Dyeing involves using dyes that have an affinity for fibers. Dyes are soluble colored compounds that can penetrate fibers and form bonds with them. The type of bond formed depends on the fiber and dye, and stronger bonds lead to better fastness. There are several types of dyes like direct dyes, reactive dyes, vat dyes, acid dyes, metal complex dyes, and basic dyes that differ in their properties and how they interact with fibers. Key factors that affect dyeing include dye properties, fiber properties, temperature, time, liquor ratio, and process used.

1. CHEMICAL
PROESSING
DYEING
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2. Dye
Coloured compounds (organic)
Soluble in water or can be solubilized
Posses affinity for the substrate
Penetrate / diffuse in fiber X-section during dyeing
Depending on nature of fiber & nature of dye, suitable dye fiber bonds are formed which retain the dye on the fiber
Nature & strength of dye fiber bonds determines the fastness of the dye
H- bond energy: 7 – 10 Kcal/mole
Van der Waals: 4 Kcal/ mole
Covalent bond: 80 – 100 Kcal/mole
TR

3. Pigment
Colouring compounds (organic/ inorganic)
Insoluble in water
No affinity to the substrate
No interaction with fiber
Used in mass colouration

4. Auxochromes:
Chromophores
(provides colour –
unsaturated grps.)
Chromogens:
(To which chromophore
is attached)
(Modify the hue / solubility –
conjugated system)
Phenyl, Naphthyl, etc.
-NH2
-NHR
-NR2
-OH
Saturated functional groups attached to -OR
-SO3

5. Chromophore
Chromogen
Auxochrome

8. Cellulosic fibres

9. Protein Fibres

10. Polyamide Fibres
Synthetic fibres

11. Synthetic fibres

12. Direct dyes
As anionic dye which has affinity for cellulosic fibre and are generally
dyed with water in presence of salt.
These sulphonate groups molecules are soluble in water
Dyes with a high affinity for cellulose fibres
Substantive dyes: dye molecules are attracted by physical forces at the
molecular level to the textile substrates
Cheap

13. Electrolyte (SALT):
Salt Sensitive dye
Durazol Fast Blue 4GS
40%
20%
0%

14. Temperature
Dyeing (exothermic) – lesser exhaustion at higher temp
Temperature
increases
the rate of
diffusion of
dyes in the
fibre
Temperature
lowers
the
equilibrium
dye uptake
of the fibre
Temperature: 900 – 100 0C, for 1 – 2 hrs.

15. Time

16. Liquor
M:L

17. BATCH DYEING
Dye should have very high affinity
Partition co-efficient should be high
CONTINUOUS: Pad – Fixation
Fixation – dry heat / steam
If high affinity, - tailing effect
SEMI-CONTINUOUS: Pad– Batch
Pad is continuous, for 1 – 2 sec.
Fixation is in batch process, for 30 min – 1 hr.
Dye of low affinity should be used

18. Diazotization and Development
Coupling with Diazonium salt
Treatment with Metal Salts
Treatment with Formaldehyde
Treatment with cationic fixing agent

19. Reactive dye
Reactive Dyes are coloured compounds that contain groups
capable of forming covalent bonds to a given substrate.
Overall affinity for cotton is poor, necessitating dyeing
for prolonged time along with excess of salt

21. Dyeing temp. 30 – 40 0C (Cold brand dye, M),
pH: 10-11
60 -70% dyes react with cotton
30-40% of dyes react with H2O
•Dyeing temperature: 60 – 700 / 80 -90 oC
•pH: 11

22. 6
5
4
3
2
1
0
1312109
20
10
30
40
11

23. Dye Variables : Substantivity
Exhaustion Profile of a Reactive Dyes
50
0
100
80
0.5 h
Time h
1.5 h

25. 100
50
0
0
Dye on Fibre
Dye in Bath
30 60 90 120 180
Time, min
0
100
50
0 30 60 90 120 180
Time, min
Dye on Fibre
Dye Fixation
Mobile Dye on Fibre
Hydrolyzed Dye

26. 100
50
0
0 30 60 90 120 180
Time, min
Exh.
% Dye on Fibre
Dye Fixation
Rate of Fixation
4% per 6 min
100
50
0
0 18030 60 90 120
Time, min
Exh.
%
Dye on Fibre
Dye Fixation
Rate of Fixation
30 % per 6 min

27. Two bath pad steam process
Two bath pad batch process
Two bath wet fixation process
One bath pad dry process
One bath pad dry steam process
One bath pad steam process
One bath silicate pad batch process

28. Vat dyes
Indigoid
Indigo on reduction – colourless or light yellow (Leuco form)
Poor fastness property
Oxidation of –C=C- happens easily
Anthraquinoid
Best washing fastness and light fastness prop.
Resistant to alkaline wash / oxidation
Dyeing with vat dyes is based on the principle of converting
a water-insoluble keto-substituted colorant by reduction to
a water-soluble enolate leuco compound that is substantive
to cellulose.

