Preparation Of A New Natural Hair Dye And Initial Research On Dyeing Theory

Nowadays we witness a renewed interest in natural dyes, as natural dyes are neither toxic nor polluting and could be considered as a suitable alternative to synthetic dyes which have been known to cause health hazards due to their carcinogenic effects. These appealing features provide an opportunity for reintroduction of naturally occurring dyes. Especially for the popularity of dyeing hair using natural dyes in recent years, the preparation of natural dyes and optimization of the hair dyeing technology in the dyeing process is thus of great importance.In this work, two kind of natural dyes hematoxylin and catechu which are commonly used in the field of wool dyeing have been systematically studied. First, the extraction methods of these dyes and their corresponding dyeing performance on human hair were investigated. The impacts of dyeing temperature, time, pH value and mordant concentration on dyeing process were inspected. By means of test of orthogonal experimental design (four factors and three levels) and using video zoom microscope and computer color matching system, optimum extraction and dyeing process were found.Second, the color stability, the relative dynamics and thermodynamic properties of the dyed were investigated to explore the dyeing mechanism between hematoxylin and hair. The results show that the dyes undergo adsorptions and desorptions process on the hair constantly during the dyeing process. During the process of hemotoxylin dyeing, the adsorption rule between hair and hematoxylin meets the Second dynamic model. The Freundlich equation and Langmuir equation were used to simulate the process of hemotoxylin dyeing, and found that Freundlich model can give a better description of the adsorption between hair and hematoxylin. Equilibrium adsorption amount of dyeing increased at the beginning and then decreased slightly. The adsorptions process of the dye is an exothermic reaction and it can occur spontaneously, as far as the dyeing process of the hair is concerned.Finally, the interaction mechanism between hematoxylin pigment and the hair was studied by the quantum chemistry method. The calculation was performed with the Gaussian 03 program suite on P4-2.6G computers based on the density functional theory (DFT) at the B3LYP/6-31G* level. The results indicate that the different pH value of the dyeing process may cause different functional groups on the hair to interact with the hematoxylin dye. Under acidic conditions, the functional group of amino on the hair plays a major role in the dye-hair interaction system. In contrast, dyeing under alkaline conditions, the functional group of carboxyl plays the major role, while the contribution of the amino group in the dye-hair interaction system may be secondary. Above all, the hair dyeing in the alkaline environments may have good results from the perspective of theoretical level.