Textile chemical processing 1st full.pptx

Textile chemical processing, 1st full

1. Fabric inspection

2. Process layout in pretreatment section Grey section Fabric receiving & recording Inspection Grey store Lot making Singeing Bleaching Scouring Desizing Mercerizing/ causticizing

3. Shearing and Singeing Processes

4. Shearing What is shearing Shearing is an operation consists of cutting the loose strands of fibers or loops from either surface of a fabric with a sharp edged razoror scissors. Objectives of shearing process To remove projecting yarns and filaments from the surface of fabric To give clean and smooth appearence to the fabric. By manipulating shearing it is possible to cut designs into pile fabrics. Good cropping is perhaps, the simplest way of reducing the tendency of blended fabrics to pill. Precautions In case of cotton fabrics, care should be taken to see that the shearing blades do not scratch the surface of the fabric, which otherwise can cause dyeing defects during subsequent dyeing.

5. Shearing Types of fabrics for shearing Shearing machine can process a wide range of knitted fabrics but not in tubular form . Shearing the pile of a raised fabric: used to shorten and equalise the height of a raised fabric. Cutting the yarn of a terry towel or of a knitted velour: a knitted fabric made with a terry machine, will have loops on its surface, if we cut the loops, a very nice effect of velvet will be the result. Pattern shearing: if we relace the cutting stand with a roller that bears a pattern design, only those parts of the fabric that correspond to the pattern will be sheared. Other application cover the fields of cleaning a surface, like example in grey fabrics before printing or in worsted fabrics, to remove any hairyness.

6. Shearing Shearing machine Feeding devices for crease free feeding of fabric. Shearing unit is composed of two sharpened elements, that are working in a similar way to a scissor. First element is a roller, with a certain numbers of blades (10 to 24 can be less or more) fixed on it with a helical displacement, this roller is rolling on a flate blade, the contact between the helical blades and flate blade is giving the cutting function. This contact point is also called cutting point. The cut fibers are removed by vacuum suction. The fabric is brought in cutting point by cutting stand, its shape depends on kind of fabric. The distance between the cutting point and cutting stand is called shearing height. This is the height, that fabric have after shearing. Shearing unit is equiped with handwheels and screws to adjust shearing height. Seam joint sensors, which lift the shearing rolls away from fabric when a seam passes. Metal detectors Modern machines upto 100 m/min

7. Shearing Machine Shearing machine 4 cutter cropping machine

8. Shearing Machine

9. Shearing Machine

10. Singeing What is singeing ? Singeing is defined as process carried out for the purpose of removing the loose hairy fibers from the surface of the cloth. Objectives of singeing To remove projecting or protruding fibers by burning Surface structure becomes better visible More even appearence after dyeing Sharper contoures in textile printing Less trouble in dyeing and printing due to fluffing Reduced soiling in sebsequent processing steps Reduction of pilling Better brightness

11. Singeing

12. Singeing There are two methods for singeing Direct method Indirect method Direct method Gas singeing (1200-1300  C, 80-100 m/min, one sided/two sided) Indirect method Heated ceramic, IR-radiations (50-200 m/min, gentle) Contact singeing: heated plates or rotary-cylinder (750  C, 70-80 m/min)

13. Plate Singeing Machine In this type of singeing machine, the cloth passes over and in contact with one or two heated curved copper plates. The thickness of the plates ranges from 1 to 2 inches. The heating of the plates is done by a suitable burning arrangement of gas mixed with air. The plates are heated to bright redness and the cloth passes over and in contact with these plates at a speed ranging from 150 to 250 yards per minute.

14. The passage of the cloth can be arranged in such a manner that one or both sides of the fabric may pass over and in contact with the heated plate(s), in order to accomplish singeing of one or both sides of the fabric in a single passage. Disadvantages Uneven singeing due to local cooling of hot metal surface Groove formation on the plate surface Remedies In order to avoid local cooling of a certain part of the plate(s) by constant passage of cloth over it, an automatic traversing mechanism is fitted to the machine. This mechanism brings the cloth into contact with a constantly changing part of the plate(s), not only to avoid local cooling but also local wearing of the plate(s).

15. Rotary-Cylinder Singeing Machine In this type of singeing machine, the cloth passes over and in contact with a heated rotary cylinder made of copper or cast iron. The rotary cylinder has internal firing and revolves slowly so that constantly a fresh surface of the roller comes in contact with the cloth. The direction of rotation of the cylinder is opposite to the direction of the fabric so that the protruding fibres of the fabric are raised. This type of machine is particularly suitable for the singeing of velvets and other pile fabrics

16. If the singeing of both sides of the fabric is required, then two cylinder are employed, one for each side of the fabric. Line diagram of rotary-cylinder singeing machine  

17. Singeing Principle of singeing One sided or two sided singeing

18. Gas Singeing Machine

19. Singeing Machine Gas singeing-cum-desizing machine for woven fabrics

20. Gas Singeing Machine

21. Singeing Gas singeing parameters: Singeing effect can be varied by altering any one or more of the following Flame intensity: amount and outlet speed of the gas air mixture Fabric speed: heavier fabrics, low speed. Light fabrics, high speed Singeing position Distance between flame burner and fabric: Intensity decreases with increasing distance. Flame width: flame width can be adjusted according to width of fabric.

22. Singeing positions Singeing positions Singeing onto free guided fabric: This position is usually recommended for singeing of fabrics with all natural fibers (e.g. cotton), regenerated fibers and blended fabrics, which have been tightly woven and have weights over 125 g/m 2 . Singeing onto water cooled roller: This position avoids the penitration of flame into the fabric. For heat sensitive fabrics. This position is usually recommended for all blended and synthetic fabrics as well as for fabrics having weights less than 125 g/m 2 and fabrics with open structure. Tangential Singeing: The flame touches only the protruding fibers without having any significant contact with the main fabric body. This position is usually recommended for very light weight and sensitive fabrics as well as fabrics with broken filaments. 

23. Singeing faults On the other hand there are singeing faults which are not visible and once occurred can no longer be repaired. They are: In the cotton system singeing is done on the grey cloth, but for blended fabrics containing synthetic fibres grey state singeing is not advisable because small globules of melted synthetic fibres absorb dye preferentially, giving cloth a speckled appearance There is a possibility of thermal damage to temperature sensitive fibres Stop-offs can cause heat bars on fabrics. Creasing produces streaks which are magnified when dyed Uneven singeing effect can cause streaks when the fabric is dyed.

24. Singeing Effectiveness Over singed fabric may give a harsher feel. By performing pilling test of singed fabric, and comparing it with unsinged fabric. By looking at the singed fabric with magnifying glass, and comparing its hairiness with unsinged fabric. By sticking tape, a good singed fabric results in less number of fibers sticking on the tape.

25. Questions

26. Sizing Purpose of Sizing The purpose of sizing is to form coating of sufficiently strong and elastic film around the cotton warp yarns so as to stand the tension during the weaving and reduce breakage.

27. Desizing Desizing and Objective of desizing Desizing is the process in which the size applied to the warp yarn before warping is removed to facilitate the penetration of dyes and chemicals in subsequent wet processing operations. Apart from film forming materials, the size recipe many times also contains other additions such as lubricants. Traditionally starch-and tallow based lubricants (triglycerides) have been used as sizing components for cotton, being readily available, relatively cheap, and based on natural, sustainable materials. The removal of hydrophobic part of the size (lubricants) is often problematic and not removed during desizing but during alkali scouring.

