Segment Separation
Phase transition in segmented polyurethanes describes the grouping of highly polar polymer segments into ordered crystalline domains. In elastane yarn production, hard segment crystallization is essential for forming the physical cross-links that give the fiber its high elastic recovery and thermal resistance. These crystals act as lock points that prevent the polymer chains from sliding past each other permanently when the fiber is stretched.
Proper phase separation ensures the yarn can withstand the heat of downstream fabric finishing without losing its stretch.
Thermal Treatment
Stenter heat-setting temperatures must be selected carefully to avoid melting these crystalline regions. If the processing temperature exceeds the melting point of these domains, the hard segment crystallization is disrupted. This disruption leads to a severe loss of elastic recovery in the finished fabric.
Molecular Architecture
The balance between hard and soft blocks determines the mechanical properties of polyurethane fibers. Hard segment crystallization provides the high melting point and strength, while soft segments provide the extensibility. This combination of properties makes elastane yarns unique.
Quality Testing
Differential scanning calorimetry allows technicians to monitor the melting and crystallization behavior of elastane samples. This testing ensures that the hard segment crystallization has occurred correctly during fiber extrusion. It helps spinners maintain consistent yarn performance for their knitting customers.
