Textured Yarns

Textured Yarns

 

yarns of synthetic fibers that differ from ordinary textile yarns in their greater bulk, strong crimp, loose structure, and, in some cases, high stretchability.

The production of textured yarns stemmed from the need to broaden the area of use of synthetic fibers; applications of such fibers had previously been limited by the fibers’ low hygroscopicity and smooth surfaces, which had an unpleasant, glassy sheen. Texturing improves the use characteristics and hygienic properties of synthetic yarns.

Textured yarns are used for manufacturing a wide variety of textile products: hosiery, knitted underwear and outer wear, and shape-retaining knitted fabrics for men’s and women’s suits and overcoats. They are also used in the production of artificial fur, carpets, blankets, and drapery and upholstery fabrics. As of 1975, world production of textured yarns was approximately 1.5 million tons a year.

The following types of textured yarns are distinguished by production method, properties, and use: high-tensile, low-tensile, crimped, loop, shaped, bicomponent, combination, and high-bulk yarns.

High-tensile yarn is called elastik in the USSR; abroad, the trade name “Helanca” is usually used. It is produced by the twisting of compound synthetic fibers (polyamide, polyester, and other fibers) up to 2,500–5,000 twists per meter, heat setting of the twisted yarn, and untwisting of the set yarn. The yarn assumes a spiral shape and acquires high stretchability (up to 400 percent) and fluffiness.

Low-tensile yarns differ from high-tensile yarns in their greater bulk, high crimp, and fluffiness, with little elastic elongation. In the USSR, low-tensile yarns produced from capron (polyamide) fibers are called meron, and those made from lavsan (polyester) fibers are called melan; abroad, the trade names “Saaba” and “Astralon” are often used. Such yarns are produced by additional heat treatment of high-textile yarns. (See alsoLOW-TENSILE TEXTURED YARNS.)

Crimped yarns are usually obtained by goffering from synthetic yarns that are tightly packed into a special chamber and subjected to heat treatment. The term gofron is used in the USSR for such yarns; it corresponds to the trade names “Ban-Lon” and “Textralized” used abroad. Crimped yarns are marked by a zigzag crimp, softness, high bulk, and comparatively low stretchability. In a second method, a synthetic yarn is drawn across the sharp edge of a steel plate. The yarn undergoes complex deformation, and the individual fibers acquire a spiral shape. In the USSR such yarn is known as rilon; the trade name “Agilon” is used abroad. Crimped yarns are also produced by the knitting method. Ordinary thermoplastic compound yarns are used on high-speed knitting machines to produce a fabric that is subsequently subjected to heat treatment, as a result of which the yarns acquire a permanent twist after the cloth is removed.

Loop yarns are obtained by exposing a composite yarn to a jet of air at the moment it passes through the orifice of a device to which air is supplied under pressure. In the USSR, the term aeron is used for such yarns; it is analogous to the trade name “Taslan” used abroad.

Shaped yarns (polyamide, polyester, and other types) are formed by spinnerets with shaped orifices rather than round ones. As a result, yarns with various cross sections or with internal channels are produced. With ordinary stretchability, they have a lower weight for a given volume, a matte finish, and increased hygroscopicity. Yarns similar in appearance and properties to natural yarn can be obtained by this method.

Bicomponent yarns are formed from two or more polymers. The orifices of the spinnerets are separated by a partition into two or more sections, and a different spinning mixture is fed to each section. The yarns formed consist of several, chemically different parts. After drawing, they are subjected to heat treatment. The polymers exhibit different degrees of shrinkage, and the yarns thus acquire a crimp, greater bulk, and a loose structure.

Combination yarns are obtained from the combined texturing of different yarns, for example, acetate and capron, by twisting textured yarns with different structures and properties, or by twisting ordinary composite or high-tensile yarns with staple fibers.

High-bulk yarn is produced by combining a low-shrink fiber with chemical staple fibers (primarily polyacrylonitrile) having a shrinkage of 20–30 percent. Heat treatment of such yarn in a free state shortens the high-shrink fibers but leaves the low-shrink fiber virtually unchanged in length. The low-shrink fiber is bonded to the high-shrink fibers by friction, and the fibers are bent, which gives the yarn a fluffy appearance.

The ever increasing demand for textured yarns fosters the development of new texturing methods and the improvement of existing ones. Technical progress in texturing methods is being carried out in the following directions: increasing equipment productivity; developing new texturing principles, for example, separating jointly twisted yarn without using complicated and expensive false-twisting equipment; combining several processes, such as shaping, drawing, and texturing, in one unit; increasing the capacity of yarn packages; mechanizing and automating operations, such as the loading of machines, the eliminating of breaks, and the removal of the finished packages; and automatic control of production parameters by means of programming devices.

REFERENCE

Usenko, V. A. Pereabotka khimicheskikh volokon. Moscow, 1975. Pages 255-396.

V. A. USENKO

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