How does the spandex pre-drafting multiple affect the strength and elongation of air-coated yarn?

Spandex air-coated yarn uses spandex filaments as elastic core material, and the outer fiber filaments form a periodic network structure through aerodynamic action. Its unique composite structure makes it widely used in the textile field. Among the many factors that affect the mechanical properties of the yarn, there is a close and complex relationship between the spandex pre-drafting multiple and the strength and elongation. The inherent mechanism of this relationship profoundly affects the actual application performance of the yarn.

Spandex pre-drafting refers to the process step of applying a certain external force to the spandex filaments before they enter the air-coated yarn production process to make them stretch and deform. In this process, the arrangement of the spandex molecular chains changes significantly. When not stretched, the spandex molecular chains are in a disordered curled state; as the pre-drafting multiple increases, the molecular chains are gradually straightened and oriented, and the interaction between molecules is enhanced. When the spandex yarn and the outer fiber filament enter the air coating device together and form a coating structure under the action of high-pressure airflow, the pre-stretched spandex yarn can more effectively transfer the external force to the outer fiber. The synergistic effect of the two significantly improves the overall resistance of the yarn to stretching. Therefore, within a certain range, the increase in the spandex pre-stretching multiple directly leads to the enhancement of the strength and elongation of the spandex air-coated yarn.

However, this positive correlation does not extend infinitely. When the spandex pre-stretching multiple exceeds the critical value, the strength and elongation of the yarn decreases instead. This is because excessive stretching causes the spandex molecular chain to reach the limit orientation state, and the intermolecular force is close to the fracture threshold. At this time, the elastic recovery ability of the spandex yarn is greatly weakened. When it is stretched by external force, it is not only difficult to effectively absorb and disperse stress, but also very easy to break. At the same time, excessive stretching causes the spandex yarn diameter to become thinner, the contact area with the outer fiber is reduced, and the friction and cohesion between the two are reduced, making the outer fiber more likely to slip when subjected to force, and unable to form a stable synergistic force system with the spandex yarn, thereby seriously affecting the strength and elongation of the yarn.

The strength and elongation of spandex air-coated yarn are also closely related to the yarn structure. Changes in the spandex pre-drafting multiple will affect the winding morphology and network point distribution of the outer fiber filaments on the spandex surface. When pre-drafted appropriately, the elastic deformation of the spandex yarn is compatible with the winding structure of the outer fiber, and the network points are evenly distributed and have high fastness, which can effectively transmit external force and enhance the overall strength and elongation of the yarn. However, when the pre-drafting multiple is too large and the spandex yarn is over-elongated, the winding tension of the outer fiber will be unbalanced, the formation and distribution of the network points will be disturbed, and some network points will become loose or even missing, unable to fully play the role of fixation and support, thereby reducing the strength and elongation of the yarn.

From the perspective of practical application, it is very important to accurately grasp the relationship between the spandex pre-drafting multiple and the strength and elongation. When producing sportswear fabrics, if the yarn needs to have high elasticity and strength to adapt to the frequent stretching of the human body during exercise, it is necessary to reasonably control the spandex pre-draft multiple, so that it can ensure the strength and elongation while taking into account good elastic recovery performance, ensuring that the clothing can still maintain its shape and comfort after multiple wears and washings. When producing some fabrics with high requirements for softness and drape, although the spandex pre-draft multiple can be appropriately reduced to reduce the rigidity of the yarn, it is also necessary to carefully weigh it to avoid damage or deformation of the fabric during use due to insufficient strength and elongation.

The spandex pre-draft multiple has an important influence on the strength and elongation of spandex air-coated yarn by affecting the spandex molecular chain structure, the interaction between the fibers inside the yarn, and the overall structural morphology. Understanding and mastering this relationship is of key significance for optimizing the production process of spandex air-coated yarn, improving product quality, and expanding its application in different fields. In the future development of textile technology, in-depth exploration of this performance correlation mechanism will help develop spandex air-coated yarn products with better performance and more in line with market demand.