28. Desizing Sizing agents on natural bases Starch and its derivatives: native, degraded, and chemically modified Cellulose derivatives: Carboxymethylcellulose (CMC), methylcellulose, oxyethylcellulose . (for regenerated cellulose and manmade fibers e.g acetate and nylon) Protein seizes: glue, gelatin (For regenerated cellulose) Fully synthetic sizing agents Synthetic fibers are stronger and hence increasing strength by sizing is not the aim and adhesion of the sizing material to yarn is also very difficult. Polyacrylates Modified polyesters Polyvinyl alcohols (Solubility of PVA can be impaired by heat applied during sizing, grey fabric heat setting or singeing, which influence desizing )

29. Desizing Sizing agents on natural bases About 75 % of the sizing agents used throughout the world today consist of starch and its derivatives because of its low cost. Chemically starch is composed of amylose and amylopectin. Amylose molecule is in the form of helix with six glucose units per turn. Low molecular weight of amylose (20-30 % ) is water soluble, amylopectin (70-80 % ), which is difficult to remove from cotton due to its higher molecular weight. Amylopectin Amylose

30. Desizing Mechanism of desizing Long, high molecular weight chains are converted into short, low molecular chains through hydrolysis or oxidative degradation Dextrins  are a group of low-molecular-weight carbohydrates produced by the hydrolysis of starch. Factors on which the desizing efficiency depends Type and amount of size applied, Viscosity of the size in solution, fabric construction, method of desizing, method of washing off. Starch (Insoluble) Dextrin (Insoluble) Soluble dextrin (soluble)

31. Desizing Classification of Desizing Methods

32. Hydrolytic Desizing Rot Steeping Oldest and cheapest method Fabric is impregnated with warm water (at 40 °C ) and padded and squeezed to about 100 % expression. The cloth is then allowed to stand for days in pits or cemented tanks. Micro-organisms, naturally present in the water multiply and secrete starch liquefying enzymes which solubilize starch. Cloth is fully washed to remove dextrins.

33. Hydrolytic Desizing Acid desizing The cloth is impregnated with a solution of dilute sulphuric acid or dilute hydrochloric acid (0.25 % owf ) followed by batching for about 8-12 hours and washing. Hydrolysis of starch is exothermic reaction, the temperature of bath may rise to higher side, even to 50  C, but at this temperature dilute acid doesn’t attack or hydrolyse cellulose. Cloth is covered to prevent evaporation, otherwise due to evaporation localized drying occurs and causes increase in acid concentration, which can cause fabric damage. By increasing acid concentration up to 2 %, reaction time can be minimize.

34. Hydrolytic Desizing Enzymatic Desizing Most widely used desizing process of starch degradation. Enzymes are complex organic, soluble biocatalysts formed by living organisms that catalyze chemical reactions in biological processes. Enzymes are quite specific in their action on a particular substrate. α -and β - Amylases are used for starch Amylases is the enzymes that hydrolysis and reduce the molecular weight of amylose and amylopectin in starch, making it water soluble enough to be washed off the fabric.

35. Hydrolytic Desizing Enzymatic Desizing

36. Lock and key mechanism

37. Hydrolytic Desizing Enzymatic Desizing Enzymes are sensitive to temperature and pH values, outside their optimum ranges, they can be denatured, resulting in activity reduction Most enzymes function best near neutral pH and temp. between 40-60  C, pH of bath adjusted by adding alkali or acid. Depending on nature of material, different enzymes are used, e.g for gelatine, Gelatase is used; for cellulose, Cellulase is used.

38. Hydrolytic Desizing Enzymatic Desizing Effect of pH and temperature on enzymes activity

39. Hydrolytic Desizing Enzymatic Desizing Decrease in activity of enzymes with time at 60  C of different amylases.

40. Oxidative Desizing 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, through which Cl 2 gas is passed. Cl 2 + H 2 O  2HCl + [O] 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. 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.

41. Oxidative Desizing 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 ). Sodium Chlorite desizing In this method Sodium chlorite (NaClO 2 ) is used under acidic condition for oxidizing the starch

42. Oxidative Desizing

43. Desizing Machines, Singeing-cum-Desizing

44. Desizing Efficiency Test Weight loss after desizing TEGEWA Rating Reagents: Potassium iodide and iodine in water and ethanol. Spot drop wise solution onto fabric, rub gently, assess change of color Fabric should be at room temperature, with neutral pH. Assessment No change of color = no starch present Bluish, purple black = starch present

45. Questions

46. Scouring The loom state cotton fabric contains about 8-12 percent natural impurities of the total weight of the fiber. These impurities mainly consists of waxes, proteins, pectic substances and mineral matters. In addition to this, the mechanically held impurities called motes are present containing seed coat fragments, aborted seeds and leaves that cling to fibers. Apart from these, loom state fabric is also contaminated with oils such as machine oils, tars, greases etc.

47. Scouring Pectic Substances Motes

48. Scouring, Objectives Scouring is a purifying treatment of textiles, the objective of scouring is to reduce the amount of impurities sufficiently to obtain level and reproducible results in dyeing and finishing operations. Saponify fats and waxes Break down of proteins and pectins Complex formation of minerals substances containing Ca, Mg, Fe, Cu. So that they do not react with saponification products Increase the absorptive capacity Improve the degree of whiteness and reduce the seed husk contents Extraction of reactions by-products.

49. Scouring, Agents used for Scouring

50. Scouring, Agents used for Scouring The type of scouring agent generally depends on the kind of fibers i.e. cotton or wool; fabric type i.e. woven or knitted, thick or thin; texturized or non-texturized and the extent of impurities present in the fiber. For example, silk and wool dissolved by alkali, whereas acetate and triacetate are converted back to their original cellulose form.

51. Scouring, Mechanism of Removal of Impurities Fats and waxes are removed by the action of alkali and surface active agents, in some cases use of solvent and surfactants mixtures may be necessary. Lipases are also used for scouring purpose. Lipase is an enzyme that catalyzes the hydrolysis of fat. Pectins and related substances are solubilized by the action of alkali, usually NaOH, which also acts as swelling agent to facilitate removal. Minerals and heavy metals are removed by producing more soluble salts e.g. acids demineralization or by use of sequestering agents. Amino acids or proteins are solubilized by producing corresponding sodium salt. Modern lubricants/mineral oils usually contains their own self emulsification system, i.e. knitting yarn in cotton weft knitted fabrics contains lubricants which replace the size on woven fabrics.

