Keiko Sakata

Oxidative Reaction of Oxidative Dye Intermediates adsorbed into Wool Fabrics

The reactivity of oxidative dye intermediates penetrated into wool fibers was investigated. The wool fabrics which were treated in p-phenylenediamine, p-phenylenediamine/p-amino-o-cresol, and p-phenilendiamine/resolcinol aqueous solution at 30°C for 10 minutes were oxidized by hydrogen peroxide. The adsorbed intermediates were found to be able to react inside the fiber by the oxidative effects. However, these fabrics were unevenly colored, and the concentration of oxidative dyes developed by reacting among the oxidative dye intermediates inside wool fibers were much lower than that of them in the fibers dyed with the same precuser/coupler/H2O2 dyeing system under the similar conditions. In particular, the K/S-λ curve of the wool fabric that were dyed by pPDA/RC solution including EDTA and ascorbic acid followed by the treatment with hydrogen peroxide was definitely different from that of the wool fabric dyed with pPDA/RC/H2O2 dyeing system. Consequently, it was suggested that the reaction among the oxidative dye intermediates inside the wool fiber is side reaction for the mechanism of oxidative dyeing under the precuser/coupler/H2O2 dyeing condition for keratin fiber.

Effects of Dyeing Conditions on Discoloration Behavior for Oxidative Dyed Wool Fabrics

The effect of air function on discoloration behavior of oxidation dyes in wool fibers at ordinary temperature and humidity in dark room was investigated. The samples dyed under three different dyeing conditions and dyed with the different mixed ratios of precursor and copular were used in experiment. In the color change defined by chromaticity diagram (a* and b*) and color tone diagram (L* and C*), the color tone of samples dyed under dyeing system including alkali and hydrogen peroxide changed more significant than that of samples dyed in the performed oxidation dye solution. The discoloration of samples dyed with the different mixed rations of precursor and copular is scarcely dependent on mixed ratio, except for the couple system of p-diaminotoluene/p-amino-o-cresol. The modifications of physical and chemical structure of wool fibers had no effect on the decreasing rate of K/S value for the samples dyed using three precursor / copular systems.

The Effects of Air Oxidation on the Surface Color of Silk fabrics dyed with Hematoxylin

In order to clarify whether the colorless hematoxylin absorbed in the silk fiber is oxidized to hematein by oxygen in air, the time-course of K/S-λcurve of the silk fabric dyed at the different pH with hematoxylin was investigated by keeping them at ambient temperature and humidity for 40 days. Either of the silk fabrics dyed at pH3.9 and 4.9 were colorless and, if these fabrics were exposed by air for 40days, colored to brownish yellow, implying that hematoxylin inside the fiber was oxidized to hematein. In addition, it was found that a portion of hematein absorbed in silk fabrics dyed at over pH5.9 was faded by oxygen in air. Consequently, the color yield of fabrics during storage was considered to result from a balance of the oxidation of hematoxylin and the discoloration of hematein.

Functions of Trace Metals in Fibers on Dyeing of Wool Fiber with Oxidation Dyes

To clarify what components of CMC contribute to the oxidation reaction, the effects of pretreatment of wool fibers using ethylenediaminetetraacetic acid (EDTA) solution and premordanting with the solution of metal salts on the dye uptake of the dinuclear oxidation dyes into wool fibers were investigated. The dye uptake of the wool samples pretreated with EDTA solutions decreased apparently compared to that of the intact wool sample. On the contrary, the wool samples premordanted with copper, iron and nickel salts allowed the dye uptake of oxidation dye inside the wool fiber to increase. These findings indicate that the metal ions presented primarily within the intercellular materials play an important role in developing the colored oxidation dye on⁄into the fiber. The presence of transition metal ions in the intercuticular material causes hydrogen peroxide to undergo radical decomposition, leading to oxidizing species by means of Haber-Weiss mechanism. They take part as initiator of oxidation reaction, where the dye precursor is electrochemically oxidized to its corresponding Wurster salt.