Shrinkage of fabric refers to the percentage of fabric shrinkage after washing or soaking. Shrinkage is a phenomenon that the length or width of textiles changes after washing, dehydration, drying and other processes in a certain state. The degree of shrinkage involves different kinds of fibers, the structure of fabrics, different external forces on fabrics during processing, and so on.
Synthetic fibers and blended fabrics have the smallest shrinkage, followed by wool, linen and cotton fabrics, while silk fabrics have a larger shrinkage, while viscose fibers, artificial cotton and artificial wool fabrics have the largest shrinkage. Objectively speaking, there are shrinkage and fading problems in all cotton fabrics, and the key is the back finishing. Therefore, the fabrics of home textiles are generally pre shrunk. It is worth noting that after pre shrinkage treatment, it does not mean that there is no shrinkage, but that the shrinkage rate is controlled within 3%-4% of the national standard. Clothing materials, especially natural fiber clothing materials, will shrink. Therefore, when choosing clothes, we should not only choose the quality, color and pattern of the fabric, but also understand the shrinkage of the fabric.
01.Influence of fiber and weaving shrinkage
After the fiber itself absorbs water, it will produce a certain degree of swelling. Generally, the swelling of fibers is anisotropic (except nylon), that is, the length is shortened and the diameter is increased. Usually, the percentage of the length difference between the fabric before and after water and its original length is called shrinkage. The stronger the water absorption capacity, the stronger the swelling and the higher the shrinkage, the worse the dimensional stability of the fabric.
The length of the fabric itself is different from the length of the yarn (silk) thread used, and the difference is usually expressed by the fabric shrinkage.
Fabric shrinkage (%) = [yarn (silk) thread length - fabric length] / fabric length
After the fabric is put into water, due to the swelling of the fiber itself, the length of the fabric is further shortened, resulting in shrinkage. The shrinkage of fabric varies with its shrinkage. The fabric shrinkage varies with the fabric structure and weaving tension. Weaving tension is small, the fabric is compact and thick, and the shrinkage is large, so the shrinkage of the fabric is small; If the weaving tension is large, the fabric will be loose and light, the fabric shrinkage will be small, and the shrinkage of the fabric will be large. In the dyeing and finishing process, in order to reduce the shrinkage of fabrics, preshrinking finishing is often used to increase the weft density and improve the shrinkage in advance, so as to reduce the shrinkage of fabrics.
02.Causes of shrinkage
① When the fiber is spinning, or the yarn is weaving, dyeing and finishing, the yarn fiber in the fabric is stretched or deformed by external forces, and at the same time, the yarn fiber and fabric structure produce internal stress. In the static dry relaxation state, or static wet relaxation state, or dynamic wet relaxation state, full relaxation state, the release of internal stress to varying degrees, so that the yarn fiber and fabric return to the initial state.
② Different fibers and their fabrics have different shrinkage degrees, which mainly depends on the characteristics of their fibers – hydrophilic fibers have a large shrinkage degree, such as cotton, hemp, viscose and other fibers; Hydrophobic fibers have less shrinkage, such as synthetic fibers.
③ When the fiber is in the wet state, it will swell under the action of the soaking liquid, which will increase the fiber diameter. For example, on the fabric, it will force the fiber curvature radius of the weaving point of the fabric to increase, resulting in the shortening of the fabric length. For example, when cotton fiber is expanded under the action of water, the cross-sectional area increases by 40~50% and the length increases by 1~2%, while synthetic fiber is generally about 5% for thermal shrinkage, such as boiling water shrinkage.
④ When the textile fiber is heated, the shape and size of the fiber change and contract, and it cannot return to the initial state after cooling, which is called fiber thermal shrinkage. The percentage of length before and after thermal shrinkage is called the thermal shrinkage rate, which is generally expressed by the percentage of fiber length shrinkage in boiling water at 100 ℃; Hot air method is also used to measure the percentage of shrinkage in hot air above 100 ℃, and steam method is also used to measure the percentage of shrinkage in steam above 100 ℃. The performance of fibers is also different under different conditions such as internal structure, heating temperature and time. For example, the boiling water shrinkage of processed polyester staple fiber is 1%, the boiling water shrinkage of vinylon is 5%, and the hot air shrinkage of nylon is 50%. Fibers are closely related to textile processing and the dimensional stability of fabrics, which provides some basis for the design of subsequent processes.
03.The shrinkage of general fabrics
Cotton 4% – 10%;
Chemical fiber 4% – 8%;
Cotton polyester 3.5%–5 5%;
3% for natural white cloth;
3-4% for wool blue cloth;
Poplin is 3-4.5%;
3-3.5% for calico;
4% for twill cloth;
10% for labor cloth;
Artificial cotton is 10%.
04.Reasons affecting shrinkage
1. Raw materials
The shrinkage of fabrics varies with the raw materials. Generally speaking, fibers with high hygroscopicity will expand, increase in diameter, shorten in length, and have a large shrinkage after soaking. For example, some viscose fibers have a water absorption of 13%, while synthetic fiber fabrics have poor water absorption, and their shrinkage is small.
2. Density
The shrinkage of fabrics varies with their density. If the longitude and latitude density are similar, the longitude and latitude shrinkage is also close. Fabrics with high warp density have large warp shrinkage. Conversely, fabrics with greater weft density than warp density have large weft shrinkage.
3. Yarn thickness
The shrinkage of fabrics varies with the yarn count. The shrinkage of cloth with coarse count is large, and that of fabric with fine count is small.
4. Production process
The shrinkage of fabrics varies with different production processes. Generally speaking, in the process of weaving and dyeing and finishing, the fiber needs to be stretched many times, and the processing time is long. The fabric with large applied tension has a large shrinkage, 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 expand, so the shrinkage is large, while wool is easy to felted due to the scale structure on the fiber surface, affecting 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 of plain fabrics is generally smaller than that of flannel fabrics; In knitted fabrics, the shrinkage of plain stitch is smaller than that of rib fabrics.
7. Production and processing process
Because the fabric will inevitably be stretched by the machine in the process of dyeing, printing and finishing, there is tension on the fabric. However, the fabric is easy to relieve tension after encountering water, so we will find that the fabric shrinks after washing. In the actual process, we usually use pre shrinkage to solve this problem.
8. Washing care 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 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 great influence on the shrinkage of the fabric.
The commonly used drying methods are dripping drying, metal mesh tiling, hanging drying and rotating drum drying. The dripping drying method has the least influence on the size of the fabric, while the rotating barrel arch drying method has the greatest influence on the size of the fabric, and the other two are in the middle.
In addition, choosing a suitable 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. However, the higher the temperature, the better. For synthetic fibers, high-temperature ironing can not improve its shrinkage, but will damage its performance, such as hard and brittle fabrics.
————————————————————————————————-From Fabric Class
Post time: Jul-05-2022