Dyeing of Cotton With Azoic Dye

Theory

Azo dyes are organic compounds that contain the insoluble "azo" group (-N=N-). These dyes are not found in ready-made form. They are produced by a reaction between two components, coupling (naphthol) and diazo components. It is also called magic color in view of its versatility. Different colors are obtained by combining different bases with the same naphthol; again, using the same base with different naphthol. Thus, many shades are produced.

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Recipe

Processes	Chemicals / Parameters	Required Amount
Naphtholation	Naphthol	3%
	NaOH	2 g/L
	Common salt	10 g/L
	Wetting agent	1 g/L
	Sequestering agent	1 g/L
	Temp ✕ Time	40℃ ✕ 30 minutes
	pH	8-9
	M: L	1: 40
	Sample weight	10 gm
Diazotization	Base	3%
	HCl	2 g/L
	NaNO₂	2 g/L
	Acetic acid	2 g/L
	Wetting agent	1 g/L
	Sequestering agent	1 g/L
	Leveling agent	1 g/L
	Temp ✕ Time	0-5℃ ✕ 30 minutes
	M: L	1: 40

Functions of the Chemicals Required

Naphthol: Naphthol is regarded as the most important chemical intermediate based on naphthalene. It is manufactured by fusing 2- naphthalene sulfonic acid with caustic soda and is converted into numerous dyes. During dyeing, the substantivity increases with an increase in the molecular size of the naphtholate ion, but the diffusion rate in the fibers and solubility in dilute aqueous alkali decrease. The addition of salt promotes better exhaustion of the bath.

Caustic soda: Used for solubility of naphthol and keeping proper alkalinity of naphthol bath.

Common salt: Works as an electrolyte for the exhaustion of naphthol during naphtholation and prevents the desorption of naphthol in the bath during the rinsing and development phase.

Wetting agent: It accelerates the wettability of material in solution, thus helping to easy penetration of chemicals into the substrate. It reduces the surface tension of water to allow it to spread drops on a surface, increasing the spreading abilities of a liquid.

Sequestering agent: A sequestering agent is a substance that suppresses as property or reaction of metal ions without the removal of that metal from the system.

Leveling agent: Levelling agent tends to slow down the dye uptake on the fibers, helping to produce a more uniform color in the textile fiber.

Acetic acid: Its function is to control the pH and neutralize the solution of the dye bath.

Sodium nitrate: Produces nitrous acid in the diazotization process.

Base: A base containing an amino group (-NH2) reacts with sodium nitrite and the excess amount of concentrated HCl to form diazonium salt.

HCl: Dissolution of base and produces nitrous acid in the diazotization phase.

Recipe Calculation

Here, M:L=1:40

Sample weight: 10 gm

Total liquor : 10 ✕ 40 = 400 ml

Naphthol;

100 gm fabric needed 3 gm

So, 10 gm fabric needed (3 ✕ 10) / 100 = 0.3 gm

Chemicals = (g/L ✕ Total liquor) / 1000

NaOH = (2 ✕ 400) / 1000 = 0.8 gm

Common salt = (10 ✕ 400) / 1000 = 4 gm

Wetting agent = (1 ✕ 400) / 1000 = 0.4 ml

Sequestering agent = 0.4 gm

Total chemicals = 0.4 ml

Freshwater = (400 – 0.4) = 399.6 ml

Diazotization:

Base = (3 ✕ 10) / 100 = 0.3 gm

NaNO₂ = (2 ✕ 400) / 1000 = 0.8 ml

HCl = (2 ✕ 400) / 1000 = 0.8 ml

Acetic acid = 0.8 ml

Wetting agent = (1 ✕ 400) / 1000= 0.4 ml

Sequestering agent = 0.4 gm

Levelling agent = 0.4 ml

Total chemicals = (0.8 + 0.8 + 0.4 + 0.4) = 3.2 ml

Freshwater = (400 – 3.2) = 396.8 ml

Shade Attachment

Azoic Dyed Cotton Sample

Dyeing Curve

Azoic Dyeing Curve

Conclusion

Naphthols are the only icy water dyes available to home dyers, which makes them ideal for wax resists application. Mostly used in the handloom industry and is suitable for cotton, silk, and rayon.

Ahmedabad