Why does spandex fabric turn yellow

Characteristics of Spandex

1. Spandex fiber has excellent elasticity, and its elastic elongation is the highest among textile fibers, which can reach 400% to 500%; the elastic recovery rate is also high, which can reach 95% to 99%.

2. Spandex is a thermoplastic fiber, with a softening point of 160°C, a safe ironing temperature <150°C, and a heat setting temperature between 185°C and 190°C.

3. Spandex is a hydrophobic fiber with low moisture absorption.

4. The relative density of spandex is low, about 1.20, so the texture of spandex is looser.

5. The surface friction factor of spandex is very large, about 0.7 to 1.30, which is 5 to 7 times that of wool (about 0.14 to 0.17 for wool), and 3 to 4 times that of synthetic fibers such as polyester and nylon. Therefore, when spinning spandex yarn, a large amount of silicone emulsion should be used in the spinning finish to facilitate stretching and winding.

6. Spandex is not resistant to ultraviolet rays and is easy to turn yellow after prolonged sun exposure, but it will not cause immediate loss of strength. Polyether spandex is more prone to yellowing than polyester spandex.

7. Spandex is resistant to dilute acids and alkalis at room temperature, and its acid resistance is much better than alkali resistance; it is resistant to reducing agents, as well as oxidizing agents and bleaching agents that do not contain effective chlorine.

Reasons for yellowing of spandex fabrics

1. Since the spandex molecular chain contains a large number of reactive groups such as amino groups, it is easy to turn yellow during high temperature setting or storage, which affects the quality of finished products, especially fluorescent whitening fabrics and light-colored fabrics.

2. In order to improve the spinning performance of spandex, silicone oil lubricants and other additives are used in the weaving process. These additives will naturally degrade over time and cause the fiber to turn yellow.

3. Spandex is not resistant to ultraviolet rays, it is easy to turn yellow after prolonged exposure to sunlight, but it will not cause immediate loss of strength. Polyether spandex is easier to yellow than polyester spandex. When spandex is subjected to dry heat treatment, if the time is too long or the temperature is too high, it will also cause yellowing, and will cause the loss of strength and elasticity. This is because the soft segment of polyether is Caused by oxidation. Certain nitrogen oxides, sulfur oxides, aldehydes and flue gas in the atmosphere can also cause yellowing of spandex and affect the appearance of finished products. Certain unsaturated oils, unsaturated fatty acids and certain fatty substances in skin secretions have an extracting effect on certain stabilizers in spandex yarns, which will increase the sensitivity of spandex to photooxidation, and make spandex more likely to yellow after sun exposure. .

4. Spandex will also turn yellow if it comes into contact with chemicals containing available chlorine, so it is best to cover it with polyethylene film during storage.

5. In addition, spandex itself is not easy to color, that is, conventional dyes cannot color spandex. Therefore, after the fabric is dyed, the so-called yellowing phenomenon will also occur if the reduction and cleaning are not sufficient.