Chain Flexibility
Amorphous, low-melting polymer blocks within a block copolymer provide the high stretchability and flexibility characteristic of elastomeric fibers. In spandex or polyurethane yarns, the soft segment consists of polyether or polyester chains that exist in a highly coiled state at rest. These chains uncoil easily when a tensile force is applied to the textile.
Elastomeric Behavior
Rapid extension and recovery of synthetic stretch fabrics depend on the mobility of these flexible molecular chains. When the pulling force is released, the soft segment recoils to its disordered, high-entropy state, pulling the entire fiber back to its original dimensions. This action provides the necessary compression and fit in athletic clothing.
Material Composition
Polyether types of these blocks offer superior resistance to hydrolytic degradation compared to their polyester counterparts. A manufacturer selects the specific chemistry of the soft segment based on the intended application of the elastomeric yarn. For swimwear, polyethers are preferred because they resist chlorine and wet conditions better than polyesters, preventing the premature breakdown of the elastane yarn under pool conditions.
Thermal Limit
Extreme heat can cause these amorphous domains to flow or degrade, ruining the elastic recovery of the finished yarn. When the textile undergoes hot finishing processes, the soft segment must remain below its degradation temperature to avoid permanent damage.
