Polymer Termination
Chemical degradation during polyester extrusion creates polymer chains populated by carboxyl end groups rather than hydroxyl counterparts. Mills measure this specific concentration to quantify thermal history degradation during yarn spinning. High counts signal excessive moisture presence in polymer pellets prior to melting.
Extrusion temperatures exceeding standard processing parameters accelerate polymer chain scission. Excess thermal energy breaks ester linkages and multiplies terminal acid sites across the batch.
Acid Titration
Laboratory technicians dissolve polyester chips in benzyl alcohol for quantitative analysis. Phenolphthalein indicator dye guides the titration process against standardized sodium hydroxide solution. Operators record the volume consumed to calculate milliequivalents of acid per kilogram of polymer.
Solvents must reach precise thermal equilibrium before the endpoint color change occurs. Endpoint observation requires strict adherence to lighting standards to avoid false readings.
Yarn Degradation
Elevated terminal acidity directly reduces intrinsic viscosity values in polyester multifilament yarns. Hydrolysis attacks these vulnerable chain ends during high temperature alkaline dyeing cycles. Weakened polymer chains snap under mechanical tension during high speed weaving operations.
Filament breakage forces frequent loom stoppages and generates excessive second quality fabric rolls. Subsequent ultraviolet exposure yellows the affected apparel during outdoor wear testing phases.
Degradation Threshold
Commercial apparel specifications enforce strict limits on terminal acid concentration before yarn acceptance. Standard textile contracts cap acceptable limits below thirty equivalents per million grams. Higher levels demand immediate rejection by the quality assurance receiving department.
Suppliers adjust solid state polymerization residence times to consume excess terminal sites. Post condensation reactors successfully reduce acid numbers back toward baseline parameters.
