Thermal Transition
The breakdown of the crystalline domain structure in polyurethane elastomers at elevated temperatures marks a critical phase change in synthetic elastic fibers. This thermal transition, referred to as hard segment dissociation, occurs when the hydrogen bonds holding the polar segments together are disrupted by heat.
Molecular Disorganization
Crystalline regions within the polymer melt or lose their ordered arrangement during thermal processing. When hard segment dissociation takes place, the polymer loses its virtual cross-links and begins to flow as a viscous liquid. This change allows the fiber to be heat-set into new shapes, but also compromises its elastic recovery during the hot processing stage.
If the material cools slowly after this transition, the hard domains slowly reform, restoring the structural integrity and original elasticity of the yarn.
Process Limit
Temperature limits in dyeing and finishing are defined by the melting point of these crystalline structures. Exceeding this thermal boundary permanently damages the elastic properties of the fabric. Mills must monitor dryer temperatures to prevent structural damage.
Mechanical Performance
Elastic recovery behavior of stretch fabrics depends on the integrity of the polymer blocks. Maintaining these blocks below their dissociation temperature ensures the fabric does not lose its stretch.
