ANGEL COLLEGE OF ENGINEERING & TECHNOLOGYTIRUPUR 641 665

(Approved by AICTE, New Delhi and Affiliated to Anna University of Technology, Coimbatore) An ISO 9001:2008 Certified Institution

DEPARTMENT OF FASHION TECHNOLOGY

FT2255 - DYEING, PRONITING AND POLLUTION CONTROL

TWO MARK QUESTION WITH ANSWER

Branch: B.Tech Year / Sem: II / III

Unit – I BLEACHING

1. Give the function of pattern roller and bowl in calendaring m/c PATTEREN ROLLER: Lusture produced. BOWL: Flat, soft effect.

2. What is universal bleaching agent and why it’s called so? Hydrogen peroxide is a universal bleaching agent. It is used for bleaching of all kind of textile fibres.

3. What are the types of effect to be given for universal calendaring?i. Roll Effect: Flattened fabric, high coverage ratio, soft hand and moderate glaze

ii. Matt Effect: High coverage ratio, soft hand and matt effectiii. Lustrous effect: This effect originates from friction created during the passage between a smooth

and a steel roller4. What are the objectives of Bleaching cotton fabric?

To remove the natural and added colouring matters To make white

5. Why sodium hypochlorite is called as strongest oxidizing agent?Sodium hypochlorite is capable for to release the nascent oxygen (O) at room temperature during bleaching process. So that it is called as strongest oxidizing agent.

6. State object of calendaring To compress the fabric and Reduced fabric thickness. Increased fabric luster Increased fabric cover To upgrade the fabric and impart smooth silky surface feel Reduced air porosity and Reduced yarn slippage

7. Mention the conditions of bleaching with hypochlorite and peroxide.Conditions for hypochlorite bleachingTemperature - Room temp Time - 2- 3 hrspH -10.5 - 11

Conditions for peroxide bleachingTemperature - 80ºCTime - 1- 2 hrspH - 10.5 - 11

8. Which one is better bleaching process – hypochlorite or peroxide? Why? Peroxide is better bleaching Because of more whiteness, less damage, less time and combine scouring and bleaching process is

possible.9. Why is grey cotton material hydrophobic?

Grey cotton fabric consists natural impurities like oils, wax, etc. and added impurities like starch so that grey cotton materials are hydrophobic.

10. What is embossing?It’s on kind of finishing process and produce damask effects on the fabric.

11. Write the advantage and disadvantage for sodium hypochlorite bleaching Advantage

Hypochlorites are easy to handle Sodium hypochlorite, being sodium salt of hypochlorous acid, does not require any dissolving

arrangement and are ready for immediate use. Sodium hypochlorite can penetrate into the fabric more thoroughly Bleaching is cheapest one. Process temp is room temp.

Disadvantage Bleaching with sodium hypochlorite produces slight damage to cellulosic fibres Sodium hypochlorite cannot be used for the bleaching of synthetic fibres as it produces greater

damage to such fibres Bleaching with sodium hypochlorite solution requires corrosion resistant equipment. Sodium hypochlorite produces unpleasent odours in working environment. Sodium hypochlorite solution is harmful to skin in concentrated form. It produces harsh handle on fabric. Furthermore, it cannot be used on natural animal fibres. Stabilisation of sodium hypochlorite is difficult to achieve where pH varies

12. List out the advantage and disadvantage for hydrogen peroxide bleaching Advantage

Peroxide is capable of continuing the scouring action simultaneously with the bleaching action, thus a single stage combined scour and bleach or a continuous method is possible using hydrogen peroxide

Peroxide bleaching is in general less liable to have adverse effect on dyed threads. The white effect is good and permanent and there is less risk of yellowing at a later stage.

Thorough rinsing followed by scouring or antichlor treatment is required with hypochlorite bleaching, whereas with peroxide a comparatively short rinsing suffices.

With hydrogen peroxide, there is no danger of equipment corrosion, no unpleasent odours and no limitations as to processing techniques.

