Shrinkage is the percentage of fabric that shrinks after washing or soaking. Shrinkage is a phenomenon that textile changes in length or width through washing, dehydration, drying and other processes in a certain state. Shrinkage degree involves different kinds of fiber, fabric structure, fabric processing by different external forces and so on.

The shrinkage rate is the smallest is synthetic fiber and mixed textiles, followed by wool, hemp, cotton in the middle, silk shrinkage is larger, and the largest is viscose fiber, artificial cotton, artificial wool kind of fabric. Objectively speaking, how much cotton fabric has the problem of shrinking and fading, the key is the finishing behind. So the fabrics of general home spinning are pre-shrink processing. It is worth noting that through pre-shrinkage processing is not equal to not shrinking, but refers to shrinkage rate control in the NATIONAL standard 3%-4% clothing especially natural fiber clothing will shrink. Accordingly, when cloth of choose and buy, besides the quality of the fabric, colour and lustre, pattern undertakes choosing outside, to the shrinkage rate of the fabric also ought to know somewhat.

01

Influence of fiber and shrinkage

When the fiber itself absorbs water, a certain degree of swelling will occur. In general, the swelling of fibers is anisotropic (except polyamide), that is, the length is shortened and the diameter is increased. The difference between the length of a fabric before and after water and the percentage of its original length is usually 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 indicated by the weave shrinkage.

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

Fabric in water, because of the swelling of the fiber itself, the length of the fabric is further shortened, resulting in shrinkage. The shrinkage of the fabric varies with the weave shrinkage. Different fabric structure and weaving tension result in different shrinkage. The weaving tension is small, the fabric is compact and thick, the weaving shrinkage rate is large, the shrinkage rate of the fabric is small; The weaving tension is large, the fabric is loose and thin, the weaving shrinkage is small, the shrinkage of the fabric is large. In dyeing and finishing, in order to reduce the shrinkage of the fabric, the way of pre-shrinkage finishing is often used to increase the weft density and advance the shrinkage of the fabric, so as to reduce the shrinkage of the fabric.

02

Causes of shrinkage

1) fibers in the yarn, 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, make the yarn fiber and fabric back to the initial state.

(2) Different fibers and fabrics, the degree of shrinkage is different, mainly depends on the characteristics of the fiber - hydrophilic fiber shrinkage degree is larger, such as cotton, linen, viscose and other fibers; Hydrophobic fibers shrink less, such as synthetic fibers.

(3) When the fiber is wetted, the fiber diameter becomes larger due to the swelling of the immersion solution, such as on the fabric, forcing the radius of curvature of the fiber at the interweaving point of the fabric to increase, resulting in the shortening of the fabric length. For example, cotton fiber is puffy under the action of water, the cross-sectional area increases by 40~50%, and the length increases by 1~2%, while synthetic fiber is shrinkable to heat, such as boiling water, generally about 5%.

(4) Under the condition of heat, the shape and size of textile fibers change and shrink, and can not return to the initial state after cooling, which is called fiber thermal shrinkage. The percentage of length before and after thermal shrinkage is called thermal shrinkage, generally by boiling water shrinkage test, in 100℃ boiling water, fiber length shrinkage percentage as a representation; There is also a hot air method to measure the percentage of shrinkage in hot air over 100℃, and a steam method to measure the percentage of shrinkage in steam over 100℃. The performance of fiber is also different 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 fiber is 5%, and the hot air shrinkage rate of chloroylon fiber is 50%. There is a close relationship between the fiber processing and the dimensional stability of the fabric, which provides some basis for the design of the following process.

03

The shrinkage rate of general fabrics is

Cotton 4% - 10%;

Chemical fiber 4% - 8%;

Cotton polyester 3.5%-- 55.5%;

Natural white cloth 3%;

Wool blue cloth is 3-4%;

Poplin for 3-4.5%;

Cloth 3-3.5%;

Twill 4%;

Denim 10%;

10 percent for rayon.

04

Causes affecting shrinkage

1. Raw materials

The shrinkage of fabric varies with the raw material. Generally speaking, the fiber with large hygroscopicity, after soaking, the fiber expands, the diameter increases, the length shortenes, and the shrinkage rate is large. If some viscose fiber absorbs water rate is as high as 13%, and synthetic fiber fabric hygroscopicity is poor, its shrinkage rate is small.

2, density,

The shrinkage of fabric varies with its density. If the latitudinal density is similar, the latitudinal shrinkage rate is also similar. Fabrics with high warp density will shrink greatly in warp direction, and conversely, fabrics with a weft density greater than warp density will shrink greatly in weft direction.

3, yarn count thickness

The shrinkage rate of fabric yarn is different with different thickness. The shrinkage of cloth with thick yarn count is large, and that of fabric with fine yarn count is small.

4. Production process

The shrinkage of fabric varies with the production technology. Generally speaking, in the weaving and dyeing process, the fiber should be stretched many times, the processing time is long, and the shrinkage rate of the fabric with greater tension is large, 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 rate is larger. Wool is easy to felting due to the scale structure of 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 low density fabrics. Among woven fabrics, the shrinkage of plain weave fabric is less than that of flannel fabric. In knitted fabrics, the shrinkage rate of plain needle tissue is less than ribbed fabric.

7. Production and processing process

Because the fabric in dyeing, printing, finishing process, it is inevitable to be stretched by the machine, so there is tension in the fabric. However, the tension of the fabric is easily released when it meets 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 and nursing process

Washing care includes washing, 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. 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, dripping drying method, metal mesh tiling method, hanging dry drying method and rotary drying method. The dripping drying method has the least effect on the fabric size, while the rotary drum arch drying method has the most effect on the fabric size, and the other two methods are in the middle.

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