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Popular Science | Why does spandex lose elasticity?

01 How many forms of spandex elastic fiber yarn are there? Spandex elastic fiber is mixed with other fibers and spun into elastic yarn. There are currently three forms of yarn: spa…


How many forms of spandex elastic fiber yarn are there?

Spandex elastic fiber is mixed with other fibers and spun into elastic yarn. There are currently three forms of yarn: spandex core-spun yarn, spandex composite yarn Twisted yarn and spandex covered yarn. The three forms of yarn are essentially different in processing principles and structural properties. Therefore, their uses and weaving properties also vary greatly. The structural diagram of the three types of yarns is shown in the figure.


What is the origin of spandex fiber and its main properties?

Spandex fiber is a kind of elastic fiber. Elastic fiber is collectively called Spandex abroad. The product name in my country is spandex. In fact, spandex fiber is Spandex is only one major category of elastic fibers. Spandex fiber (Polyurethane Fibre) is referred to as PU fiber. There are two varieties. One is a copolymer made of aromatic diisocyanate and polyester segments containing hydroxyl groups, which is referred to as polyester spandex. The other variety is made of aromatic diisocyanate and hydroxyl-containing polyester segments. Polyether segment-embedded copolymer of hydroxyl groups is referred to as polyether spandex. The representative trade name of polyester spandex is Vyrent, and the representative trade name of polyether spandex is Lyera.

The main properties of spandex fiber are: usually an elongation of 500% to more than 700%, and good elastic recovery performance. It retracts 97% at 200% elongation and over 99% at 50% elongation.

The relative density difference of various spandex is small, generally 1.20~1.25, and the breaking strength is 4.41~8.82cN/tex (0.5~1.0g/ Denier), polyester spandex has lower strength, while polyether spandex has higher strength. The moisture absorption rate is generally 0.3%-1.2%. The moisture absorption rate of multifilament is slightly higher than that of monofilament. The heat resistance is generally between 95 and 150°C. Short-term storage will not damage the fiber. The safe ironing temperature is below 150°C.

Fiber burns slowly and forms a gelatinous residue after burning. It has excellent dyeing performance, can be dyed in a variety of colors, and has strong affinity for dyes. It has good acid and alkali resistance, can be bleached, and does not become moldy.


Spandex dyeing

Spandex can be dyed with disperse dyes and acid dyes, but the fastness of these two dyes is too poor, and experiments have shown that nylon is dyed with reactive dyes (dyed with nylon elastic Cloth) and dispersed cationic dyes (dyed CDP elastic cloth) on spandex base�Does not stain. Does this mean that these two dyes are not suitable for spandex dyeing? In fact, it is not the case. With the appropriate additives as the medium, nylon can be dyed with reactive dyes for spandex, and the fastness and depth are relatively good. excellent.

There are very few pure spandex fabrics on the market, so spandex dyeing is relatively unfamiliar. Pure spandex fabrics can be used together with low-elastic fabrics or non-elastic fabrics to increase the elasticity and resilience of the fabrics. . And when the elastic fabric is stretched or pressed, if the color of the spandex is inconsistent with the filament, there will be a problem of color leakage of the spandex, which requires dyeing the spandex.


For dyeing spandex in light colors

Yes Use acid dyes or disperse dyes for dyeing under acidic bath conditions. Under the same dye dosage, the fastness of disperse dyes to spandex is better than that of acid dyes. However, the fastness of different disperse dyes to spandex is different. Generally, the dye dosage is less than 0.5 % can be dyed with disperse dyes

Spandex is a highly elastic fiber. Considering that long-term dyeing under high temperature conditions will cause the spandex to lose elasticity, it is generally dyed below 100℃, and spandex does not It is resistant to alkali, and disperse dyes and acid dyes are suitable for dyeing under acidic conditions. Generally, spandex is dyed under acidic bath conditions, and the pH is around 5.

Various dyes can be dyed with suitable auxiliaries as a medium to dye spandex. This type of auxiliary is called spandex colorant or spandex colorant on the market, and it is mainly used for nylon. Spandex dyed with reactive dyes, acid dyes, etc. is generally zwitterionic in nature.

The working principle is roughly as follows: under acidic conditions, groups such as amide bonds in spandex are ionized and become positively charged, and the spandex coloring agent reacts with them, and the fixing agent is fixed On spandex, since the spandex colorant contains amino cations, the dye can also combine with the spandex colorant.


