Study On Electrochemical Reduction And Dyeing Process Of Vat Dye In Controllable Electric Field

Vat dye is an important dye for cellulose fabric dyeing and printing, which has bright color, completed color spectrum and comprehensive fastness. It is mainly used in high-quality fabric due to its particularly outstanding washing and light fastness. Nowadays, in most industrial dyeing process, vat dye is reduced by sodium dithionite, which will produce large amount of sulfur containing wastewater, such as sulfates and sulfites during the dyeing process and increase the cost of waste water treatment. There are numerous studies on eco-friendly dyeing process of vat dye proposed so far, in which indirect electrochemical reduction has the potential to be industrialized. However, limited contact areas of cathode plate surface and leuco dye tending to aggregation around it cause the slow diffusion rate and induce low reduction efficiency. What is more, the dyeing depth cannot be comparable to those dyed by traditional methods. As a result, indirect electrochemical dyeing still has limiting applications.Aiming at improve the indirect electrochemical reduction rate and efficiency, this research introduced controllable electric field into vat dye reduction and dyeing process. In reduction process, Fe(Ⅲ)-oxalate-calcium gluconate complex was chosen as the media and self-made electrolytic bath with additional electric field was applied during the whole process, The advantages of this method are reduction rate and efficiency increase and color depth improvement. The main research contents and conclusions are shown as below.Firstly, indirect electrochemistry reduction device was designed. The main work consisted of designing electrolytic bath and electromagnet and connecting the whole circuit.Secondly, the indirect electrochemistry reduction process of FFB in appearance of additional alternating induced electric field was studied. The effects of influence factors on K/S values and CV curves were discussed by orthogonal and single factor experiments. The best reduction conditions with additional electric field are NaOH25g/L,C2H2O6g/L,Fe2(SO4)37.5g/L, Ca(C6HnO7)14.5g/L,dye0.3g/L, reduction voltage4.5V, cathode area360cm2, induced electric strength1650N/C, frequency50Hz, reduction time19min,Under mentioned conditions, highest reduction rate and color depth can be obtained. Different dyes with different concentration were also studied under the same media.Then, dye tank with controllable induced electric field and frequency was designed for dyeing process. The reduced FFB was used to dye fabrics with the assistant of alternating electric field. The influencing factors of electric field strength, temperature, time, pH and NaCl concentration on dyeing effects were discussed from orthogonal experiment and single factor experiments by taking dyeing rate and K/S as criteria. The best dyeing conditions are electric field strength1600N/C,pH11.5,temperature45℃,time9min. Finally, compared with conventional electrochemistry and traditional sodium thiosulfate reduction process, the dyeing effects achieved by this new method are quite close in terms of level effect and dry rubbing fastness, while wet rubbing and washing fastness can improve by0.5to1grade.