What is Fabric Dimensional Stability? How to do Shrinkage Test?

• June 20, 2017
• testextextile
• Textile Testing and Certification
• 4 Comments

Fabric Dimensional Stability

In daily life, newly bought clothes, sheets, and other textiles, after water washing once or twice, which are not the original size, greatly affecting our user experience. So how did this happen? And how to prevent this embarrassing phenomenon from happening? This brings us to the dimensional stability of the fabric.

What is the Dimensional Stability of Fabrics?

The dimensional stability of fabric refers to the change of fabric size when it is used or reprocessed due to the properties of a material and the potential thermal contraction force in the process of processing. The fabric with good dimensional stability is worn and washed for many times, the original pleating and shape are unchanged, and the dimensions don’t shrink or elongated, which don’t affect the user experience. The fabric with poor dimensional stability is usually shown as shrinkage, such as shrinkage in sewing, ironing, washing and so on. Among them, the wash shrink is the problem that consumer pays close attention to very much.

Main Factors Affecting Fabric Shrinkage

The moisture absorption of fiber is the direct factor of fabric shrinkage. The tightness of yarn and fabric structure is the indirect factor of shrinkage. The tighter the structure, the expansion of the fiber cause the yarn to swell, then the warp height of the yarn in the fabric increases and the length of the yarn in the buckling state becomes shorter, so the fabric shrinks. Therefore, the higher twist and volume fraction of the yarn, the greater shrinkage of the fabric.

The processing tension of the fabric also has an effect on fabric shrinkage. If the processing tension increases, the fiber deformation increases, the internal stress and the slow elastic deformation increase, then the relaxation and retraction degree of the fabric increases after soaking, which make the shrinkage rate of the fabric increases obviously. Besides, temperature also has a great effect on fabric shrinkage, because the high temperature has the effect of relaxation and expansion, and even heat shrinkage.

Different raw materials of fabrics will affect shrinkage rate and heat shrinkage rate. Under normal circumstance, fabrics with minimum shrinkage rate are synthetic fibers and blended fabrics; secondary is linen fabrics; middle is cotton fabrics; the maximum is viscose fabrics. In addition to this, the shrinkage rate varies from fabrics density, the thickness of yarns, weaving, dyeing and finishing process. Different kinds of fabrics have been prescribed standard of shrinkage rate. In the process of dyeing and finishing, some processes like mercerization and preshrunk can reduce shrinkage rate. Synthetic fiber is easy to deform when heated, especially nylon fabrics, it shrinks more easily when heated, but it can improve its dimensional stability by hot setting.

Treatment of Fabric Shrinkage

By using the thermoplasticity of the fabric fiber, after the shrinkage of the fabric, the shrinkage fiber can be stretched back to its original state and cooling setting under the action of hot steam. This will normally restore shrunken clothing to its original state. In addition, when washing clothes of different materials, you should pay attention to some situations: when washing wool fabrics, you should add a small amount of water or use quality dry cleaning aids, if possible, dry clothes in advance. Do not dry clean PVC or clothing containing polypropylene fiber. The temperature should not be too high when drying clothes.

2. Fabric Shrinkage Rate Test

Shrinkage rate refers to the percentage that fabrics’ size presents shrink when washed or soaked, which is also an indicator of measuring the degree of fabric shrinkage. The level of fabric shrinkage rate is one of the criteria to measure product quality. The commonly used shrinkage rate test methods are mainly mechanical shrinkage method and dipping method.

A. Mechanical Shrinkage Method

a) Test Apparatus and Materials

Shrinkage Tester (Figure 5), AATCC 1993 Standard Detergent WOB, No Phosphorus ECE Standard Detergent, Oven, Scale, Sewing Thread, Pen, Fabrics, etc.

b) Test Principle

Fabrics with specified dimension are handled in water of a certain temperature in a certain time; then measure the length change in the warp and weft direction after fabrics are dried and evaluate shrinkage of fabrics. Mechanical Shrinkage Method usually adopts shrinkage tester to complete the test, and it is divided into two types: cylinder washing machine adding materials from the front door, stirring washing machine adding materials from the top.

c) Test Method

• Sample preparation.

Choose smooth sample with no obvious crease, and its size should no less than 500mm*500mm; if width is less than 500mm, complete sample can be used, whose length is at least 500mm. Sample is made 3 pairs of marks along the warp and weft direction. The space of marks should be not less than 350mm; marks from the edge of cloth should be not less than 50mm. When necessary, sample of 250mm*250mm can be used, and 3 pairs of marks are made on the sample in the length and width direction, each pair of whose space is 200mm.

• Washing accompany preparation.

Washing accompany used to type A washing machine. It is pure polyester deformed filament knitted fabric; the quality of unit area is 310g ± It comprises of four fabrics overlapping, sewing four sides and adding reinforcement line on the corner. The shape of it is square; size is (20cm ± 4cm)×(20cm ± 4cm); the quality of each sewed washing accompany is 50g ± 5g. Cotton bleach woven fabrics with crease or nylon/cotton 50/50 plain bleach woven fabrics are available. Unit area quality of the two is 155g ± 5g; size is (92cm ±5cm) * (92cm ±5cm).

