There are many manufacturers in the textile fabric functional finishing, will be worried about the fabric shrinkage have a greater impact, in fact, if the fabric itself shrinkage has been controlled, within the qualified range, then the finishing basically will not have an impact on the shrinkage of the fabric again. This article will take you to understand the textile fabric shrinkage causes analysis and testing methods!
The fibre itself will produce a certain degree of swelling after absorbing water. Usually the swelling of fibres is anisotropic (except for nylon), i.e. the length is shortened and the diameter is increased. The difference in length between the fabric before and after it has been exposed to water, as a percentage of its original length, is often referred to as the shrinkage rate. The stronger the water-absorbing 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 in terms of weaving shrinkage.
After the fabric is placed in water, the length of the fabric is further shortened due to the swelling of the fibres themselves, resulting in shrinkage. Fabrics with different weave shrinkage rates have different sizes of shrinkage. Fabric structure and weaving tension of the fabric itself is different, its weaving shrinkage rate is different. Weaving tension is small, the fabric is tight and thick, weaving shrinkage rate is large, the fabric shrinkage rate is small; weaving tension is large, the fabric is loose and thin, weaving shrinkage rate is small, the fabric shrinkage rate is large. In the dyeing and finishing process, in order to reduce the fabric shrinkage, often using the pre-shrinkage finishing to increase the weft density, in advance to improve the weaving shrinkage, thus reducing the fabric shrinkage.
Testing method
For the shrinkage of fabrics, the commonly used test methods are dry steaming and water washing. Take washing test as an example, the process and method of shrinkage test are as follows:
Sampling: take samples from the same batch of fabrics, at least 5 metres from the head of the cloth, the taken fabric samples should not affect the results of the blemish, the specimen cutting and washing width can be applied to the washing, specifications for the 70 cm to 80 cm square, natural flat 3 hours, with 50 cm * 50 cm specimen placed in the middle of the cloth, and then use the box head of the pen in the surrounding edges of the drawing line.
Scratch sample: put the specimen on a flat countertop, smooth out creases and irregularities, do not stretch, and do not use force when drawing the line to avoid going out of place.
Washing specimen: in order to prevent discolouration after washing, it should be sewn (double layer for knitted fabric, single layer for woven fabric) When sewing, the knitted fabric should be sewn only on both sides of the warp and one side of the weft, and the woven fabric should be sewn on all four sides of the car, and the thread should be suitable for loosening and tightening, and the coarse or easy to disperse fabric should be sewn on all four sides of the car with three threads. After the specimen is finished, put it into 30 degrees of warm water, wash it with washing machine, dry it with drying machine or dry it naturally for 30 minutes, after it cools down sufficiently, then measure it practically.
Calculation: Shrinkage rate = (size before washing – size after washing) / size before washing x 100%. Generally, the shrinkage rate of the fabric in both warp and weft direction should be measured.