52. Scouring, Mechanism of Removal of Impurities Natural fats, oils and lubricants tallow are mostly esters usually in the form of triglycerides. After saponification, glycerol is water soluble and soap is efficient surfactant or emulsifier. If wax is not removed, non uniform absorption of dyes and finishing agents will take place. Actually removal of wax determines the absorbency after scouring. Also alkali removes pectic acid, pectic acid is insoluble in water but soluble in alkaline solution

53. Scouring, Mechanism of Removal of Impurities Sequestering agents or chelating agents are negatively charged and are capable of forming strong ring structure with the metal ions present in hard water and in pectins. This prevents film and scum formation; precipitation of hard water. Advantages are better levelness and more brilliance in dyeing process, lower peroxide consumption, high degree of whiteness, and no catalytic damage during peroxide bleaching. Scum formation because of Ca +2 , Mg +2 , Fe +3 metal ions

54. Scouring, Mechanism of Removal of Impurities, Emulsification A surfactant is a substance, which reduces the surface tension of the water, e.g. water surface tension 72 dynes/cm to 30 dynes/cm at less than 0.1 % concentration. Only non-ionic and anionic surfactants are used in scouring. This helps in wetting as well as dispersion and suspension of soil and oils. The droplet of emulsified greases separate from the fiber due to the net repulsion of the surfactant head groups on the dirt particles and the fiber surface, resulting in complete and lasting separation

55. Scouring, Mechanism of Removal of Impurities, Emulsification An emulsion is a dispersion of a liquid in another liquid in which it is not soluble. When two immiscible liquids are mixed and shaken aggressively one of them break into small droplets and gets dispersed in other, however, such dispersion is thermodynamically unstable, hence liquids again go to two distinct continuous phase. To stabilize such dispersions, emulsifiers are used. Emulsifier is surfactants whose molecules cover the surface of two droplets. One portion of the surfactant molecule becomes compatible with one phase and other part with second phase. This way of dispersion of one liquid phase in another becomes stable, which is known as emulsion. Removal of hydrophobic impurities from textiles using surfactant in a aqueous medium by emulsification is a common mode. Agitation helps in removal of impurities.

56. Scouring, Mechanism of Removal of Impurities, Solubilization using a Solvent Using a solvent to dissolve away the hydrophobic soil. For example common dry cleaning uses organic solvents to remove hydrophobic greasy or oily soils from textile materials. At industrial scale, this has safety and logistical problems related to handling of large amount of organic solvents. Since the amount of hydrophobic impurity present on a textile substrate may be very small one can choose another approach .A solvent may be emulsified in an aqueous medium. The resultant emulsion, which may contain only a small amount of solvent may be used to remove the oily soil.

57. Scouring, Scouring with NaOH In this process cotton fabric boiled with a solution of 10 to 20 g/l (3-6 % o.w.f .) caustic soda in kier with a liquor ratio 3:1. In continuous scouring about 30 g/l of caustic soda is added in the pad-bath with a liquor pick-up of about 100 %. In continuous processes it is possible to decrease the time of post impregnation steaming to about 2 min at a temperature of 130-135  C with NaOH solution of 40-60 g/l. The rate of saponification of waxes increase as the temperature (pressure) of boiling increase, rate of chemical reaction is doubled with each 10  C rise in temperature and saponification of oil is increased sixteen times from 60 to 100  C.

58. Scouring, Scouring with NaOH Cotton is not degraded by boiling with sodium hydroxide solution up to a concentration of 20 g/l in the absence of air. If colored yarns are present in fabric, soda ash (sod. Carbonate) is used because of its low pH. Combination of soda ash and caustic soda can also be used.

59. Scouring, Scouring of Polyester and Nylon Synthetic fibers generally do not contain naturally occurring impurities like natural fibers. However spin finishes, knitting weaving oils, antistatic agents are added to improve physical as well as mechanical properties. Other are dirt etc. For polyester weak and low concentration of alkalis are used at low temperature. Special precaution is necessary when polyester is scoured with strong alkali at higher temperatures and care has to be taken not to hydrolyze the fiber. Nylons are scoured with mild alkali and detergents. Generally non-ionic detergents are used in scouring of nylons.

60. Scouring with Enzymes Why scouring with Enzymes? NaOH is not only harsh on the fabric but also on the environment Chemical Handling Excessive Rinsing Effluent Concern Possible fiber damage

61. Scouring with Enzymes How do Enzymes work? Pectinase Pectin act like glue between fibers core and the waxes. It can be removed with alkaline pectate lyase (pectinase), making the residual waxes easy to eradicate in the subsequent hot rinse. It degrades the pectin from the primary cell wall of cotton without degrading the cotton itself. Lipases They are used for the removal of natural fatty substances from cotton Proteases Catalyse the hydrolysis of proteins

62. Scouring, Assessment Drop/Spot Test In a pipette a solution of 0.1 percent direct or congo red is taken and droplet of solution put on the different places of the fabric and absorption time is observed. The standard time for the absorption of one drop of solution is 0.6 to 1 sec. Weight Loss Tensile strength (reduction indicates fiber damage during process) Cuprammonium fluidity Test To check the degree of degradation/polymerization. Fibers/fabric is dissolved into Cuprammonium hydroxide. High viscosity means high degree of polymerization and low damage.

63. Questions

64. Bleaching The aim of bleaching is to transfer colored substances (Flavone pigments) in the fibers into uncolored substances and/or to make them removable by the washing. By that the following effects should be reached The degree of whiteness shall be high and even enough for the intend use of the textile goods. The textile good shall not be damaged if possible The degree of whiteness shall be stable in storage The absorptive capacity shall be high and uniform For achieving this mainly oxidative and rarely reductive bleaching systems are used.

65. Bleaching Bleaching is important, in case of white, pastel shades, or printed background, but can be optional in case of dark shades. Dyeing an unbleached fabric in pastel shades might mask the brightness of applied color. Bleaching also removes residual impurities left by other pretreatment processes like desizing, scouring etc. In case of cotton, the motes or the seed coat fragments are visible as specks of brown or black colors on fabric. The color of these motes is also destroyed by bleaching.

66. Bleaching, Oxidative Hydrogen peroxide H 2 O 2 Sodium peroxide Na 2 O 2 Peracetic acid CH 3 -CO-O-OH Potassium permanganate KMnO 4 Ozone O 3 Sodium Chlorite NaClO 2 Sodium hypochlorite NaOCl

67. Bleaching, Reductive Sodium Sulphite Na 2 SO 3 Sodium bisulphite NaHSO 3 Sodium dithionite Na 2 S 2 O 4 Oxalic acid HOOC-COOH

68. Bleaching, Auxiliaries Auxiliaries, facilitate and accelerate bleaching and provide protection against fiber damage. Wetting agents: Sulphonated oils, fatty alcohol sulphates , fatty acid condensates Stabilizers: Very important for the bleaching with hydrogen peroxide, suitable products are sodium silicate (water glass), phosphates, organic complexing agents, etc. Activators for bleaching with sodium chlorite: Inorganic and organic acids, phosphates, nitrates etc. Corrosions inhibitors for sodium chlorite bleaching: fatty acids condensates, nitrates and phosphates.

69. Bleaching with Hydrogen Peroxide (H 2 O 2 ) It is today the most frequently used bleaching agent for textiles. It is a chemical compound that has mostly an oxidative effect. It is a weak acid, that has only a low bleaching power. If alkali is added to an aqueous hydrogen peroxide solution, perhydroxyl anions (HOO - ) are formed. From perhydroxi -anions (HOO - ), superperoxide radical ( . O-O - ) is formed, which is active bleaching agent. In addition to the bleaching agent and alkali (as activator) the bath consists always washing-off and wetting agents for improving the process and a stabilizer. Stabilization of peroxide is important for an even bleaching effect and preventing the fiber damage.

