Lycra

Use of 1,3 cycloaHphatic diamines in polyamides may be similarly limited by internal amide dehydration of the conformationaHy labile cis isomers to form a tetrahydropyrimidine (38) rather than high molecular weight polyamide. 1,3-Cyclohexanediamine is, however, a component of Spandex polyureas Du Pont uses the hydrogenation product of y -phenylenediamine [108-45-2] (24) captively to produce Lycra (see Fibers, elastomeric). 

One partieular form of thermoplastic polyurethane elastomers is the elastic fibre known as spandex fibre. Like the usual thermoplastic rubbers these materials consist of hard and soft segments but to qualify for the term spandex by the US Federal Trade Commission the polymer used should contain at least 85% of segmented polyurethane. The first commercial material of this type was introduced by Du Pont in 1958 (Lycra). Several other similar materials have since been introduced including Dorlastan (Bayer), Spanzelle (Courtaulds) and Vyrene (US Rubber). 

Both polyethers and polyesters may be used as polyols. For example, Du Pont use polytetrahydrofuran for Lycra whilst US Rubber originally used a polyester of molecular mass of about 2000 obtained by condensing adipic acid with a mixture of ethylene and propylene glycols. A polyether-based mixture was used for Vyrene 2 introduced in 1967. All the polyols have terminal hydroxyl groups. 

Various elastic elements are added to disposable sanitary products. Strands of lycra, natural rubber, polyurethane foam, and other elastic laminates are applied to provide good fit and avoid leakage. These are attached with adhesives. While non-PSA formulas such as polybutene-based [64] and polyamide [65] adhesives have shown utility, as well as benefits in terms of resistance to baby oils and lotions, adhesives based on styrenic block copolymers still dominate. SBC-based... 

Polyurethane elastomeric fibers17 are known generically in the United States as spandex (elastane in Europe). These were developed by Bayer under the tradename Dorlastan and by Du Pont as Lycra. These materials are highly elastic and can withstand elongation of several hundred percent before breaking. They are exttuded into filaments for textiles and are commonly used in elastic fabrics, especially sportswear. 

The main application of spandex (e.g., Lycra ) is for stretched apparel clothing. It is used to make yarns when combined with other natural and synthetic fibres. 

The generic name given, in the USA, to stretch fibres based on elastomeric long-chain polyester polyurethanes. Trade names are, e.g., Lycra and Vyrene . 

Attempts were made later on to prepare synthetic stretch fibres based on polyurethane. At present many such fibres are marketed as "Spandex", "Lycra , etc. 

Spandex Segmented polyurethane, 85% or more Light, soft, smooth, resistant to body oils, can be stretched often, retain original form, abrasion-resistant Girdles, bras, slacks bathing suits, pillows Lycra... 

DuPont and Shell have developed a new polyester, poly(trimethylene terephthalate) (PTT) (structure 19.38) that is structurally similar to PET, except that 1,3-propanediol (PDO) is used in place of ethylene glycol. The extra carbon in Sorona allows the fiber to be more easily colored giving a textile material that is softer with greater stretch. Further, it offers good wear and stain resistance for carpet use. The ready availability of the monomer PDO is a major consideration with efforts underway to create PDO from the fermentation of sugar through the use of biocatalysts for this conversion. Sorona and Lycra blends have already been successfully marketed. Sorona is also targeted for use as a resin and film. 

Principal brands Glospan/Cleerspan , Globe (multifilamem) Lycra . DuPont (coalesced monofilament)... 

Figure 7.6 SEM micrograph of knitted cotton/Lycra fabric (original magnification 600x) Cotton fibers dominate the image. (Photo R. C. Janaway.)...

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