29. Vatting:
Dissolving the dye under alkaline reducing condition,
mostly with sodium hydrosulphite or sodium dithionite
(Na2S2O4) and caustic soda (NaOH).
Dyeing:
Impregnation of the materials with the dissolved dye.
Oxidation:
The insolubilisation of dye to the original insoluble, non-
substantive pigment form inside the fibre.
Soaping: Removal of Superficial dyes, Dye aggregation

31. After treatment- Oxidation
Skying in air
Hydrogen Peroxide (H2O2)
Sodium Perborate (NaBO3·H2O)
Sodium m - nitrobenzenesuphonate (Ludigol)
Potassium Dichromate (K2Cr2O7)

32. Acid dyes
2 8 10
0.25
0.20
0.15
0.10
0.05
4 6
pH of the Dyebath
Aciddyesorbed/meqkg-1

33. Zone-1 → a regular titration region with an anion of high
affinity;
Zone-2 → a region of electrostatic saturation where there is a
reasonable correlation between amine end group content and
amount of sulphonic acid dye bound;
Zone-3→ a region where electrostatic saturation is exceeded
and where dye uptake has no apparent maximum.

34. Nylon: 2.7
Wool: 4.6
Silk: 3.5
Hydrolysis of amide groups to primary amine and carboxylic
groups at low pH
Reduction in DP
More accessible fibre (more dye sites)
Applied from acidic pH and also the dye contains acidic
group in their structure
- +
CO-NH COOHH+
3N
DSO3
-

36. Barre effect
Physical variations’‐ could be:
Fine – difference introduced drawing, heat setting,, etc. of the
filament yarns.
Gross – due to variations in the count or the crimp of the
yarns or Fibres.
Chemical variations’
During polymer spinning or blending of yarns of
different AEG (amino end grp.) content.

37. Interactions
1 Electrostatic Interaction: This interaction is between the protonated amino
groups of the fibre and the negatively charges anionic dyes.
HOOC ------------NHCO----------------
NH + DYE –
SO3
3
2. Hydrogen Bonding: This interaction is between the amino, amido and
carboxlic acid groups of the fibre and the azo and other hydrogen bonding
groups of the anionic dyes.
3
HOOC ------------NHCO----------------
NH +
3
N = N Ph – SO
2 2- 2 2
2
HOOC ------------NHCO-CH -CHCH -CH -CH
-NH
3
3. Hydrophobic Interactions: This interaction is between the aliphatic groups
of the fibre and the hydrophobic groups of the anionic dyes.
+
2 2
-CH -CH -CH -Ph-N = N-Ph -
3

38. Metal complex dyes
Reaction of 1 atom of metal with molecule of dye produces 1:1
metal–complex dye.
Very low affinity
Thus Conc. H2SO4 is used in dyeing (it degrades the wool ,
becomes rough).
Reaction of1 atom of metal with 2 molecules of dye produces
1:2 metal– complex dyes.
Dye has high affinity (Neutral Dyeing Metal Complex dye)

39. Like acid dyes, these anionic dyes form ionic bond
with protonated amino groups (Dye– +H3N-Wool)
Powerful Van der Waals’ forces may act between the big dye
molecules and the fibre.
Dye-SO3 – +H3N-Wool
Dye-Cr+ –OOC-Wool
Dye-Cr ←NH-Wool

40. Basic dyes
Cationic dyes are basic dyes. They are so-named because they
are derived from organic bases. They are also called cationic
dyes as they ionise in water producing coloured cations
Brilliance and colour intensity
With alkali, these dyes become colourless bases.

41. Temperature effect
Temperature, 0C TD = 95.60C
Df(mmolkg-1)

42. With retarding agent

43. pH effect
4
SO - groups only
Fibre with COO–
groups

44. End of dyeing
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