• Washing accompany used to type B washing machine. As Table 6 shows.

Table 6 Washing Accompany of Type B Washing Machine

• Test Procedure

1. Detergent is put in washing machine. AATCC 1993 standard detergent (not contain fluorescent brightener) suits for Type B washing machine adding materials from the top, while No Phosphorus ECE Standard Detergent (contain fluorescent brightener) suits for Type A and Type B washing machine.

2. Washing temperature, water level, and washing time are set. Prepared sample and washing accompany are put in detergent, handled as chosen washing program.

3. After fabrics are washed, you can choose one of the following 6 drying methods to dry it:

Hanging dry — after dehydration, fabric is perpendicular to the ground in the length direction, hanging on a string or smooth pole and drying in room temperature and stationary air.

Drip dry — Sample without dehydration is perpendicular to the ground in the length direction, hanging on a string or smooth pole and drying in room temperature and stationary air.

Flattened dry — sample is flattened on the drying rack with horizontal screen, removed wrinkles to make it flat but not to let it deform or extend, dried in the room temperature.

Flat pressing — sample is put on the flat pressing machine, removed bigger wrinkles by hands. As request of drying sample, putting down the pressing head, sample is hot pressed in a or more short periods until it is dried. Choose apposite temperature and record temperature and pressure used.

Tumbling drying — sample and washing accompany is put in tumbling dryer (Figure 6), and choose the drying stall. As for fibers which are sensitive to hot, a lower temperature is better.

Oven drying — sample is mounted flat on filter screen in oven, noticing not to make it deform or extend. The temperature of oven is set in 60℃ ± 5℃, and drying it.

4. Measurement and Calculation

Soaking, sample is flattened horizontally on table at a state of no tension. Under the condition that no any tension is applied to it, shrinkage rate is measured directly by shrinkage scale; or scale is used to measure the length (accurate to 1mm) between 3 pairs of marks in warp and weft direction of fabric, then take averages respectively and replace the data to the following formula to calculate fabric shrinkage rate:

Shrinkage rate = (the length of latitude and longitude before washing − the length of latitude and longitude after washing) ÷ the length of latitude and longitude before washing

B. Dipping Shrinkage Method

a) Test Apparatus and Materials

Scale, Sewing Thread, Wetting Agent, Blankets, Pen, fabrics, etc.

b) Test Principle

Dipping shrinkage method is fitted to textiles improper to wash sharply. Before washing, sample should mark the size. The shrinkage of fabrics is judged by the size change of marks before and after washing.

c) Test Method

• Soaking fabric is put on a 600mm*600mm*600mm glass without tension.
• Another glass with same size is covered by the sample.
• The distance between each pair of marks is measured, accurate to 1mm.
• Sample is soaked in 15~20℃ water in a free state for 2h after measured. Liquid level should be higher than the sample at least 25mm. 0.5 g/L efficient wetting agent is added in water. Water should be soft water or hard water whose thickness is no more than 5/100000 calcium carbonate.
• Sample is taken out. Four angles of fabrics are folded toward the center and move it to the blanket. Another blanket is covered on the sample, pressing to remove extra water.
• Sample is dried in a condition of 20℃±5℃.
• The dried sample is humidified in standard atmosphere. Achieving the balance, the distance of each pair of marks should be measured again.

d) Result Calculation

Shrinkage rate = [(the length of latitude and longitude before soaking − the length of latitude and longitude after soaking) ÷ the length of latitude and longitude before soaking]×100%

C. Steam Shrinkage Test

a) Test Apparatus and Materials

Sleeve Steam Meter, Sewing, Scale, Several Fabrics.

b) Test Principle

Fabric is influenced by steam under the condition with no pressure. The size change of fabric before and after steamed reflects the shrinkage of steamed fabrics.

c) Test Method

• Sample Preparation

Four samples are taken from longitude and latitude respectively. Sample size: length is 300mm; width is 50mm. No obvious spot is on the fabric. Through pre-humidified (temperature is no more than 50℃, relative moisture is 10%~25%) for 4h later, sample is humidified in a standard atmosphere (temperature is 20℃±2℃, relative moisture is 65%±2%) for 24h.

• Test Procedure

1. Two marks are made symmetrically on the two sides of fabric whose distance is 250mm.
2. The length between marks measured is length before steamed, accurate to 0.5mm.
3. The steam goes through the steam cylinder at the speed of 70 g/min (tolerance is 20%) for at least 1 min to pre-heat the cylinder. If temperature in cylinder is too low, pre-heating time should be extended appropriately. Steam valve should be open in the test.
4. Four humidified samples are mounted flat on wire stent of each layer, put in cylinder right away and kept in 30s.
5. Sample is removed from the cylinder, cooled in 30s and then put in cylinder again. Sample is put in and out of the cylinder repeatedly for three times.
6. After recycling for three times, sample is put on the smooth plane to cool down.
7. After pre-humidified and humidified, the length between marks measured is the length after steamed, accurate to 0.5 mm.

• Result Calculation

Steam Shrinkage rate = [(the length before steam – the length after steam)÷ the length before steam]×100%

The average value of steam shrinkage rate in the longitude and latitude should be calculated respectively and retained one number after the decimal point.

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