Textile chemical processing 1st.pdf

Tp 1 slides

1. Shearing and Singeing
Processes

2. 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(یلوگ یک یئاود).
•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.

3. 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.

4. 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

5. Shearing Machine
Shearing machine
4 cutter cropping machine

6. Shearing Machine

7. Shearing Machine

8. 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

9. Singeing

10. Singeing
•There are two methods for sigeing
•Direct method
•Indirect method
•Direct method
•Gas singeing (1200-1300 C, 300 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)

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

12. Gas Singeing Machine

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

14. Gas Singeing Machine

15. 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.

16. 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
fabricsas well as fabrics with broken filaments.

17. 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.

18. 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.

19. Questions

20. 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.

21. 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.

22. 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 fiberse.gacetate 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)

23. 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

24. Desizing
•Mechanism of desizing
•Long, high molecular weight chains are converted into short, low molecular
chains through hydrolysis or oxidative degradation
•Dextrinsare a group of low-molecular-weightcarbohydratesproduced by
thehydrolysisofstarch.
•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)

25. Desizing
•Classification of Desizing Methods

26. 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.

27. 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.

28. 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.

29. Hydrolytic Desizing
Enzymatic Desizing

30. 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.gfor
gelatine, Gelataseis used; for cellulose, Cellulaseis used.

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

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

33. Oxidative Desizing
•Chlorine desizing
•The active agent in case of chlorine desizing is gaseous chlorine.
•For the Cl
2desizing, open width cloth is impregnated with water and
squeezed at required percentage expression. The squeezed fabric is passed
through a chamber, through which Cl
2gas is passed.
Cl
2+ H
2O →2HCl + [O]
•In this case Cl
2reacts 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
2gas passed and time
of contact.

34. Oxidative Desizing
•Bromitedesizing
•Sodium bromite, is used for the desizing is a salt of bromousacid, HBrO
2 (like
sodium chlorite, the salt of chlorousacid, HClO
2).
•Sodium Chlorite desizing
•In this method Sodium chlorite (NaClO
2) is used under acidic condition for
oxidizing the starch

35. Oxidative Desizing

36. Desizing Machines, Singeing-cum-Desizing

37. 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

38. Questions

39. 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.

40. Scouring
Pectic Substances
Motes

41. 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.
•Saponifyfats 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.

42. Scouring, Agents used for Scouring

43. 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.

44. 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.

45. 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

46. Scouring, Mechanism of Removal of
Impurities
Sequesteringagentsorchelating
agentsarenegativelychargedandare
capableofformingstrongring
structurewiththemetalionspresent
inhardwaterandinpectins.This
preventsfilmandscumformation;
precipitationofhardwater.Advantages
arebetterlevelnessandmore
brillianceindyeingprocess,lower
peroxideconsumption,highdegreeof
whiteness,andnocatalyticdamage
duringperoxidebleaching.
ScumformationbecauseofCa
+2
,Mg
+2
,
Fe
+3
metalions

47. Scouring, Mechanism of Removal of
Impurities, Emulsification
Asurfactantisa
substance,whichreduces
thesurfacetensionofthe
water,e.g.watersurface
tension72dynes/cmto
30dynes/cmatlessthan
0.1%concentration.Only
non-ionicandanionic
surfactantsareusedin
scouring.Thishelpsin
wettingaswellas
dispersion and
suspensionofsoiland
oils.
Thedropletofemulsifiedgreasesseparate
fromthefiberduetothenetrepulsionof
thesurfactantheadgroupsonthedirt
particlesandthefibersurface,resultingin
completeandlastingseparation

48. 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.

49. Scouring, Mechanism of Removal of
Impurities, Solubilizationusing 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.

50. 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.

51. 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 sod. Caustic soda can also be used.

52. 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.

53. 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 demage

54. 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
•Catalysethe hydrolysis of proteins

55. Scouring, Assessment
•Drop/Spot Test
•In a pipette a solution of 0.1 percent direct or congored 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)
•Cuprammoniumfluidity Test
•To check the degree of degradation/polymerization.
•Fibers/fabric is dissolved into Cuprammoniumhydroxide. High viscosity
means high degree of polymerization and low damage.

