Textile wet processing_unit_i

preparatory process in detail - The wet processing is a term that involves the mechanical and chemical treatment to improve the aesthetic value of the fabric, yarn, fiber.

1. TEXTILE WET PROCESSING PREPARATORY PROCESS R.SUBHA, ASSISTANT PROFESSOR

2. PRODUCTION PROCESS INTRODUCTION: Textile fibers provided an integral component in modern society and physical structure known for human comfort and sustainability. Man is a friend of fashion in nature. The desire for better garment and apparel resulted in the development of textile fiber production and textile manufacturing process.

3. GENERAL SEQUENCE OF PROCESS

4. GREY CLOTH The grey cloth —woven cotton fabric in its loom-state—not only contains impurities, including warp size, but requires further treatment in order to develop its full textile potential. It may receive considerable added value by applying one or more finishing processes

5. SINGEING Singeing is designed to burn off the surface fibres from the fabric to produce smoothness. The fabric passes over brushes to raise the fibres, then passes over a plate heated by gas flames

6. DESIZING Desizing is the process of removing the size material from warp yarns after a textile fabric is woven.

7. SCOURING Scouring, is a chemical washing process carried out on cotton fabric to remove natural wax and non-fibrous impurities (e.g. the remains of seed fragments) from the fibres and any added soiling or dirt. Scouring is usually carried in iron vessels called kiers . The fabric is boiled in an alkali , which forms a soap with free fatty acids ( saponification ). A kier is usually enclosed, so the solution of sodium hydroxide can be boiled under pressure, excluding oxygen which would degrade the cellulose in the fibre. Preparation and scouring are prerequisites to most of the other finishing processes. At this stage even the most naturally white cotton fibres are yellowish, and bleaching, the next process, is required

8. BLEACHING Bleaching improves whiteness by removing natural coloration and remaining trace impurities from the cotton; the degree of bleaching necessary is determined by the required whiteness and absorbency. Cotton being a vegetable fibre will be bleached using an oxidizing agent , such as dilute sodium hypochlorite or dilute hydrogen peroxide . For white bed sheetings and medical applications, the highest levels of whiteness and absorbency are essential

9. MERCERIZING A further possibility is mercerizing, during which the fabric is treated with caustic soda solution to cause swelling of the fibres. This results in improved lustre, strength and dye affinity. Cotton is mercerized under tension, and all alkali must be washed out before the tension is released or shrinkage will take place. Mercerizing can take place directly on grey cloth, or after bleaching.

10. COLOURING - Dyeing, printing, and coating are the coloration processes to produce beautiful motif and color effect on textile A dye can be considered as a substance that can be fixed to a material that has these properties. The colour it reflects is defined by the structure of the molecule, and particular the parts of the chromogen molecule called the chromophore group . Cotton is an absorbent fibre which responds readily to colouration processes. Dyeing is commonly carried out with an anionic direct dye by completely immersing the fabric (or yarn) in an aqueous dyebath according to a prescribed procedure. For improved fastness to washing, rubbing and light, other dyes such as vats and reactives are commonly used. These require more complex chemistry during processing and are thus more expensive to apply.

11. PRINTING Printing is the application of colour in the form of a paste or ink to the surface of a fabric, in a predetermined pattern. It may be considered as localised dyeing. Printing designs on to already dyed fabric is also possible. The common processes are block printing , roller printing and screen printing

12. FINISHING Mechanical finishin g Raising Another finishing process is raising. During raising, the fabric surface is treated with sharp teeth to lift the surface fibres, thereby imparting hairiness, softness and warmth, as in flannelette. Calendering Calendering is the third important mechanical process, in which the fabric is passed between heated rollers to generate smooth, polished or embossed effects depending on roller surface properties and relative speeds. Chemical finishing Many other chemical treatments may be applied to cotton fabrics to produce low flammability, crease resist and other special effects.