70. Bleaching with Hydrogen Peroxide (H 2 O 2 )

71. Bleaching with Hydrogen Peroxide (H 2 O 2 )

72. Bleaching with Hydrogen Peroxide (H 2 O 2 ), Process Parameters Operation of peroxide bleaching depends on Nature and quality of goods to be bleached The amount of bleaching required Equipment available Following general variables are considered to be important Effect of pH At pH 1-3 peroxide is stable, but at 11.5 to 13. it has least stability Bleaching take place around pH 10.5 to 10.8

73. Bleaching with Hydrogen Peroxide (H 2 O 2 ), Process Parameters Effect of Temperature Normally bleaching is carried out at 90-100 C, but temperature can be increased to 120 C in case of a pressurized equipment. Increase in temperature results in decrease process time. This means rate of bleaching increases with increase in temperature. But at higher temperatures, cellulose is more prone to decompose Effect of Time The time is inversely proportional to the temperature of the bleaching bath. Cotton may be bleached in open kiers by circulating heated hydrogen peroxide solution (88-95 C) for 6 to 10 hours.

74. Bleaching with Hydrogen Peroxide (H 2 O 2 ), Process Parameters Effect of concentration of liquor Concentration of peroxide depend on liquor ratio, temperature, and class of fibers. In kier boiling 2-4 percent (o.w.f) peroxide is sufficient. In continuous process, fabrics saturated with bleach bath containing 1-2 percent peroxide. Very high concentration of peroxide may damage the fiber.

75. Bleaching with Sodium chlorite (NaClO 2 ) Sodium chlorite bleaching is fiber protective, rapid bleaching effect, usable for CO, CV, PAN and other synthetic fibers and blends with cotton. Sodium chlorite is chlorine containing bleaching agent, it remains stable at high pH and has to be activated with acids or acid liberating agents to bring down pH, when bleaching take place. Acid generators (activators) include sodium chloroacetate, triethanol amine, ammonium persulphate etc. One disadvantage of chlorite bleaching is formation of toxic and corrosive gas ClO 2 (even stainless steel) at pH below 6.

76. Bleaching with Sodium chlorite (NaClO 2 ) Advantages Can be used for both cotton and synthetic fibers, suitable for fibers, which are unstable at alkaline pH. As it takes place at acidic pH, hardness of water and metal ions do not impair the process. Cause low or no cellulose damage. Disadvantages More expensive than NaOCl or H 2 O 2 . It can not used to bleach silk and wool (pink coloration). ClO 2 corrosive and toxic gas. It takes place at acidic pH, so removal of wax is not satisfactory.

77. Questions

78. Mercerization Mercerization was discovered by John Mercer in England and the process is named after him: Mercerizing. Mercerization is a process of impregnating the textile material with a concentrated solution of cold NaOH for some time with or without tension, and subsequently rinsing it. Generally mercerization is carried out at 18-24 % NaOH concentration and low temperature 15-20  C with a suitable wetting agent. Mercerization increases the absorbency, dye-uptake, lustre and tensile strength of the fibers. Cellulose undergoes chemical, physio-chemical and structural modifications with caustic soda.

79. Mercerization Mechanism: Mercerization causes swelling in fiber. Swelling causes cross-section to become rounder, loss of convolution and detwisting leading to more lustrous surface. Stage 1-5 swelling of cross section, stage 6 and 7 removal of NaOH from fiber Mercerization causes opening of fiber structure, this increases amorphous content due to de-crystallization Higher number of –OH groups available as compared to un-mercerized cotton Higher moisture regain, dye-uptake and reactivity. Gradual change in cross section of cotton fiber on mercerization

80. Mercerization Increase in tensile strength Removal of convolutions results in removal of weak spots at the point of reversal. Fiber have more uniform, circular and smooth cross section after mercerization. Fiber alignment along fiber axis is better in case of tension mercerization as compared to slack mercerization. Shrinkage When fiber swells, the fiber shrinks in length, in absence of tension. Effect of Tension Tension mercerization results in more lustrous product as compared to a slack mercerization.

81. Mercerization Neutralization after mercerization Normally with a suitable acid Test method to determine degree of mercerization Although there are many methods to do this, one quantitative test based on the ability of mercerized cotton to absorb barium hydroxide is widely used. Mercerized cotton can absorb more Barium hydroxide than un-mercerized cotton and this is the basis for this test.  For completely mercerized cotton the value of BAN is around 155 and for semi mercerized cotton it varies in between 115 and 130.

82. Mercerization Mercerization machines Pad chain mercerizing machine: Saturator (NaOH)- padder ( sequeeze )-airing rollers (time for swelling)-saturator (NaOH)- padder-stenter clips/chain –sprinkling of fabric with water (reduction of NaOH conc. below 60 g/l)-washer for rinsing and neutralization. Chainless mercerizing machine Clip chain mercerizing machine for woven fabrics

83. Questions

84. Colorants Difference between dyes and pigments Both are colorants In terms of their chemical composition, one primary distinction between dyes and pigments is that pigments are insoluble in water as well as most other solvents. In general dyes are either water soluble or soluble in another type of solvent. Dyes require some sort of physical or chemical reaction in order for dyeing process to occur. Unlike dyes, dyeing with pigments requires a binding or dispersion agent in which pigment itself is suspended. Before coloring process pigments are usually ground as finely as possible, resulting in a powder of pigments particles of few microns. Since coloring process with dyes occurs by means of physical and chemical reaction, it is necessary to understand dyes at molecular level.

85. Dyestuff Dyes are colored, unsaturated organic chemical compounds. Capable to dye substrate with sufficiently fastness. Distinguish itself from the pigments, which require a binder. Color is caused by the interaction of an π -electron system (dye chromophore) with light. Chromophore gives a dye its particular color, by absorbing a light of particular wavelength. They can represent as C, N, O and S can have alternative single and double bonds. Auxochrome are responsible for dye solubility and cohesiveness, and is attached to a chromophore which modifies the ability of that chromophre to absorb light, e.g –OH, -NH2, -CHO

86. Dyestuff

87. Classification of dyes Dyes can be classified in several ways, each class has a very unique chemistry, structure and particular way of bonding. Some dyes can react chemically with the substrates forming strong bonds in the process, and others can be held by physical forces. Some of the prominent ways of classification are given below Natural / Synthetic Organic / Inorganic By area and method of application Chemical classification - Based on the nature of their respective chromophores. According to the dyeing methods Anionic (e.g. for Protein fibre ) Direct (e.g. for Cellulose) Disperse (e.g. Polyester, Polyamide fibres)

88. Classification of dyes US International Trade Commission has advocated the most popular classification of dyes. which are given below: Group Application Direct Cotton, cellulosic and blended fibres Vat dyes Cotton, cellulosic and blended fibres Sulphur Cotton, cellulosic fibre Organic pigments Cotton, cellulosic, blended fabric, paper Reactive Cellulosic fibre and fabric Disperse dyes Synthetic fibres Acid Dyes Wool, silk, paper, synthetic fibres, leather Azoic Printing Inks and Pigments Basic Silk, wool, cotton

89. Dyes for Cellulose Water soluble dyes, e.g. direct (substantive), reactive, and vat leuco ester dyes. Water insoluble dyes, e.g. vat and Sulphur dyes, first transfer into water soluble form. Insoluble colorants, e.g. colored pigments, require a binder to bind onto fibers. Dyeing is the process of coloring textile materials by immersing them in an aqueous solution of dye, called the liquor. Normally the dye liquor consists of dye, water and an auxiliary.

