Research Of Ultrasound Electrochemical Reduction Of Indigo And Dyeing

Indigo as one of the oldest dyes has been applied in dyeing industry for thousand years,which plays a very important role in denim industry.Demand of indigo holds very large in future due to its excellent all-around fastness to cellulosic fibers,particularly to light,washing and chlorine bleaching.But indigo faced some technical problems due to its water insolubility.Generally indigo needs to be reduced to its water soluble leuco form in the alkaline solution before indigo applied in dye-stuff.Sodium dithionite is served as mainly reducing agent to reduce indigo.But its harmful reduction products produced in dyeing process such as sulpHite,sulpHate,thiosulpHate and toxic SulpHur,which would cause serious air pollution and water pollution becoming one of the largest pollution in denim production.Many studies had been carried out to overcome these issues through developing alternative eco-friendly reducing systems.Some researches proposed to adopt some greener chemistry as reducing agent to replace the sodium dithionite,while the lower deoxidization efficiency and the higher costing restricted its further developments.Electrochemical has been considered as one of the most effective methods for reducing vat dyes,including indigo because it replaces the sodium dithionite in a stable redox mediator system.This method make it easier for process control and reproducibility of the dyeing process by the adjustment of redox potential.Compared with the previous studies,this paper firstly uses ultrasound electrochemistry reduction of indigo in China and uses the new iron-triethanolamine-calcium gluconate(Fe-TEA-Ca)complex as a medium to accelerate the mass transfer,Cleaning the electrode surface that improves the electrochemical activity and current efficiency.And for the first time found in the subsequent dyeing study Fe ions attached to the fiber surface,affecting the dyeing effect.In this regard,this article provides an experiment to solve the problem and simulate the dyeing process of the factory on medium-sized machinery and equipment,providing technical parameters and theoretical guidance for the electrochemical dyeing technology in the future industrialization.Polarization curves and current efficiency tests showed that the nickel electrode has higher corrosion resistance and exhibits excellent performance in electrochemical processes.The electrode surface could be cleaned by ultrasound that would improve the current efficiency and electrochemical activity.This view was corroborated by galvanostatic scanning and electrode surface characterization.By cyclic voltammetry analysis of Fe-TEA-Ca complex system,found that its stronger peak current and better electrochemical activity than other systems.The electrochemical reduction was carried out under the ultrasonic condition.The current efficiency was discussed on the ultrasonic frequency,current density,NaOH concentration,ferric sulfate concentration,TEA concentration,calcium gluconate concentration and reaction temperature.The best electrochemical reduction process was obtained.The current density was 1 A/dm~2,NaOH concentration was 20 g/L,ferric sulfate concentration was 5 g/L,TEA concentration was 30g/L,calcium gluconate concentration was 5 g/L,tempreture was 50?,500 W ultrasonic power and 60 HZ ultrasonic frequency,the electrochemical reduction current of indigo dye is the best.On this basis,the electrochemical dyeing of indigo was discussed.The effect of each drug concentration on the dyeing effect was discussed.The surface of the dyed fabric was characterized and found that Fe ions attached to the fabric surface and the fabric was washed with oxalic acid,which was good for wiping off Fe ions.Results showed that the content of iron ions on the surface of fabric decreased to one fifth after the oxalic acid treatment,which improved the electrochemical dyeing effect and enhanced the rubbing fastness.