13. IMPURITIES PRESENT IN GREY CLOTH WAXES, OILS, FATS, STARCH, PECTIN

14. PLATE SINGEING

15. SINGEING

16. DESIZING DESIZING IS THE PROCESS OF REMOVING THE SIZE MATERIAL FROM WARP YARNS AFTER A TEXTILE FABRIC IS WOVEN. SIZING COMPONENTS SUCH AS VEGETABLE OILS, STARCH ETC ARE APPLIED ON THE WARP YARN TO STRENGTHEN IT BEFORE WEAVING.

17. OBJECTIVES OF DESIZING

18. MECHANISM INVOLVED IN DESIZING DEXTRIN (Insoluble) SOLUBLE DEXTRIN (Soluble) STARCH (Insoluble in water) MALTOSE (Soluble) ALPHA GLUCOSE (SOLUBLE)

19. DESIZING MATERIALS

20. METHODS OF DESIZING

21. HYDROLYTIC METHODS

22. ROT STEEP DESIZING METHOD

23. ROT STEEP

24. ADVANTAGES AND DISADVANTAGES OF ROT STEEP

25. ACID DESIZING

26. ENZYMATIC DESIZING

27. PROCESS

28. DESIZING PROCESS

29. Oxidative desizing

30. Chlorine desizing : The active agent in case of chlorine desizing is gaseous chlorine . For the Cl 2 desizing, open width cloth is impregnated with water and squeezed at required percentage expression . The squeezed fabric is passed through a chamber , which is provided with a false bottom, through which Cl 2 gas is passed . In this case Cl 2 reacts with water present in the cloth producing nascent oxygen and this nascent oxygen attacks starch , there by solubilizing it. Cl 2 + H 2 O 2HCl + [O] Since cellulose is difficult to oxidize than starch, the oxidation of cellulose is prevented or minimized by controlling the quantity of Cl 2 gas passed and time of contact.

31. The Cl 2 gas may be replaced by dilute hypochlorite solution of 1-2 g/l available Cl 2 . For this sodium hypochlorite (NaOCl) or bleaching powder (CaOCl 2 ) is used. For this method the cloth is impregnated with bleaching solution at 30・C (room temperature), squeezed and allowed to stand for one hour at room temperature. It is then washed and afterwards antichlor with HCl.

32. S odium chlorite desizing In this method Sodium chlorite (NaClO 2 ) is used under acidic condition for oxidizing the starch present in the grey cloth. Sodium chlorite in the presence of ammonium sulphate gives good desizing efficiency. Sometimes pH of desizing bath may be adjusted between 4 - 4.5 with the help buffer of Sodium acetate and acetic acid. Cotton fabric is padded at room temperature with an expression of 100% with an aqueous solution of 15g/l Sodium chlorite and 10 g/l ammonium sulphate and 1g/l of wetting agent. Then fabric is heated to 80-90 C for 1 hour. Then it is washed and neutralized.

33. Bromite Desizing Sodium bromite, is used for the desizing - is a salt of bromous acid, HBrO 2 (like sodium chlorite, the salt of chlorous acid, HClO 2 ). This has a powerful oxidising action on the starch. This is due to the combined effect of bromous acid, HBrO 2 and hypobromous acid, HOBr. This is accompanied by the conversion of bromine dioxide into oxygen and bromine . Hydrolysis of this bromine produces more hypobromous acid and the nascent oxygen generated is responsible for the oxidation of starch. There are different methods of oxidation, but the most likely one is the breaking of most stable ether linkage of the glucose ring by sodium bromite.

34. SCOURING The process of removing naturals (oil, wax, fats, gum etc) as well as added impurities (during fabrication process) to produce hydrophilic and clean textile materials is called scouring . It is very vital process of wet processing. Objectives of Scouring : The main purpose of scouring is to remove impurities from the textile materials. To make the fabric highly hydrophilic. To make the textile materials in a highly absorptive condition without undergoing chemical or physical damage significantly. To produced a clean material by adding alkali. To remove non-cellulosic substance in case of cotton. To make the textile material suitable for the subsequent bleaching operations.

35. Changes occurred during scouring : Free fatty acids are converted into soap. Unsaponifiable oils and waxes are emulsified. Proteins are hydrolyzed into soluble products. Pectose and pectin are changed into soluble salts of pactic acid . Mineral matter is dissolved. Dust particles are removed. Residual sizing materials are broken down into soluble products. Scouring process depends on : Types of fabric. Color of fabric. Cleanliness of fabric. Twist of the fabric. Count of the fabric. Construction of the fabric.