90. Dyes for Cellulose Direct dyes can be defined as water soluble, with the specific ability to dye cellulose fibers without any special arrangements, that means direct. There are no reactive groups, neither other chemically activated substituents, nor special pretreatment of the fibers, e.g. in the form of a mordant, are necessary. They have affinity for cellulose, therefore also known as substantive dyes. They have poor wet colorfastness. Direct dyes can also dye wool, nylon.

91. Most commercial direct dyes belong to the azo series and can be described by the following general formula Solvation in water is due to sulfonate groups (anion) Planar highly conjugated molecular structure Many direct dyes are sodium salts of sulphonic acids. Structural features of direct dyes Direct Yellow 50

92. Dyeing with direct dyes Dissolving in the water

93. Dyeing with direct dyes

94. Dyeing with direct dyes Addition of salt: the edition of electrolyte to the dye liquor is essential to obtain adequate exhaustion of the dye molecules by the fiber polymer system. Application of the heat: to the dye liquor increases the energy of the components of the dye liquor, swells the fibers and accelerate the rate at which dyeing occurs.

95. Dyeing with direct dyes

96. Dyeing with direct dyes

97. Dyeing with direct dyes Properties of direct dyes Light fastness Dyed and printed direct colors have a moderate light fastness, the light fastness rating being about 3. Wash fastness The wash fastness rating of direct dyes is about 2-3. The comparatively poor wash fastness of cellulosic textile materials dyed with direct dyes is due to Direct dyes anions are attached to the cellulose polymers by hydrogen bonds and van der Waals forces both of which are weak. Which may be hydrolyzed by water molecules resulting in the removal of these dyes from polymer. Relatively large no. of auxochrome in direct dye anion which contribute to poor wash fastness.

98. Dyeing with direct dyes Improving wash fastness All after treatments to improve wash fastness aim to increase the molecule size of the dye molecule one it is located within the polymer system of the fiber. The large dye molecule size increases the forces of attraction between the dye molecule and the polymer The increased molecular size makes it more difficult for the dye to be removed from the polymer system. Some methods are Diazotisation : Increases the size of dye molecule, also changes the hue of color. Copper after treatment: Cu Forms a metal complex with dye, thus size increases. Cationic agent: cation attaches to the dye, which results increase in size. But light fastness decreases. Formaldehyde after treatment: dye molecules appear to be joined together by methylene cross links, giving very large molecule complexes.

99. Questions

100. Dyeing with Reactive dyes Reactive dyes are so called because their molecules react chemically with the fiber polymers to form a covalent bond between the dye molecule and fiber polymer. Fibers, which are dyed with reactive dyes are Man made (acetate) and natural cellulosic fibers Synthetic nylon Natural protein fibers The covalent bond is formed between the dye molecules and the terminal –OH group of cellulosic fibers or in case of protein fibers –NH 2 group of polyamide or wool fibers.

101. Dyeing with Reactive dyes, reaction mechanism Triazine Anchor Dichlorotriazine , Procion Cold reactive dyes (30 C) Monochlorotriazine , Cibacron Hot reactive dyes (80 C) First step: Substantive absorption, like direct dyes with salt ( NaCl , Na2SO4). The dye diffuse towards the interior of fiber, where it is absorb by the cellulose chains by secondary type forces Step two: Reaction in alkaline liquor with the cellulose and water hydroxyl groups. Step three: Elimination of the hydrolyzed dye that is not fixed covalently to the cellulose.

102. Dyeing with Reactive dyes, reaction mechanism Hydrolyzed dye

103. Dyeing with Reactive dyes, reaction mechanism Vinyl Sulphone dyes Ramazol (40 C)

104. Dyeing with Reactive dyes

105. Dyeing with Reactive dyes Properties of reactive dyes Lightfastness Have very good light fastness properties about 6. Wash fastness Have very good wash fastness properties about 4-5 because of strong bond. Effect of acids The formation of covalent bond between dye and fiber occurs under alkaline conditions. Presence of acid may reverse this process. Perspiration and atmospheric pollution which are both slightly acidic may affect textile materials color.

106. Questions

107. Dyeing with Sulphur dyes Sulphur dyes contain Sulphur atoms in their molecules. The fibers mostly colored with Sulphur dyes are the natural and man-made cellulosic fibers. They are cheap, generally have good wash-fastness and easy to apply. Sulphur dyes are predominantly black, brown, and dark shades. They are like vat dyes highly colored and water insoluble. The range of colors covers all hue except a true red. As a rule, the hues are dull compared with other dye classes. Sulphur dyes are insoluble in water, in order to make them soluble, they should be reduced first. For reduction sodium sulphide /sodium hydrosulphite is used. In some cases addition of alkali may be necessary to obtain required pH.

108. Dyeing with Sulphur dyes In this reduced and leuco form, Sulphur dyes are substantive to cellulosic fibers. To achieve adequate exhaustion, it is necessary to add an electrolyte such as sodium chloride to the dye liquor. To obtain adequate penetration and a satisfactory rate of dyeing, the dye liquor is heated. This increases the energy of the molecules and thus increases the rate of dyeing and ensures proper penetration of dye into the fiber polymer system. Once the dye is within the fiber polymer, reduced Sulphur dye is converted back to its original insoluble form. This is achieved by an oxidation treatment with a mild reagent such as sodium perborate.

109. Dyeing with Sulphur dyes

110. Dyeing with Sulphur dyes

111. Dyeing with Sulphur dyes Light Fastness Light fastness is about 4, which can be increased by after treatment with metallic salts about 5. The fair lightfastness is due to UV degradation of chromophore. Wash Fastness Wash fastness is about 3-4. This fair fastness is because of large dye molecule and insolubility of dye (lack of polar groups). Bronzing Sulphur dyed textiles may show a metallic or bronze sheen, which is referred to bronzing. This effect is usually present in heavy or dark shades. The causes of this, are exposure of textile to the atmosphere during dyeing causing premature oxidation of dye, failure to remove excess dye liquor after dyeing, insufficient amount of Na2S in dye liquor to keep the dye in its soluble form. This effect can be minimized by after treatment with dilute Na2S, which will remove excess dye molecules that are present on the surface.

112. Questions

113. Dyeing with Vat dyes Water insoluble dyes. The name was derived from the large wooden vessel from which vat dyes were first applied. Vat dyes provide textile materials with the best colour fastness of all the dyes. The fibers most readily colored with vat dyes are the natural and man made cellulosic fibers.

114. Dyeing with Vat dyes Vat dyes are based on indigo and anthraquinone. The excellent fastness properties of textile material colored with vat dyes is attributed in part to the very large size of the vat dye molecule and in part to its aqueous insolubility. In general, vat dyes based on anthraquinone have better fastness properties than the vat dyes derived from indigo. Indigo, C.I Vat Blue 1 C.I Vat Green 8, Anthraquinone type

115. Dyeing with Vat dyes The application of vat dyes to cellulosic materials occurs in five steps Aqueous dispersion: The insoluble vat dye is dispersed in water. Vatting : This step involves the chemical reduction of vat dye to produce soluble, reduced or leuco form of the dye. This is achieved by sodium hydrosulphite , sodium hydroxide and water. Vatting stage also alters the original color of the dye. Absorption of the dye molecules by fibers: The vatted dye molecules are substantive to the cellulosic material. To achieve adequate exhaustion an electrolyte is added to the dye liquor and the temperature may be increased depending on the specific vat dye. During this stage textile material must be kept immersed in the dye liquor to prevent the premature oxidation of the leuco compound. Reoxidation : Once dye in the polymer system of the fiber, vatted form of the dye has to be oxidized and converted back to its original color and the insoluble form of the dye. Soaping: Insoluble vat dye, which during previous stage may be deposit on the surface of the textile material, has to be removed to prevent poor rub-fastness as well as a possible change of shade due to subsequent removal of this surface deposit. Material is boiled in presence of some suitable detergent.

