Pretreatment ,Impurities in natural fibre; Chemistry and practice of preparatory processes for cotton, wool and silk; Mercerization of cotton; Preparatory processes for manmade fibres and their blends,Carbonization ,Scouring barium acitivity number .

1. CHEMICAL
PROCESSING
pretreatment

2. Introduction
Textile pretreatment is a series of cleaning operations that removes impurities:
1) Natural
2) Added
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3. Sizes: Natural
polymers/derivatives
Starch and its derivatives (75%)
Starch has two components:
• Amylose: Relatively lower mol. wt. & water soluble
(20%)
• Amylopectin: Higher mol. wt. and difficult to remove
(80%)
In case of sizes based on natural polymers, add-on is of the order
of ~15% and they generally require removal by chemical
degradation. This results in high pollution of discharge

4. Sizes based on Synthetic Polymers
• Polyvinylics
• Polyacrylates
• Poly vinyl aclohol

5. Removal of impurities
Solubilization
Emulsification
Chemical breakdown by
• Hydrolysis
• Oxidation

6. Important parameters:
• Temperature
• pH
• Time
• Concentration
• M:L ratio

7. Cotton
Cotton consists of practically pure cellulose and may
be chemically described as poly (1, 4-B-D-
anhydroglucopyranose).
The helical reversal structure of natural cellulose
shows the constantly recurring cellobiose unit,
consisting of two glucose units each with six carbon
atoms. The length of unit cell along the fibre axis is
10.4A calculated for the cellobiose unit.
In natural cellulosic fibres there are 3000 - 5000 C6
or glucose units joined together. This corresponds
to a molecular weight of the order of 300,000 -
500,000.

9. Proteins
Nitrogenous compounds:
• Present in primary cell wall and lumen
• Yellow colour of cotton is due to presence of
proteins and
• some colouring matter

10. Some amino acids:
▪ Leucine
▪ Valine
▪ Proline
▪ Alanin

11. Fats and waxes
The wax present in the primary cell wall of cotton
protects the fibre from environmental agencies
Responsible for the smooth handle and is a source of
hydrophobicity.
In the presence of wax, cotton has poor wettability.
The wax consists of long chains of fatty alcohols,
fatty acids, their esters, cholesterin & hydrocarbons

12. Pectins
Derivatives of pectic acid
Found in the cover of citrus fruits
Polymer of high molecular weight
Pectin is a polysaccharide that acts as a cementing
material in the cell walls of all plant tissues. It is a
polymer of α-Galacturonic acid with a variable number of
methyl ester groups.
Some COOH groups are present as Ca and Mg salts.

13. Wool
• Keratin
• Suint
Suint is mainly water soluble constituents of raw fleece and is normally
neutral or slightly alkaline in reaction. It contains potassium and to a certain
extent sodium ions.
• Other impurities

14. CH2SSCH2 Cysteine

15. Silk
The average composition of raw silk is 70-75%
fibrion (C15H23N5O8), 20-25% sericin, 2-3% waxy
substances extractable by ether and alcohol and 1 to
1.7% mineral matter.
Sericin is amorphous and dissolves in hot soap
solution.

16. Fibrion is the form of a filament thread and dissolves
in 5% sodium hydroxide solution at boil.
Both fibrion and sericin are protein substances built
up of 16-18 amino acids, out of which only glycine,
alanine, serine and tyrosine make up the largest
part of the silk fibre
It is 65-70% crystallne

17. Silk

18. Silk polymer occurs only in beta -configuration. The
important chemical groupings of the silk polymer are
the peptide groups which give rise to hydrogen bonds,
the carboxyl end amine groups which give rise to salt
linkages and the Van der Waals' forces. It has high
degree of molecular orientation which accounts for
the excellent strength of the silk fibres.

19. Singeing
To remove protruding fibres from the surface of a fabric smooth appearance
Passing/exposing one or both sides of a fabric over a gas flame
Singeing of yarns is called “gassing”.
In Grey State (Economical) ‐ As one dry step is avoided
Slight Yellowing Occurs ‐ Removed on bleaching
Singed with maximum burner intensity
Polyester melts at 260-280°C, but burns at 500°C.
Normal flame forms fused polymer at fabric surface
So, powerful flame for quick burning

20. Direct: Flame contact
• Hot Plate
• Rotary Cylinder
• Gas
Indirect: No Flame Contact, Uniform Singeing
• Radiation Singeing

