Elastane (EL), (in the USA and Asia spandex fiber) is an extremely stretchable chemical fiber with high elasticity, which is spun as filament yarns (mostly as multifilaments, yarn count 11-2 600 dtex) and processed into textile products. The underlying block copolymer has a mass fraction of at least 85 % polyurethane. Even when stretched to three times its original length, the fiber returns to almost its original length after the load has been released. It is similar to rubber, but has a higher strength and is more durable.
The first fibers made from elastane came onto the market in 1959 as Fiber K after Joseph Shivers developed a process for large-scale production at the American chemical company DuPont. It was glued multifilament yarn made of polyurethane. From 1962, Fiber K was sold in large quantities under the Lycra brand, which has been held in Germany by the Invista company since January 28, 2005. Two years later, Bayer AG began manufacturing Dorlastan, a multifilament yarn made from polyester urethane. Other brands are creora (Hyosung), Linel (Fillattice) and Elaspan (Invista).
Manufacture and construction
The most common manufacturing process for elastane filaments is multi-stage. First, simple linear polyurethanes are formed using the diisocyanate polyaddition process. The production of a polyurethane from butylene glycol and hexamethylene diisocyanate is well suited for fiber production. To form the elastomeric polyurethane block copolymer, a segmented polyurethane, a large part of the glycol is replaced by long-chain dihydroxy compounds (macrodiols) based on polyether or polyester with terminal OH groups during the polyaddition reaction. The macrodiols result in an amorphous structure (the soft segments) and are very mobile under load and are therefore the cause of the very high elongation of a few 100 %. If they are converted into macrodiisocyanates (diisocyanate prepolymers) via the terminal OH groups with diisocyanates, these can be chain-extended with short-chain diamines (e.g. ethylenediamine or m-xylylenediamine) or dialcohols (ethylene glycol or 1,4-butanediol) be converted into segmented polyurethanes (block copolymers). The bridges that form within the linear macromolecules between the long-chain soft segments result in the hard segments as short-chain crystalline urea or carbamide structures. They determine the strength and thermal properties of the elastane filaments. The length of the short-chain crystalline area is approximately 2.5-3 nm, that of the soft chains approximately 15-30 nm.
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