ASTM standards to determine the shrinkage rate of spandex

When determining the shrinkage rate of spandex fibers, it's crucial to understand that spandex is rarely used alone as a pure fiber in textile products. It's almost always blended with other fibers (like cotton, polyester, nylon, etc.) to impart stretch and recovery properties to the fabric. Therefore, the shrinkage is measured typically by the dimensional change of a fabric containing spandex, rather than the inherent shrinkage of individual spandex fibers in isolation.

However, ASTM has introduced several standards to determine the shrinkage rate of isolated spandex fibers. These include:

1. Individual spandex fibers (or filaments)

• ASTM D5104: Standard Test Method for Shrinkage of Textile Fibers (Single-Fiber Test)
• Scope: This method covers the measurement of shrinkage of crimped or uncrimped single staple fibers when exposed to hot air or near-boiling water.
• Relevance to spandex: While this standard is for single fibers, it can be applied to individual spandex filaments removed from tow or yarn. It helps understand the inherent thermal shrinkage behavior of the spandex itself, independent of fabric structure.
• Procedure: A single fiber is measured under a specified load, then subjected to a hot air or hot water treatment for a defined period. After reconditioning, the fiber length is remeasured, and shrinkage is calculated as a percentage.
• Important Note: ASTM D5104-02 has been withdrawn, but it was the primary standard for single fiber shrinkage. Even though withdrawn, its principles are still relevant, and labs might use similar in-house methods based on it.

2. Spandex yarns (containing spandex)

• ASTM D2259: Standard Test Method for Shrinkage of Yarns
• Scope: This test method determines the shrinkage of yarns in skein form when treated in boiling water, dry heat, saturated steam, or solvents.
• Relevance to spandex: While the standard notes it's generally "not recommended for elastomeric yarns and those yarns that stretch more than 5% under the tension loadings prescribed, although it has been used for the latter," it can still be a valuable tool to assess the shrinkage of yarns that contain spandex, especially if the spandex content is not excessively high or if specific tension parameters are agreed upon.
• Procedure: Yarn skeins are prepared, an initial length is measured under specified tension, and then they are subjected to a chosen treatment (e.g., boiling water, dry heat). After conditioning, the final length is measured, and shrinkage is calculated.

3. Fabrics containing spandex:

• ASTM D1966: Standard Test Method for Dimensional Stability of Textile Fabrics to Laundering
• Scope: This standard provides procedures for determining the dimensional changes (shrinkage or growth) of various textile fabrics (including woven, knitted, nonwoven, and felted fabrics) after repeated washing and drying cycles.
• Relevance to spandex: This is arguably the most practical and widely used standard when dealing with spandex, as spandex's primary impact is on the dimensional stability of the fabric. The interplay between spandex and other fibers, and how they react to laundering conditions, is critical.
• Procedure: Fabric specimens are marked with precise benchmarks, measured, then subjected to specified laundering conditions (washing machine type, water temperature, detergent, drying method). After conditioning, the benchmarks are re-measured, and the percentage of shrinkage or growth is calculated in both warp/length and weft/width directions.

Considerations for spandex shrinkage

• Relaxation: Spandex fibers and fabrics have a strong tendency to return to their original, relaxed state. Proper relaxation and conditioning of samples before initial measurements are crucial for accurate shrinkage determination.
• Heat setting: Spandex-containing fabrics are often heat-set during manufacturing to stabilize their dimensions. The effectiveness of this heat-setting directly impacts the subsequent shrinkage.
• Laundering conditions: High temperatures in washing and especially drying are major contributors to shrinkage in spandex blends. The test method chosen should reflect the intended care instructions for the product.
• Tension: Spandex's elastic nature means that the tension applied during measurement can significantly influence the apparent length. Standards specify minimal or controlled tension to ensure reproducible results.
• Blend composition: The percentage and type of fibers blended with spandex will heavily influence the overall fabric shrinkage. Cotton-spandex blends might show more shrinkage than polyester-spandex blends, for example.

To get the most accurate and relevant shrinkage rate for spandex in a textile product, focusing on fabric-level standards like ASTM D1966 or AATCC TM135, and understanding the specific laundering conditions, is generally the most practical approach.