Spandex polymers properties

In much the same way, natural polymeric fibers like wool, cotton, silk, etc., are often touted as superior to anything that is man-made or synthetic. But is this fair There is no doubt that natural fibers have a unique set of properties that have withstood the test of time (e.g., it is difficult, but not impossible, to match silk s feel or cotton s ability to breathe ). On the other hand, consider Lycra , a completely synthetic fiber produced by DuPont (Figure 1-12) that has a truly amazing set of properties and is the major component of Spandex (a material that keeps string bikinis on ). Or consider the wrinkle-free polyester fibers used in clothing and the stain proof nylon and polyacrylonitrile polymers used in carpets. The point here is that polymers, be they natural" or synthetic, are all macromolecules but with different chemical structures. The challenge is to design polymers that have specific properties that can benefit mankind. 

As a general rule, for linear polymers all the properties, such as tensile strength, elongation, elasticity, melting points, glass transition temperature (Tg), modulus and increase of the MW, increase up to a limited value, where all the properties remain practically constant. This behaviour is valuable for linear polymers, in our particular case in linear polyurethanes (PU elastomers, spandex fibres, etc). 

One of the most important uses of polyurethanes is in fabrics with elastic properties, such as spandex (Lycra ). These materials are block copolymers in which some of the polymer segments are polyurethanes, some are polyesters, and some are polyamides. The blocks of polyurethane are soft, amorphous segments that become crystalline on stretching (Section 28.7). When the tension is released, they revert to the amorphous state. 

In 1970, anidex fibers were introduced as an elastomeric fiber by Rohm and Haas with the trade name Anim. Anidex fibers are defined as fibers containing polymers that are at least 50%of one or more polymerized acrylate esters. Anidex fibers are formed through emulsion copolymerization of acrylate esters with reactive crosslinkable comonomers such as N-methyl ol-acrylamide. The resulting copolymer emulsion is mixed with a filler and wet spun to form a fiber which is heated to crosslink the polymer chains and provide the necessary elastomeric properties. The morphology and elastomeric action of the fiber resemble spandex and rabber, but anidex generally has a lower elongation at break than these fibers. It has a round... 

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