Elastic fibers are bundles of silk with high extensibility and high resilience. Most classic definition for the association of American material experiment ASTM given: "at room temperature, for the original material is repeatedly stretched to at least 2 times, and after tension release, can quickly return to the original long" type of fiber, and for pu material, is refers to stretch up to the original length after 3 times, release tension can quickly restore the original length of fiber. In addition, there are other definitions, depending on the country and region.
In the function of many varieties, elastic fiber, as a "sunrise industry" by can give human good touch feeling, in such aspects as the wearing comfort of clothing, soft warm plays an irreplaceable role, so in China and the world textile industry occupies a stable position, endows textile fabrics and elastic take textiles has become an inevitable trend.
One, diene elastic fiber (rubber silk)
Diene elastic fiber commonly known as rubber wire or elastic wire, elongation is generally between 100 %~300 %. The main chemical composition is vulcanized polyisoprene, which has good chemical and physical properties such as high temperature resistance, acid and alkali resistance and wear resistance. It is widely used in knitting industry such as socks and rib cuffs. Rubber silk is an elastic fiber used in the early stage, because it is mainly made into thick yarns, so its application in weaving fabric is limited.
Two, polyurethane fiber (spandex)
Polyurethane elastic fiber refers to a kind of block copolymer made of polyurethane as the main component, which is referred to as Spandex in China. The original product in the United States was Spandex, and later renamed as Lycra, Elastane in Europe, Neolon in Japan, and Dorlastan in Germany. Its elasticity comes from the fact that its molecular structure is a network of block copolymers consisting of so-called "soft" and "hard" chains. With the different block copolymers, the spinning process is different, forming different "block" network structure, elasticity and dyeing and finishing properties are different.
The spinning methods of spandex include dry spinning, wet spinning, chemical reaction spinning and melt spinning. Dry spinning technology is the most common method for spandex industrial production at present. It has the advantages of fast spinning speed (1000 m/min), small spinning size, good product quality and small workshop area, but at the same time, it has the disadvantages of serious environmental pollution and high cost. On the contrary, melt spinning technology, no use of solvents, coagulants, no waste water treatment problems, low production cost, has great development potential, is one of the current research hot spots.
Spandex is the earliest developed and most widely used elastic fiber with the most mature production technology.
Polyether ester elastic fiber
Polyether ester elastic fiber is an elastic fiber made of polyester and polyether copolymer by melt spinning. It was first produced by Japan Teiren company in 1990. Polyether ester elastic fiber is similar to polyurethane elastic fiber in structure and has "segment" structure. "Soft" chain is mainly polyether chain, good flexibility, long chain, easy elongation deformation; The "hard" segment is a polyester segment, which is relatively stiff and easy to crystallize. The short chain acts as a node when the fiber is stressed and deformed, giving elastic recovery and determining the strength and heat resistance of the fiber.
Polyether ester elastic fiber is not only of high strength, but also of 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 high. When blended with PET fiber, it can be dyed at 120~130 ℃, so polyester fiber can also be processed into elastic textiles. In addition, their excellent light resistance, chlorine bleaching resistance, acid and alkali resistance are better than ordinary spandex. Because of good acid and alkali resistance, the fabric composed of polyester and it can also be processed by alkali reduction to improve the drape of the fabric.
This kind of fiber also has the advantages of cheap raw material, easy production and processing, and is a kind of fiber with a promising future.
Four, polyolefin elastic fiber (DOW XLA fiber)
Polyolefin elastic fibers are prepared by melt spinning of polyene thermoplastic elastomers. XLA, launched by DOW Chemical in 2002, is the first commercial polyolefin elastic fiber, which is prepared by melting spinning of ethylene - octene copolymer (POE) catalyzed by metallocene catalyst. It has good elasticity, 500% breaking elongation, 220℃ high temperature resistance, chlorine bleaching and strong acid and alkali treatment, and has a strong uv degradation performance. Its production process is simpler, the raw material price is lower than spandex, and the production process produces almost no pollution and is easy to recycle.
Polyolefin elastic fibers have been widely used in recent years because of their excellent properties.
Five, composite elastic fiber (T400 fiber)
CONTEX (ST 100 composite elastic fiber, the market collectively T400 elastic fiber) is a kind of duPont Sorona as the main raw material, and ordinary PET through advanced composite spinning process made of two-component new composite elastic fiber; With natural permanent spiral crimp and excellent bulking, elasticity, elastic recovery rate, color fastness and special soft handle, it can be pure woven alone, or interwoven with cotton, viscose fiber, polyester, nylon, etc., to form a variety of styles. It not only solved the traditional fiber silk is not easy to dyeing, elastic excess, weaving complex, fabrics, size is not stable, and easy ageing, and many other problems in use process, and can be directly on the jet, water jet, shaft loom weaving, don't must be made as spandex coated before computer weaving yarn, reduce the cost of yarn, improve the quality of the product homogeneity.
Hard elastic fiber
All the elastic fibers mentioned above are soft elastic fibers, which deform and recover greatly under low stress. From the perspective of thermodynamics, elasticity comes from the degree of freedom (or chaos) 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. But under the condition of special processing of some fibers, such as polypropylene (PP), polyethylene (PE), such as fiber, while under low stress is not easy to deformation (because they have higher modulus), but under high stress, especially at low temperature, also has good flexibility, so this kind of fiber is called hard elastic fibers.
The deformation and recovery of hard elastic fibers are obviously different from those of elastic fibers. For example, hard elastic PP fiber after stretching recovery immediately after the second stretching, its modulus and strength to drop a lot, but if the removal of stress after placing for a period of time, or increase the temperature to make it fully relaxed after the second stretching, the deformation recovery and the first curve is basically close. This is because when the hard elastic fiber is stretched and recovered, not only the stretching and retraction deformation of the long chain segment of the soft elastic fiber winding molecule mentioned above occurs, but also some changes of micropore structure and their wafer network structure occur during the stretching process. Only after these structural changes are gradually recovered can they return to their original state, so they can be deformed and recovered under higher pressure, which is called hard elastic fibers.
At present, hard elastic fiber is seldom used in textiles, but its elastic characteristics are different from soft elastic fiber, so some special textiles can be developed.