One of the Appearance Properties of Textile Fabrics: Dimensional Stability

One of the Appearance Properties of Textile Fabrics: Dimensional Stability

The dimensional stability of a fabric refers to its property of shortening or elongating in length during wearing, washing, and storage.

New fabrics tend to shrink during use. There are three types of shrinkage: natural relaxation shrinkage, thermal shrinkage, and shrinkage due to water absorption (often simply called shrinkage). Natural relaxation shrinkage refers to the contraction of fabric from the time it leaves the factory until it is used. Thermal shrinkage occurs during ironing;  synthetic fibers are thermoplastic polymers and will shrink if the ironing temperature is too high. The  noticeable type of shrinkage is the shrinkage that occurs when fabric comes into contact with water, commonly referred to as shrinkage.

Main Causes of Shrinkage:

(1). Swelling of Yarns: When fibers absorb moisture, they swell. This increases the crimp height of the warp and weft yarns within the fabric, meaning the yarns become more wavy, leading to a contraction in the fabric's length and width. Fibers with high moisture absorption generally have higher shrinkage rates; conversely, fibers like polyester and polypropylene have very low moisture absorption, resulting in minimal shrinkage from this cause.

(2). Recovery from Tensile Deformation: Fabrics are subjected to mechanical tension during processing, which stretches the fibers, yarns, and the fabric itself. When this external force is removed, the fabric has a tendency to relax and contract naturally. This recovery from deformation is accelerated and becomes more pronounced when the fabric is wetted.

The degree of shrinkage is a key factor considered when determining the ease allowances in garment making. For fabrics with high shrinkage, it is advisable to pre-shrink them before cutting. Most modern fabrics undergo stabilization treatments during finishing to prevent both thermal shrinkage and shrinkage due to water.

Shrinkage is typically expressed using the shrinkage rate:
Shrinkage Rate = (Length before shrinkage - Length after shrinkage) / Length before shrinkage × 100%

Testing for shrinkage can be categorized into four types: Natural Relaxation Shrinkage Test, Dry Ironing Shrinkage Test, Spray Damping Shrinkage Test, and Immersion Shrinkage Test.

1. Natural Relaxation Shrinkage Test
   Natural relaxation shrinkage refers to the contraction that occurs when a fabric roll is unpacked and allowed to relax. The entire roll is removed from its packaging, and its length and width are initially measured and recorded. The fabric is then loosely spread out, allowed to relax for 24 hours, after which its length and width are measured again. The warp-wise and weft-wise shrinkage rates are calculated based on these measurements.

Environmental Conditions for Fabric Relaxation: Standard atmospheric pressure, temperature of 20°C, and relative humidity of 65%. Generally, fabrics with a looser structure tend to have higher natural relaxation shrinkage.

2. Dry Ironing Shrinkage Test
   Dry ironing shrinkage measures the degree of contraction in the warp and weft directions when the fabric is subjected to heat via ironing, without any water treatment. This method is commonly used for silk fabrics or materials like vinylon fabrics and tussah silk, which may develop water spots if dampened.

Test Procedure: A test sample, 50cm in length and the full width of the fabric, is cut from a point at least 2 meters from the fabric end (to avoid the less stable end portion). The sample is ironed for 15 seconds using an iron set to the highest temperature the fabric can withstand. After allowing it to cool completely, the length and width of the sample are measured, and the warp and weft shrinkage rates are calculated.

3. Spray Damping Shrinkage Test
   Spray damping shrinkage measures the degree of contraction in the warp and weft directions after the fabric is sprayed with water and then ironed.

Test Procedure: Sampling is done using the same method as described above. The sample is evenly sprayed with clean water, then gently crumpled by hand. After smoothing it out (without stretching), it is left to air dry. Once dry, it is ironed flat (again, without pulling it into shape). The final length and width are measured, and the warp and weft shrinkage rates are calculated.

4. Immersion Shrinkage Test
   Immersion shrinkage involves soaking the fabric completely in water to determine the shrinkage in its length and width after wetting. This method is widely used in practice and is also common for testing interlinings and other accessories.

Test Procedure: Sampling is done using the same method as described above. The sample is immersed in clean water at approximately 60°C. It is gently kneaded by hand to ensure complete saturation. After soaking for 15 minutes, it is removed and excess water is pressed out (without wringing or twisting). The sample is smoothed out, air-dried, and then its final length and width are measured to calculate the warp and weft shrinkage rates.