The Secret of Textile Shrinkage

Textiles shrink when they change in length or width. This happens after washing, dehydration, or drying. Shrinkage depends on fiber type, fabric structure, and forces on the fabric. Shrinkage has different forms.

What is shrinkage

Fabric is a fibre fabric. The fibre absorbs water and swells. This shortens the length and increases the diameter. Typically, we refer to the difference in length as the shrinkage rate. It’s the difference between the fabric before and after the water. It’s the percentage of its original length. Fabric with higher water-absorbing capacity swells more. It also shrinks more. So, it has worse dimensional stability. The fabric’s length differs from the yarn’s length. The difference is due to weaving shrinkage. Weaving shrinkage (%) = (original yarn length – fabric length) / original yarn length. After putting the fabric in water, it shrinks more. This is because the fibers start to dissolve. Fabrics with different weaving shrinkage rates have different sizes of shrinkage. The fabric’s structure and weaving tension are different. So, its weaving shrinkage rate is different. Weaving tension is low and the fabric is tight and thick. Weaving shrinkage is high, but fabric shrinkage is low. When weaving tension is high, the fabric is loose and thin. Weaving shrinkage is low, but fabric shrinkage is high. In dyeing and finishing, to cut fabric shrinkage, we often use pre-shrinkage finishing. This process boosts the weft density to cut the weaving shrinkage. That, in turn, cuts the fabric shrinkage.

The reason of fabric shrinkage

① Forces affect fibers in spinning, and forces affect yarn in weaving, dyeing, and finishing. External forces stretch or deform the yarn and fabrics. The yarn and fabric’s structure generates internal stress. The body releases stress in the dry or wet relaxation states, or in the dynamic wet relaxation state. This lets the yarn and fabrics return to their initial state.

② Different fibers and their fabrics shrink differently. The degree of shrinkage depends on the fibers’ characteristics. Hydrophilic fibers, like cotton, shrink more. Hydrophobic fibers, like synthetics, shrink less.

③ Wet fiber swells due to the soaking liquid. This makes the fiber’s diameter larger, as in the fabric. It forces the interweaving points of the fabric closer. So, the fiber’s curvature radius increases, shortening the fabric. For example, cotton fiber expands in water. Its cross-sectional area increases by 40 to 50%. Its length increases by 1 to 2%. Synthetic fibers shrink when heated, such as in boiling water. They shrink by about 5%.

④ When heated, textile fibres change shape and size. When they cool, they shrink and can’t return to the initial state. Fibre heat shrinkage is the term for this. Heat shrinkage is the change in length that occurs before and after heating. It is usually tested by boiling the fabric. In 100 ℃ boiling water, the fabric shrinks. The shrinkage is the percentage change in length. Hot air above 100 ℃ and steam above 100 ℃ are also used to measure the shrinkage. Fibers shrink due to their structure and heat. Times and other conditions also vary. For example, polyester shrinks 1% in boiling water. But, polyvinyl chloride shrinks 5%. And, chlorine hot air shrinks 50%. Fibre in textile processing and its stability are closely related. They affect the design of the next process. They provide some basis.

Shrinkage test method

We test fabric shrinkage by using dry steaming and water washing. These are the common methods. Take washing test as an example, the process and method of shrinkage test are as follows:

① To sample: take fabric samples from the same batch, at least 5 meters from the head. The samples should not affect the blemish results. Cut and wash 70 to 80 cm squares. Let them lay flat for 3 hours. Place a 50 cm * 50 cm sample in the middle of the cloth. Then, use the pen to draw a line along its edges.

② Scribe: Put the specimen on a flat countertop. Smooth its creases and bumps, but do not stretch it. Draw the line gently, so it stays in place.

③Washing specimen: Sew it to prevent color fading. For knitted fabric, sew two layers. And for woven fabric, sew one layer. For knitted fabric, sew the warp and latitude. For woven fabric, sew four sides. Use the right elastic thread. For rough cloth, beat the edge with three lines. After the specimen is ready, put it in 30 degrees of warm water. Wash it with a washing machine. Dry it with a drying machine or let it dry naturally for 30 minutes after it cools. Then, measure it.

④The shrinkage rate is the difference in size before and after washing. It’s divided by the size before washing and then multiplied by 100%. Generally, you should measure how much fabrics shrink. You should do this in the warp and weft.

Influence of Shrinking Machines and Their Test Methods on Fabric Shrinkage Rate

1. The shrinking machine‘s structure affects fabric shrinkage rate. First, the YG701 Shrinking Machine washes using three rounded bars. They are on the inner wall of the washing cylinder. They push the specimen and cloth. This causes the specimen and cloth to roll at a certain height without external pressure. The rinsing goes forward for 12 seconds. Then, it stops for 3 seconds. After that, it goes backward for 12 seconds and stops for 3 seconds. This design keeps the specimens from tangling and wrinkling. It also reduces fabric deformation and shrinkage.

①The M988 shrinking machine washes by turning the stirring wheel inside the box. This drives the water and specimens to rotate. The wheel always turns the same way. This causes the specimens to tangle, deforming them and affecting the shrinkage value. This makes it easy for the specimens to tangle. This deforms them and affects the shrinkage rate.

② YG701 type shrinkage machine is a horizontal drum. Its wings are evenly distributed. When it runs, the force on the specimen is uniform. This makes it hard to deform, so it reduces the shrinkage rate. The M988 type shrinkage machine has a blade on the side wall. When it rotates, the blade causes the force on the fabric to be uneven. This deformation affects the shrinkage rate.

