiber (T400 fiber)

CONTEX (ST 100 composite elastic fiber, collectively referred to as T400 elastic fiber in the market) is a new bi-component composite elastic fiber made of DuPont Sorona as the main raw material and ordinary PET through advanced composite spinning process; it has a natural permanent spiral Curl and excellent bulkiness, elasticity, elastic recovery rate, color fastness and particularly soft hand feel, can be woven alone or interwoven with cotton, viscose, polyester, nylon, etc. to form a variety of types style. It not only solves many problems such as the traditional spandex yarn is not easy to dye, has excess elasticity, complex weaving, unstable fabric size, and easy aging during use, but also can be directly woven on air-jet, water-jet, and arrow shaft looms, not like spandex In this way, the covered yarn must be made before weaving on the machine, which reduces the cost of the yarn and improves the quality uniformity of the product.

6. Hard elastic fibers

The above elastic fibers are all soft elastic fibers, which will deform and recover greatly under lower stress. From the perspective of thermodynamics, the elasticity comes from the degree of freedom (or disorder) of the molecular chain, that is, the change of the entropy value of the system, so the crystallinity of the above fibers is very low. However, some fibers made under special processing conditions, such as polypropylene (PP), polyethylene (PE) and other fibers, although not easily deformed under low stress (because of their higher modulus), but at higher Under stress, especially at lower temperatures, it also has better elasticity, so this type of fiber is called hard elastic fiber.

The deformation and recovery of hard elastic fibers are obviously different from those of elastic fibers. For example, if the hard elastic PP fiber is stretched for the second time immediately after recovery, its modulus and strength will drop a lot. extension, its deformation recovery is basically close to the first curve. This is because when the hard elastic fiber is stretched and recovered, not only the stretching and retracting deformation of the long chain segment of the crimped molecules of the soft elastic fiber occurs, but also accompanied by some changes in the microporous structure during the stretching process. The wafer network structure has also changed. Only after these structural changes are gradually restored, can they return to their original state, so they deform and recover under higher pressure, which are called hard elastic fibers.

At present, hard elastic fibers are not widely used in textiles, but because their elastic characteristics are different from soft elastic fibers, some special textiles can be developed.