| Nowadays,vat dyes,especially for indigo,are demanded in large.Because of a number of jeans are dyed in indigo.But these dyes are indiscerptible in water.Reductant which makes vat dye solvent in water is demanded.In general,the main reductant heavy demanded in dyeing process is rongalite and generate much sulphur waste water of deep colour and peralkaline and undegradation.If the waste water is inappropriately treated,it may result in pollution.In this experiment,indigo is reduced by electrochemical method which is a better attempt to the environmental protection.It can avoid much waste water containing sulfur produced by chemical reducers such as sodium hydrosulfite.An electrochemical setup of 300mL for reducing and dyeing has been designed.Copper (Cu),reticulate Titanium and Ag/AgCl electrodes covered by precious metals oxide are chosen as working electrode,the auxiliary electrode and a reference electrode,respectively. Sulfuric acid solution is used as the anode solution while NaOH,TEA and Fe2(SO4)3·6H2O solutions are chosen as the cathode solutions.And adopting Nation film as membrane material,indigo is electrochemically reduced and dyed by applied voltage.Firstly,the best process of reducing and dyeing is determined.A better dyeing effect can be obtained.With cathode area of cupper 20cm2,anode solution concentration of sulfuric acid solution 35g/L,cathode solution concentration of NaOH 9g/L,triethanolamine(TEA) concentration 30g/L,solution concentration of Fe2(SO4)3·6H2O 5g/L,temperature 35℃, reaction time 70min,external applied voltage 5V,indigo solution concentration 0.2 g/L and liquor ratio 100:1.Next,the influencing factors in dyeing processes are considered in experiment.It shows that K/S value rapidly rises with an increase in applied voltage;when it exceeds 5V,K/S value would decrease.Increaseing Fe2(SO4)3·6H2O concentration,K/S value would obviously rises with an increase in Fe2(SO4)3·6H2O concentration;when it exceeded 5g/L,K/S value would gradually decrease.K/S value increases with an increase in triethanolamine concentration; when TEA concentration exceeds 30g/L,K/S value decreases.When NaOH solution has a higher concentration,K/S value would be bigger;after concentration of NaOH has reached 9g/L,K/S value goes down with concentration of NaOH solution rising.With an increasing in cathode area,K/S value increases;when the cathode area exceeds 20cm2,K/S value decreases. K/S value increases with reducing and dyeing temperature rising;when the temperature exceeds 35℃,K/S value gradually decreases.K/S value increases with reducing dyeing time going on;when time exceeds 70rain,K/S value gradually decrease.Finally,the effect of the electrolyte solutions on pH value and dyeing potential is analyzed. It is experimentally shown that both pH value and dyeing potential depend on the concentration of NaOH solution.The dyeing potential almost retains constant when the concentration of NaOH solution is less than 9g/L.However,the dyeing potential increases when the concentration of NaOH solution is larger than 9g/L.The better dyeing effect can be obtained when the concentration of NaOH solution is 9g/L and pH value is 11.5.Moreover, the curves of rates of dye-uptake,levelness,colour fastness to washing between the electrochemical reducing dyeing and conventional method are compared.It demonstrates that the curve of rate of dye-uptake of electrochemical process is lower than the conventional dyeing method at beginning of dyeing process while the rate of dye-uptake of electrochemical process is higher than conventional dyeing method at last;levelness of the electrochemical method is better than one of the conventional dyeing method.The same colour fastness to washing can be obtained by the two dyeing methods.Then,it can be concluded that the dyeing effect of the electrochemical reducing and dyeing is better than the conventional one. |
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