The level of shrinkage involves different types of fibers, fabric structure, different external forces experienced during fabric processing, etc., and has different performances.
The smallest shrinkage material is synthetic fiber and blended textiles, then by wool, linen, and cotton fabrics in the middle, silk fabrics shrink larger, and the largest is viscose fiber, rayon, and artificial wool fabrics. Generally speaking, all cotton fabrics have the problem of shrinking and fading. The important is the finishing. Therefore, home textile fabrics need pre-shrinked. It is worth noting that the pre-shrinking treatment does not mean that the shrinkage is controlled within 3%-4% of the national standard.
1.Reasons of shrinkage
1), During spinning, weaving, dyeing and finishing, the yarn 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 levels of shrinkage, which mainly depends on the characteristics of their fibers, hydrophilic fibers have a greater shrinkage, such as cotton, hemp, viscose and other fibers; while hydrophobic fibers have a smaller shrinkage, such as synthetic fibers.
3),When the fiber in the wet state, the fiber will expand due to the action of the immersion liquid, which will increase the fiber diameter. For example, on the cloth, the fiber curvature radius of the interweaving point of the fabric is forced to increase, caused 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 is about 5%.
4) When the textile fiber under heated, the shape and size of the fiber will change and shrink, and it will not return to the initial state after cooling, which is called heat shrinkage. The percentage of length before and after heat shrinkage is called heat shrinkage. Generally, it is expressed by boiling water shrinkage test. During 100℃ boiling water, the percentage of fiber length shrinkage is expressed. Hot air is also used, hot air more than 100℃ the percentage of shrinkage can be measured , and the steam method can also be used to measure the percentage of shrinkage 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 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 has a close relationship with the textile processing and the dimensional stability of the fabric, which provides some basis for the design of subsequent processes.
2. Factors that cause fabric shrinkage
1) Different fabric materials have different shrinkage rates. Generally speaking, the fibers with high moisture absorption, after being immersed in water, the fiber expands, its diameter increases, its length decreases, and its shrinkage rate is large. If some viscose fibers have a water absorption rate as large as 13%, while synthetic fiber fabrics have poor moisture absorption, their shrinkage rate is small.
2) Yarn is made of fibers arranged by twisting the yarn axis. The size change in water is not only related to the nature of the fiber, but also related to its structure such as twist and tightness. Generally speaking, different yarn counts have different shrinkage rates. The shrinkage rate of fabric with thick yarn count is large, and the shrink rate of fine yarn count is small.
3) The density of the fabric is different, and the shrinkage rate is also different. If the warp and weft density is similar, the warp and weft shrinkage rate is also close. Fabrics with high warp density will shrink in the warp direction. Conversely, fabrics with a weft density greater than warp density will shrink in the weft direction. In general, the dimensional stability of high-density fabrics is better than that of low-density fabrics.
4) Different fabric production processes have different shrinkage rates. Generally speaking, in the process of weaving and dyeing and finishing the fabric, the fiber has to be stretched many times, and the processing time is long. The shrinkage rate of the fabric with larger applied tension is larger.In order to control the width of the fabric, in the actual process, we generally use pre-shrinking to solve this problem.
5) Washing care, including washing, drying and ironing, each of these three steps will affect the shrinkage of the fabric. For example, the dimensional stability of hand washing is better than machine washing, and the washing temperature will also affect its dimensional stability. Generally speaking, the higher the temperature, the worse the stability.
Choosing an appropriate 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 a high temperature to improve their size shrinkage. But not all higher temperature is better, for synthetic fibers, high-temperature ironing will not only improve its shrinkage, but will damage its performance, such as hard and brittle fabrics.
Shrinkage of general fabric
"Shrinkage" is officially called "dimensional washing change", which refers to the percentage of textiles that shrink after washing or immersion in water.
Shrinkage= (size before washing-size after washing) / size before washing × 100%
Under normal situations:
Cotton is 4%-10%;
Cotton mercerized plain weave: shrinkage rate is 3.5% in warp direction and 3.5% in weft direction;
4% for twill;
Cotton mercerized twill: shrinkage rate of 4% in warp direction, 3% in weft direction;
Cotton plain fabric: shrinkage rate of 6% in warp direction, 2.5% in weft direction;
Cotton polyester 3.5%-5 5%;
Chemical fiber 4%-8%;