21. Plate singeing machine
The plates are heated to bright red from the opposite
side
Fabric speed up to 200 yard/min
Fabric is run into water immediately after singeing
Hollow cylinder rotates slowly in opposite direction
Fired internally

22. Rotary cylinder machine
A hollow cylinder which revolves slowly in the
opposite direction
The hollow cast iron or copper cylinder may be fired
internally.
The cloth is drawn through the machine by a
powerful squeezer nip, singed, run through water bath
and plaited

23. Gas singeing machine
Flame has high thermal and mechanical energy
Can loosen the fibre ends
Flame temp‐1300°C

24. Tangential singeing
Singeing onto water cooled rollers
Singeing into the fabric

25. Desizing
Desizing is the process of removal of size material
applied on warp threads of a fabric to facilitate the
process of weaving.
•Hydrolytic desizing
•Oxidative desizing

26. • Starch sizes
• Modified starches
• Cellulose derivatives
• CMC (carboxymethyl cellulose)
• Sizes based on polyvinyl alcohol (PVA)
• Polyacrylates (PAC)

27. • Galactomannans (GM)
• Polyester sizes (PES)
• Vinyl, acrylic and styrene homo- and copolymers
• Waxes and fats
• Paraffins, silicones, softeners, fungicides and
others

28. Representative partial structure of amylopectin
(70-80%)
 -(1-4) linkage
Representative partial structure of amylose
(20-30%)
 -(1-6) linkage
Starch

29. Hydrolytic desizing
• When the ‘1‐4 linkage’ is attacked and broken by
hydrolysis, the desizing is called hydrolytic desizing.
• Initial starch degradation product is insoluble
dextrin, which on further hydrolysis is converted to
soluble dextrin and finally glucose.

30. Rot steeping
Steeping in water at 30 - 400C, starch swells
Swollen starch is attacked by enzymes secreted by
microorganisms in environment
Hydrolyzed starch is removed by normal washing
Low capital investment
Slow, low reproducibility, risk of cellulose being attacked

31. Acid desizing
The 1-4 linkage can be broken by acid hydrolysis also
Mineral acids are used
H2SO4/HCl (5 – 10 gpl) is needed at 400C for 3-4 hrs.
(> 40 0C & 10 gpl acid concentration
The fabric is padded with acid solution and stored
(batched)

32. Enzyme desizing
Vegetable, Bacterial, Animal (Diastase, Amylase,
Rapidase, etc.)
Since enzymes act optimally at specific conditions of
temperature and pH, it is important to maintain
narrow range of conditions for best results.

33. Effect

35. Oxidative degradation
Synthetic polymer or is a mixture of synthetic and
natural polymers size is removed by oxidative
degradation
• Sodium chlorite (NaClO2)
• Sodium bromite (NaBrO2)

36. • Hydrogen peroxide (H2O2)
• Sodium and Potassium persulphate (Na2S2O8,
K2S2O8)
• Peroxy monosulphuric acid (H2SO5)

37. Sodium Chlorite NaClO2 and Sodium bromite (NaBrO2)
Sodium bromite is a powerful oxidant for starch
Breaks glucose ring by breaking C2‐C3 link and produces a
dialdehyde. The dialdehyde dissolves in alkaline solution. hence
desizing is followed by an alkaline wash
Acts best at pH 10
Works at room temperature for short durations and is highly
efficient
However, 50% of the bromite reacts with impurities and increases
pollution problem of the effluent

38. Peroxy monosulphuric acid (H2SO5) / Hydrogen
peroxide (H2O2)
Peroxy compounds are sensitive to presence of heavy
metal ions, a sequestering agent is usually employed.
Hydrogen peroxide may be used in a similar way.
Conditions are generally kept mild (pH‐6‐8) and
washing is done in alkaline conditions.

39. Methods Chemical Temp.
(oC)
Time pH
Rot None 30 (RT) 16 -24 hrs. 7.0
Acid HCl
(0.5 -1.0 %)
30 - 60 2 -8 hrs. 1.0 -2.0
Enzyme 0.5 -1.0% 60 - 70 1 -2 hrs. 6.0 -7.0
Oxidative
(Persulphate)
0.3 -0.5% 100 10 min 14.0

40. TEGEWA rating
Reagent preparation
Put potassium iodide [10 g of KI (100%)] in 100 ml of water; then add 0.6358 g
of iodine (100%).
Stir well until iodine is completely dissolved in the KI solution. After this, add
800 ml of ethanol. Then by adding water the volume should be raised to 1000
ml.
Testing Method
Put one or two drops of the above solution on a fabric. Rub it gently and then assess
the colour change as per the TEGEWA scale. Before testing, the fabric should be cold
and there should not be any residual alkalinity in it

41. No Colour Change = No starch is present
Pale blue to bluish violet = Presence of starch size or
a blend of starch+ synthetic size
Brown = Presence of modified starch or a blend of
modified starch/PVAsize

42. Starch Test:
Add Iodine-KI reagent to
a solution of starch or to
starch. A blue-black
colour results if starch is
present. If starch amylose
is not present, then the
color will stay orange or
yellow. Starch
amylopectin does not give
the colour, nor does
cellulose, nor do
disaccharides such as
sucrose in sugar.

