Abstract
A colorimetric investigation was performed on the analysis of the color of wool substrates dyed by the
reaction between p -aminophenol(pAP) or p -phenylenediamine(pPDA) and p -amino- o -cresol (pAOC) in the presence of
hydrogen peroxide and in media at different pH values. In particular, it was investigated the L ∗ a ∗ b ∗ color variations,
namely the reflectance of the formed color, that take place on the wool in dependent on different reaction conditions.
The oxidation of a mixture of pAP or pPDA and pAOC results in the formation of an orange-red indo-phenol and a
bluish purple indo-aniline, respectively. From the color changes with increasing dyeing time in the a ∗ b ∗ diagram and
the L ∗ C ∗ diagram, it was found that the dyed fabrics changed dark shades at longer dyeing time, suggesting that these
oxidative dyes formed easily the molecular aggregates with increasing dyeing time. Furthermore, in the case of pPDA/
pAOC binary mixture, the obtained reflectance curves of the dyed wool fabrics indicated the presence of indo-dyes
produced by the self coupling of pPDA. The rate of an amount of uptake of self coupling dyes increased largely, with
decreasing pH, over the pH range 8 to 10. Although one has been believed that the diamines and monoimines produced
from pPDA and pAP, respectably, react preferentially with pAOC to produce indo-dyes which adsorbed into fibers over
the pH range 8 to 10, these colorimetric results obtained for the both dyeing system suggested that the oxidative reaction
occurred in the solution contacted with the fiber surface included the self coupling reaction considered negligible in the
bulk solution.
