The smallest shrinkage rate was synthetic fibers and blended textiles, followed by woolen, hemp, and cotton fabrics, silk fabrics had a larger shrinkage, and the largest were viscose fibers, rayon, and artificial wool fabrics.
Objectively speaking, there is a problem of shrinkage and fading in cotton fabrics. The key is the finishing. Therefore, the fabrics of home textiles are generally pre-shrinked.
It is worth noting that after the pre-shrinking treatment is not equal to not shrinking, it means that the shrinkage rate is controlled at 3% -4% of the national standard. Underwear, especially natural fiber, will shrink. Therefore, when choosing clothing, in addition to selecting the quality, color, and pattern of the fabric, the shrinkage rate of the fabric should also be understood.
First, the effect of fiber and shrinkage
The fiber itself swells to some extent after it absorbs water. Generally, the swelling of fibers is anisotropic (except nylon), that is, the length decreases and the diameter increases. 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 (filament) thread used, and the difference between the two is usually expressed by the shrinkage rate.
Weaving shrinkage rate (%) = [yarn (silk) thread length-fabric length] / fabric length
After the fabric is launched, due to the swelling of the fiber itself, the length of the fabric is further shortened, resulting in a shrinkage rate. Different shrinkage rates of fabrics have different shrinkage rates. Different fabric structures and weaving tensions have different shrinkage rates. 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 weaving tension is large, 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 of the fabric, a pre-shrinking method is often used to increase the weft density and increase the weaving shrinkage in advance to reduce the shrinkage of the fabric.
Two. Reasons for shrinkage:
(1) When the fiber is spinning, or when the yarn is woven and dyed, the yarn fibers in the fabric are stretched or deformed by external forces, and at the same time, the internal stress of the yarn fibers and the fabric structure is generated, and the static dry relaxation state , Or static wet relaxation state, or in dynamic wet relaxation state, full relaxation state, the release of stress to varying degrees, so that the yarn fiber and fabric return to the original state.
(2) Different fibers and their fabrics have different degrees 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; and hydrophobic fibers have a shrinkage To a lesser degree, such as synthetic fibers.
(3) When the fiber is in a wet state, the fiber swells due to the immersion solution, which makes the fiber diameter larger. For example, on the fabric, the fiber curvature radius of the interlaced point of the fabric is increased, resulting in a shortened fabric length. For example, cotton fiber swells under the action of water, its cross-sectional area increases by 40-50%, and its length increases by 1-2%, while synthetic fibers shrink to heat, such as boiling water, and so on, generally about 5%.
(4) Under the condition of heating of textile fibers, the shape and size of the fibers change and shrink, and they cannot return to the original state after cooling, which is called fiber thermal shrinkage. The percentage of length before and after heat shrinkage is called the heat shrinkage rate. It is generally expressed by the boiling water shrinkage test. In 100 ° C boiling water, the percentage of fiber length shrinkage is expressed. It is also possible to use hot air to heat the air at temperatures exceeding 100 ° C. The percentage of shrinkage can be measured in the middle of the steam, and the percentage of shrinkage can also be measured in steam over 100 ° C. The fiber also behaves differently under different conditions such as internal structure and 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 shrinkage of chloroflon hot air is 50%. Fibers are closely related to the dimensional stability of textile processing and its fabric, and provide some basis for the design of subsequent processes.