43. Scouring
To reduce the amount of impurities sufficiently to
obtain level results in dyeing & finishing operations
by bringing the substrate to a highly absorbent
state.

44. Different Agent Descriptions
Alkali Mainly Sodium
sometimes mix
(washing soda)
of
hydroxide
NaOH and
(NaOH),
Na2CO3
Wetting agent To reduce the surface tension of scouring
liquor so as to wet out the goods uniformly,
generally anionic surfactants are used.
Emulsifier To emulsify non-saponifiable wax, generally
nonionic surfactants are used.

45. Impurities Mechanism of removal
Fats and waxes Saponification:
The saponifiable parts of waxes (fatty
acid, glycerides and esters) are
converted in to soap.
Emulsification:
The non-saponifiable parts of the waxes
such as alcohols and hydrocarbons are
emulsified by the soap formed.
Pectin & related
Substances
Pectins are converted to water soluble
salts of pectic acid

46. Impurities Mechanism of removal
Proteins and
Amino acids
Proteins are hydrolyzed with the
formation of soluble sodium salts of
amino acid.
Amino compounds are hydrolyzed to
ammonia by alkali.
Minerals &
heavy metals
•Partially dissolve in NaOH
•By use of sequestering or chelating
agents

47. Impurities Mechanism of removal
Hemicelluloses Dissolution: Hemicelluloses with low DP
are dissolved in NaOH
Motes •Cellulose of low crystallinity swells in
alkali and becomes sodium cellulosate,
water soluble.
•Residual motes are destroyed in
bleaching.
Other organic
compounds
Cellobiose, Cellotriose, Organic acid (i.e.
Malic acid, etc.)

48. Chemicals Amount
NaOH 4% owf for normal fabric.
6% owf for heavier fabric
Wetting Agent 1 – 3 gpl
Emulsifying agent Non-ionic surfactant (1-3 gpl)
Temperature 130 oC

49. Trichloro ethylene
(B.P. : 121 oC, Non-flammable)
Trichloroethylene (TCE)
Perchloro ethylene
(B.P. : 87oC, Non-flammable)
Perchloroethylene (PCE)

50. • Pressure kier (batch system)
• J-BOX (continuous system)
• Vapor loc System (continuous)

51. It is a continuous system
Fabric is fed from one end and the scoured fabric comes out
from the other end.
The capacity is such that sufficient residence time, allowed
inside the machine for degradation and removal of impurities.
Inside temperature: 100 oC
Saturation of fabric with recipe before treatment in the J-Box.
Time: 40 – 60 min.

52. Assessment of scouring efficiency
Practical tests of absorbency
Measurements of:
Weight loss
Protein content
Residual wax content
Methylene blue absorption (removal of pectic substances)

53. Copper Number, defined as grams of cupric copper reduced
to cuprous oxide by 100 g of cellulose under standard
conditions of boiling in alkaline medium.
The formed cuprous oxide is dissolved in a solution of iron
alum and sulphuric acid for reducing an equivalent amount of
iron to the ferrous state.
The reduced iron is then determined by titration with a
standard solution of ceric ammonium sulphate.
(Ortho ferrous phenathroline is used as an indicator)

54. V is the ml of ceric ammonium sulphate
solution consumed after deducting blank
reading
N is the normality of ceric ammonium sulphate
solution
W is the weight of the bone dry cellulose sample

55. Cuprammonium is a measure of molecular chain length
of cellulose.
(By measuring the fluidity of cotton material
dissolved in cuprammonium hydroxide
solution)
The degradation, in terms of reduction of the degree of
polymerization, can be assessed by measuring fluidity.
The DP of a polymer is directly proportional to the
viscosity of its solution.
Substrates Fluidity
Unbleached cotton 2
Bleached cotton 5 or less
unbleached viscose 10

56. Dyeing with Basic dye
blue absorptionMethylene
method is based on the
principle that the carboxyl
groups present in cellulose
are able to absorb
methylene blue dye cations
(quantitatively from a
solution of methylene blue
dye)

