DYEING OF NATURAL FIBRE

Question 1

1. List the various phases in the process of dyeing.

Answer 1

• Absorption
• Penetration and
• Fixation

Question 2

2. Give the properties of reactive dyes

Answer 2

• Reactive dyes are cationic dyes, which are used for dyeing cellulose, protein fibres.
• Reactive dyes are found in power, liquid and print paste form.
• Reactive dyes are soluble in water.
• They have very good light fastness with rating about
• Reactive dye gives brighter shades and has moderate rubbing fastness.
• Reactive dyes are comparatively cheap

Question 3

3. List any four properties of direct dyes.

Answer 3

• Direct dyes give bright shades but exhibit poor wash fastness.
• Their ionic nature is anionic
• They are soluble in water
  *

Question 4

4. Why are reactive dyes so called? Classify the reactive dyes with examples on the basis of application?

Answer 4

Its chemically react with cellulose fibre to form a covalent bond. So that it is called as reactive dyes.
* Hot brand
* Cold brand
* VS brand

Question 5

5. What are the advantages of reactive dyes over other dyes classes with respect to dyeing cellulosic material

Answer 5

• Good washing fastness due to formation of covalent bond between the fibres and dyes
• Bright colour and more shades are possible
• Low cost
• Easy to apply

Question 6

6. During washing, the colour is bleed from dyed fabric. How do you sort out the problem during reactive dyeing process?

Answer 6

using soaping treatment

Question 7

7. Define: Shade percentage.

Answer 7

• The quantity of dyestuff taken for a dyeing expressed as a percentage of the dry weight of the fibre to be dyed. Shade percentage is 2 means 2 gram of dyes taken for dyeing of 100g of a textile material.

Question 8

8. What dyeing assistants are used in reactive dyeing? State their functions.

Answer 8

Exhausting agents – To promote exhaustion process or dye up take. Ex. Common salt
Fixing agents - To increase the pH value to 10 to11 (alkaline pH)

Question 9

9. Indicate the fibres for which the following dyes have affinity: a. Reactive dyes b. Acid dyes c. Vat dyes d. Disperse dyes e. Direct dyes

Answer 9

• Reactive dyes – cotton, wool, silk, polyamide and viscose rayon
• Acid dyes – silk and nylon
• Vat dyes – cotton
• Disperse dyes – polyester and acrylic
• Direct dyes – cotton and wool

Question 10

10. What steps are involved in the application of a reactive dye to a cellulose fibre?

Answer 10

• Preparation fabric
• Preparation of dye solution
• Dyeing
• Exhaustion
• Fixation
• Washing
• Soaping
• Washing

Question 11

11. List the Properties of VS reactive dyes

Answer 11

• The VS dyes have extremely good solubility.
• They have excellent brightness of shade.
• They are versatile, being applicable both by dyeing and printing.
• The dyes posses good all round fastness.

Question 12

12. Mention Properties of acid dye

Answer 12

• Acid dyes are highly soluble in water
• Acid dyes are properly work on proteins fibres such as wool, silk, nylon.
• Acid dyes are ionic in nature.
• Acid dyes have molecular weights in the range 300–1000 g mol-1.