Polymer Degradation
The breakdown of synthetic elastomer structures in wet-processing environments results in the release of non-crosslinked polymer chains. A phenomenon called polyurethane soft segment leaching occurs when the low-molecular-weight polyol components of spandex fibers are dissolved and extracted during high-temperature washing or dyeing. This leaching degrades the elastic properties of the fabric, leading to permanent deformation.
It is a major cause of performance loss in stretch garments.
Degradation Mechanism
Spandex fibers consist of alternating hard segments that provide strength and soft segments that provide elasticity. The soft segments, typically made of polyethers or polyesters, are vulnerable to hydrolytic cleavage when exposed to hot water, alkaline scour baths, or chlorinated water. As these chains are cleaved, they dissolve in the processing liquor, leaving behind a weakened polymer skeleton.
This degradation is accelerated by high temperatures and extended processing times, especially during the aggressive wet-processing stages of industrial laundering.
Performance Loss
The loss of these soft segments directly reduces the recovery power of the elastic yarn, causing the fabric to bag or sag after stretching. Garments lose their shape-retention capability, particularly in high-stress areas like knees and elbows. This degradation is visible as a loss of modulus and an increase in permanent set during tensile testing.
It also makes the fiber more brittle, increasing the likelihood of fiber breakage during sewing.
Prevention Method
Mills prevent this leaching by using protective chemical finishes. Reducing the duration of wet treatments preserves the soft segments. This step is crucial for high-durability swimwear.