56. Questions

57. 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.

58. 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.

59. Bleaching, Oxidative
•Hydrogen peroxide H
2O
2
•Sodium peroxide Na
2O
2
•Peraceticacid CH
3-CO-O-OH
•Potassium permanganateKMnO
4
•Ozone O
3
•Sodium Chlorite NaClO
2
•Sodium hypochlorite NaOCl

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

61. Bleaching, Auxiliaries
•Auxiliaries, facilitate and accelerate bleaching and provide protection
against fiber damage.
•Wetting agents: Sulphonatedoils, 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.

62. Bleaching with Hydrogen Peroxide (H
2O
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, perhydroxi-
anions (HOO
-
) are formed.
•From perhydroxi-anions (HOO
-
), superperoxideradical (
.
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.

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

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

65. Bleaching with Hydrogen Peroxide (H
2O
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

66. Bleaching with Hydrogen Peroxide (H
2O
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.

67. Bleaching with Hydrogen Peroxide (H
2O
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.

68. 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, trietahnol
amine, ammonium persulphateetc.
•One disadvantage of chlorite bleaching is formation of toxic and
corrosive gas ClO
2(even stainless steel) at pH below 6.

69. 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 NaOClor H
2O
2.
•It can not used to bleach silk and wool (pink coloration).
•ClO
2corrosive and toxic gas.
•It takes place at acidic pH, so removal of wax is not satisfactory.

70. Questions

71. 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
0
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

72. 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

73. 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.

74. 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.

75. Mercerization
•Mercerization machines
•Pad chain mercerizing machine: Saturator (NaOH)-padder(sequeeze)-airing
rollers (time for swelling)-saturator (NaOH)-padder-stenterclips/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

76. Questions

77. 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.

78. 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 represented as C, N, O and S can have
alternative single and double bonds.
•Auxochromeare 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

79. Dyestuff

80. 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)

81. 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

82. 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.

83. 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.

84. •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 sulphonicacids.
Structural features of direct dyes
Direct Yellow 50

85. Dyeing with direct dyes
•Dissolving in the water

86. Dyeing with direct dyes

87. Dyeing with direct dyes
Additionofsalt:the
editionofelectrolyte
tothedyeliquoris
essentialtoobtain
adequateexhaustion
ofthedyemolecules
bythefiberpolymer
system.
Applicationoftheheat:tothedyeliquorincreasesthe
energyofthecomponentsofthedyeliquor,swellsthe
fibersandacceleratetherateatwhichdyeingoccurs.

88. Dyeing with direct dyes

89. Dyeing with direct dyes

90. 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.

91. 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.

92. Questions

93. 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.

94. Dyeing with Reactive dyes, reaction mechanism
TriazineAnchor
Dichlorotriazine, Procion
Cold reactive dyes (30
0
C)
Monochlorotriazine, Cibacron
Hot reactive dyes (80
0
C)
Firststep:Substantiveabsorption,likedirect
dyeswithsalt(NaCl,Na2SO4).Thedyediffuse
towardstheinterioroffiber,whereitisabsorb
bythecellulosechainsbysecondarytypeforces
Steptwo:Reactioninalkalineliquorwiththe
celluloseandwaterhydroxylgroups.
Stepthree:Eliminationofthehydrolyzeddye
thatisnotfixedcovalentlytothecellulose.

95. Dyeing with Reactive dyes, reaction mechanism
Hydrolyzed dye

96. Dyeing with Reactive dyes, reaction mechanism
Vinyl Sulphonedyes
Ramazol(40
0
C)

97. Dyeing with Reactive dyes

98. 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.

99. Questions

100. 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
hydrosulphiteis used. In some cases addition of alkali may be necessary to
obtain required pH.

101. Dyeing with Sulphur dyes
•In this reduced and leucoform, 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.

102. Dyeing with Sulphur dyes

103. Dyeing with Sulphur dyes

104. 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.

105. Questions

106. 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.

