False-twist textured yams

Atkinson C. False twist textured yams principles, processing and applications. Cambridge Woodhead Publishing Ltd 2012. 

In false twist texturing (FTT), shown schematically in Figure 7, a device twists yam upstream of its location as the threadline passes across a heater, and the yam untwists downstream from the device and is wound up. If the yam is not heated downstream from the twist device, it has bulk and high elasticity (stretch). If the yam is heated downstream from the twist device, it has bulk, but much less stretch. FTT machines initially used two steps to sequentially draw and texture. Later machines combined those steps to simultaneously draw and texture (92). Initial machines used pin spindles as the false twist device. Texturing speeds were about 150 m/min and slowly increased to about 300 m/min. As POY quaUty and stmctural stabiUty improved, new... 

The air jet textured yam process is based on overfeeding a yam into a turbulent air jet so that the excess length forms into loops that are trapped in the yam stmcture. The air flow is unheated, turbulent, and asymmetrically impinges the yam. The process includes a heat stabilization zone. Key process variables include texturing speed, air pressure, percentage overfeed, filament linear density, air flow, spin finish, and fiber modulus (100). The loops create visual and tactile aesthetics similar to false twist textured and staple spun yams. 

Commercial textured yams cover a range of yam sizes and end uses. The 1.7—3.3-tex (15—30 denier) yams for hosiery are false-twist-textured, as is the 4.4—22.2-tex (40—200 denier) yams for apparel. The 56—333-tex (500—3000 denier) yams for carpets, upholstery, and soft-sided luggage are air- and fluid-jet-textured. 

False-twist textured Crimp, flat character - Air-textured Staple fiber yam-like character... 

PTT POY yams were textured by the false-twist method at 140 to 160 °C. Crimp development was almost twice as high as PET, with crimp contraction reaching about 50 %. When PTT yams with a high level of crimp contraction are knitted into stretch fabrics, the amount of stretch achieved is equivalent to PET stretch fabrics incorporated with 6 to 8 % of Spandex [89], In addition to stretch, PTT fabrics tend to have softer hand and better drape than PET. Since they do not absorb moisture like nylon, PTT fabrics also have a desirable dry touch and comfort. 

Bicomponent stretch fiber such as T400 also can be used in the classification of stretch and recovery properties, which positions it between elastane and standard mechanically textured yams. Self-crimp fibers behave like natural wool with a textured appearance. The crimps are from a composite of two parallel attached fibers with differing shrinkage or expansion properties. Usually, the crimp is generated by either false-twist or air-texturing on the fiber via mechanical deformation of the fiber as a 2D zig-zag crimp. A combination of various polyester materials can be used, for example, PET (polyethylene terephthalate), PTT, and PBT. 

Textured yams give low to medium elongation and elastic recovery in sportswear. The current methods commonly used for sportswear yam production include false-twist, air jet, and BCF. 

The threads used to lead to the velour stmcture in a fabric are texturized, usually by the false-twist method, and heat set so that they are pre-shrunk. These threads are also fed at a higher rate and lower tension than are the threads that form the rest of the fabric. The latter are plain, that is, untexturized, and not heat set. The warp comprises both types of yarn, and the fill may be of the unshrunk, untexturized, yam alone or may be used in combination with pre-shrunk, texturized yam, the two types twisted together (in the fill only) prior to weaving. When the tubular fabric is heat set to develop corrugations, only the unshrunk threads will shrink, not the pre-shmnk texturized yarns. This will cause the latter to form projected loops. 

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