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.
Hard Segment Enthalpy
Thermal Measure
Energy absorbed during the melting of the crystalline domains in a segmented polyurethane polymer defines a critical transition point for synthetic elastomeric yarns. Specifically, hard segment enthalpy quantifies the heat required to disrupt the ordered regions formed by diisocyanate and chain extender molecules. This thermodynamic value represents the strength and degree of molecular order within the structural segments of the polymer.
Crystalline Phase
The presence of structured physical crosslinks determines the heat capacity of these elastic domains. During thermal analysis using differential scanning calorimetry, a distinct endothermic peak reveals the temperature range over which the hard domains melt. Stronger intermolecular hydrogen bonding increases the energy needed to transition from an ordered state to a disordered melt.
This transition affects the elasticity of the yarn at elevated temperatures.
Elastic Property
Higher values of this thermodynamic metric correspond to superior recovery behaviour in spandex and elastane fibres. When the material is stretched, the high melting temperature of the hard domains prevents them from slipping past one another. The fabric retains its original shape over multiple laundry and wear cycles.
Low enthalpy values result in permanent bagging and sagging at elbows and knees in stretch denim. This recovery is essential for high-performance athletic apparel.
Processing Limit
Excessive thermal exposure during heat setting can permanently diminish the structural melting energy of the polyurethane. Manufacturers must control stenter temperatures to prevent melting of the elastomeric core during finish curing.