116. Dyeing with Vat dyes

117. Dyeing with Vat dyes

118. Dyeing with Vat dyes

119. Dyeing with Vat dyes

120. Dyeing with Vat dyes

121. Dyeing with Vat dyes Lightfastness Light fastness rating of vat dyes is about 7. the excellent light fastness f textiles colored with vat dyes is attributed to the stable electron arrangement in chromophores of the vat dye. Washfastness The Washfastness rating of the vat dye is about 4-5. The excellent Washfastness of textile dyed with vat dyes is attributed to the large vat dye molecule as well as its aqueous insolubility. Solubilized vat dyes As with Sulphur dyes a solubilized form of vat dye has been developed. This has made vat dyes easier to handle and results in more level dyeings .

122. Questions

123. Dyeing with Disperse dyes Disperse dyes are used to dye synthetic as well as modified fibers such as polyester and cellulose acetate, because of their hydrophobic nature. Disperse dyes are traditionally non-ionic chemicals with sparing solubility in water. They have better substantivity for hydrophobic fibers such as polyester, nylon and acetate. For the sake of efficient diffusion into textiles, the particles of disperse dyes should be as fine as possible. Disperse dyes are often substituted azo, anthraquinone or diphenylamine compounds which are non-ionic and contain no water solubilizing groups.

124. Dyeing with Disperse dyes The dye particles are thus held in dispersion by the surface-active agent and the dyes themselves are called disperse dyes. The disperse dye committee of the society of dyers and colorists (SDC) has now classified the dyeing characteristics of disperse dyes according to the results of several tests which can be performed on the dyes. Small dye molecules with low polarity are levelling, rapid dyeing, dyes with poor heat resistance are called low energy disperse dyes. More polar higher molecular weight dyes have low dyeing rates, poor migration during dyeing but good heat and sublimation fastness.

125. Dyeing with Disperse dyes Mainly azo and anthraquinone structures Water solubility: 30 mg/l, supported by following substituents OH-groups NH2-groups Aromatic bound halogen, etc.

126. Dyeing with Disperse dyes Structure and properties of Polyester N= 80-150; mean molar mass: 15200-28500 Melting area: 256-275 C Surface tension: 39.5 mN/m Glass transition temperature: 80 C Dyeing only possible with disperse dyes.

127. Dyeing with Disperse dyes Disperse Dyeing Mechanism

128. Dyeing with Disperse dyes Dispersing agent is added to water with dye to form a aqueous dispersion. The insolubility of the disperse dyes enables them to leave the dye liquor as they are more substantive to the organic fiber. Heating dye liquor increases the energy of the dye molecules and accelerate the dyeing. Heating swells the fiber to some extent and assist the dye to penetrate the fiber polymer system resulting in dye being located in the amorphous regions of the fiber. One dye in polymer system, the dye molecules are held by hydrogen bonds and van der Waals forces. Polyester fibers are extremely crystalline and hydrophobic and it is difficult to achieve even lighter shade at boil. In order to obtain medium to dark shades polyester fibers are dyed using carriers or by using high temperature dyeing techniques.

129. Dyeing with Disperse dyes Dyeing with carriers Application of disperse dyes by exhaust dyeing with the addition of carrier. Carrier are able to loosening the structure of the polymeric chains, so that the diffusion rate of dye molecules will increase. Disadvantages: High price, harmful substances (health, environment) bad wash out ability.

130. Dyeing with Disperse dyes High temperature dyeing This dyeing technique is carried out at temperatures above the boil in the rage 100-130 C and under pressure ranging from 0 to 170 kPa . This method of dyeing is also called pressure dyeing. Thermosol dyeing process

131. Dyeing with Disperse dyes

132. Dyeing with Disperse dyes Light fastness Fair to good light fastness and is about 4-5. Benzene or aromatic structure gives them a relative stable structure. Wash fastness Have moderate to good wash fastness properties and is about 3-4. This is due to insolubility of dye in water. Sublimation These dyes have ability to undergo sublimation. That is they can be vaporized without significant change in their color.

133. Questions

134. Acid Dyes Acid dyes are so called because they are usually applied under acidic conditions. The fibers most readily colored with acid dyes are manmade, synthetic and natural fibers e.g. Nylon, Silk, Wool. There are large number of amino groups in wool fibers. Dark shades can readily be obtained on wool because of the highly amorphous nature of the fiber, which results in relatively easy penetration of the fiber polymer by the dye molecule. As a guide there are 20 times as many as amino groups on wool as on nylon and five times as many amino groups on wool as on silk.

135. Acid Dyes

136. Acid Dyes Mainly acid dyes are salt of sulphonic and/or carboxylic acids. (containing SO 3 H, COOH or OH groups) Good water solubility Excellent affinity for wool, silk and polyamide. Easy to dye generally good levelling properties Fabric handle and lustre are unaffected. Addition of acids accelerate rate of exhaustion. Addition of salt retard the rate of exhaustion. When dyeing is correctly carried out, the dyebath exhaustion is generally complete (clear liquor)

137. Acid Dyes

138. Acid Dyes The application of acid dyes to protein fibers results in an ionic bond or salt link between the dye molecule and fiber polymer. In case of Nylon, the greater crystalline structure compared with wool as well as the relative lower number of amino groups means that dark shades on Nylon can not be achieved with acid dyes. In addition to ionic bond, hydrogen bond and van der Waal’s forces will be formed between acid dye molecule and the fiber polymer system.

139. Acid Dyes Acid dyes have high substantivity for protein fibers, so dye move very fast towards polymer and non-uniform dyeing will be the result. To overcome this problem, a retarder needs to be added to the dye liquor. Electrolyte acts as retarder such as sodium sulphate. As sulphate radical is negatively charged and smaller than the dye anion it can move more rapidly in liquor and occupies positively charged fiber polymers. The dye molecules have greater affinity for the fiber polymer but the sulphate radicals retard the rate at which the dye molecules occupies the dye sites. This produces the uniform dyeing. The application of heat assists the dyeing process by increasing the kinetic energy of the dye molecules which are slowly overcoming the retarding effect of the sulphate radicals. The dye anions will gradually replace the sulphate radical that has been attached to the dye site.

140. Acid Dyes Lightfastness The lightfastness of fabrics dyed/printed with acid dyes is about 4-5. Washfastness The Washfastness of these dyes are about 2-3 for dyes with good levelling characteristics, 3-4 for those with average levelling and 4-5 for those with poor levelling characteristics. Acid dyes molecules attaches itself by ionic and hydrogen bonds to nylon and wool fibers polymers, these bonds may be hydrolyzed in water. Acid dye molecules which are held loosely or which are not penetrated the polymer sufficiently may be removed from the polymer system. Dye molecules are acidic in nature and are resistant to acids, being acidic they can combine with alkalis such as the detergents used for washing.

