Presence of Colorless Oxidation Dye Intermediates in Fiber in Oxidation Dyeing for Wool

In order to clarify whether the colorless oxidation dye intermediate mixture in the fiber is present, the timecourse of K/S-Ramda curve of the wool fabric dyed for the different dyeing time with p-phenylenediamine (pPDA) alone, pPDA/ p-amino-o-cresol (pAOC) and pPDA/ resorcinol (RC) dyeing system was investigated by keeping them in a dark room at ambient temperature and humidity for 30 days. The dyeing was carried out using hydrogen peroxide as oxidant at pH 10 and 30 degree for 30 min. In the sample dyed with pPDA alone system and pPDA/pAOC couple system included ethylenediaminetetraacetic acid (EDTA) and ascorbic acid, the colorless oxidation dye intermediate mixture is scarcely substantive inside the fiber dyed for the different dyeing time,whereas in the sample dyed with pPDA/RC couple system included EDTA and ascorbic acid the presence of the colorless oxidation dye intermediate mixture within the fiber was confirmed. However, the time-course of K/S-Ramda curve of the wool fabric dyed with pPDA/RC couple system excluded EDTA and ascorbic acid indicated that there is no presence of the colorless oxidation dye intermediate mixture inside wool fibers. On taking all the results into consideration, we reached the conclusion that the oxidation dye intermediates presented inside the wool fiber are the colorless leucoindo dyes as a discrete entity. We concluded, furthermore, that the presented leucoindo dyes result from inhibiting the oxidative reaction of the leucoindo dyes by the anti-oxidative function of ascorbic acid, and deductively that, in the greater part of the precursor/coupler dyeing system, the oxidative reaction of the leucoindo dye occurred principally at the outside regions of fiber surface and the produced indo dye penetrated into the intercuticlar region of the wool fiber.