Sometimes customers complain about spandex-containing fabrics sent out by printing and dyeing factories. The main complaints are that the fabric surface is poor, rungs appear, and the spandex turns yellow. There are some issues that really make people confused. The raw materials come from large factories, and the dyeing factory that makes the goods is also a standard dyeing factory. Moreover, this cloth has been shipped in many large quantities, and no customers have reported any problems. To know where these problems lie, we need to first understand the character of spandex.
01 Characteristics of spandex
1. Spandex fiber has excellent elasticity and its elastic elongation It is the highest among textile fibers, reaching 400% to 500%; the elastic recovery rate is also high, reaching 95% to 99%.
2. Spandex is a thermoplastic fiber with a softening point of 160°C. The safe ironing temperature is <150°C. The heat setting temperature is preferably between 185 and 190°C.
3. Spandex is a hydrophobic fiber with low hygroscopicity.
4. The relative density of spandex is low, about 1.20, so the texture of the entire spandex is loose.
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 (wool is about 0.14 to 0.17), and 3 to 3 times that of synthetic fibers such as polyester and nylon. 4 times. Therefore, when spinning spandex yarn, a large amount of silicone emulsion should be used in the spinning oil to facilitate stretching and winding. 6. Spandex is not resistant to ultraviolet rays and will easily turn yellow after being exposed to the sun for a long time, but it will not cause immediate loss of strength. Polyether spandex is more likely to yellow than polyester spandex. 7. Spandex can resist dilute acid and dilute alkali at room temperature, and its acid resistance is much better than alkali resistance. It is resistant to reducing agents, and is also resistant to oxidants and bleaches that do not contain available chlorine.
02 Reasons for the 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 running performance of spandex during spinning, silicone oil lubricants and other additives are used in the weaving process. These additives will naturally degrade over time causing the fiber to turn yellow.
3. Spandex is not resistant to ultraviolet rays and will easily turn yellow after long-term sunlight exposure, but it will not cause immediate loss of strength. Polyether spandex is more prone to yellowing 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 loss of strength and elasticity. This is because the polyether soft segment is Caused by oxidation. Certain nitrogen oxides, sulfur oxides, aldehydes and smoke in the atmosphere can also cause spandex to turn yellow and affect the appearance of the finished product. Some unsaturated oils, unsaturated fatty acids and certain fats in skin secretions have an extraction effect on certain stabilizers in spandex yarns, which will increase the sensitivity of spandex to photooxidation and make spandex more likely to turn yellow after being exposed to the sun. .
4. Spandex will also turn yellow if exposed to chemicals containing available chlorine, so it is best to wrap it with polyethylene film during storage.
5. In addition, spandex itself is not easy to color. That is to say, conventional dyes cannot color spandex. Therefore, after the fabric is dyed and the restoration and cleaning is insufficient, so-called stains may also occur. yellowing phenomenon.
03 Reasons for indentation
In order to improve the running performance during spinning, spandex is used in the weaving process. Silicone lubricants and other additives. These additives will naturally degrade over time, causing the fibers to turn yellow and the fabric’s elasticity to decrease. At the same time, spandex-containing fabrics will form “cold setting” during long-term storage, causing the fabric to produce permanent wrinkles that cannot be eliminated during post-processing. Therefore, in addition to reducing the storage time of spandex-containing knitted fabrics, it is more important to open the width immediately after weaving and then roll it in an open width to avoid the chance of creasing. </p
