Dye Transport
Physical movement of disperse dye molecules from inside synthetic fibre cores to the fibre surface occurs during high-temperature thermal processing and finishing. In polyester dyeing, thermomigration reduces washfastness and rubfastness when dyed fabrics undergo heat setting or application of non-ionic silicone softeners. Thermal energy mobilizes dye molecules, causing them to dissolve in surface chemical finishes and accumulate on the outer cuticle.
The phenomenon occurs exclusively in dyed synthetic fibres and does not affect natural cellulose or protein fibres.
Mechanism Description
High temperatures applied during stenter drying or garment pressing accelerate dye diffusion through the relaxed polymer matrix toward surface finishes. When dyed polyester fabrics are treated with silicone softeners at elevated temperatures, thermomigration causes dye molecules to migrate into the softener film on the fibre surface. Surface-extracted dye molecules wash off easily during subsequent laundering, resulting in unexpected color loss and staining of adjacent white fabric panels.
Laboratory fastness testing verifies surface dye concentration after thermal finishing treatments.
Fastness Degradation
Migration of dye to the fibre exterior causes severe drops in washing fastness and rubbing fastness metrics. Standard fastness ratings drop significantly when surface dye accumulations remain uncleaned following thermal finishing operations.
Process Control
Dyehouses manage thermal dye movement by selecting low-migration disperse dyes and optimizing stenter curing temperatures. Reduction clearing treatments using sodium hydrosulfite remove surface dye accumulations following heat setting operations. Quality control laboratories test finished fabric lots for colorfastness after every thermal finishing process to ensure compliance with buyer specifications.