141. Questions

142. Basic Dyes There are also called cationic dyes. These dyes in solution ionize and become positively charged. The fibers most readily colored with basic dyes are mainly the synthetic acrylic and modacrylic fibers. Basic dyes are applied to acrylic fibers from a slightly acidic dye liquor.

143. Basic Dyes

144. Basic Dyes Ionic nature: The ionic nature of these dyes is cationic. Shade range: These dyes exhibit an unlimited shade range with high strength, brightness and many colors are having fluorescent properties. Solubility: The solubility of these dyes is very good in water ,in the presence of glacial acetic acid. Leveling properties: These dyes have a very high strike rate , therefore leveling is poor. Affinity:  These dyes shows a very affinity towards silk and cationic dye able acrylic, but have no affinity towards cellulosic. To dye cellulosic with basic dyes the material must be treated with suitable mordanting agents

145. Basic Dyes Lightfastness Dyed and printed acrylic textiles using basic dyes have excellent lightfastness and is about 6-7. This attributed to hydrophobic nature and resistance to sunlight of acrylic fibers. Washfastness Fabrics dyed with basic dyes have good Washfastness and is about 4-5. This may be attributed in part to the good substantivity of basic dyes for acrylic fibers and the hydrophobic nature of acrylic fibers. Bright Colors These dyes are characterized by their brilliance and intense hues.

146. Questions

147. Printing The printing of textile materials is the application of color according to a predetermined designs or patterns. In properly printed fabrics the color is bonded with the fibers, as to resist the washing and friction. Textile printing is related to dyeing but, whereas in dyeing the whole fabric is uniformly covered with one color, in printing one or more colors are applied to it in certain parts only, and in sharply defined patterns. In printing, wooden blocks, stencils, engraved plates, roller or silkscreens are used to place colors on the fabric.

148. Printing Colorants used in printing contain dyes, thickened to prevent the color from spreading by capillary attraction beyond the limits of the pattern or design.

149. Printing, Printing Procedures The typical steps involved in textile printing are Preparation of a pattern form (using different techniques) Preparation of printing color paste (based on dyes or pigments) Application of the paste to the substrate (i.e. cellulose, synthetic or protein fibers) Fixation of the color to the substrate (e.g. by the action of steam or hot air) Optional after treatment such as washing and drying of the printed substrate.

150. Printing, Printing Methods Resist printing Discharge printing Transfer printing Two-phase printing

151. Printing, Resist Printing In case of resist printing, a special printing paste (called resist) is printed onto certain areas of the fabric to prevent dye fixation. In case of physical resist, the material is printed with an impermeable resin, which inhibits the penetration of a dye applied in second stage On the other hand, with a chemical resist, dye fixation is prevented by a chemical reaction.

152. Printing, Discharge Printing If the etched and previously dyed area becomes white, then the process is called white discharge. If a colored pattern is to be obtained in the etched area after the destruction of the previously applied dye, the process is called color discharge. The printing paste must contain a reduction-resist dye along with the chemicals needed to destroy the previous one. The pre-dyed background is destroyed according to a pattern and the dye, which is resistant to reduction, takes it place.

153. Printing, Discharge Printing

154. Printing, Transfer Printing In transfer printing, the pattern is first created on an intermediate carrier (e.g. paper) using selected disperse dyes and then transferred from there to the textile. The dye is usually fixed by placing the printed paper in contact with the fabric into a thermal pressure system. Under the influence of the heat, the dye sublimates and diffuses from the carrier into the fibers of textile substrate. There is no need for further treatment such as steaming, washing, etc. This technique is applied for polyester, polyamide, and some acrylonitrile fibers, using selected disperse dyestuffs according to the specific type of fibers.

155. Printing, Stencil (Screen) Printing Stencil printing is a technique in which the pattern surface of the printing form are permeable for the color paste. The printing paste needs therefore to be passed by squeezing, through the pores of a stencil and to be applied on the textile substrate.

156. Printing, Pigment Printing Pigment printing systems are based upon three equally important components Pigment dispersion Binders and crosslinking agents Thickeners and auxiliary agents giving the required rheology. Pigment dispersions Most of the pigments used in textile printing are synthetic organic materials, except for carbon black, titanium dioxide, copper and aluminum alloys etc. Synthetic organic pigments include azo , anthraquinone, naphthalene pigments etc. Particle size must be 0.03-0.5 µ, if pigments are not fine enough, the prints are dull and grey, but particle size must not less than wavelength of light.

157. Printing, Pigment Printing Binder System The binder is a film forming substance made up of long chain macromolecules which when applied to the textile together with the pigment, produce a three dimensionally linked network. The links are formed during fixing process, which usually consists of dry heat and a change in pH value, causing either self-crosslinking or reaction with suitable crosslinking agent. The degree of crosslinking should be limited, to prevent macromolecules becoming too rigidly bonded, thus preserving some extensibility. Important criterion: pigment within crosslinked binder should fast to wear and cleaning; Elasticity Cohesion and adhesion to the substrate Resistance to hydrolysis, absence of swelling in the presence of dry cleaning agents.

158. Printing, Pigment Printing Thickening System The colloidal polysaccharide thickening agents, such as starch, cellulose ether, alginates or gums have been used successfully throughout the history of textile printing in printing pastes for various dyes. But they are not suitable for pigment printing, because their flow properties are unsuitable and films they formed are brittle. It is necessary for pigment printing pastes to have pseudo-plastic (shear-thinning) flow, for easy transfer on to the textile material, but their penetration is limited. Flow occurs under shear, but when the shear is removed the pastes return to the consistency of a solid on the surface of the textile. So they produce much better color value, a sharp mark and brilliance of color. In addition, because of superficial coating of the fabric with printing paste, the textile yarns are not bonded to each other by binders and crosslinking agents, this results in better handle to the printed goods.

159. Printing, Reactive Printing The formation of covalent bond between dye and fiber makes it possible to use dyes which, unlike the vat and direct dyes, are of small molecular size and good solubility. These dyes can be brighter, faster diffusing and in the hydrolyzed form easily removed in the washing off process. When selecting reactive dyes for printing, attention must be paid to print paste stability and staining of the ground during washing-off. Thickener: Alginates are the only natural thickeners suitable for use in printing with reactive dyes. All other carbohydrates react with the dye and this results in low color yield.

160. Printing, Reactive Printing Sodium alginate also contains hydroxyl groups but it reacts very little, presumably because the ionized carboxyl groups on every ring of the polymer repel the dye anion. Advantages of the alginates include ease of removal in after-wash, resulting in a printed fabric with a soft hand, and also low sensitivity of the thickening effect towards electrolyte in the print paste. Alkali: Alkali is essential to produce ionization of accessible cellulose hydroxyl groups, which can then react with reactive dye. Sodium bicarbonate is the preferred alkali because it is cheap and gives sufficient print paste stability.

161. Printing, Reactive Printing Fixation: In textile printing, it is most important that the fixation and hydrolysis proceed to completion, so that no dye in reactive form remains to stain the white ground. The fixation of the most reactive dyes is effected by saturated steam at 100-103 C within 10 min. the most highly reactive dyes may require only 1 min. Addition of Urea in printing paste: Urea holds water very strongly, when fabric enters the steamer, this provides solvent required for the dye-fiber reaction to occur. In the absence of urea color yields are low.

