Spandex yarns are so elastic because their polymer chains are made up of low- and high-melting amorphous 'soft' segments embedded with crystalline 'hard' segments. The molecular chains of the flexible segment form a certain network structure through certain cross-links. Since the interaction force between the molecular chains is very small, they can expand and contract freely, resulting in a large elongation. The resultant force of the molecular chain in the rigid segment is relatively large, the molecular chain will not be stretched infinitely, and the resilience is high. The cross-section of radon wire is mostly dog-bone-shaped, and some wires have a smooth or jagged surface. All textile fibers have low breaking strength, a small range of moisture absorption, and heat resistance varies greatly with different varieties. Most of the fibers are stored in the range of 90 ~ 150° for a short time, and the fibers will not be damaged. The safe ironing temperature is below 150°, and it can be heated and disturbed and wet cleaned. Excellent dyeing performance, can be dyed into various colors. The dye has strong affinity to fibers, can adapt to most kinds of dyes, and has good chemical resistance. It is resistant to most acids and bases, chemical agents, organic solvents, dry cleaning and bleaching agents, as well as sunlight and snow, but it is not resistant to oxidizing agents, which yellow the fibers and reduce their strength.
Spandex yarn is generally not used alone, but added to fabrics in small amounts. This fiber has both rubber properties and fiber properties, and is mostly used in core-spun yarns with spandex as the core thread, called elastic core-spun yarns. The main features of this type of yarn are: 1. Good hand feel and appearance can be obtained, and the outer fibers composed of natural fibers have good hygroscopicity. 2. Only 1-10% of spandex filament can be used to produce high-quality stretch yarn. 3. The elastic percentage is controlled at 10%-20%, and different elastic values can be selected according to the product use.
As people put forward new requirements for fabrics, such as lightness, fit and comfort, and soft texture, the proportion of low-denier spandex yarns in synthetic fabrics is increasing. There are also naked spandex yarns and twisted yarns formed by combining spandex with other fibers, which are mainly used in various warp-knitted and weft-knitted fabrics, woven fabrics and elastic fabrics.