The dye which is capable of reacting chemically with a substrate to form a covalent dye-substrate linkage is known as reactive dye.
D-SO2-CH2-CH2-OSO3Na + OH-Cell →D- SO2-CH2-CH2-O-Cell + NaHSO3
- Reactive dyes are cationic dyes.
- Found in powder or liquid form.
- Forms covalent bond.
- Soluble in water.
- Very good light fastness properties.
- Very good wash fastness properties.
- Dyeing method of reactive dye is very easy.
- Comparatively cheap.
- Exhaustion & fixation occurs.
Assistant used for reactive dyes:
- Salts are used to increase the affinity of dye to fibre.
- Decreases hydrolysis rate of dyes.
- Neutralisis electronegativity of fibre surface.
- Creates extra energy to push dye inside fibre polymer.
- Alkali :
- Alkali is used to maintain proper pH in dye bath.
- It is used as a dye fixing agent.
- Strength of alkali depends on the reactivity of dyes.
- NaOH→(12.5 – 12) – Strong Alkali
- Na2CO3→(11 – 12) – Medium Alkali
- NaHCO3→(10 – 11) – Weak Alkali