57. Bleaching
To destroy the natural or acquired coloring materials
to bring the textiles in a white state.
For dyeing in dark shades, it is an optional process
Increased absorbency

58. NaOCl is sodium salt of Hypochlorus acid (HOCl)
having redox potential of 1400-1550 mV.
Strongest oxidizing agent
Active chlorine is a unit of chlorine concentration used
for hypochlorite bleaching
Active chlorine is determined by adding excess
potassium iodide to sample of bleach solution
Titration of iodine with standard sodium thiosulfate
solution

59. Bleaching with Sodium Hypochlorite (NaOCl):
pH effect
50
100
Concentration
%
0
1 2 3 4 5 6 7 8 9 10 11 12 13 pH
Cl2
HOCl
OCl−
Safe pH
for
Bleaching
9-11

60. Bleaching with Sodium Hypochlorite (NaOCl): pH effect
Rate of oxidation of cellulose in terms of the consumption of
half of the total available chlorine.
•Rate of oxidation at
around pH 7 is the highest
•pH-7 is an unsafe zone
for bleaching

61. Sodium Chlorite Bleaching
Concentration
%
0
50
100
1 2 3 4 5 6 7 8 9 10 pH
ClO2
HClO2
ClO2−
Optimum
pH for
Bleaching
3.0-4.5

62. ClO2 is a toxic corrosivegas
No silk and wool (yellowish pink color) bleaching
possible

63. H2O2
An eco-friendly bleaching agent: by-products only
water and oxygen
Redox potential: 810 – 840 mV
Universal bleaching agent–most of the fibres can be
bleached
Provides permanent bleaching action

64. Perhydroxyl ion (HO2 )
–
In alkaline medium H2O2 decomposes as: H2O2 + OH–
OOH– + H2O
Above pH 10.8, formation of HO2ions is rapid.
–
Stable in acidic pH
Decomposes in presence of alkalis or UV light
Sodium hydroxide (NaOH) is commercially used as an
activator
Sodium Silicate as stabilizer

65. H2O2 (50%) : 1 – 2%
Activator (TSP): 2 – 3% (to adjust the pH 10.5)
Stabilizer (Sodium silicate):1 – 2%
Non-ionic surfactant: 3 gpl
Metal chelating agent (EDTA): 0.01%
Temp: 1-2 hrs.(@ 95 0C)

66. Comparison of sample against a standard of
magnesium oxide or barium sulphate
The standard: 100% reflectance at all wavelengths
Bleached samples: 70 - 75% reflectance at 460 nm
Unbleached cotton: 55% reflectance at 460 nm (blue
region)
Good bleached fabric: WI >75

67. Mercerization
Improved lustre (silky look, in tension mercerization
only)
Improved tensile strength
Improved dimensional stability
Increased uniformity of dyeing & improving color
yield (savings in dyestuff
Improved Elasticity or Stretch material (in
slack mercerization only)

68. Mercerization causes swelling in fibre. Swelling causes
cross- section to become rounder, loss of convolutions &
de-twisting leading to more lustrous surface
Opening of fibre structure
Increase in amorphous content due to de-crystallization
Although mercerization is accompanied by swelling, it
more closely related to internal modification of fiber.
(Effect is observed at 18 - 25 % w/w NaOH solutions). (48
– 52 0Tw)
Higher no of –OH groups available as compared to un-
mercerized cotton
Higher moisture regain, dye-uptake and reactivity

69. At different
alkali concentration
and temperature

70.  During regeneration, it gets converted to a
different crystalline form, known as Cellulose-II.
During mercerization also, some native cellulose
gets converted to cellulose-II.
The native form of cellulose which occurs in cotton and
other natural cellulosic fibres
 It has it’s unique crystal diffraction pattern.
 It is a thermodynamically less stable form of cellulose.
When cellulose is converted to regenerated cellulosic fibres
like viscose, dissolution of cellulose is an intermediate step.
Cellulose-I
Cellulose-II

71. •

72. Saturation of cotton with NaOH under relaxed
conditions (50oC to boiling point) for 4-20 seconds
Controlled hot stretching
Cooling the stretched material to less than 25 oC
temp.
Tension controlled washing (till NaOH concentration
in fabric falls below 60 gpl level)
Final washing under relaxed conditions

73. Pad chain
Fabric is saturated with alkali solution and padded.
The saturated fabric passes over a set of rollers (airing rollers)
Fabric is again saturated and squeezed and passed in to a stenter
Length and widthwise tension is applied
Widthwise tension applied using stenter clips on chain

74. Chainless
• Fabric passes through a number of rollers without the use of a
clip stenter
• In Chainless mercerizing machine bowed rollers are used to
apply widthwise tension.
• Weft direction tension is mainly determined
by warp wise tension
• Warp wise tension is controlled by oscillating rollers.
• Other features are more or less similar to chain
mercerization units.

