Shrinkage is the percentage of the fabric that shrinks after washing or soaking. Shrinkage is a kind of phenomenon in which the length or width of a textile is changed in a certain state through washing, dehydration and drying. The degree of shrinkage relates to different types of fibers, fabric structure, different external forces during fabric processing, and so on.

Shrinkage rate is the smallest synthetic fiber and mixed textiles, followed by wool, hemp, cotton fabrics in the middle, silk fabrics shrink larger, and the largest is viscose fiber, artificial cotton, artificial wool fabric. Objectively speaking, the number of all cotton fabrics have the problem of shrinkage and fading, the key is the finishing behind. So the general home textile fabrics are pre - shrinkage processing. It is worth noting that the pre-shrinkage treatment is not equal to not shrink, but refers to the shrinkage rate control in the national standard 3%-4% clothing materials, especially natural fiber clothing materials will shrink. Accordingly, when dress material of choose and buy, besides the quality of the fabric, colour and lustre, pattern undertakes to choose outside, the shrinkage rate of the fabric also ought to understand somewhat.

Influence of fiber and shrinkage

When the fibers themselves absorb water, they swell to a certain extent. Usually the swelling of the fiber is anisotropic (except nylon), that is, the length of the shortened, the diameter of the increase. Usually the length difference between the fabric before and after water and the percentage of its original length is called shrinkage. The stronger the water absorption capacity, the more intense the swelling, the higher the shrinkage rate, 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 difference is usually expressed by the rate of weave.

Shrinkage ratio (%) =[yarn (silk) thread length - fabric length]/ fabric length.

Fabric in water, due to the swelling of the fiber itself, the length of the fabric is further shortened, resulting in shrinkage. The shrinkage rate of the fabric varies with the weaving shrinkage rate. The shrinkage rate of the fabric varies with its structure and weaving tension. Weaving tension is small, the fabric is compact and thick, the shrinkage rate is large, the shrinkage rate of the fabric is small; Weaving tension is big, fabric is loose and frivolous, knit shrinkage rate is small, the shrinkage rate of fabric is big. In the dyeing and finishing process, in order to reduce the shrinkage rate of the fabric, the pre-shrinkage finishing method is often used to increase the weft density, improve the shrinkage rate in advance, so as to reduce the shrinkage rate of the fabric.

The cause of shrinkage

(1) fiber during spinning, or yarn in weaving and dyeing and finishing, the fabric of the yarn fiber elongation by external force or deformation, stress in fiber yarn and fabric structure at the same time, in the static dry relaxation state, or static wet relaxation condition, or in a dynamic wet relaxation condition, total relaxation condition, different degree of internal stress release, To make the yarn fiber and fabric back to the original state.

(2) Different fibers and their fabrics have different degree of shrinkage, mainly depending on the characteristics of their fibers - hydrophilic fibers have a greater degree of shrinkage, such as cotton, hemp, viscose and other fibers; The degree of shrinkage of hydrophobic fibers, such as synthetic fibers, is less.

(3) When the fibers are wet, they expand under the action of the immersion solution, which causes the diameter of the fibers to increase. For example, on the fabric, the radius of curvature of the fibers at the interweaving point of the fabric to increase, resulting in the length of the fabric to shorten. For example, cotton fiber puffing under the action of water, cross-sectional area increases 40~50%, length increases 1~2%, and synthetic fiber is on the heat contraction, such as boiling water contraction, generally about 5%.

(4) Under the condition of heating, the shape and size of textile fibers change and shrink, and can not return to the initial state after cooling, which is called thermal shrinkage of fibers. The percentage of the length before and after the thermal shrinkage is called the thermal shrinkage rate. It is generally tested by the shrinkage of boiling water. In the boiling water at 100℃, the percentage of the fiber length shrinkage is expressed. It can also be used to measure the percentage of shrinkage in hot air over 100℃, and it can also be used to measure the percentage of shrinkage in steam over 100℃. Fiber performance is also different under different conditions such as internal structure, heating temperature and time. For example, the boiling water shrinkage rate of polyester staple fiber is 1%, the boiling water shrinkage rate of vinylon is 5%, and the hot air shrinkage rate of chlorofiber is 50%. There is a close relationship between the dimensional stability of the fabric and the fiber in the textile process, which provides some basis for the design of the subsequent process.

The shrinkage rate of general fabrics is:

Reasons that affect shrinkage rate

1. Raw materials

The material of fabric is different, the shrinkage rate is different. Generally speaking, the fiber with big hygroscopicity, the fiber after soaking water expands, diameter increases, length shortening, shrinkage rate is big. If some viscose fiber bibulous rate is as high as 13%, and synthetic fiber fabric hygroscopic sex is poor, its shrinkage rate is small.

2, density,

The shrinkage rate varies with the density of the fabric. If the longitude and latitude density are similar, the longitude and latitude shrinkage rate is also close. For fabrics with high warp density, the warp shrinkage will be greater; on the contrary, for fabrics with a weft density greater than the warp density, the weft shrinkage will be greater.

3. Thickness of yarn

The shrinkage rate is different when the yarn count is different. Shrinkage rate of coarse yarn is large, and shrinkage rate of fine yarn fabric is small.

4. Production technology

The shrinkage rate of fabric varies with the production process. Generally speaking, the fabric is in weaving and dyeing and finishing process, the fiber should be drawn for many times, processing time is long, the fabric shrinkage rate with larger exertion tension is large, and conversely small.

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 rate is larger, while wool is easy to felt due to the scale structure on the fiber surface, which affects its dimensional stability.

6. Fabric structure

In general, the dimensional stability of woven fabric is better than that of knitted fabric. The dimensional stability of high density fabrics is better than that of low density fabrics. In the woven fabric, the shrinkage rate of plain weave fabric is smaller than that of flannel fabric. In knitted fabrics, the shrinkage rate of plain knitting is smaller than that of ribbed fabrics.

7. Production and processing process

As the fabric is in the process of dyeing, printing and finishing, it will inevitably be stretched by the machine, so there is tension on the fabric. Fabrics, however, easily dissolve in water, so we may find that the fabric shrinks after washing. In practice, we usually use pre-shrinkage to solve this problem.

8, washing care process

Catharsis nursing includes catharsis, dry, ironing, each of these 3 steps can affect the shrinkage of the fabric. For example, the dimensional stability of the hand-washed sample is better than that of the machine-washed sample, and the washing temperature will also affect its dimensional stability. In general, 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.

Commonly used drying methods are, drip drying method, metal mesh tiling method, hanging dry drying and drum drying method. The drip-drying method has the least effect on the fabric size, while the dry-arching method has the largest effect on the fabric size, and the other two kinds are in the middle.

In addition, according to the composition of the fabric to choose a suitable ironing temperature, can also improve the shrinkage of the fabric. Cotton and linen fabrics, for example, can be ironed at high temperatures to improve their shrinkage. But not be the temperature had been better, to synthetic fiber, high temperature ironing not only cannot improve its shrink rate, can destroy to its performance somewhat instead, if fabric hair is hard hair is crisp.