Fabric 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 ratio of the difference between shrinkage and original size is the fabric shrinkage rate. Fabric shrinkage involves different types of fibers, the structure of the fabric, the different external forces that the fabric is subjected to during processing, etc. The shrinkage rate is small for synthetic fiber 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 following. tidy. 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 within the national standard of 3% to 4%. Underwear materials, especially natural fiber fabrics, 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.
Shrinkage rate of general fabrics:
Cotton 4%-10 %; chemical fiber 4%-8%; cotton polyester 3.5%-5 5%; natural white cloth 3%; poplin 3-4.5%; twill 4%; denim 10%; rayon: 10%; rayon 5-9% ; Tencel fabric 2-4%; Modal fabric 3-6%.
1. Fabric shrinkage is affected by fiber and weave shrinkage
After the fiber itself absorbs water, Some degree of swelling will occur. 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. The difference between the two is usually expressed by the shrinkage rate. 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.
The shrinkage rate of fabrics will be different depending on the fabric shrinkage rate. The fabric’s own tissue structure and weaving tension are different, and its shrinkage rate is different. The weaving tension is small, the fabric is tight and thick, the weaving shrinkage is large, and the shrinkage of the fabric is small. If the weaving tension is large, the fabric will be loose and light, and if the weaving shrinkage is small, the shrinkage rate of the fabric will be large.
In dyeing and finishing, in order to reduce the shrinkage of fabrics, pre-shrinking finishing is often used to increase the weft density and increase the weaving shrinkage in advance, thereby reducing the shrinkage of the fabric. Rate.
2. Reasons for fabric shrinkage
1. Fiber in When 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 results in a static dry relaxation state or a static wet relaxation state. state, or in the dynamic wet relaxation state or the 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 degree, such as cotton and linen. , viscose and other fibers; while hydrophobic fibers shrink less, such as synthetic fibers.
3. When the fiber is in a wet state, it will expand due to the action of the soaking liquid, making the fiber diameter larger. For example, on a fabric, it will force the fiber curvature at the interweaving point of the fabric. The radius increases, resulting in the shortening of the fabric length. 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 fiber thermal shrinkage. 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. There is also a hot air method to measure the shrinkage percentage in hot air exceeding 100°C, and a 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 in textile processing and the dimensional stability of fabrics, which provides some basis for the design of post-processes.
3. Factors affecting fabric shrinkage
1. Raw materials
Due to different raw materials, fabric shrinkage rates are different. 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. Different densities lead to different fabric shrinkage rates.
If the longitudinal and latitudinal densities are similar, the longitudinal and latitudinal shrinkage rates are also similar. Fabrics with a higher warp density will shrink more in the warp direction. Conversely, fabrics with a weft density greater than the warp density will shrink more in the weft direction.
3. Thickness of yarn count
The thickness of yarn count is different, the fabric Shrinkage rates are also different. Fabrics with thick thread count will shrink more, and fabrics with fine thread count will shrink more.The shrinkage rate is small.
4. Production process
Due to different production processes, the fabric shrinkage rate 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
Natural plant fibers (such as cotton, Compared with synthetic fibers (such as polyester, acrylic), hemp) and plant regenerated fibers (such as viscose) are easy to absorb moisture and expand, so the shrinkage rate is larger, while wool is easy to felt due to the scale structure on the fiber surface, affecting its Dimensional stability.
6. Fabric structure
Generally, woven fabrics The dimensional stability of high-density 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 is dyeing and printing , During the finishing process, it will inevitably be stretched by the machine, so tension exists on the fabric. However, fabrics easily release tension when exposed to water, so we may find fabric shrinkage after washing. In actual processes, we generally use pre-shrinking to solve this problem.
8. Washing care process
Washing care includes washing and drying , 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 fabric shrinkage. 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 based on the composition of the fabric can also improve fabric shrinkage. For example, cotton and linen fabrics can be ironed at high temperatures to improve their dimensional shrinkage. 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 damage its performance, such as making the fabric hard and brittle.