Thermodynamic Analysis of Hydrolyzed Polyurethane Filament Failure during Dyeing
Hydrolytic polyurethane breakdown during high-temperature dyeing occurs via acid-catalyzed ester cleavage, requiring polyether backbones and strict pH control.
Soft Segment Phase Separation
Morphological Segregation
Microphase segregation of incompatible polymer blocks in segmented polyurethanes determines the mechanical elasticity of synthetic stretch fibres. During polymer solidification, soft segment phase separation occurs when the flexible polyether or polyester blocks isolate from the rigid diisocyanate domains. This structural arrangement generates a dual-phase morphology that allows spandex yarn to stretch and recover.
Elastomeric Recovery
The degree of segregation directly influences how well the elastic yarn returns to its original length after stretching. When the soft domains are well separated from the hard blocks, they form a highly flexible matrix that deforms easily under tension. The hard domains act as physical anchor points that pull the soft chains back into their coiled state when the load is released.
Poorly separated systems lead to permanent deformation and loss of recovery in stretch apparel.
Thermal Behavior
Temperature changes alter the compatibility of the different blocks and can force them to mix or separate. High temperatures during heat setting of elastomeric fabrics promote phase mixing, which temporarily lowers the elastic performance. Cooling allows the segments to segregate again and restore the microphase structure of the yarn.
Measuring this phase transition temperature provides a clear picture of the thermal stability of the fabric. This analysis uses differential scanning calorimetry to detect structural transitions.
Spinning Effect
Spinning speeds and subsequent drawing during yarn formation affect the final phase morphology of the filaments. Rapid cooling and high drawing rates freeze the polymer in a highly segregated state to maximize elastic efficiency.