162. Questions

163. Chemical Finishing of Textiles Chemical finishing can be defined as the use of chemicals to achieve desired fabric property. Chemical finishing also referred as wet finishing, includes processes that change the chemical composition of the fabric that they are applied to. Typically chemical finishing take place after coloration (dyeing and printing) but before fabrics are made into garments or other textile articles. Chemical finishing can be durable, i.e. undergo repeated laundering or dry cleanings without losing effectiveness. non-durable i.e. intended when only temporary properties are needed or when the finished textile typically is not washed or dry cleaned for example some technical textiles.

164. Chemical Finishing of Textiles In nearly all cases, the chemical finish is a solution or emulsion of the active chemical in water. The actual method of finish application depends on the particular chemicals and fabrics involved and the machinery available. Chemicals that have strong affinities for fiber surfaces can be applied in batch processes by exhaustion in dyeing machines e.g. softeners, ultraviolet protection agents and some soil release finishes. Chemicals that do not have an affinity for fibers are applied by a variety of continuous processes that involve either immersing textile in a solution of finishing chemical or applying the finishing solution to fabric by some mechanical means.

165. Chemical Finishing of Textiles After application of the chemical finish, the fabric must be dried and if necessary, the finish must be fixed to the fiber surface, usually additional heating in a curing step.

166. Chemical Finishing of Textiles, Softening Finishes Textile materials are subjected to many processes during the transformation of fiber to fabric and during the manufacture of the final product. During the many stages fibers undergo, they may be damaged and in some cases natural fats may be removed from the fibers resulting in harsh and undesirable handle. The restoration of a satisfactory handle can be achieved through the addition of suitable chemical compounds. With chemical softeners, textiles can achieve an agreeable, soft hand, some smoothness, more flexibility and better drape and pliability.

167. Chemical Finishing of Textiles, Softening finishes Other properties improved by softeners include the feeling of added fullness, antistatic properties and sewability. Disadvantages sometimes seen, include reduced crockfastness, yellowing of white goods, change in hue of dyed goods and fabric structure slippage. Softeners provide their main effect on the surface of fibers. Small softener molecules, in addition penetrate the fiber and provide an internal plasticization of the fiber forming polymer by reducing the glass transition temperature.

168. Chemical Finishing of Textiles, Softening finishes The physical arrangement of softener molecules on fiber surface depends on ionic nature of softener. Cationic softeners orient themselves with their + vely charged ends towards partially – vely charged fibers, creating new surface of hydrophobic carbon chains that provide excellent softening and lubricity. Anionic softeners, on the other hand orient themselves with their - vely charged ends repelled away from the – vely charged fiber surface. This leads to higher hydrophilicity but less softening.

169. Chemical Finishing of Textiles, Easy-care finishes Cellulosic textiles materials crease readily. Wrinkling after washing is overcome by a very important type of finish. It is difficult to find the one best term describe this class of finishes. Some of the words and phrases that have been used in the past include easy-care, permanent press, shrink proof, easy to iron, non iron, durable press finish, wash and wear, wrinkle free minimum care. The most technically correct description would be cellulose anti swelling or cellulose crosslinking finishes. Easy care finishes are generally applied to cellulose and cellulose blends, but other fibers can benifit from these finished also.

170. Chemical Finishing of Textiles, Easy-care finishes An unavoidable side effect of the cellulosic crosslinking finishes is a reduction in the elasticity and flexibility of cellulose fibers. This produce a considerable decrease in abrasion resistance and tear and tensile strengths of natural cellulose fibers. Mechanism of easy care and durable press finishing absorbed moisture in cellulosic fibers facilitate internal polymer chain movements in the amorphous fiber areas by lubricating. It disrupts the internal hydrogen bonding between these polymer chains. When stress in applied, polymer chains are move to relieve the stress. Hydrogen bonds can reform between the polymer chains in their shifted positions, in effect locking in the new configuration and this remains until additional processes (e.g. ironing) aplly adequate moisture and mechanical forces to overcome the internal forces.

171. Chemical Finishing of Textiles, Easy-care finishes Two different chemical approaches have been used commercially to produce non-sweling or durable press cellulose fabrics. The incorporation of a polymerized finish in the pores of the fibers, so that water moleculea cannot easily penetrate the fibers. The newer approach is the reaction of multifunctional crosslinking agents with the –OH groups of adjacent cellulose molecules that hinder the swelling of the cellulose fibers. One special use of the cellulose crosslinking finshes are wash permanent chintz articles, produced by the heat and high pressure of calendering the impregnated fabrics. Urea-formaldehyde, melamine-formaldehyde, dimethylol-dihydroxyethylene urea are examples of formaldeyde containing crosslinking agents. Dimethyl-dihydroxyethylene urea is an example of formaldehyde free crosslinking agent.

172. Chemical Finishing of Textiles, Flame retardant finishes Most textile materials burn readily and rapidly. For example cellulose materials will burn readily once they are ignited. The great danger with cellulose fibers is afterglow, which may remain if the flame has been completely extinguished. Afterglow often reignite a flame in the textile material. Synthetic fibers may melt rather than burn. Hot thermoplastic fiber will cause severe burns and intense shock to victim wearing cloth of such fibers. For a commercially successful flame retardant textile product Meeting flammability requirements Having little or no adverse effect on textile physical properties Retaining the textiles aesthetic physiological properties Should be durable to washing, dry cleaning and tumble drying Can be produce with available commercial equipment and inexpensive chemicals

173. Chemical Finishing of Textiles, Flame retardant finishes Combustion is an exothermic process that requires three components, heat, oxygen and a suitable fuel. When left unchecked the combustion becomes self catalyzing and will continue until the oxygen, the fuel or the excess heat is depleted. Suggested reasons of the effectiveness of flame retardant finishes are These chemicals alter the course of decomposition, less flammable tars and reduce volume of flammable gases are produced and amount of non volatile, non flammable carbonaceous material produced is increased. These chemicals may on heating yield inert gases. As these inert gases are nonflammable and will act as flame retardant by reducing amount of atmospheric oxygen. The heat generated by the burning by the burning may be dissipated by endothermic changes in chemical applied. This will reduce amount of heat for further propagation.

174. Mechanical Finishing of Textiles Mechanical finishing involves the application of physical principles such as friction, temperature, pressure, tension etc. to achieve desired effect. Calendering A process of passing cloth between rollers (or "calendars"), usually under carefully controlled heat and pressure, to produce a variety of surface textures or effects in fabric such as compact, smooth, supple, flat and glazed.  Sanforizing or Pre-Shrinking Sanforizing is a process where by the fabric is run through a sanforizer ; a machine that has drums filled with hot steam. This process is done to control the shrinkage of the fabric. The fabric is given an optimum dimensional stability by applying mechanic forces and water vapour.

175. Mechanical Finishing of Textiles Raising The raising of the fiber on the face of the goods by means of rollers covered with card clothing (steel wires) that are about one inch in height. Action by either method raises the protruding fibres and causes the finished fabric to provide greater warmth to the wearer, makes the cloth more compact. Causes the fabric to become softer in hand or smoother in feel; increase durability and covers the minute areas between the interlacing of the warp and the filling.

176. Questions