ANGEL COLLEGE OF ENGINEERING & TECHNOLOGY

TIRUPUR 641 665

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

DEPARTMENT OF FASHION TECHNOLOGYFT6404 & TEXTILE CHEMICAL PROCESSING ITWO MARK QUESTION WITH ANSWERBranch: B.Tech

Year / Sem: II / VI

Unit I 1. What are the objectives of Bleaching cotton fabric?

To remove the natural and added colouring matters

To make white

2. 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.3. Mention the conditions of bleaching with hypochlorite and peroxide.

Conditions for hypochlorite bleaching

Temperature - Room temp Time - 2- 3 hrspH

-10.5 - 11Conditions for peroxide bleaching

Temperature - 80C

Time - 1- 2 hrs

pH

- 10.5 - 11

4. 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.

5. 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. 6. 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

7. 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.

8. 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.

9. 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.

10. How are the Bleaching method classified? Bleaching method

Half bleaching

Full bleaching

11. write down a typical recipe for H2O2 bleaching

Typical recipe for H2O2 bleaching

H2O2

2 -8 %

NaOH

0.4-0.6%

Na2Sio3

3%

Na2Co3

0.8 - 6%

Temp - 80C, Time 2 hrs, pH 10.5 to 1212. What is M: L: R for dyeing machine?

Jigger 1: 5

Winch 1: 20 to 1: 4013. State the concentration of bleaching agent, the temperature and pH to be maintained while sodium chlorite bleaching

Sodium chlorite: 0.5 2 gpl

Temp: 85-90C

pH: 4 0.2

Time: 90-120 min.

14. 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 damage

If concentration is decrease. No reaction

15. What is the role of sodium silicate in scouring and bleaching? In scouring:

To prevent the formation of iron stains in scoured fabric

In bleaching Act as stabilizer To maintain the pH during scouring and bleaching process16. 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 hydrosulphite17. 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 fabric18. 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 successfullyin winch dyeing machine without exerting any tension.

Embroidery fabrics may be dyed in winch dyeing machine without affecting theembroidery 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 theadditional chemicals are provided more when compared to jigger.Heat and chemical losses are more because of the wider open tank.

19. List out the objectives of scouring process.

To make the fabric highly hydrophilic.

To remove impurities such as oils, waxes, gum, husks as nearly as possible.

To increase absorbency of fabric or textile materials without physical and chemical damage.

To produce a clean material by adding alkali.

To make the fabric ready for next process.

To remove non-cellulosic substance in case of cotton.20. What you understand by grey cloth?It directly comes from loom without involved any chemical treatment.it have natural and added impurities and colour.21. Write the properties of mercerized yarn. Improve Luster.

Increase ability to absorb dye.

Improve reaction with a verity of chemicals.

Improve stability of form.

Improve strength/elongation.

Improve smoothness.

It has been shown that the increase in the luster occurs because of an effect.

22. What is saponification? Soaponofication is the process in which fats are treated with caustic and lead the formation of hydrophilic soaps (sodium salts of fatty acids).23. What are the changes take place during scouring process

Saponifiable oils and free fatty acids are converted into soaps.

Pectins and pectoses are converted into soluble salts of pectic acid.

Proteins are degraded to simple soluble amino acids or ammonia.

Mineral matters are mostly dissolved.

Non-saponifiable oils are emulsified by the soluble soaps generated from the saponifiable oils.

Additive dirts are removed.

Residual sizing materials are broken down into soluble products.24. Write the role of stabilizer in hydrogen peroxide bleaching.The role of stabilizer is to control the pH level in solution so its help for control the rate of nascent oxygen release.25. Write the chemical used in scouring process.

Main chemicalsUse

Caustic sodaNeutralize acidic materials, saponify glycerides (waxes and oil), solubilise silicates

SurfactantsReduce surface tension & minimize interfacial tension.

DetergentsEmulsify oil, fats, and waxes and remove oil-borne stains.

Chelating agentDeactivate metal ions.

Sodium silicatePenetrate & break drown lignins

Soda ashMaintain pH

Assist emulsification by dissolving oily materials.

26. Classify the scouring agent.

27. Define scouring

Scouring is the process by which all natural and additive impurities such as oil, wax, fat, hand dust etc. are removed to produce hydrophilic and clean textile material. It is one of the vital processes of wet processing.28. Write the recipe for silk fabric bleaching.Hydrogen peroxide 10-20 ml/l (35% strength )

Sodium silicate - 2-3%

Sodium pyrophosphate 1-2%

29. Define. Carbonising Carbonising is done to remove the cellulosic impurities from wool by treatment with acid or acid producing salts.

30. What are the steps involved for Carbonising The conventional carbonising process comprises five main stages:

Scouring

Acidizing

Drying and Baking

Burr crushing and Dedusting Neutralising

31. Write the advantages of solvent scouring.

Solvent processing has been established due to reduced water pollution, reduced energy cost and consumption apart from effective removal of impurities. Solvent preparation gives excellent results in terms of uniformity, reproducibility and high absorbency.32. Name the different methods used for degumming process. Degumming of silk in water

Degumming of silk with alkali and acid

Degumming of silk with soap

Degumming of silk with synthetic detergents

Enzymatic degumming of silk

Foam degumming

33. What are optical brightening agents?Its colour less dye. To improve the brightness of the fabric.34. What do you mean by peroxide killer?