107. Dyeing with Vat dyes
Vatdyesarebasedonindigo
andanthraquinone.The
excellentfastnesspropertiesof
textilematerialcoloredwith
vatdyesisattributedinpartto
theverylargesizeofthevat
dyemoleculeandinparttoits
aqueousinsolubility.In
general,vatdyesbasedon
anthraquinonehavebetter
fastnesspropertiesthanthe
vatdyesderivedfromindigo.
Indigo, C.I Vat Blue 1
C.I Vat Green 8, Anthraquinone type

108. 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
leucoform of the dye. This is achieved by sodium hydrosulphite, sodium hydroxide and water.
Vattingstage also alters the original color of the dye.
•Absorption of the dye molecules by fibers: The vatteddye 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 leucocompound.
•Reoxidation: Once dye in the polymer system of the fiber, vattedform 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.

109. Dyeing with Vat dyes

110. Dyeing with Vat dyes

111. Dyeing with Vat dyes

112. Dyeing with Vat dyes

113. Dyeing with Vat dyes

114. 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.

115. Questions

116. 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.

117. 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.

118. Dyeing with Disperse dyes
•Mainly azo and anthraquinone structures
Watersolubility:30
mg/l,supportedby
followingsubstituents
•OH-groups
•NH2-groups
•Aromatic bound
halogen, etc.

119. Dyeing with Disperse dyes
•Structure and properties of Polyester
•N= 80-150; mean molar mass: 15200-28500
•Melting area: 256-275
0
C
•Surface tension: 39.5 mN/m
•Glass transition temperature: 80
0
C
•Dyeing only possible with disperse dyes.

120. Dyeing with Disperse dyes
Disperse Dyeing Mechanism

121. Dyeing with Disperse dyes
•Dispersingagentisaddedtowaterwithdyetoforma
aqueousdispersion.
•Theinsolubilityofthedispersedyesenablesthemto
leavethedyeliquorastheyaremoresubstantivetothe
organicfiber.
•Heatingdyeliquorincreasestheenergyofthedye
moleculesandacceleratethedyeing.
•Heatingswellsthefibertosomeextentandassistthe
dyetopenetratethefiberpolymersystemresultingin
dyebeinglocatedintheamorphousregionsofthefiber.
•Onedyeinpolymersystem,thedyemoleculesareheld
byhydrogenbondsandvanderWaalsforces.
•Polyesterfibersareextremelycrystallineand
hydrophobicanditisdifficulttoachieveevenlighter
shadeatboil.
•Inordertoobtainmediumtodarkshadespolyester
fibersaredyedusingcarriersorbyusinghigh
temperaturedyeingtechniques.

122. 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.

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

124. Dyeing with Disperse dyes

125. 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.

126. Questions

127. 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.

128. Acid Dyes

129. Acid Dyes
•Mainly acid dyes are salt of sulphonicand/or carboxylic acids.
(containing SO
3H, 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)

130. Acid Dyes

131. Acid Dyes
•Theapplicationofaciddyesto
proteinfibersresultsinanionic
bondorsaltlinkbetweenthedye
moleculeandfiberpolymer.
•IncaseofNylon,thegreater
crystallinestructurecompared
withwoolaswellastherelative
lowernumberofaminogroups
meansthatdarkshadesonNylon
cannotbeachievedwithacid
dyes.
•Inadditiontoionicbond,
hydrogenbondandvander
Waal’sforceswillbeformed
betweenaciddyemoleculeand
thefiberpolymersystem.

132. 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.

133. 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.

134. Questions

135. 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.

136. Basic Dyes

137. 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 mordantingagents

138. 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.

139. Questions

140. 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.

141. 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.

142. 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.

143. Printing, Printing Methods
•Resist printing
•Discharge printing
•Transfer printing
•Two-phase printing

144. 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.

145. 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.

146. Printing, Discharge Printing

147. 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.

148. 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.

149. 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.

150. 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.

151. 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.

152. 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.

153. 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.

154. 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
0
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.

155. Questions

156. 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.

157. 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.

158. 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.

159. 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.

160. 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.

161. 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 +velycharged ends
towards partially –velycharged 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 –velycharged fiber surface. This
leads to higher hydrophilicity but less softening.

162. 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.

163. 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.

164. 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.

165. 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

166. 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.

167. 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.

168. 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.

169. Questions