Study On The Mechanism Of Hematoxylin Dyeing Deep Dlack On Cotton Fabrics

Natural dyes are gradually recognized by people for their unique environmental protection and functional advantages,but their color spectrum is incomplete,especially the black series are scarce.Therefore,the method of dyeing black with natural dyes should be further studied to enrich the shades of natural dyes.Natural dye of Sappanwood can use to development of a variety of color shades for its wide range of colors,which offers the possibility of dyeing black.At present,the research of natural dye of Sappanwood is mainly in its extraction and dyeing process,but its mechanism research were rarely reported.Therefore,In this paper,hematoxylin were selected as the research object,and its dyeing performance?black dyeing method?dyeing mechanism on cotton fiber was discussedFirstly,the acid-base stability,temperature stability,reducing agent stability and metal ion resistance stability of hematoxylin in aqueous solution was investigated.The result showed that hematoxylin is extremely unstable in solution and sensitive to the p H value of the solution and easy to be oxidized under alkaline conditions;In an acidic solution with acetic acid as the p H regulator,the hematoxylin can also be oxidized by increasing the system temperature,but the stability in the acidic reducing agent system is better,which can effectively prevent hematoxylin from being oxidized;Hematoxylin is difficult to complex with metal ions to develop color;And then,its dyeing mechanism under the citric acid system was investigated.The result showed that the hematoxylin has poor dyeability on modified cotton fiber.Secondly,using high performance liquid chromatography and liquid chromatography-mass spectrometry to analyze the chemical structure changes after hematoxylin alkali treatment,it is found that hematoxylin is easily oxidized to hematein under alkaline conditions,and the effective dyeing substance is Hematein.The process of using alkali solution method to preparing hematein was researched,and the optimal preparation conditions were determined as:T=20?,p H=9,t=80 min,The resulting solution is called pre-oxidation dye solution for the oxidation rate of hematoxylin was 67%.Thirdly,the cotton fabric was dyed with the pre-oxidation dye solution,and the results showed that the pre-mordant dyeing of modified cotton fabric with ferric sulfate as a mordant can dye dark black.And then,the effect of mordant dosage,dye dosage,dyeing time,dyeing temperature,dyeing p H value are analyzed by single factor and orthogonal optimization experiment.The results show that the pre-oxidized dye liquor is dyed with 6%(o.w.f)iron using the pre-mordant dyeing method,The best process for dyeing black is:dyeing p H is 7,dyeing temperature is 60?,dyeing time is 40min,dye dosage is 3%(o.w.f);The fastness of dyed black cotton fabric is good,even up to level 4 or above,it also has anti-ultraviolet performance for UPF=2000?UVA=0.05%.Finally,the black dyeing mechanism of hematoxylin was studied.The results show that Fe₂(SO₄)₃ has strong oxidizing properties,which can oxidize hematoxylin in the solution,and the complex reaction can undergo between the reduction product ferrous sulfate and the dye,as result that the fabric was dyed with the blue color in the same medium.But during the pre-medium dyeing process,iron sulfate is first adsorbed on the fiber and complexed with the fiber,the oxidation ability of Fe³⁺is inhibited,and the,it complexes with hematein to appear black.The results of dyeing thermodynamics and kinetics under the citric acid system show that the process of dyeing cotton fabrics with hematein conforms to the quasi-secondary model,and the thermodynamic fitting results conform to the Langmuir model.Therefore,the dyeing process of hematein belongs to chemical adsorption;As the temperature increases,the half-dyeing time is shortened,and the dyeing affinity decreases,therefore the dyeing equilibrium adsorption capacity decreased with the increase of temperature;The dyeing heat of hematein was-11.504k J·mol^-1·K^-1,the dyeing entropy is 0.0818 k J·mol^-1·K^-1,and the dyeing process is an exothermic reaction with entropy increase.