Viscoelastic Stress Relaxation Profiles in Heat Set Polyurethane Stretch Wovens
Controlled stenter dwell at 185-195°C stabilizes polyurethane hard segments to minimize viscoelastic force decay and garment bagging in stretch wovens.
Hysteresis Loss
Energy Dissipation
Elastic recovery in loaded fabrics involves both the storage of mechanical energy and its release during unloading. In the evaluation of stretch fabrics, hysteresis loss measures the energy dissipated as heat when the textile is subjected to a load-unload cycle. This phenomenon occurs because the polymeric chains undergo internal friction and rearrangement during extension.
When the fabric fails to return this energy, the efficiency of the stretch-recovery cycle is reduced, indicating potential bagging in finished garments.
Mechanical Test
Standard laboratory testing requires cycling the fabric between fixed elongation limits to evaluate its elastic performance. During these tensile tests, hysteresis loss is calculated from the area between the loading and unloading curves. Technical specifications for high-performance apparel usually define a maximum allowable percentage for this value.
Mill quality control uses this metric to verify that finishing treatments have not damaged the elastomeric core.
Production Impact
Garment durability depends on the consistency of the stretch material under repeated use. High hysteresis loss indicates that the fabric will lose its tension quickly during active wear. This leads to a loss of shape and compression in performance garments.
Fabric construction and fiber quality are the primary factors that determine this behavior.
Performance Limit
Industrial finishing processes can alter the elastane performance through heat and chemical exposure. Uncontrolled temperature in the drying stage increases hysteresis loss by degrading the polyurethane crosslinks. This degradation restricts the elastic recovery of the final product.
Quantifying Physical Degradation Limits in Synthetic Elastomeric Knits
Thermal setting over 190°C and jet nozzle pressures above 0.30 MPa degrade polyurethane cores, causing permanent set and elasticity loss in synthetic knits.