Study On The Photo Fading Mechanism Of Madder Natural Dye

Natural dyes have always been the focus of research in the textile industry.Its environmental protection and health advantages have attracted extensive attention from researchers in the textile field.However,fabrics dyed with natural dyes often have obvious color fading and color change after light irradiation,and studies on the fading mechanism of such fabrics are relatively limited.In this paper,the natural dyes of rubidium alizarin were selected as the research object,and the mechanism of the fading of rubidium alizarin and its dyed fabrics was discussed under the light or without light,and light conditions by simulating the sunlight with xenon arc lamp.The effects of high temperature,oxidant,acid and base on alizarin were investigated,and the light stability and photooxidation products of alizarin under different p H value,solvent,oxygen and photosensitizer were emphatically analyzed.Studies have confirmed that quercetin was oxidized by DPPH?1,1-diphenyl-2-trinitrophenylhydrazine?and other Strong oxide in preference when it was mixed into the solution of alizarin,indicating that quercetin and other substances had a protective effect on alizarin.Oxygen plays an important role in the photodegradation of alizarin and participates in its photochemical reaction.The stability of alizarin in different solvents is different,and the light stability of alizarin in acetic acid,ethyl acetate and other acidic or neutral solvents is strong,but the stability of alizarin in ethylenediamine and other basic solvents is very poor.Further investigation found that the change of p H value changed the ionization state of phenolic hydroxyl of alizarin molecule,which could make alizarin show a colorful color change from yellow to red to blue.The higher the p H value was,the easier the phenolic hydroxyl group was to be ionized,and the more unstable the molecular structure was,which may be the fundamental reason for the photodegradation of alizarin.The photodegradation of alizarin was accelerated when diphenylketone and other photosensitizers were added to alizarin solution.In the photodegradation of alizarin,180?C₉O₄H₈?,170?C₇O₅H₆?,166?C₈O₄H₆?,142?C₆O₄H₆?,208(C₁₀O₅H₈)and other colorless small molecule compounds are mainly generated,leading to discoloration.Secondly,the color stability of alizarin-mordant and mordant-cotton fabric was studied.The results show that the mordant itself is unstable,whether it is the premordant fabric or the mordant-alizarin complex,the acid will dissolve the metal ions in the complex,and the base will promote the metal ions to hydrolyze,resulting in the discoloration.Under the condition that the premordant fabric has a high liquid content,after photothermal treatment and then dyeing,the yield of the premordant fabric decreases significantly,indicating that the premordant fabric is unstable.In the system of alizarin mordant,the optical stability of alizarin-Al³⁺complex was the worst,while the opticalThirdly,the light stability of dyed fabrics was studied.The results show that the ternary complex system of alizarin-mordant-cotton fabric still exhibits similar characteristics to that of its unary or binary system,and the water,acid and alkali in the fabric still play an important role in the process of fading.The dyeing p H value is controlled between 7-9,which can improve the color depth and light resistance of the dyed fabric to some extent.The light resistance of different metal ions as mordant varies greatly,zinc sulfate is the worst,copper sulfate and ferrous sulfate are better.The dye structure analysis of the dyed fabric after light showed that the photodegradation behavior of alizarin on the fabric was the same as that of alizarin in solution.Finally,the light resistance of dyed fabrics with different light sources,air humidity and different finishing agents was studied.The results show that ultraviolet light is not the only reason for the fading of dyed fabrics,and visible light can also cause the same degree of fading of alizarin dyed fabrics.Dry environment can significantly improve the light stability of dyed fabrics,30%air humidity,can accelerate the light fading behavior of alizarin dyed cotton fabrics;Alizarin has different fading degree on different fibers,and its light fastness on polyester fiber is obviously higher than that of cellulose and protein fiber,which is obviously related to the combination state of dye and fiber and the structure of fiber aggregation state.When dyed fabrics are treated with different finishing agents,polycarboxylic acids such as tannic acid can improve the light resistance of dyed fabrics.The light resistance of dyed fabrics treated with anion softener finishing fabrics better than cationic or non-ionic softener.