Carrier Dyeing at Atmospheric Pressure
topic
Carriers are organic compounds (biphenyl, methylnaphthalene, butyl benzoate) that swell and plasticise PET, depressing Tg to <100°C enabling atmospheric-pressure dyeing (98°C). Mechanism: carrier partitions into amorphous regions, increasing free volume and reducing activation energy for dye diffusion. Environmental concerns: many traditional carriers (chlorinated aromatics) are toxic and persistent. Carrier-free dyeing (HT) now preferred; carriers limited to heat-sensitive blends (PET/wool).
Role
Carrier dyeing theory illustrates the free-volume mechanism of polyester dyeing and its dependence on amorphous phase mobility. It is academically important despite declining industrial use due to the environmental chemistry of carrier compounds.