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.
Ester Bond Scission
Chemical Cleavage
Hydrolytic and thermal reactions that divide the ester linkages in polyester fibers reduce the molecular weight of the polymer. In ester bond scission, water molecules attack the carbonyl carbon atoms at elevated temperatures. This break in the chain shortens the polymer length.
Lower polymer length reduces the overall strength of the yarn.
Degradation Pathway
Degradation progresses rapidly when moisture is present during high-temperature melt extrusion or wet processing. The reaction generates free carboxylic acid groups that act as catalysts for further hydrolysis. This self-accelerating cycle can destroy the load-bearing capacity of the fiber in a short time.
Controlling humidity in dry storage is necessary to stop polymer breakdown before processing begins.
Mechanical Consequence
Loss of fiber tenacity and increased brittleness are the direct outcomes of polymer chain fragmentation. Synthetic yarns become prone to dusting during knitting and tearing during high-speed winding. This damage cannot be repaired by subsequent chemical finishes or softeners.
The fabric loses its durability and is prone to premature tearing.
Prevention Strategy
Limiting the exposure of polyester to alkaline media at high temperatures remains the primary method for maintaining structural integrity. Spinners ensure that the raw polyester chips are dried to a moisture level below zero point zero one percent prior to spinning. In dyebaths, using protective buffers protects the polymer.
These actions maintain the life and durability of the finished product. Processors monitor the rinse water to confirm that all reactive agents are fully neutralized before heat setting.