Nylon active Rules for dyeing spandex with dyes (adding spandex coloring agent)

1. The general rules for the fastness of spandex after dyeing: water washing>perspiration (acid)>water immersion, and the wet rubbing fastness is much better than the dry rubbing fastness. Analyzing the reason, after spandex is colored, the dye or the combination of spandex coloring agent and dye will migrate under wet conditions under the long-term action of external pressure, and it is a slow process (spandex is a hydrophobic fiber, and water molecules will not quickly enter the interior of the fiber, and the dye will not migrate quickly), so its washing fastness is better. Secondly, under the acidic conditions of sweat stains, it is beneficial to the ionization of the amide bonds on the spandex or the amino groups on the spandex colorant, which can capture the migrating It is a combination of dye or spandex coloring agent and dye, so the acid perspiration fastness is better than the neutral water immersion color fastness. Under the action of friction, dry grinding will generate heat, causing the dye on the surface of spandex to thermally migrate, which does not occur under wet conditions.

2. Boiling soda ash after dyeing spandex will reduce its fastness by about 0.5 levels. This is because under alkaline conditions, the combination of spandex coloring agent with fiber and dye will be damaged, resulting in reduced fastness. Secondly, after spandex is dyed, cationic fixatives are used to fix the color. The fastness improvement is greater than that of anionic fixatives. The cationic fixatives can react with the water-soluble groups (-SO3-) produced by the dye and block the water-soluble groups. The water solubility of the dye is reduced, and the fixing agent forms a film on the fiber surface, which can isolate the dye, and the dry rubbing fastness is accordingly improved.

3. The light fastness of spandex dyed with acidic, dispersed and nylon reactive dyes is worse than that of polyester or nylon. Silk. The main reason is that spandex has low crystallinity and is in a high elastic state at room temperature. Air can easily enter the fiber and change color under the influence of sunlight. Furthermore, spandex itself will turn yellow under the influence of sunlight. , which is also the reason for the low light fastness


When cotton stretch fabric is dyed black

Spandex will To expose the white, you can generally add a small amount of disperse or acid black to the dye bath to dye spandex, but you should pay attention to the fastness problem. Secondly, for the problem of black spandex color exposure when polyester elastic and nylon elastic fabrics are dyed, a small amount of spandex coloring agent of about 0.3% can be added to the dye bath when dyeing polyester elastic fabrics. When dyeing nylon elastic fabrics, spandex coloring agent can be added directly to the dye bath. Dyeing, so that the problem of color exposure of spandex can basically be solved. The problem of color exposure of spandex in other colors can be deduced according to the above analogy.


Why does denim spandex lose elasticity?

Low elasticity and high elasticity materials of spandex core-spun yarn in denim fabrics are becoming more and more common, and the elasticity of spandex directly determines the denim washing process In addition to its poor quality and easy elasticity, spandex elastic yarn is also affected by many external factors.

1. Enzyme powder in the enzyme washing process

Due to Enzyme powder is a multi-component compound, and the differences in its internal chemical components will affect the elasticity loss of spandex, especially the anti-dyeing powder component. The enzyme powder used basically does not have this phenomenon.

2. Sodium hypochlorite (bleach)

Since spandex itself is not resistant to chlorine, the elasticity of spandex is greatly damaged during the chlorine bleaching process, and the concentration, pH and other reactions of the bleaching water Speed ​​also plays an important role in the elastic damage of spandex, and heavy bleaching causes greater damage.

The following are some suggestions for easing the elasticity loss of spandex:

1. For denim garments that require chlorine bleaching, use 1-3g of spandex chlorine bleaching anti-brittle agent in advance /L (1/10 of the bleaching water), run in the water bath for 1-2 minutes, gradually raise the temperature to 40°C, add the bleaching water three times, add 1/5 of the total amount of bleaching water for the first time, and 2/5 of the total amount of bleaching water for the second time The total amount, add the remaining 2/5 of the bleaching water for the last time, and operate according to the actual bleaching time.

2. After bleaching, drain water and add water at the same time. The water temperature will gradually drop. The reason for this is to prevent the spandex from being brittle and elastic due to a sharp drop in temperature.

3. Soft

Due to various Auxiliary manufacturers have different formulations of softeners and silicone oils. Some softeners and silicone oils can damage the elasticity of spandex, mainly due to the small amount of solvents in their components, which have little effect on the elasticity of spandex. It does not contain this solvent and has no effect on the elasticity of spandex. Choose appropriate silicone oil for softening.

4. Solvent

Since the spandex weaving process contains silicone oil, its The oil agent needs to be removed during the dyeing and finishing process, and many scouring agents contain solvents, which have a great impact on the elasticity of spandex.

5. Physical cutting

Since the characteristic of denim is nostalgia, many of them need to be physically damaged and cut. The damage will cause uneven stress on the spandex elastic yarn. This results in blistering of the spandex, and the exposed yarn is easily broken, resulting in loss of elasticity.

6. Drying temperature

Generally, the drying temperature of denim fabrics containing spandex elastic yarn is


Author: clsrich