Fabric shrinkage refers to the percentage of fabric shrinkage after washing or soaking in water. Shrinkage is a phenomenon in which the length or width of textiles changes in a certain state through washing, dehydration, drying and other processes. The degree of shrinkage involves different types of fibers, the structure of the fabric, the different external forces that the fabric is subjected to during processing, and so on.

Synthetic fibers and blended textiles have the smallest shrinkage rate, by wool fabrics, linen fabrics, and cotton fabrics. Objectively speaking, all cotton fabrics have the problem of shrinking and fading, the key is the finishing. Therefore, the general home textile fabrics are pre-shrinked. It is worth noting that pre-shrinking treatment does not mean that it does not shrink, but that the shrinkage rate is controlled at 3%-4% of the national standard. Underwear fabrics, especially natural fiber fabrics, will shrink. Therefore, when purchasing fabrics, in addition to selecting the quality, color and pattern of the fabric, the shrinkage rate of the fabric should also be understood.

1 The influence of fiber and weaving shrinkage

After the fiber itself absorbs water, it will swell to a certain extent. Usually the swelling of fibers is anisotropic (except for nylon), that is, the length is shortened and the diameter is increased. Usually, the percentage of the difference between the length of the fabric before and after it is launched and 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) thread used, and the difference between the two is usually expressed by the shrinkage rate.

Weaving shrinkage (%) = [yarn (silk) line length - fabric length] / fabric length

After the fabric is in 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, and the size of the shrinkage rate is different. The tissue structure and weaving tension of the fabric itself are different, and the shrinkage rate is different. When the weaving tension is small, the fabric is compact and thick, and the weaving shrinkage rate is large, and the shrinkage rate of the fabric is small; the weaving tension is large, the fabric is loose and thin, the weaving shrinkage rate is small, and the shrinkage rate of the fabric is large. In the dyeing and finishing process, in order to reduce the shrinkage rate of the fabric, pre-shrinking is often used to increase the weft density and increase the shrinkage rate in advance, thereby reducing the shrinkage rate of the fabric.

2 Reasons for shrinkage

①When the fiber is spinning, or when the yarn is weaving and dyeing, the yarn fiber in the fabric is stretched or deformed by external force, and the yarn fiber and the fabric structure generate internal stress, in a static dry relaxation state, or In the static wet relaxation state, or in the dynamic wet relaxation state and the full relaxation state, the release of internal stress of different degrees makes the yarn fibers and fabrics return to the original state.

②Different fibers and their fabrics have different degrees of shrinkage, mainly depending on the characteristics of their fibers - hydrophilic fibers have a larger degree of shrinkage, such as cotton, hemp, viscose and other fibers; while hydrophobic fibers have a higher degree of shrinkage Less, such as synthetic fibers, etc.

③When the fiber is in a wet state, it will expand due to the action of the immersion liquid, which will increase the fiber diameter. For example, on the fabric, the fiber curvature radius of the interwoven point of the fabric is forced to increase, resulting in a shortening of the fabric length. For example, cotton fibers expand under the action of water, the cross-sectional area increases by 40~50%, and the length increases by 1~2%, while synthetic fibers shrink by heat, such as boiling water shrinkage, generally about 5%.

④ Under the condition of heating of textile fibers, the shape and size of the fibers change and shrink, and they cannot return to the original state after cooling down, which is called thermal shrinkage of fibers. The percentage of length before and after heat shrinkage is called the heat shrinkage rate, which is generally measured by boiling water shrinkage. In boiling water at 100 °C, the percentage of fiber length shrinkage is expressed; hot air is also used. The percentage of shrinkage is measured in the steam method, and the percentage of shrinkage is measured in the steam exceeding 100 ℃. Fibers behave differently due to different conditions such as internal structure, heating temperature and time. For example, the boiling water shrinkage rate of processed polyester staple fiber is 1%, the boiling water shrinkage rate of vinylon is 5%, and the hot air shrinkage rate of vinylon is 50%. Fibers are closely related to the dimensional stability of textile processing and fabrics, which provide some basis for the design of subsequent processes.

3 The shrinkage rate of general fabrics is

Cotton 4%--10%;

Chemical fiber 4%--8%;

Cotton polyester 3.5%--5 5%;

Natural white cloth is 3%;

The wool blue cloth is 3-4%;

Poplin is 3-4.5%;

Flower cloth is 3-3.5%;

4% for twill;

Labor cloth is 10%;

Rayon is 10%.

4 Reasons Affecting Shrinkage Rate

(1) Raw materials

The raw material of the fabric is different, and the shrinkage rate is different. Generally speaking, fibers with high hygroscopicity will expand after soaking in water, their diameter will increase, and their length will shorten, and their shrinkage rate will be large. If some viscose fibers have a water absorption rate of up to 13%, while the synthetic fiber fabrics have poor moisture absorption, their shrinkage rate is small.

(2) Density

The density of the fabric is different, and the shrinkage rate is also different. If the warp and weft densities are similar, the warp and weft shrinkage rates are also similar. The fabric with high warp density will shrink greatly in the warp direction. On the contrary, if the weft density is greater than that in the warp density, the shrinkage in the weft direction will be large.

(3) Yarn thickness

The thickness of the yarn count of the fabric is different, and the shrinkage rate is also different. Fabrics with coarse yarn counts have higher shrinkage rates, while fabrics with fine yarn counts have lower shrinkage rates.

(4) Production process

Different fabric production processes have different shrinkage rates. Generally speaking, in the process of weaving and dyeing and finishing of fabrics, the fibers need to be stretched many times, the processing time is long, and the shrinkage of the fabric with greater tension is greater, and vice versa.

(5) Fiber composition

Compared with synthetic fibers (such as polyester and acrylic), natural plant fibers (such as cotton, hemp) and plant regenerated fibers (such as viscose) are easy to absorb moisture and expand, so the shrinkage rate is larger, while wool is due to the scale structure on the surface of the fiber. And it is easy to felt, which affects its dimensional stability.

(6) 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 smaller than that of flannel fabrics; and in knitted fabrics, the shrinkage rate of plain knitted fabrics is smaller than that of rib fabrics.

(7) Production and processing process

Because the fabric is inevitably stretched by the machine in the process of dyeing, printing and finishing, there is tension on the fabric. However, the fabric is easily de-tensioned when 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.

(8) Washing and nursing process

Laundry care includes washing, drying, and ironing, each of which affects the shrinkage of fabrics. For example, the dimensional stability of hand-washed samples is better than that of machine-washed samples, and the washing temperature also affects its dimensional stability. In general, the higher the temperature, the worse the stability. The drying method of the sample also has a great influence on the shrinkage of the fabric.

Commonly used drying methods include drip drying, metal mesh tiling, hanging drying and tumble drying. Among them, the drip drying method has the least effect on the size of the fabric, while the drum drying method has the greatest effect 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 high temperatures to improve their dimensional shrinkage. But it is not the higher the temperature, the better. For synthetic fibers, high-temperature ironing will not only improve its shrinkage rate, but will damage its performance, such as the fabric being hard and brittle.

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