③YG701 type shrinkage machine has a low washing rate of 53r/min. In the shrinkage test, the force on the specimen is small. So, the fabric shrinks and deforms only a little. M988 type fabric shrinkage machine has a high washing rate of 500r/min. The force on the specimen in the shrinkage test is large. It causes big deformation that affects the shrinkage rate.

2. The influence of test method on shrinkage rate

(1)YG701 type fabric shrinkage machine tests shrinkage. The sample weight must not exceed 210g (not counted in pieces). The rest of the test cloth is polyester, double size 30cm × 30cm. We add 5g sodium perborate and 18g low-foam washing powder. Place the sample flat in the washing drum with the test cloth. Heat the drum to (40±3)℃. Then, wash it for 12 minutes. After that, we discharge the water. Rinse 4 times, and finally shake 6min, take out and dry.

(2) The shrinkage test uses an M988 fabric shrinkage machine (with a bath ratio of 1:50). Add water to the box to the specified mark and heat it to (45±2)℃. The specimen is not heavy enough. You can add the test cloth to make it weigh 800g. The test cloth is square and is usually about 60cm. Turn on the motor. It will make the specimen and test cloth rotate in the solution. 30 minutes later, the specimen had both hands out of cold water. It was in the dehydrator, dehydrating. The moisture content was (50 ± 10)%.

(3) Analysis of two specimen methods

① The shrinkage test uses the YG701 fabric shrinkage machine. The specimen is separate by the test cloth that comes with it. This keeps the fabrics from touching and getting tangled. The test cloth is small (30cm×30cm) and made of polyester. It causes less friction than cotton. So, the fabrics are unlikely to get tangled. This keeps the fabrics from getting deformed. With the M988 fabric shrinkage machine, it’s used to test fabric shrinkage. The fabrics get tangled. The test cloth is large and gets tangled with the sample. This makes the sample deform and affects the shrinkage rate.

② In the YG701 fabric shrinkage test, the final specimen’s moisture is generally over 80% (daily data). In the M988 type test, the cotton fabric must have (50 ± 10)% moisture. The moisture content is high. The gravity when drying is high. So, the shrinkage will be low. Thus, the test method is different and also affects the shrinkage rate.

③Verification experiment. Using the above methods, we test ten fabrics. The same fabric shrinks different amounts in different machines. This happens with different test methods. The results fit the law described above.

Shrinkage rate of different fabrics

In terms of shrinkage, the smallest are synthetic fibers and blends. Next are woolen and linen fabrics. In the middle are cotton. Then, silk. The largest are viscose, rayon, and artificial wool. The general fabric shrinkage rate is:

Cotton 4% – 10%;

Chemical fibre 4% – 8%;

Cotton polyester 3.5% – 5.5%;

Native white fabric is 3%;

Woolen blue cloth is 3-4%;

Poplin 3-4.5%; 3-3.5 per cent for floral fabric;

4 per cent for twill;

10 per cent for labour cloth;

10 per cent for rayon.

Factors affecting the shrinkage rate

① Raw material:

Fabrics made from different raw materials shrink at different rates. In general, fibres with high moisture absorption will swell. They will get wider and shorter after soaking in water. They will also shrink a lot. Viscose fiber absorbs up to 13% water. But, synthetic fibers absorb poorly. They also shrink less.

② Density:

The density of the fabric is different, the shrinkage rate is different. If the density of the warp and weft to similar, the warp and weft to the shrinkage rate is also close. Fabrics have warp density, and it shrinks a lot. The weft density is higher than the warp’s. The weft shrinks a lot too.

③ Yarn thickness:

Fabric yarn thickness is different, shrinkage rate is different. Yarn thick fabric shrinkage rate is large, yarn fine fabric shrinkage rate is small.

④ Production process:

Fabric production process is different, shrinkage rate is also different. In the weaving and dyeing process, it is generally necessary to stretch the fiber many times. The process takes a long time. The fabric shrinks a lot when you pull it hard. It shrinks a little when you pull it gently.

⑤ Fibre composition:

Natural plant fibers, like cotton and hemp, absorb and expand with moisture. Regenerated plant fibers, like viscose, do this as well. This is unlike synthetic fibers, like polyester and acrylic. So, they shrink more. Wool felts easily because its fibers have a scaled surface. This affects its size.

⑥ Fabric structure:

Woven fabrics are more stable than knitted ones. High-density fabrics are more stable than low-density ones. In woven fabrics, plain fabrics shrink less than flannel. In knitted fabrics, flat-needle groups shrink less than ribbed ones. Production and processing: Dye, print, and finish fabrics. This process stretches them. So, tension is present on the fabrics. However, it is easy to release the tension after the fabric gets wet. So, we will find the fabric shrinking after washing. In the actual process, we generally use pre-shrinkage to solve this problem.

⑦ Wash care process:

Wash care includes washing, drying, and ironing. Each of these steps will affect how much the fabric shrinks. For example, hand-washed samples are more stable than machine-washed ones. Also, the wash’s temperature affects its stability. In general, the higher the temperature, the worse the stability.

The drying method of the samples also has a greater influence on the fabric shrinkage. People commonly use drip drying, metal mesh laying, hanging dry, and rotary drying. The drip drying method has the least effect on fabric size. The rotary drying method has the greatest effect. The other two are in the middle.

Also, picking the right ironing temperature for the fabric’s composition can reduce shrinkage. For example, you can iron cotton and linen fabrics at high temperatures. This improves their shrinkage. However, higher temperature is not better. For synthetic fibers, ironing at high temperature does not reduce shrinkage. Instead, it harms the fabric, making it hard and brittle.

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