The shrinkage of fabric 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 after washing, dehydration, drying and other processes in a certain state. The degree of shrinkage involves different types of fibers, the structure of the fabric, the different external forces exerted on the fabric during processing, etc.
The shrinkage rate is small for synthetic fibers and blended fabrics, followed by woolen fabrics, linen fabrics, and cotton fabrics in the middle. Silk fabrics have a larger shrinkage, and the larger ones are viscose fiber, artificial cotton, and artificial wool fabrics. Objectively speaking, all cotton fabrics have the problem of shrinkage and fading. The key is the subsequent finishing. Therefore, most home textile fabrics are preshrunk. It is worth noting that pre-shrinking does not mean that there is no shrinkage, but that the shrinkage rate is controlled to be below the national standard of 3%-4%. Underwear materials, especially natural fiber clothing materials, will shrink. Therefore, when purchasing clothing materials, 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 fibers and shrinkage
When 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 shortens and the diameter increases. The percentage of the length difference between the fabric before and after it is washed and its original length is usually called shrinkage. The stronger the water absorption capacity, the more intense the swelling, the higher the shrinkage, 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 rate is usually used to express the difference between the two.
Shrinkage (%) = [Yarn (silk) thread length – Fabric length] / Fabric length
After the fabric is put into the water, due to the swelling of the fiber itself, the length of the fabric is further shortened, resulting in shrinkage. Different shrinkage rates of fabrics result in different shrinkage rates. The fabric’s own organizational structure and weaving tension are different, and its shrinkage rate is different. If the weaving tension is small, the fabric will be tight and thick, and if the weaving shrinkage rate is large, the shrinkage rate of the fabric will be small; if the weaving tension is high, the fabric will be loose and light, if the weaving shrinkage rate is small, the shrinkage rate of the fabric will be large. In the dyeing and finishing process, in order to reduce the shrinkage of the fabric, pre-shrinkage finishing is often used to increase the weft density and increase the weaving shrinkage in advance, thereby reducing the shrinkage of the fabric.
2. Reasons for shrinkage:
(1) When the fiber is spinning, or when the yarn is weaving, dyeing and finishing, the yarn fibers in the fabric are elongated or deformed by external forces. At the same time, the yarn fibers and the fabric structure generate internal stress, which is in a static dry relaxation state. , or in a static wet relaxation state, or in a dynamic wet relaxation state, or a full relaxation state, the internal stress is released to varying degrees, causing the yarn, fiber and fabric to return to their original state.
(2) Different fibers and their fabrics have different shrinkage degrees, which mainly depend on the characteristics of the fibers – hydrophilic fibers shrink to a greater extent, such as cotton, linen, viscose and other fibers; while hydrophobic fibers shrink To a lesser extent, such as synthetic fibers, etc.
(3) When the fiber is in a wet state, it will swell due to the action of the soaking liquid, making the fiber diameter larger. For example, on a fabric, it forces the fiber curvature radius at the interweaving point of the fabric to increase, causing the length of the fabric to shorten. For example, cotton fiber expands under the action of water, and its cross-sectional area increases by 40 to 50% and its length increases by 1 to 2%, while synthetic fibers shrink by heat, such as boiling water, generally about 5%.
(4) When textile fibers are heated, the shape and size of the fibers change and shrink, and they cannot return to their original state after cooling, which is called thermal shrinkage of the fibers. The percentage of length before heat shrinkage and after heat shrinkage is called heat shrinkage rate. It is generally measured by boiling water shrinkage. In boiling water at 100°C, the percentage of fiber length shrinkage is expressed. It can also be expressed by hot air method, in hot air exceeding 100°C. To measure the shrinkage percentage, you can also use the steam method to measure the shrinkage percentage in steam exceeding 100°C. Fibers behave differently due to their internal structure and heating temperature, time and other conditions. For example, the boiling water shrinkage rate of polyester staple fiber processing is 1%, the boiling water shrinkage rate of vinylon is 5%, and the hot air shrinkage rate of chlorine fiber is 50%. Fibers are closely related to textile processing and the dimensional stability of fabrics, which provides some basis for the design of post-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%;
Wool blue cloth is 3-4%;
Poplin is 3-4.5%;
Floral cloth is 3-3.5%;
Twill is 4%;
Labor cloth is 10%;
Rayon is 10%.
4. Reasons affecting shrinkage
1. Raw materials
Different raw materials of fabrics have different shrinkage rates. Generally speaking, fibers with high hygroscopicity will expand when soaked in water, increase in diameter, shorten in length, and have a large shrinkage rate. For example, the water absorption rate of some viscose fibers is as high as 13%, while synthetic fiber fabrics have poor hygroscopicity and their shrinkage rate is small.
2. Density
Fabrics with different densities have different shrinkage rates. If the latitude and longitude densities are similar, the longitude and latitudinal shrinkage willThe rate is also close. Fabrics with a high warp density will have a large shrinkage in the warp direction; conversely, fabrics with a greater weft density than warp density will have a large shrinkage in the weft direction.
3. Thickness of yarn count
Fabrics with different yarn counts have different shrinkage rates. Fabrics with a thicker yarn count will have a greater shrinkage rate, while fabrics with a finer yarn count will have a smaller shrinkage rate.
4. Production process
Fabric production processes are different and shrinkage rates are also different. Generally speaking, during the weaving, dyeing and finishing process of fabrics, the fibers have to be stretched many times, and the processing time is long. The shrinkage of fabrics with greater tension will be greater, and vice versa.
5. Fiber composition
Compared with synthetic fibers (such as polyester, acrylic), natural plant fibers (such as cotton, linen) and plant regenerated fibers (such as viscose) are prone to moisture absorption and expansion, so the shrinkage rate is larger, while wool is due to the scale structure on the fiber surface. It is easy to felt, which affects its dimensional stability.
6. Fabric structure
Generally speaking, 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. Among woven fabrics, the shrinkage rate of plain weave fabrics is generally smaller than that of flannel fabrics; while among knitted fabrics, the shrinkage rate of plain knitted fabrics is smaller than that of ribbed fabrics.
7. Production and processing process
Since the fabric will inevitably be stretched by the machine during the dyeing, printing, and finishing processes, tension will exist on the fabric. However, fabrics easily release tension when exposed to water, so we may notice shrinkage in the fabric after washing. In actual processes, we generally use pre-shrinking to solve this problem.
8. Washing and care process
Laundry 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 will also affect its dimensional stability. Generally speaking, the higher the temperature, the worse the stability. The drying method of the sample also has a relatively large impact on the shrinkage of the fabric.
Commonly used drying methods include drip drying, metal mesh laying, hang drying and drum drying. Among them, the drip drying method has a small impact on the size of the fabric, while the drum drying method has a large impact on the size of the fabric, and 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, the dimensional shrinkage of cotton and linen fabrics can be improved by high-temperature ironing. But it is not that the higher the temperature, the better. For synthetic fibers, high-temperature ironing will not only not improve its shrinkage, but will also damage its performance, such as making the fabric hard and brittle.
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