Elastic polyurethane fibers

Not all copolymers which are produced by step-growth processes are random in nature. Block copolymers are also of major interest. An example of the synthesis of elastic polyurethane fibers was given in Section 1.5.4. Block and graft copolymers of polysiloxane-poly(alkylenc ethers) with segments like5-9 are used as surfactants in the production of polyurethane foams with uniform cell sizes. 

Low-molar-mass products are viscous oils, the high-molar-mass polymers are crystalline. Polymers with two hydroxyl end groups and molar masses of about 2000 g/mol are used as soft segments for elastic polyurethane fibers or polyether ester elastomers. 

Elastomeric Fibers. Elastomeric fibers are polyurethanes combiaed with other nonelastic fibers to produce fabrics with controlled elasticity (see Fibers, elastomeric). Processing chemicals must be carefully selected to protect all fibers present ia the blend. Prior to scouriag, the fabrics are normally steamed to relax uneven tensions placed on the fibers duriag weaving. Scouriag, which is used to remove lubricants and siting, is normally conducted with aqueous solutions of synthetic detergents and tetrasodium pyrophosphate, with aqueous emulsions of perchloroethylene or with mineral spidts and sodium pyrophosphate. 

Mixtures of isocyanates are commonly used for convenience in commercial production of the diisocyanate, since the pure toluene 2,4-diisocyanate is more expensive to produce. The resulting prepolymer is then mixed with either a glycol, such as 1,6-hexanediol, or a deactivated (sterically hindered) diamine plus pigment if required, and then promptly poured into a preheated mold of the desired shape. In about half an hour the mixture sets to a pliable shape with stiffness and elasticity controlled by the components and processing details used [29]. Similar procedures produce high-strength polyurethane fiber (e.g., Perlon U) or elastomeric fibers (e.g., Spandex and Lycra). 

Polyurethane fibers are another niche application. These elastanes, the basis of Lycra , have nearly taken over the textile industry, displacing rubber threads (elastodienes) in the process. The high popularity of PU fibers is attributable to the good tensile strength and elasticity of highly segmented polyurethanes. In addition, elastanes can be processed in a variety of sizes, either as continuous filaments (yarns) or as shorter fibers. Rubber threads, on the other hand, are available solely as monofilaments. ... 

The preparation, sjHnning, and drawing of copolymers PET—PEG were invest tigated more recently and it was ascertained that by incorporation under optimum conditions of about 5 mol % PEG (mol. wt. 4000) into PET, the polyglycol reacts with the terephthalic group and the copolymer obtained can be easily spun and drawn. However, fibers prepared in this way are far from having the elasticity of polyurethane fibers (e.g. Lycra) (Table 2). 

Shape memory polyurethane fiber Comfort elasticity Body temperature active... 

Spandex Generic name for fibers from elastic polyurethanes ... 

The more flexible blocks are derived from low-molecular-weight (MW 1,000 to 4,000) polyesters or polyethers with —OH groups at each end of their chains. Polyurethane fibers are fairly soft and elastic and have found use as spandex and Lycra , the stretch fabrics used in bathing suits, leotards, and undergarments. 

Figure 4.3 AFM micrograph of aligned polyurethane fibers produced by soft molding (Section 3.2) and lying on silicon, and scheme of a scanning probe tip used for collecting force-displacement curves during elastic nanoindentation and hence fiber compressive modulus. Inset scheme of the elastic compression of the polymer surface, and of the z vertical coordinate system of the AFM system, radius of the contact paraboloid, A/ indentation. Adapted with permission from Ref 26, Appl. Phys. Lett., 2005, 87, 123109. Doi 10.1063/1.2046731. Copyright 2005, American Institute of Physics.

Other elastomeric-type fibers iaclude the biconstituents, which usually combine a polyamide or polyester with a segmented polyurethane-based fiber. These two constituents ate melt-extmded simultaneously through the same spinneret hole and may be arranged either side by side or ia an eccentric sheath—cote configuration. As these fibers ate drawn, a differential shrinkage of the two components develops to produce a hehcal fiber configuration with elastic properties. An appHed tensile force pulls out the helix and is resisted by the elastomeric component. Kanebo Ltd. has iatroduced a nylon—spandex sheath—cote biconstituent fiber for hosiery with the trade name Sidetia (6). 

More recentiy, melt-spun biconstituent sheath—core elastic fibers have been commercialized. They normally consist of a hard fiber sheath (polyamide or polyester) along with a segmented polyurethane core polymer (11,12). Kanebo Ltd. in Japan currentiy produces a biconstituent fiber for hosiery end uses called Sideria. 

Different materials can be used such as nylon, polyester (TS), and epoxy, but TS polyurethane (PUR) is predominantly used. Almost no other plastic has the range of properties of PUR. Modulus of elasticity range in bending is 200 to 1,400 MPa (29,000-203,000 psi) and heat resistance from 90 to over 200°C (122-392°F). The higher values are for chopped glass-fiber-reinforced RIM (RRIM). 

We can tune the physical characteristics of polyurethanes over a wide range by careful selection of their components. Polyurethanes are used extensively as foams, which range from soft and resilient to rigid. Solid polyurethanes range from soft moldings and elastic fibers to rigid injection molded items. Other uses of polyurethanes include coatings, sealants, and adhesives. 

Another widespread use of polyurethane elastic fibers is in disposable diapers and adult incontinence garments. Elastic strands are incorporated into waistbands and side panels made of non-woven fabrics where they improve fit and reduce leakage. 

There are several interesting applications reported in the literature, such as insulated wire and cable, UV cross-linking of drawn fibers, and tapes from ultra-high-molecular-weight polyethylene. Semi-interpenetrating networks (IPNs) from acrylates and polyurethanes are suitable as UV curable adhesives with high elasticity, good impact resistance, and excellent adhesion to a variety of substrates. ... 

Elastomeric Fibers. Elastomeric fibers are polyurethanes combined with other nonelastic fibers to produce fabrics with controlled elasticity. See also Fibers Elastomeric. Processing chemicals must be carefully selected to protect all fibers present in the blend. 

Elastane. The DuPont Company commercialized the first manufactured elastic fiber, Lycra, in 1958. Originally categorized as a span-dex fiber, the name elastane has become more common around the world. This specialty fiber is described as a segmented polyurethane that contains hard and soft segments their ratio determines the amount of stretch built into the fiber. Elastane fibers are formed by dry-spinning or solvent-spinning. The continuous filaments can be coalesced multifilaments or monofilaments, depending on the manufacturer. 

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