Increasing strict control over the discharge of AOX from chlorine bleaching liquors has led to a greater advantage of peroxide processes for bleaching cellulosic fibres

Disadvantages Bleaching with peroxide is costlier than that of hypochlorite or bleaching powder. Hydrogen peroxide bleaching requires stabilisation usually with silicates which brings the risk of

forming resist stains in subsequent dyeing, and causes a build-up of hard crystalline deposits on plant and machinery causing abrasion damage to the fabric during passage.

Catalytic damage' occurs during hydrogen peroxide bleaching of cotton fabrics and results in small spots of unevenly dyed fabric or even, in severe cases, the formation of small holes.

There is limitation in white obtained on acrylic fibres. It also causes deleterious effect on skin when used in a concentrated form.

13. Mention the advantage and disadvantage for sodium chlorite bleaching Advantage

High brightness degree Negligible degradation of fibres (1-2% weight loss for cellulosic fibres and no attack to the

polymeric chains in the synthetic fibres) Lower environmental impact of wastewaters (negligible level of AOX and COD). Versatile bleaching agent for cellulosics, synthetics and blends, especially poly-cotton blends. It is

also safe for those synthetic fibers which are sensitive to alkali. Non sensitive to metal ions such as iron and Water hardness under acidic conditions.

Disadvantages It is expensive as compared to hydrogen peroxide. It cannot be used for wool and silk. Chlorine dioxide is highly corrosive to metals and toxic in nature. Bleaching in neutral and acidic pH damage cotton. 

14. Why the bleaching agents used in textile industry are oxidizing agents and not used for reducing agents? Oxidizing bleaching agents provide the permanent whiteness compare to reducing bleaching agents.

15. How are the Bleaching method classified? and write down a typical recipe for H2O2 bleachingBleaching method Half bleaching Full bleaching

Typical recipe for H2O2 bleaching H2O2 – 2 -8 %NaOH – 0.4-0.6%

Na2Sio3 – 3%Na2Co3 – 0.8 - 6%Temp - 80ºC, Time – 2 hrs, pH 10.5 to 12

16. What is M: L: R for dyeing machine?Jigger – 1: 5Winch – 1: 20 to 1: 40

17. State the concentration of bleaching agent, the temperature and pH to be maintained while sodium chlorite bleaching Sodium chlorite: 0.5 – 2 gpl Temp: 85-90°C pH: 4 ± 0.2 Time: 90-120 min.

18. What is the role of peroxide concentration in bleachingTo maintain the 2 volume of hydrogen peroxide concentration solution to provide the better effect. If Concentration is increase, fabric will damageIf concentration is decrease. No reaction

19. What is the role of sodium silicate in scouring and bleaching? Stabilizer To maintain the pH during scouring and bleaching process

20. What do you mean Antichlor Treatment? Anti chlorine treatment is to remove the chlorine content present in the hypochlorite bleached fabric to avoid the yellowise problem due to formation of chloramines by using sodium bisulphate or sodium thiosulphate or sodium hydrosulphite

21. What do you mean Souring? Bleached fabric is treated with diluted hydrochloric acid or sulphuric acid with 30 mins to make neutral condition for bleached fabric

22. Mention the merits and demerits of winch and jigger dyeing machine.Jigger Merits The cloth can be dyed in open width form of full width form. Chemical and heat loses are less when compared to winch dyeing machine The material to liquor ratio is 1:3 (or) 1:4 which saves considerable amount of chemical cost and

steam cost.

Demerits It exerts lot of tension in the warp direction and because of this normally woolen, knitted fabrics, silk

etc are not dyed in jigger dyeing machine.

Winch Merits (advantages)Thin and light weight fabrics like knitted fabrics, voile cloth etc, can be dyed successfully in winch dyeing machine without exerting any tension. Embroidery fabrics may be dyed in winch dyeing machine without affecting the embroidery designs.Demerits (disadvantages)Fabrics are dyed in rope form, so there are more chances for uneven dyeing. Therefore, we will get even dyeing only when retarding / leveling agent is added to the dye liquor. The material to liquor ratio is very high i.e. 1:30 or 1:40. Therefore the heat and the additional chemicals are provided more when compared to jigger. Heat and chemical losses are more because of the wider open tank.

23. List out the function of friction calender To produces high degree of lusture on one side of the fabric and Closing up the interlacing threads