Shrinkage is a phenomenon in which the length or width of textiles undergoes washing, dehydration, and drying in a certain state. The degree of shrinkage involves different types of fibers, fabric structure, and different external forces experienced during fabric processing."Synthetic fibers and blended textiles have the smallest shrinkage rate, followed by wool, linen, and cotton fabrics in the middle, silk fabrics have more shrinkage, and the largest shrinkage is viscose, rayon, and artificial wool fabrics." Objectively speaking, all cotton fabrics have the problem of shrinking and fading. The key is the finishing. Therefore, general home textile fabrics are pre-shrinked. It is worth noting that the pre-shrinking treatment does not mean that the shrinkage rate is controlled within 3% to 4% of the national standard, and the underwear material, especially the natural fiber clothing material, 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. The shrinkage rate of general fabric。
Chemical fiber: 4%~8%;
Cotton polyester: 3.5%~5 5%;
natural white cloth: 3%;
Labor cloth: 10%;
After the fiber itself absorbs water, it will swell to a certain extent. Generally, the swelling of fibers is anisotropic (except nylon), that is, the length is shortened and the diameter is increased. The percentage of the difference between the length of the fabric before and after it is launched and its original length is usually 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 express 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 tight and thick, and the shrinkage rate is large, and the shrinkage rate of the fabric is small.If the weaving tension is large, the fabric will be loose and light, and the shrinkage rate will be small, and the shrinkage rate of the fabric will be large. In the dyeing and finishing process, in order to reduce the shrinkage rate of the fabric, pre-shrinkage finishing is often used to increase the weft density and increase the weaving shrinkage rate in advance to reduce the shrinkage rate of the fabric.
The cause of shrinkage 1. When the fiber is spinning, or when the yarn is weaving, dyeing and finishing, 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 the static dry relaxation state, Either in the static wet relaxation state, or in the dynamic wet relaxation state or fully relaxed state, the internal stress is released to different degrees, so that the yarn fibers and fabrics return to the original state. 2. 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 a degree of shrinkage Less, such as synthetic fibers. 3. 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 curvature radius of the interweaving point 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%. 4. When the textile 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 heat shrinkage. The percentage of length before heat shrinkage and after heat shrinkage is called heat shrinkage rate. Generally, it is measured by boiling water shrinkage test. In 100℃ boiling water, the percentage of fiber length shrinkage is expressed. is also available in the hot air method to measure the percentage of shrinkage in hot air above 100°C, and steam method to measure the percentage of shrinkage in the steam above 100°C. Fibers perform differently under 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 polyvinyl fiber is 50%. Fiber is closely related to the textile processing and the dimensional stability of the fabric, which provides some basis for the design of subsequent processes. Causes affecting the shrinkage rate
1, raw materials Different fabric materials 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.
2, density The density of the fabric is different, and the shrinkage rate is also different. If the density in the warp and weft directions is similar, the shrinkage rate in the warp and weft directions 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.
3, yarn thickness Different fabric yarn counts have different shrinkage rates. The shrinkage rate of fabric with thick yarn count is large, and the shrink rate of fabric with fine yarn count is small.
4, 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 processing time is long. The shrinkage rate of the fabric with greater applied tension is greater, and vice versa.
5. Fiber composition Compared with synthetic fibers (such as polyester and acrylic), natural plant fibers (such as cotton and hemp) and plant regenerated fibers (such as viscose) are easy to absorb moisture and swell, so the shrinkage rate is larger, while wool is due to the scale structure on the fiber surface It is easy to felt and affects its dimensional stability.
6. Fabric structure Generally, 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.
7. Production process As the fabric is inevitably stretched by the machine during the process of dyeing, printing, and finishing, there is tension on the fabric. However, the tension of the fabric is easily relieved after it meets water, so we will find the fabric shrinks after washing.