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. They are 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.
{getToc} $title={Table of Contents}
Recipe
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 ©Textile Pad |
Dyeing Curve
 |
| Azoic Dyeing Curve ©Textile Pad |
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.