36. SAPONIFICATION AND EMULSION

37. TYPES OF KIER Open kier Closed kier Some are vertical/ horizontal. Depending on methods of heating kier divided into 3 types: Heated by direct steam within kier Heated by indirect steam within kier Heated by indirect steam outside the kier

38. Heated by direct steam within kier - rate of heat transfer from the steam to the liquor is maximum (because of its direct contact) - but there is condensation of a part of steam which dilutes the liquor and increases the volume of liquor , generates hydraulic pressure - oxygen dissolved in water which degrades. Therefore hydrazine is added to the water. (H 2 N - NH 2 + O 2 N 2 + 2H 2 O). Heated by indirect steam within kier - liquor is heated with closed steam coils inside the kier - therefore the efficiency of heat is lower than first type but there is no dilution of the liquor and not increase in its volume and no increase in pressure.

39. Open kier Certain goods containing coloured effect threads i.e. fabrics containing dyed yarns for warp and weft along with white yarns for producing coloured woven designs are boiled in open kier - since most of the colour of these threads is destroyed in boiling and bleaching. In handloom industry grey yarns are mostly boiled in open kier under atmospheric pressure using 2% caustic soda, 1% soap and 1% sodium silicate (1:20) for 4 hours - yarn has to be completely immersed in liquor throughout and left overnight and washed with water thoroughly

40. Kier Boiler is a cylindrical long, mild steel or a cast-iron container fitted with two tubular perforations (disc with several holes). One of them is on the ground, and one is on the top. These disks are linked to the upper compartment with a number of tunes which bring the liquor. Steam is carried through the center of the bay. Thus, the liquor pipes are surrounded by steam that heats them.

41. Pressure kier Boiling Cylindrical vessel capable of holding 1-3 tons of cloth. A 2 ton kier of 2.7m height amd 1.95 in diameter is commonly used for boiling. Either open kier or closed kier are in use. When lid of kier is removed, it serves as open kier working at atmospheric pressure. Kiers are made of mild steel plated 0.6cm thick joined by welding. They are provided with a pressure gauge and a safety valve. High pressure kier have manholes through cloth is introduced. Lime wash is given to interior part of kier to avoid formation of rust stains on the cloth which come in contact with the inner kier.

42. Loading of Kier Grey fabric after desizing is loaded into kier uniformly by piling either automatic or by manual piling. The kier should not filled beyond 80 and 85% of its rated capacity (overfilling create hydraulic pressure and also compress the fabric at the top of the kier, hindering the circulation of the liquor thereby increasing the temperature. Small quantities of cloth should not be boiled in larger kier, the kier should be atleast half - full or else the cloth may entangle. It is important to ensure that the goods are evenly and regularly packed in the kier. After the material is piled in the kier, heavy stones are placed on it to prevent from being tossed up during boiling. Jute cloth may be placed between the material and the stones. The cloth may be impregnated with alkaline liquor before entering the kier, in a trough and mangled to ensure even treatment of the cloth.

43. Removal of Air from Kier After loading the fabric in the kier, the liquor is let-in from the bottom of the kier to sweep out air. Material liquor ratio (M.L.R) i a kier is usually 1:4 or 1:5. There should be enough liquor for efficient circulation by the pump. Air is often removed by heating the liquor, allowing it to come from bottom, closing the lid and by keeping the air valve open . After opening the air valve, direct steam is turned ON when the liquor boils and expels the dissolved air. Subsequently direct steam is stopped and the air valve is closed, only partial air is removed this way. For satisfactory removal of air, the liquor is circulated for 15 minutes and stopped, again restarted when kier liquor starts coming out from air valve.

