Although acid-and basic-dyeable variants of polyester have been developed, the majority of PET fibres are dyed with disperse dyes. It is generally accepted that the mechanism of aqueous phase transfer of disperse dyes is identical for all hydrophobic fibres. While the greater portion of the disperse dye is in dispersion in the dyebath, a small amount of disperse dye forms an aqueous solution . Monomolecular dye is adsorbed on to the surface of the fibre from the aqueous dye solution situated at the fibre surface. As dye molecules diffuse, monomolecularly, from the surface to the interior of the fibre, dye particles from the bulk dispersion dissolve in the depleted aqueous dye solution, which is thus replenished with monomolecular dye that can be further adsorbed on to the fibre surface. This process continues until either the dyebath is exhausted of the dye or the fibre is saturated with dye.
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