Spandex yarn is a kind of fiber made of block copolymer with polyurethane as the main component. It has the characteristics of high elongation, high elastic recovery, low elastic modulus and good fatigue resistance. This paper introduces the reasons for the high elasticity of spandex fiber and its main varieties.

1.Reasons for spandex yarn high elasticity

The high elastic properties of polyurethane fibers are different from those of ordinary elastic fibers, which depend on the composition of polymer macromolecules and the characteristics of supramolecular structure. The flexible soft segment is composed of aliphatic polyester or polyether, which can be regarded as a spring that is easy to stretch; The rigid segment is composed of carbamate and urea group, just like a rigid ball. The net formed by connecting springs with small balls is an elastomer with certain strength. The two segments are linked by covalent bonds. Because each single bond in the soft chain segment makes different degrees of internal rotation around the adjacent single bond, the long chain segment with curved shape is like a messy thread group, and its shape is constantly changing. Macromolecules have great adaptability under the action of external forces, and there is also a lot of room for extension in length, which gives spandex yarn the characteristics of high elongation and high elastic recovery.

2.Main varieties of spandex yarn

The main varieties of spandex yarn include bare silk, core spun yarn, covered yarn and twisted yarn.

Naked silk is the earliest developed variety. It can be used for processing and production without spinning. Because the friction coefficient of bare silk is large and the slippage is poor, it is not used directly in weaving fabrics. It is usually suitable for knitting machines to interweave with other chemical fiber filaments. The main textiles include tights, sportswear, leggings, surgical bandages, etc.

Core spun yarn is the most widely used variety in spandex. It takes spandex as the core yarn and is wrapped with one or several non elastic staple fibers (cotton, wool, acrylic, polyester, etc.).

The core yarn provides excellent elasticity, and the peripheral fibers provide the necessary surface properties. For example, the textile fabric of wool core spun yarn not only has the appearance and warmth retention of general wool fabric, but also can stretch freely when wearing.

Wrapped yarn is also called wrapped yarn. It takes spandex as the core and is wrapped by synthetic filament or yarn in a spiral way to form an elastic yarn. Its handle is hard, the yarn is thick, and the fabric is thick. It is mainly used for elastic fabrics such as socks, elastic belts, leg guards, etc.

Twist yarn, also known as ply yarn, is produced by combining the drafting of spandex with the twisting of other two strands of inelastic yarn. Twisted yarn is mostly used for weaving thick fabrics, which has a hard hand feel.

Spandex yarn is a kind of highly elastic man-made fiber, which is made of linear polymer material containing more than 85% polyurethane chain segments. Mastering the relevant knowledge of spandex fiber is conducive to the better use of this material.