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What is the shrinkage rate of textile fabrics 2020.08.12

In daily life, a word is often mentioned-shrinkage. Sometimes when washing clothes, it is emphasized that the clothes can be washed but not washed, because some materials of clothing will shrink, so what shrinking phenomenon What is it, and what is the cause of this daily phenomenon? Let's take a look at the shrinkage rate of fabric.

The shrinkage rate of fabric refers to the percentage of fabric shrinkage after washing or immersion in water. Shrinkage is a phenomenon in which the length or width of a fabric product undergoes washing, dehydration, and drying in a certain state. The degree of shrinkage involves different types of fibers, the structure of the fabric, and the different external forces experienced when the fabric is finished.
The smallest shrinkage rate is synthetic fiber and blended chemical fiber fabrics, followed by wool, linen, and cotton fabrics in the middle, silk fabrics shrink more, and the largest is viscose, rayon, and artificial wool fabrics. Objectively speaking, Cotton fabrics have the problem of shrinking and fading. The key is the subsequent finishing. Therefore, general home textile fabrics are pre-shrinked. It is worth noting that the pre-shrinking treatment does not mean that it does not shrink, but refers to the shrinkage rate of 3%-4% in the national standard. Underwear materials, especially natural fiber clothing, will shrink.

Therefore, when purchasing clothing, in addition to selecting the quality, color, and pattern of the fabric, you should also understand the shrinkage rate of the fabric.

1. The influence of fiber and weaving
After the fiber itself absorbs water, it will swell to a certain degree. Generally, the swelling of fibers is anisotropic (except for nylon), that is, the length is shortened and the diameter is increased. Usually the difference between the length of the fabric before and after the water and the percentage of its original length is called the shrinkage rate. The stronger the water absorption capacity, the more severe the swelling, the higher the shrinkage rate, and the worse the dimensional stability of the fabric.

The length of the fabric itself is different from the length of the yarn (silk) used, and the shrinkage ratio is usually used to indicate the difference between the two.

Shrinkage rate (%) = [Yarn (silk) thread length-fabric length] / fabric length

After the fabric is launched into the water, the length of the fabric is further shortened due to the swelling of the fiber itself, resulting in a shrinkage rate. The shrinkage rate of the fabric is different, the size of the shrinkage rate is different. The structure and weaving tension of the fabric itself are different, and the shrinkage rate is different. The weaving tension is small, the fabric is dense and thick, the shrinkage rate is large, the shrinkage rate of the fabric is small; the weaving tension is high, the fabric is loose and thin, and the shrinkage rate is small, and the shrinkage rate of the fabric is large. In dyeing and finishing, in order to reduce the shrinkage rate of the fabric, pre-shrinkage finishing is often adopted to increase the weft density, increase the weaving shrinkage rate in advance, and reduce the shrinkage rate of the fabric.

2. Reasons for shrinkage

When the fiber is spinning, or when the spinning yarn is weaving and dyeing and finishing, the spinning fiber in the fabric is stretched or deformed by external force. At the same time, the spinning fiber and the fabric structure generate internal stress, in the static dry relaxation state , Or static wet relaxation state, or dynamic wet relaxation state, full relaxation state, the release of internal stress to different degrees, so that the spun yarn fiber and fabric return to the original state.
Different fibers and fabrics have different degrees of shrinkage, which mainly depends on the characteristics of their fibers-hydrophilic fibers have a greater degree of shrinkage, such as cotton, hemp, viscose and other fibers; while hydrophobic fibers have less shrinkage , Such as synthetic fibers.
When the fiber is in the wet state, the fiber will expand due to the action of the immersion liquid, which makes the fiber diameter larger. For example, on the fabric, the fiber radius of curvature at the interlaced points of the fabric is forced to increase, resulting in the shortening of the fabric length. For example, cotton fiber expands under the action of water, the cross-sectional area increases by 40-50%, and the length increases by 1-2%, while the synthetic fiber shrinks by heat, such as boiling water shrinkage, generally about 5%.
When the fabric fiber is heated, the shape and size of the fiber will change and shrink, and it will not return to the original state after cooling, which is called fiber thermal shrinkage. The percentage of length before and after thermal shrinkage is called thermal shrinkage. Generally, it is expressed by boiling water shrinkage test. In 100℃ boiling water, the percentage of fiber length shrinkage is expressed; hot air is also used. Hot air at over 100℃ The percentage of shrinkage can be measured in the steam method, and the percentage of shrinkage can be measured in steam above 100℃. Fibers perform differently under different conditions such as internal structure, heating temperature and time. For example, the boiling water shrinkage rate of finishing polyester staple fiber is 1%, the boiling water shrinkage rate of vinylon is 5%, and the hot air shrinkage rate of vinylon is 50%. The fiber has a close relationship between the fabric finishing and the dimensional stability of the fabric, providing some basis for the design of the subsequent process.