Peroxide killer

To remove the traces of the peroxide content in bleached fabric using vigorous rinsing or using inorganic reducing agents.

35. Write short notes on Enzymatic degumming of silk

Enzyme which can hydrolyse the sericin is classified as proteolytic enzymes. The proteolytic enzymes cleave the peptide/amide linkages and convert them into amino acid. Mainly there are three types of proteolytic enzymes such as

Zinc protease (e.g. carboxy peptidase A),

Serine protease (Chymotrypsin, Trypsin, Thrombin) and

Thiol protease (acts as cystine residue in the protein).

The function of proteolytic enzymes in their degree of degumming depends on the pH of the bath and the optimum activity is found to be different at different pH for different enzymes.

Usually enzymatic desizing of silk is a two stage process. In pre-degumming stage, the cloth is treated with a solution containing soda-ash (1 g/l) at 95C for 20 min at a liquor ratio of 30.

In the second stage, further degumming is carried out by treatment in a solution containing protein enzyme (0.06-0.1 g/l), non-ionic detergent (1 g/l) for 30 min at 55 to 60C.

It is usually impossible to achieve full degumming of silk by enzymes. A short-time treatment in a third bath containing soda-ash or soap may be given for the removal of the remaining sericin.

36. What physical and chemical changes take place in cotton fiber after mercerization in fabric form?A. Fiber level1. Swelling

2. Cross sectional morphology changes from beam shape to round shape.

3. Shrinkage along with longitudinal direction.

B. Molecular level1. Hydrogen bond readjustment

2. Orientation (parallelization) of molecular chains in amorphous region along the direction of fiber length.

3. Orientation of the crystallinity in the direction of the fiber length.

4. Increased crystallinity

C. Chemical Changes1. Increased rate of reaction on hydrolysis and oxidation

2. Liberation of heat during the caustic treatment.(heat of sorption and heat of reaction)

3. Increase in the alkali absorption.4. Increase in the absorption of iodine.

37. What is mercerization? Mercerization is afinishingtreatment of cotton with a strong caustic alkaline solution in order to improve the luster, hard and other properties, was names after its discoverer, JohnMercer, and has been in use for some time. It has been seeing an increase in application recently. John Mercer invented a process which gives cotton a lustre resembling silk - a process known as 'mercerization'. 38. Why there is increase in luster of yarn after mercerization?

The cotton hair swells in strong caustic soda solution, which change its cross section from squashed circular pipe shape to an oval shaped. If the fibers are placed under a tension or stretched position in the swollen state and then washed to reduce the caustic concentration below a particular limit, then there is an increase in the luster of the fiber.

39. Mention the step involved in mercerization process.

Impregnation of the material in in relaxed state, cold caustic solution of required strength and wettability..

Stretching while the material is still impregnated in the caustic solution.

Washing off the caustic soda from the material while keeping the material still in the stretch state.

40. Give conditions of mercerizing a cotton fabric. Time

: 30-60 seconds

Temp

: 18-20o CConcentration : 48o - 56 o Tw.

41. Mention the different types of Mercerization

Mercerization is Two Types:

1. Tension MercerizationThe purpose of mercerization is to increase luster of Cotton fibers

The fiber untwists and swells, lumen becomes rounder in cross-section and it gains luster. Dye affinity and chemical reactivity increase. Fabric becomes stronger and smoother.

2. Slack MercerizationNot as lustrous as tension method

Elongation and recovery properties improve and thus have been used to produce comfort stretch garments and fabric bandages, which need to conform to body shapes.42. Define. Mercerization

It is a treatment for cotton articles and/or natural fibres composed by cellulose in a concentrated solution of caustic soda (300 g/l), under tension and ambient temperature.

43. How can we quantify the mercerizing effect?

There are several tests which are done to quantify the mercerizing effect,

1. X ray analysis showing changes in the fine structure

2. Increased reactivity

(a) Reactivity ratio

(b) Hydrolysis number

3. Absorption Methods

(a) Moisture absorption or regain

(b) Dyestuff absorption

(C) Absorption from alkaline solutions

(i)Sodium hydroxide absorption

(ii) Barium Hydroxide absorption or Barium Number

(iii) Cuprammonium hydrate

4. Counting methods

(a) Deconvolution count

(b) Cross section count

5. Lusture

6. Shrinkage or Swelling

7. Mechanical properties

(a) Breaking load

(b) Extension or elongation at break

(c) Dimensional stability of yarn

44. List out factors involved for mercerization. Twaddle

Temperature

Tension

Time

(1) Twaddle (Concentration of NaOH):

If the concentration of NaOH is increased above 56oTw improvement inluster will be attained but if it is decrease below 48o Tw. The quality of luster willbegin to be adversely affected.

(2) Temperature:

High degree of luster is attained at temperature 18-20oC. As thetemperature is increased the quality of luster is adversely affected but onlowering the temperature no improvement in the luster is obtained.

(3) Tension:For acquiring better luster the material must be stretch to its originaldimension (both in warp and weft direction during mercerization). If the materialis allowed to shrink duringmercerizingthen quality of luster will be impaired onthe other hand if the material is stretched more no improvement in luster isachieved.

(4) Time:The optimum time for mercerizing is 30-60 seconds by increasing theduration of time no applicable improvement in the quality of mercerization can beachieved but if the time limit is less than 30 seconds in the quality ofmercerization will be improved.