The performance of spandex

Elasticity

Spandex fiber has great elasticity. Under normal circumstances, it can be stretched to 4 to 7 times of its original length, and its recovery rate is almost 100% when stretched by 2 times, and its resilience rate is 95 when stretched by 500%. ~99%, which is unmatched by other fibers. Generally speaking, in the molecular structure of spandex fiber, the larger the molecular weight of the soft segment, the stronger the elasticity and rebound rate of the fiber. Polyether spandex has higher elasticity and rebound rate than polyester spandex; chemically crosslinked spandex Its resilience is better than that of the physical cross-linking type.

Strength

Because of its elasticity, spandex cannot be tested for strength in the same way as other fibers. When the fiber is stretched to the maximum length, the fiber becomes thinner, and the strength measured at this fineness is the effective strength. Due to the different structure of spandex, its strength is about 4 to 5 cN/dtex, while the breaking strength is 0.44 to 0.88 cN/dtex in dry state and 0.35 to 0.88 cN/dtex in wet state. Since the moisture absorption of spandex fiber is extremely low (0.3% to 1.3%), the plasticizing effect of water on spandex is not obvious, so its wet strength is only slightly lower than the dry strength. When the breaking strength of spandex fiber is close to 0.88cN/dtex, its elongation energy can reach 350% to 600%. Of course, the breaking elongation of spandex is large, and its breaking work is also great.

Heat resistance

The softening point of spandex is 205～210℃, it turns yellow at 150℃, and its strength decreases at 190℃, even sticky. Therefore, the general setting temperature of spandex fabric should not exceed 175～180℃. Due to the difference between the structure of the fabric and the winding method of spandex and other fibers, the setting temperature of covered yarn fabrics generally does not exceed 180℃, the setting temperature of core-spun thin fabrics can reach 190℃, and the setting temperature of core-spun thick fabrics can reach 195. ～210℃.

Dyeing performance

For core-spun yarns, covered yarns, and twisted yarns, since spandex is almost completely covered by external fibers after dyeing, it is generally not necessary to consider the color of spandex, but spandex itself can be directly dyed, vat dyes, acid dyes, and disperse Dyes, reactive dyes, etc. However, the color fastness of direct dyes and reactive dyes is poor (especially for dark colors). If the bare silk of spandex fiber or spandex fiber is not completely covered by the external phase fiber, the dyeing of spandex must be considered.

Chemical resistance

Spandex is resistant to most acids, alkalis and chemical solvents, especially polyether spandex. Whether it is core-spun yarn, covered yarn or twisted yarn, during dyeing and finishing such as scouring, bleaching and mercerizing, most of spandex has been covered by external fibers, and the exposed surface area is very small, so it can be dyed with external fibers. Finishing process.