3. The shrinkage rate of general fabric

Cotton 3%-10%
Chemical fiber 4%-8%
Cotton polyester 3.5%-5.5%
3% for natural white cloth
Wool blue cloth is 3-4%
Poplin is 3-4.5%
Floral cloth is 3-3.5%
4% for twill
Labor cloth is 10%
Rayon is 10%

4. Reasons that affect the shrinkage rate
Raw materials
Different fabrics have different shrinkage rates. Generally speaking, for a fiber with high moisture absorption, the fiber expands after being immersed in water, the diameter increases, the length decreases, and the shrinkage rate is large. If the water absorption rate of some viscose fibers is as high as 13%, while the synthetic fiber fabric has poor moisture absorption, its shrinkage rate is small.

density
The density of the fabric is different, the shrinkage rate is also different. If the warp and weft density is similar, the warp and weft shrinkage rate is also close. A fabric with a high warp density will shrink in the warp direction. Conversely, a fabric with a weft density greater than the warp density will shrink in the weft direction.

Yarn count thickness
Different fabric yarn counts have different shrinkage rates. The shrinkage rate of fabrics with thick yarn counts is large, and the shrinkage rate of fabrics with fine yarn counts is small.

Production Process
Different fabric production processes have different shrinkage rates. Generally speaking, in the process of weaving, dyeing and finishing of the fabric, the fiber has to be stretched many times, and the finishing time is long. The shrinkage rate of the fabric with larger applied tension is larger, and vice versa.

Fiber composition
Compared with synthetic fibers (such as polyester and polyacrylonitrile), natural plant fibers (such as cotton and hemp) and regenerated plants (such as viscose) simply absorb moisture and expand, so the shrinkage rate is larger, while wool is due to the surface of the fiber. The scale structure and simple felting affect its dimensional stability.

Fabric structure
In general, the dimensional stability of woven fabrics is better than that of knitted fabrics; the dimensional stability of high-density fabrics is better than that of low-density fabrics. In woven fabrics, the shrinkage rate of plain weave fabrics is generally less than that of flannel fabrics; while in knitted fabrics, the shrinkage rate of plain stitches is less than that of ribbed fabrics.

Production finishing process
As the fabric is stretched by the machine in the process of coloring, printing, and finishing, there will be tension on the fabric. However, it is easy to release the tension after the fabric is exposed to water, so we will find that the fabric shrinks after washing. In the actual process, we generally use pre-shrinking to solve this problem.

Cleaning care process
Cleaning care includes washing, drying and ironing. Each of these three steps will affect the shrinkage of the fabric. For example, the dimensional stability of hand-washed samples is better than that of machine-washed samples, and the cleaning temperature will also affect its dimensional stability. Generally speaking, the higher the temperature, the worse the stability. The drying method of the sample has a relatively large impact on the shrinkage of the fabric.

Commonly used drying methods include drip drying, metal mesh tiling, hanging drying and rotating drum drying. Among them, the drip drying method has the least influence on the size of the fabric, while the drum arch drying method has the greatest influence on the size of the fabric, and the other two are in the middle.

In addition, choosing a suitable ironing temperature according to the composition of the fabric can also improve the shrinkage of the fabric. For example, cotton and linen fabrics can be ironed at a high temperature to improve their size shrinkage. But it is not that the higher the temperature, the better. For synthetic fibers, high-temperature ironing will not only improve its shrinkage, but will damage its performance, such as the cloth becoming hard and brittle.

 
 
 
 
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