False-twisting

The film is fibrillated mechanically by mbbing or bmshing. Immiscible polymers, such as polyethylene or polystyrene (PS), may be added to polypropylene to promote fibrillation. Many common fiber-texturing techniques such as stuffer-box, false-twist, or knife-edge treatments improve the textile characteristics of slit-film fibers. 

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. 

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. 

The yarn elasticity plays a minor role, unless the elasticity of the yam is very low or very high (high-elastic false twist yarns, elastomeric yams). 

Spun nylon Textured nylon False twist nylon False twist nylon... 

Crimp rigidity test. A form of crimp rigidity test used in the UK for the testing of false-twist textured nylon yarns. 

A) Mechanical crimping is carried out by false twisting, compression in a stuffing box, knitting, edge bending, by gears, and hot blows "... 

Such procedures may be u ful for crimping continuous filament yams instead of eitifdoying false twist, which requires expensive equipment. 

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. 

False-twist texturing depends on setting fibers in a kind geometry and then changing to another, which generates elongation that can be recovered by bulking. Another method is to set fibers in the required crimped form. This was the basis for stuffer-box and other methods. 

---