The shrinkage rate of synthetic fibers and blended textiles is the smallest, followed by wool, linen and cotton fabrics in the middle, silk fabrics shrinkage is larger, and the largest is viscose, man-made cotton and man-made wool fabrics.
Objectively speaking, there are shrinkage and fading problems in cotton fabrics, the key is the finishing behind. So the fabric of home textile is pre-shrinked.
It is worth noting that the shrinkage of underwear, especially natural fibers, is not equal to non-shrinkage after pre-shrinkage treatment, but means that the shrinkage of underwear, especially those of natural fibers, will shrink when the shrinkage rate is controlled within 3% - 4% of the national standard. Therefore, when choosing clothes, besides selecting the quality, color and pattern of the fabric, the shrinkage rate of the fabric should also be understood.
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I. The influence of fibers and shrinkage
When the fibers absorb water, they will swell to a certain extent. Usually, the swelling of fibers is anisotropic (except nylon), that is, the length is shortened and the diameter is increased. The shrinkage rate is usually defined as the percentage of the difference between the length of the fabric before and after launching and its original length. The stronger the water absorption, the stronger the swelling, the higher the shrinkage, the worse the dimensional stability of the fabric.
The length of the fabric itself is different from that of the yarn (silk) yarn used, and the difference is usually expressed by the shrinkage ratio.
Shrinkage (%)= [Yarn (Silk) Line Length-Fabric Length]/Fabric Length
After the fabric is drained, the length of the fabric is further shortened due to the swelling of the fiber itself, resulting in shrinkage. The shrinkage of fabrics varies with the fabric shrinkage. The shrinkage rate varies with the fabric's structure and weaving tension. Weaving tension is small, the fabric is compact and thick, the shrinkage rate is large, the shrinkage rate of the fabric is small; Weaving tension is large, the fabric is loose and thin, the shrinkage rate is small, and the shrinkage rate of the fabric is large. In dyeing and finishing process, in order to reduce the shrinkage of fabric, pre-shrinkage finishing is often used to increase weft density and pre-increase the shrinkage of fabric, so as to reduce the shrinkage of fabric.
2. Causes of shrinkage:
(1) During spinning, weaving and dyeing and finishing, the yarn fibers in the fabric are elongated or deformed by external forces. At the same time, the yarn fibers and fabric structures produce internal stresses, which vary in different degrees in the static state of dry relaxation, static state of wet relaxation, or dynamic state of wet relaxation and full relaxation. The release of the product restores the yarn fibers and fabrics to their original state.
(2) The shrinkage degree of different fibers and their fabrics is different, mainly depending on the characteristics of their fibers - hydrophilic fibers shrink more, such as cotton, hemp, viscose and other fibers; hydrophobic fibers shrink less, such as synthetic fibers.
(3) When the fibers are wetted, they swell under the action of soaking solution, which makes the diameter of the fibers bigger. For example, on the fabric, the curvature radius of the interlacing point of the fabric is increased and the length of the fabric is shortened. For example, when cotton fibers are expanded under the action of water, the cross-sectional area and length of cotton fibers increase by 40-50% and 1-2%, while the thermal shrinkage of synthetic fibers, such as boiling water shrinkage, is generally about 5%.
(4) When textile fibers are heated, the shape and size of the fibers change and shrink, and can not return to the initial state after cooling, which is called thermal shrinkage of the fibers. The percentage of shrinkage of fibers before and after thermal shrinkage is called thermal shrinkage, which is usually measured by boiling water shrinkage test. In boiling water at 100 C, the percentage of shrinkage of fibers is expressed by the percentage of shrinkage of fibers. It is also useful to measure the percentage of shrinkage of fibers in hot air at more than 100 C by hot air method, and also by steam method in steam at more than 100 C. The percentage of contraction was measured. The performance of the fibers varies under different conditions, such as boiling water shrinkage of 1%, boiling water shrinkage of 5% and hot air shrinkage of 50% for polyester staple fibers. Fibers are closely related to textile processing and dimensional stability of fabrics, which provides some basis for the design of subsequent processes.
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3. Shrinkage of general fabrics:
Cotton 4%--10%;
4%-8% of chemical fibers;
Cotton and polyester 3.5%-55%;
Natural white cloth 3%;
Blue wool cloth 3-4%; < br />
Poplin is 3-4.5%;
Flower cloth is 3-3.5%,
Twill is 4%;
Labor cloth is 10%;
Artificial cotton is 10%.
FourReasons affecting shrinkage:
1. Raw materials
The shrinkage of fabrics varies with the raw materials. Generally speaking, the fibers with high moisture absorption expand after immersion, increase diameter, shorten length and shrinkage rate. If some viscose fibers absorb water up to 13%, while synthetic fabrics have poor hygroscopicity, their shrinkage is small.
2, density
The shrinkage rate varies with the density of the fabric. If the density of longitude and latitude is similar, the shrinkage of longitude and latitude is also close. If the warp density is high, the warp shrinkage will be large. On the contrary, if the weft density is greater than the warp density, the weft shrinkage will be large.
3. Thickness of yarn
The shrinkage rate varies with the yarn count. The shrinkage of yarn count thick cloth is larger, and that of yarn count fine cloth is smaller.
4. Production technology
Fabric shrinkage varies with different production processes. Generally speaking, in the process of weaving and dyeing and finishing, the fibers need to be stretched many times, the processing time is long, the shrinkage rate of the fabric with greater tension is large, and vice versa is small.
5. Fiber composition
Natural plant fibers (such as cotton, hemp) and regenerated plant fibers (such as viscose) are easier to absorb moisture and expand than synthetic fibers (such as polyester and acrylic), so shrinkage rate is higher, while wool is easier to felting due to the scale structure on the surface of the fibers, which affects its dimensional stability.
6. Fabric structure
In general, the dimensional stability of woven fabrics is better than that of knitted fabrics, and that of high density fabrics is better than that of low density fabrics. In general, the shrinkage of plain weave fabric is less than that of flannel fabric, while in knitted fabric, the shrinkage of plain knitted fabric is less than that of rib fabric.
7. PRODUCTION AND PROCESSING PROCESS
As fabric is inevitably stretched by machine during dyeing, printing and finishing, tension exists on the fabric. However, it is easy for the fabric to release tension when it meets water, so we will find that the fabric shrinks after washing. In practical process, we usually use pre-shrinkage to solve this problem.
8. Washing nursing process
Washing 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 washing temperature also affects the dimensional stability. Generally speaking, 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.
The commonly used drying methods are drip drying, metal mesh laying, hanging drying and rotary drying. The drip drying method has the least influence on the size of the fabric, while the rotary cylinder arch drying method has the greatest influence on the size of the fabric, the other two are in the middle.
In addition, choosing an appropriate 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 temperature to improve their dimensional shrinkage. But not the higher the temperature, the better. For synthetic fibers, high temperature ironing not only can not improve its shrinkage, but also can damage its performance, such as brittle and hard fabrics.