44. Complete immersion of material and the removal of air is most essential to prevent the formation of oxy cellulose, rapidly produced by action of air on cotton. For kier boiling, a mixture of 2% caustic soda, 1% soap and 1% sodium silicate on the weight of the material is used along with any heating assistant, boiling under 1.5kg per sq.cm pressure for 6- 10 hours is adequate for most goods, also varies according to type of fabric. Goods to be sold in white state are boiled twice, first with - sodium hydroxide and then with sodium carbonate, which takes normally 2 hours to reach the required pressure in the kier. https://www.youtube.com/watch?v=3a3ro4X6eVo

45. Bleaching Process by which the natural colouring matter and any other colouring matter are removed. In scouring all the colouring matters are removed except natural colouring matter, which diminishes the whiteness. Classified into two groups - 1. Oxidizing bleaching agents 2. Reducing bleaching agents

46. Oxidizing bleaching agents Chlorine (CL) Hypochlorous acid (HOCL) Hydrogen Per Oxide (H 2 O 2 ) Potassium Permanganate (KMnO4) Per Sulphates (K2S2O8) Pen borates (KrO4) Ozone (O3) These agents directly or indirectly use oxygen for bleaching purpose. Nascent oxygen decompose colouring matter completely into simpler compounds - can be washed and do not give trouble at later stage.

47. Reducing Bleaching Agents Sulphur dioxide (SO 2 ) Sulphurous acid (H 2 SO 3 ) Sulphite (Na 2 S 2 O 4 ) Bisulphates (NaHSO 3 ) In this the nascent oxygen combines with colouring matter to produce a colorless compound which remains in the fabric. This gradually gets oxidized back to the original colouring matter upon exposure to the air. Hence the whiteness produced is not permanent.

48. Hypochlorite bleaching Cotton goods to be bleached are to be kier -boiled and then packed in a cylindrical or rectangular vessel, may be made of wood, stone cement lining or stainless steel. The vessel have a perforated false bottom with an outlet to a tank below which has an equal capacity. The liquor in tank is made into desired concentration of available chlorine with bleaching power or sodium hypochlorite solution. It is then pumped up and spread, through which percolates to find its way ultimately into tank again. The concentration of chlorine required in the bleach liquor varies between 1 to 3 gram/ litre, but for good results 1.5g/litre is recommended.

49. Peroxide Bleaching For bleaching woven goods, series of washers, padding mangles and J - boxes operated in line and synchronized. The fabric may be handled either i the open width or in rope form. Four unit operations are involved in the process. They are Wetting out and saturating the fabric with peroxide solution. Heating the chemically saturated fabric to 930 C to 100 0 C by applying steam. Store the heated fabric for sufficient period to allow the chemical reactions to take place. Washing the heated cloth to remove the products of decomposition and untreated chemicals.

50. One stage process Grey cloth is first singed, desized and washed . It is squeezed to about 20% expression and fed into the saturator, where it is impregnated with 3 and 4% hydrogen peroxide. The saturator has a set of squeeze rollers on the exit and to remove the excess chemicals and ensure proper degree of saturation to the cloth. Cloth is then processed in the heater tube - an integral part of J - box. The heating assembly is built in form of U with reels at he top and bottom of the enclosed unit, so the cloth can freely travel through the heater. Then dry saturated steam at atmospheric pressure is admitted to the heater tube.

51. After the cloth is heated, it falls into the J- box. As it is a large stainless steel chute provided with a cloth piling device and is large enough to hold the heaviest cloth to be processed at highest speed for an hour. The heated cloth is taken from the J - box and fed into the washer where it is thoroughly washed.

52. Two Stage Method Caustic scouring and peroxide bleaching. Caustic Saturator - first stage carried out here - contains caustic liquor and the cloths are dipped into the caustic liquor 6 -8 times. The concentration of NaOH in the saturator can be maintained at 4%. Before entering into the saturator the cloth is squeezed to about 85 - 90 % expression. The saturator consists of rollers, gives cloth more dips for even wetting, when cloth leaves the saturator, it contains 100 - 110% of caustic solution.

53. T he caustic treated goods are steamed in a J-box for an hour at about 100 0 C - it is a large stainless steel chute provided with a cloth piling - in device and is large enough to hold the cloth for an hour. Before entering into the peroxide saturator it is necessary to remove NaOH solution. If it retained in the cloth means the pH of the peroxide solution increased and the solution become unstable. Hence bleaching efficiency will be lowered.

