Study On Dyeing Mechanism And Properties Of Natural Indigo Dyeing By Reducing Agent SRP

Natural indigo has attracted extensive attention because of its excellent clothing and unique medicinal function.Therefore,it is of great significance to study on natural indigo dyeing.Natural indigo is a vat dye.Because of it is insoluble,it can't be used for fabric dyeing directly.It can be used after reduced by reducing agent under alkaline conditions.At present,the most commonly used reducing agent of natural indigo in industry is the sodium hydrosulfite.However,the chemical property of the sodium hydrosulfite is very active.It easily react with oxygen in the air,which reduced the reducing capacity and influenced the result of use.And it is considered environmentally unfavourable because of the resultant contaminated wastewater.In recent years,thiourea dioxide and glucose have been studied to replace sodium hydrosulfite as reducing agent.However,their application is limited because of their unsatisfactory reduction and dyeing properties.This paper used a kind of reducing agent SRP.The dyeing process of natural indigo was optimized by orthogonal experiments after single factor testes.Comparison of reduction and dyeing properties of natural indigo after reduced by thiourea dioxide,glucose,redutase and sodium hydrosulfite.The reducing agent SRP has strong reducing power,good stability,good properties of natural indigo dyed fabric.In order to know the mechanism of natural indigo dyeing with reducing agent SRP,the components and the reduction potential of reducing agent SRP were studied.Through evaluating the K/S values of fabrics and color fastness,it was found that the optimal process was that the natural indigo was 5%(owf),reduced at 60 ? for 15 minutes with reducing agent SRP 30 g/L and caustic soda 3.33 g/L and dyed at 20 ? for 75 minutes with sodium chloride 70 g/L,bath ratio was 1:100.The optimized K/S value of dyed fabric was 14.32.The soaping and perspiration fastness was 4-5 grade,the rubbing fastness was above 1-2 grade.The dyeing properties of natural indigo reduced by reducing agent SRP,thiourea dioxide,glucose,redutase and sodium hydrosulfite under optimized process conditions were compared.The results showed that the reducing agent SRP had the best dyestuff enhancement property.Although had high initial dyeing rate,good levelness.The reducing properties of reducing agent SRP,thiourea dioxide,glucose,redutase and sodium hydrosulfite were compared.The results showed that the reducing agent SRP had the strongest reducing power and good stability.The reducing agent SRP was analyzed by XRD and ICP-AES.The results showed that the reducing agent SRP may contain thiourea dioxide and sodium sulfite.SRP is mainly made up of S and Na and other small amount of elements,such as Ca,K,Mg,B.This indicates that the reductant SRP is a mixture containing many components.The factors influencing reduction potential of SRP was studied.Increasing the concentration of reducing agent and caustic soda concentration,temperature and time were beneficial to increasing the value of reduction potential and K/S value.But it is not good for over negative reduction potential,the dye bath should maintain at pH 11.