The sulphur dye is reduced and dissolved to form a dye solution, and the formed dye leuco body is adsorbed by the cellulose fiber, and is subjected to air oxidation treatment to make the cellulose fiber exhibit a desired color.
The sulphur dye precursor has no affinity for the fiber, and its structure contains a sulfur bond, a disulfide bond or a polysulfide bond, and is reduced to a sulfhydryl group by a sodium sulfide reducing agent to become a leuco sodium salt dissolved in water. The reason why the leuco body has a good affinity for the cellulose fibers is that the molecules of the dye are large, and thus a large van der Waals force and hydrogen bonding force are generated between the fibers.
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