Function of Surfactants in Hair Dyeing by Oxidation Dyes 1. Effect on Colour of Hair Dyed by p-Aminophenol and 5-Amino-o-cresol

The effect of surfactants on the colour of hair dyed by an oxidation dye was studied paying attention to the difference in charge of the hydrophilic part of the surfactants. The surfactants employed in the experiments were anionic, nonionic and cationic ones. It was found that in the presence of cationic surfactants, the resulting colour of hair dyed by the p-aminophenol (PAP) and 5-amino-o-cresol (5AOC) system is more vivid than that of hair dyed without surfactants or with anionic or nonionic ones. The changing behaviour of hue, lightness and chroma with time for hair dyed by the PAP-5AOC system with cationic surfactants is different from that of other systems, which contain anionic or nonionic surfactants, or contain no surfactants. Especially the hair chroma (C*) for the cationic-surfactant-containing system increases monotonously with time, while C* for other systems increases at first and then decreases with time. The C* - L* (lightness index) relation curve for the cationic system shows a same tendency even at longer dyeing time (140 min). The C* of hair dyed by PAP-5AOC system for 40 min has maximum value at 0.03 M of cationic surfactant added, of which hydrophobic chain is hexadecyl.