Published on Feb 10, 2016
The Objective : VAT dying is a process through which all insoluble commercial VAT dyes are taken up by cotton fibers in an alkaline or base-soluble form by reduction and made insoluble again through fixation by oxidation.
In the case of the current experiment, indigo synthetic[C(16)H(10)N(2)O(2)] is the example dye used. When sodium hydrosulfite[Na(2)S(2)O(4)] is added to the solution of water, sodium hydroxide and indigo synthetic; and heated to a temperature of 75 degrees Celsius, indigo synthetic gets reduced to indoxyl [C(16)H(12)N(2)O(2)], which is a highly unstable yellow compound.
When the cotton fabric is immersed in the indoxyl solution and exposed to air to dry, the yellow coloring in the fabric gets oxidized into indigo synthetic and turns blue. Here, handling sodium hydrosulfite (hydros) is injurious to health since a toxic smell involved during dying process seriously affects the health of the dyers by irritating their eyes, nose and skin. Hence, it is thought worthwhile to study an electrolytic method for VAT dying; which is simple, economical, free from pollution and the costly handling of sodium hydrosulfite; during reduction.
The experiment is setup in a H-Type electrolytic cell. Catholyte consists of 300mL of water; 5g of sodium hydroxide; 1g of sodium sulfate and 100mg of cerous sulfate as catalysts; and a lead sheet as cathode.
Anolyte consists of 40mL of water, 1.1mL of sulfuric acid and a lead sheet as anode. The cell is heated to 75 degrees Celsius and 100mg of indigo synthetic is added.
A DC 12 volts power supply is taken; the positive alligator clip is connected to the anode while the negative alligator clip is connected to the cathode. Hydrogen gas is released in the catholyte and indigo will get reduced to indoxyl.
As the electrolysis was allowed to run for 10 minutes, the catholyte barely changed color.
But when the experiment was continued for an hour, the catholyte had slightly turned green. In order to save time, the catholyte was decanted and the sediments were found to be yellow in color.
When the sediments were allowed to dry and get oxidized, the color of sediments changed from yellow to blue.
Results show that an electrolytic method for reducing VAT dyes is indeed a very time consuming process but definitely a safe alternate method that actually works. In the years to come, this process will be further researched on how it can be sped up.
The project was to test whether or not electrolysis can reduce VAT dyes without the assistance of sodium hydrosulfite, which is the commercial toxic reducing agent used by VAT dyers.
Science Fair Project done By Uppili S. Raghunathan