54. Peroxide Saturator After washing the cloth enters the peroxide saturator, where it is impregnated with the bleaching liquor. The bath generally contains hydrogen peroxide, sodium silicate and a small amount of NaOH. The concentration of hydrogen peroxide depends on the cloth construction , weight of the fabric and cotton quality. Closely constructed fabric requires higher concentration of peroxide. Sodium silicates fixes the pH value of the bleach liquor and produces good peroxide stability for efficient bleaching. NaOH is added to avoidthe surface of the J-box to become rough due to the precipitation of silicon residues from sodium silicate when it is used alone.

55. The cloth steamed with bleaching solution is sent to the peroxide J-box where it is steamed for an hour at atmospheric pressure at 100 0 C, for uniform bleaching the cloth temperature should be uniform.

56. MERCERISATION The process of mercerization is a most satisfactory method for increasing luster on cotton materials and two particular advantages are that the process is a cheaper one and lhat the increased luster is prominent, so that it is unaffected by washing, drying and other methods of textile finishing.

57. MACHINES FOR MERCERIZATION : Yarns are mercerized on yarn mercerizing machine - batch wise process. Mercerized either on chain or chainless mercerizing machine and it is a continuous process. YARN MERCERIZING MACHINE Can be done on grey yarn or bleached yarn using yarn mercerizing machine - contains two rollers, one is movable and has pointer which move against the graduated scale, which indicates the tension applied on the yarn. There is a rubber squeezer near the fixed roller.

58. 18-22% NaOH is taken in an overhead tank which is the mercerizing liquor. The yarn in hank form is mounted on the two roller and the tension is applied, The rubber squeeze roller helps in removing excess NaOH from the yarn. Below the two rollers there is a movable tray to collect the spent NaOH and wash water. After mounting the yarn and applying required tension the machine is started - the movable roller connected to a motor starts moving. The mercerizing liquor NaOH is sprayed over the yarn with the help of perforated pipe, when yarn gets wetted with NaOH, mercerizing takes place. This treatment carried out for 2 minutes, and once the tray is filled, hot water is sprayed over the hank which removes 60% of NaOH held and the hanks are given a cold wash and soured with HCl or sulphuric acid to neutralize the alkali. For grey yarn 1% mercerizing auxiliary can be used, which helps in better penetration of the caustic solution.

59. FABRIC MERCERIZATION In this machine, both the chain and padding mangles are not found . In this machine, the fabric is not allowed to shrink, by applying the tension on the fabric during the whole process. The fabric is mercerized under tension, whereas in other method, the fabric is mercerized with shrinkage and stretching. The machine consists of an impregnating section , washing section and squeezing mangles. The rollers of impregnating section are on inclined plane and those of washing section are on horizontal plane to assist the counter current system.

60. Before mercerizing, the cloth is passed over an expander to remove all creases and then over 4 curved, rubber covered expanding rollers . Two of which may be raised of lowered thus the cloth enters the machine under tension and is held to its dimension by passing over a series of the rollers which make contact with each other during the mercerizing. In the mercerizing section, there are two rows of bowls, one above the other and the cloth runs alternatively around the top and a bottom roller. The top bowls are covered with rubber and are carried by the bottom cast iron bowls. As the cloth passes with tension in the impregnating section, the cloth will not shrink, but the luster produced on the fabric is more. The first two lower rollers carry the cloth through the sodium hydroxide solution in the trough.

61. For better impregnation, the sodium hydroxide solution circulated through two prpcs above the first two top bowls. After passing round the remaining bowls the fabric is , squeezed by the squeezing mangle. It is then taken to a washing section, where the fabric is washed in hot water from the spurt pipes.

62. CONCLUSION Textile fibers provided an integral component in modern society and physical structure known for human comfort and sustainability. A textile manufacturing process involves the production or conversion of textile fiber through a defined process in a product. The resultant textile product can be a finished product ready for consumer market, or it may be an intermediate product to be used as an input (raw material) substance to produce another textile product.

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