Study On Dyeing Property And Mechanism Of Indigo,Lawsone And Their Combination System

In recent years,the market of hair dyes in daily chemical industry has been increasing year by year.Pigments,as an important component of plant hair dyes,have always been a research hotspot.The research on the extraction of natural pigments and optimization dyeing process has a long history,and some scholars have studied the dyeing kinetics and thermodynamic behavior of single-component pigments in recent years.However,the adsorption behaviors of two-component and multi-component pigments are rarely studied.The research on the dyeing kinetics and mechanism of two-component system can provide theoretical basis for the development of plant hair dyes and the improvement of dyeing process in the future day.Hence,this research is of great significance.In this paper,two kinds of natural pigments indigo and lawsone have been selected as research objects to optimize the dyeing process.The optimal dyeing process conditions are fixed at the temperature of 50°C,pH value of 4,and the dyeing time of 60 min.Compared with the oxidation hair dyes,the surface of hair scales are still regularly dyed by indigo and lawsone,and the internal structure of hair is less damaged,which maintains good integrity of hair.Furthermore,indigo and lawsone could be mixed with different ratios under the best dyeing condition to obtain multiple colors,and enrich color tones of natural plant pigments hair dye.The adsorption kinetics and thermodynamics of single-component plant pigments on hair have been explored.The results show that the adsorption kinetics of indigo and lawsone on hair are consistent with the pseudo-second-order kinetic model,and the Freundlich isothermal adsorption could simulate the adsorption behavior properly.The adsorption process is a spontaneous endothermic process accompanying with increased entropy.The higher temperature is,the more favorable the adsorption reaction can proceed.In the two-component system,indigo and lawsone would struggle with the adsorption sites of hair,which shows that there is a competitive adsorption behavior between them.In addition,the competitive ability of lawsone is greater than indigo.The competitive adsorption capacity is not only related to the interaction between pigment and hair,but also related to the concentration of pigment molecules.Extended Freundlich could describe the competitive adsorption behavior between indigo and lawsone.The effects of washing,solar irradiation and ultraviolet radiation on the fade behavior of dyed hair were studied.The results show that washing could cause color fading of hair.The more washing times are and the higher washing temperature is,the more serious fade is.Moreover,solar irradiation,UVA and UVB could also cause the fade of hair,as well as the decrease of tensile strength and?-keratin content of hair.Six fundamental pentapeptide quasi-repeats with the form of A₁?C-C-Q-P-X?,A₂?C-C-R-P-X?,B₁?C-C-X-S-T?,B₂?C-C-X-T-S?,B₃?C-C-X-S-S?and B₄?C-C-X-T-T?have been selected as a simple model of hair.The quantum chemistry method was performed to investigate the interaction between hair-indigo and hair-lawsone.The hydrogen bonds are formed between two kinds of natural pigments and six pentapeptide models,and the lowest interaction energy is formed with the model B₂,indicating that the indigo and lawsone are most prone to binding with B₂ during dyeing process.In addition,there is a positive synergistic effect existed in the compounding system,which could promote the absorption of pigments and improve the stability of dyed hair.