Casual Sweater ManufacturerThe reason why fabrics need to be pre-shrunk is because the fabric has a shrinkage effect. According to the research of textile materials, the shrinkage effect can be mainly divided into three categories: natural shrinkage of fiber elastic recovery; fiber hydrophilic swelling and shrinkage and thermal shrinkage of fiber chemical structure . Chemical treatment of fiber shrinkage is not the scope of this article.
1. Natural shrinkage
The fabric is constantly under tension during the processing process, and the yarn and fiber produce accumulated elongation deformation. The greater the tension, the more accumulated stress deformation. After the tension disappears, the elastic deformation in the accumulated deformation will be released, making the length of the fabric smaller and producing natural shrinkage. In production, some fabrics (such as fabrics with better elasticity) usually need to be placed for a period of time (usually 24 hours) after being laid, and the purpose is to give the fabric enough time to shrink naturally. Natural shrinkage is also a method of pre-shrinking.
2. Water absorption shrinkage
The hydrophilic fiber will produce anisotropic expansion after absorbing water, which is the main reason for the water absorption shrinkage (shrinkage rate) of the fabric. The better the moisture absorption of the hydrophilic fiber, the greater the shrinkage rate of the woven fabric. The experiment pointed out that the length and diameter of the hydrophilic fiber increase when it meets water and wet, but the increase in diameter is much greater than the increase in length.
Cellulose and protein fibers have better moisture absorption and swelling properties. In contrast, cotton fibers and viscose fibers are more prominent. After the fiber absorbs water, it swells and thickens, and the yarn diameter becomes thicker and increases. After drying, the fiber and yarn basically return to their original thickness. The result of this "one piece and one relaxation" causes the accumulated elongation deformation in the fabric (Also known as residual deformation) has been fully "released"; at the same time, the original warp and weft yarns in the fabric have changed and moved due to the expansion effect. Therefore, hydrophilic fabrics tend to shrink in area, increase in thickness, and have uneven surfaces after being dried in water.
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