75. Assessment
Mercerized and un-mercerized cotton samples (2 gm each) are treated with
30 ml of N/4 Barium hydroxide for two hours at room temperature.
Preferential absorption of barium hydroxide by cotton samples reduces the
strength of Barium Hydroxide solutions.
The amount of Ba(OH)2 absorbed can be determined by taking 10 ml of
Ba(OH)2 solution from each of the flasks and titrating it with N/10 HCl,
with phenolphthalein indicator.
Blank titration also done.

76. Barium activity number
BAN = (B-M) / (B-C)*100
Where,
B = Volume of HCl (ml) required for blank titration
M = Volume of HCl (ml) required with mercerized
cotton C= Volume of HCl (ml) required with un-
mercerized cotton
For completely mercerized cotton the value of BAN
is around 155.
Semi mercerized cotton, it varies in between 115 and
130

77. Sericin is a protein which forms bulk of the gum or the
outer protective coat in a silk filament
Removal of this gummy
substance is called as:
Degumming
The process consists of cleavage of peptide bonds of sericin,
either by hydrolytic or other methods, and its subsequent
removal from fibroin by solubilization or dispersion in water

78. Extraction with water
Boil-off in soap
Degumming with alkali buffer
Degumming with organic acids
Degumming with amines
Degumming with enzymes

79. Up to 96% sericincan be removed by
extracting it with water at 115 oC for 3 hrs.
Olive oil soap (Marseille soap) is the most
widely used soap. Boil off method
Degumming depends on the alkali formed on
hydrolysis of soap and the soaps hydrolyzing the
most have the highest degumming power.

80. • With alkalis, the pH of the boiling bath maintained
between 9.5 -10.5.
Below pH 9.5, the rate of degumming is too
slow and above 10.5, the risk of chemical damage
is high.
 Hence, many times, alkaline buffers like:
 Sodium carbonate / sodium bicarbonate
 Sodium hydrogen phosphate / trisodium phosphate,
 Potassium tetraborate / boric acid
• Mineral acids may cause significant damageto
silk, hence generally only organic acids are used.

81. • The main enzymes used aretrypsin,
papain and bacterial enzymes.
• Amines show good degumming (upto 90
% sericin removal) with little loss in tensile
strength

82. Bleaching

83. Carbonization
To remove cellulosic impurities from wool by treatment with
acid / acid producing salts.
• Seeds
• Burrs
• Grass
 Removing Principle:
• Mineral acids turn cellulose into brittle
carbonaceous mass which can be removed by crushing it.

84. Treatment with(5-7%w/v) sulphuric acid and acid stable
wetting agent.
Hydro-extraction
Drying at 60 – 70 oC to low regain
Baking at 110 oC in dry heat for 2 min. (wool is relatively stable
to acidic conditions. The vegetable matter turns brown / black,
becomes brittle)
Crushing to break the degraded vegetable matter
to small fragments by passing through heavy
fluted rollers
Dusted and Neutralized with sodium bicarbonate.
Bleaching with acidic hydrogen peroxide to minimize
yellowing caused by carbonization

85. Scouring
Presence of scales on wool fibre surface leads to a
tendency to felt / shrink.
Soaps
Nonionic / Anionic detergents (Along with alkali, Na2CO3
pH: 9 – 10; Temp: 45 – 55 oC)
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86. Bleaching
Wool is bleached with hydrogen peroxide
pH: 8.5 – 9.0
Temp: 50 - 60 ᵒC.
Time: 2 hrs.
Activator: mild alkali
Stabilizers: Tetra sodium pyrophosphate or sodium tri-
polyphosphate
Wool can be damaged under alkaline condition, an
alternative is to bleach in acidic conditions using a per acid
activator (pH 5 - 6).

87. Thiourea dioxide
Sodium dithionite
Zinc formaldehyde sulphoxylate
Sodium formaldehyde sulphoxylate
Sodium dithionite is the preferred reducing agent.
Bleaching is carried out at 45 – 65 ᵒC at pH- 5.5 – 6
for 1 hour.
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88. End of pretreatment
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