Fibres polyurethane

Compared with nylon 66 fibres, the polyurethane fibres (known as Perlon U) have a tensile strength at the higher end of the range quoted for nylon 66, they are less prone to discolouration in air, are more resistant to acid conditions and they have a lower moisture absorption. On the debit side they are less easy to dye, are hard, wiry and harsh to handle and have too low a softening point for many applications. They are currently of little importance but have found some use in bristles, filler cloths, sieves and a few other miscellaneous applications. 

Whilst the crystalline fibres and their thermoplastic counterparts are no longer of importance, elastic polyurethane fibres, commonly known as spandex fibres, are of significance. These will be considered further in Section 27.4.1. 

Polyurethane fibres were made in Germany during World War II. These were later improved. Today, these fibres are sold as Spandex. They have properties like that of rubber. 

Polyurethane fibres (Perlon U) were prepared by reacting hexamethylene disocyanate with 1,4 butanediol in 1942. Because they were difficult to dye and had harsh feel so went out of the market. But these resins are used for small mechanical components like gears and bearings because of dimensional stability and retention of electrical resistance in humid conditions. 

Just as the products of polycondensation are greatly varied, so are the reaction conditions used in their production. Some are produced in the melt (many polyamides and polyesters), some initially in the melt but with extensive polymerization continuing in the solid state (polyurethane foams and elastomers), in solution (some polyurethane fibres) or in non-homogeneous liquid systems (some polycarbonates, very high melting polyamides). 

Modern polyurethanes fibres (such as Lycra ) use tetrahydrofuran as a starting material rather than butanediol. 

K GisselMt, P Flodin and B Edberg, Biodegradable polyurethane fibres svq>port natural healmg processes . Text Asia, 1998 29 52-54. 

Polyurethane fibres of a kind different to those described above have become important within the last decade these are elastomeric fibres, which are commonly called spandex fibres. These products are made either by solution spinning or by reaction spinning. In the first process, a hydroxy-terminated polyester (e.g., an adipate) or polyether (e.g., poly(oxytetramethylene) glycol) is treated with an excess of diisocyanate (e.g., tolylene diisocyanate) to give an isocyanate-terminated pre-polymer similar to those used for cast elastomers (Section 14.6.1). The pre-polymer is dissolved in a strongly polar solvent (e.g., dimethylformamide) and treated with an aliphatic diamine or hydrazine to effect chain extension with hydrazine the following reaction occurs ... 

It was claimed that the hard cyclic structure restricts chain mobility to become an effective tie-down point (thus avoiding the need for chemical cross-linking). When 65% of the formulation was the poly(tetramethylene ether)glycol, elastic fibres similar to the Spandex polyurethane fibres were obtained. 

Lin J, Han F, Shang Y, Wang F, Ding B, Yu J, Guo Z (2013) Co-axial electrospun polystyrene/polyurethane fibres for oil collection from water surface. Nanoscale 5(7) 2745-2755. doi 10.1039/c3nr34008b... 

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