In this article, we are going to know about the dyeing process of cotton fabric with vat dye. This process and recipe is followed in the lab and described below with the resulted color.
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Theory
The word vat comes from the vessel, vat dyes can be applied in a vat for coloring textile products. Vat dyes are natural coloring materials that are solubilized in a vat by the fermentation process called vatting. Vat dyes are insoluble in water, but it becomes soluble through the vatting process. The process of converting insoluble vat dye into soluble form is known as vatting. It is different from reactive dyes, disperse dyes, basic dyes, and acid dyes, but its application process is similar to Sulfur dyes. Vat dyes are used for coloring cellulose fiber, especially cotton fiber. It is widely used to run the dyeing process of cotton yarns, which are used for producing jeans or denim products.
Objectives
- To dye cotton fabric
- To know about vat dye
- To know about the process of vatting
- To know about oxidation
- To know about the importance of vatting.
Recipe
Dyeing Procedure
Vatting– Dye + Na2SO4 + NaOH – (60℃ ✕ 10 minutes)
Dyeing– (Wetting agent + Leveling agent + Sequestering agent) – (80℃ ✕ 30–50 minutes)
OxidationTemperature ✕ Time – (50℃ ✕ 10 minutes)
Neutralization: SoapingH2O2 – 2 g/L
CH3COOH – 1 g/L
Temperature ✕ Time – (50℃ ✕ 10 minutes)
Detergent – 2 g/L
Temperature ✕ Time – (70℃ ✕ 10 minutes)
After soaping, then hot wash, and after hot washing, then cold washing.
Calculation
M : L (Material : Liquor) = 1:40Fabric = 5 gm
So, Liquor = (5 ✕ 40) = 200 ml
M : L = 5 : 200
Insoluble dye, 3 %100 gm fabric required 3 gm dye
So, 5 gm fabric required (3 ✕ 5) / 100 = 0.15 gm dye
Again, Chemical = (g/L ✕ Total liquor) / (1000 ✕ Stock solution %)For 5% stock solution wetting agent required = (1 ✕ 200) / (1000 ✕ 5%) = 4 ml
For 5% stock solution, Na2SO4 = (4 ✕ 200) / (1000 ✕ 5%) = 16 ml
Thus, calculated total chemicals.
Now, Freshwater needed = (200 – Total chemicals) ml
After dyeing,For oxidation, 5% H2O2 = (2 ✕ 200) / (1000 ✕ 5%) = 8 ml
Freshwater = (200 – 8) = 92 ml
Sample of Fabric
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| Vat Dyed Cotton |
Dyeing Curve
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| Vat Dyeing Curve |
Functions of the Chemicals Required
Vat dye: Vat dyes are natural coloring dyes. It is insoluble in water, the vatting process is needed for making the insoluble vat dyes into a soluble form. The oxidation process develops the final color. Vatting is done in alkaline conditions. The fastness properties of the dyes are excellent, but their rubbing properties are not good. It is mainly used for coloring cellulose fiber. The dye is applied in a soluble, reduce form to impregnate the fiber and then oxidized in the fiber back to its original insoluble form.
Wetting agent: It accelerates the wettability of material in solution, thus helping the easy penetration of chemicals into the substrate. It reduces the surface tension of water to allow it to spread drops onto a surface, increasing the spreading abilities of a liquid.
Sequestering agent: In the absence of a water-softening plant in an industry, it is also possible to reduce the unwanted interference of heavy metal ions during soaping or dyeing by a sequestering agent. A sequestering agent is a substance that suppresses a property or reaction of metal ions without the removal of that metal from the system. The most common sequestering agent is EDTA, known as ethylenediaminetetraacetic acid.
Leveling agent: Levelling agent tends to slow down the dye uptake of the fibers, helping to produce a more uniform color in the textile fiber. They are also termed retarding agents or retarders.
NaOH (Caustic Soda): Neutralizes acidic materials, saponifies glycerides (waxes and oils), and solubilizes silicate. Maintain reducing dye in water.
Hydrose (Na2SO4): Sodium hydrosulfite or hydrose is used as a reducing agent. It turns the insoluble dye to produce a weak, acidic leuco form. It decomposes during vatting and dyeing. Decomposition increases with temperature.
Oxidizing agent: The chemical compound which provides oxygen during a chemical reaction and itself converted to oxides. It is a reactant that removes electrons from other reactants during a redox reaction. In the experiment, H2O2 acts as an oxidizing agent.