The shrinkage rate of fabric refers to the percentage o […]
The shrinkage rate of fabric refers to the percentage of fabric shrinkage after washing or immersion in water. 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.
The smallest shrinkage is synthetic fibers and blended textiles, followed by wool, linen, and cotton fabrics in the middle, silk fabrics shrink more, 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 subsequent finishing. Therefore, general home textile fabrics are pre-shrinked. It is worth noting that the pre-shrinking treatment does not mean that it does not shrink, but it means that the shrinkage rate is controlled at 3%-4% according to 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.
1. The influence of fiber and weaving
After the fiber itself absorbs water, it will swell to a certain extent. Generally, the swelling of fibers is anisotropic (except for 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 indicate the difference between the two.
Shrinkage rate (%) = [Yarn (silk) thread length-fabric length] / fabric length
After the fabric is launched into the water, due to the swelling of the fiber itself, the length of the fabric is further shortened, 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 dense and thick, and the shrinkage rate is large, and the shrinkage rate of the fabric is small; when the weaving tension is high, the fabric is loose and thin, and the 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-shrinkage finishing is often used to increase the weft density and increase the weaving shrinkage rate in advance, thereby reducing the shrinkage rate of the fabric.
2. Reasons for shrinkage:
(1) When the fiber is spinning, or when the yarn is weaving and dyeing and finishing, the yarn fiber in the fabric is stretched or deformed by external force, and the yarn fiber and fabric structure generate internal stress, which is in the static dry relaxation state. , Or in the static wet relaxation state, or in the dynamic wet relaxation state or the full relaxation 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, linen, viscose and other fibers; while hydrophobic fibers shrink To a lesser extent, such as synthetic fibers.
(3) When the fiber is in a 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 at 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 thermal shrinkage. The percentage of length before heat shrinkage and after heat shrinkage is called heat shrinkage. Generally, it is expressed by boiling water shrinkage test. In 100℃ boiling water, the percentage of fiber length shrinkage is expressed; hot air is also used. Hot air at over 100℃ The percentage of shrinkage can be measured in the steam method, and the percentage of shrinkage can be measured in 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 vinylon is 50%. Fiber is closely related to the textile processing and the dimensional stability of the fabric, providing some basis for the design of the subsequent process.
3. The shrinkage rate of general fabrics:
Chemical fiber 4%-8%;
Cotton polyester 3.5%-5 5%;
3% for natural white cloth;
Wool blue cloth is 3-4%;
Poplin is 3-4.5%;
Floral cloth is 3-3.5%;
4% for twill;
Labor cloth is 10%;
Rayon is 10%.