Quantifying Physical Degradation Limits in Synthetic Elastomeric Knits
Thermal setting over 190°C and jet nozzle pressures above 0.30 MPa degrade polyurethane cores, causing permanent set and elasticity loss in synthetic knits.
Thermo-Oxidative Yellowing
Chemical Degradation
Phenolic antioxidants and spin finish residues undergo structural changes when exposed to high temperature in an oxygenated environment. Thermo-oxidative yellowing occurs as these substances break down into quinone-based species that absorb light within the visible spectrum. The phenomenon typically presents in white or pastel synthetic fibres during drying or heat setting processes.
Process Mechanism
Heat energy lowers the activation threshold for the reaction between atmospheric oxygen and the substrate. Polymeric chains remain largely stable while low molecular weight additives react rapidly to form colored byproducts. Discoloration reaches a peak when contaminated textiles spend extended periods in hot air tenter frames.
Measurement Protocol
Technicians quantify the magnitude of chromatic shift using a spectrophotometer to derive b-star values on the CIELAB scale. High positive values indicate a pronounced shift toward the yellow region. Samples undergo testing against a control white fabric before and after controlled heat exposure to determine the severity of the reaction.
Control Mitigation
Maintaining low nitrogen oxide levels in the factory atmosphere prevents the catalytic acceleration of oxidation. Process engineers reduce operating temperatures in finishing equipment whenever product specifications allow for a cooler set. Careful selection of non-phenolic lubricants minimizes the potential for chemical transformation during thermal treatment.