3. Reactive dyes…
has a reactive group which are adsorbed on to the cellulose and than reacted with the
fiber to form covalent bonds.
Chromophore Bridging RG
General structure
Functional groups
Reactive group
4. Reactive dyes…
has a reactive group which are adsorbed on to the cellulose and than reacted with the
fiber to form covalent bonds.
Chromophore Bridging RG
General structure
Functional groups
Shade
Fastness
Levelness
Substantivity
Solubility
Application temperature
Fastness
Dischargeability
Fixation
Application temperature
5. Reactive dyes…
When put fabric and dye into the water;
Cell-OH
General reaction
Cell-O¯
HO3S-Dye-X
Cellulose:
Dye:
X-Dye-SO3¯
Electrostatic
repulsion because of
the negative charges
With addition of salt: Cell-O¯ ⁺ Na
X-Dye-SO3¯ ⁺ Na
Reduce the repulsion
6. Reactive dyes…
After addition alkaline and linking with covalent bond;
General reaction
Na ⁺ ¯O-Cell
X-Dye-SO3¯ ⁺ Na
( Soda ash, caustic …)
+
Na ⁺ ¯O3S – Dye –O-Cell + NaX
Thanks to covalent bond
Linking much more resistant to the
usual conditions of use than the
physicochemical bond between
direct dyes and cellulose.
Bond type App. Relative strength
Covalent 30.0
Ionic 7.0
Hydrogene 3.0
Other
Intermolecular
1.0
7. Reactive dyes… Description of dyeing mechanism
Exhaustion of dye in presence of electrolyte by adsorption
Fixation under the influence of alkali
Wash off the unfixed dye from material surface
T1: Addition of
alkali and start of
the fixation
8. Reactive dyes… Exhaustion
The reactive dyes is adsorbed onto the cellulose surface and than diffuses into the fiber.
This phase is fully reversible.
Dye molecules are in equilibrium between fiber and dyebath.
Any change in bath composition
affect the equilibrium
[F] Dyebath [F] Cellulose
So; affect the Substantivity
S=
[F] Cellulose
[F] Dyebath
9. Reactive dyes… Substantivity: Influencing parameters
Substantivity
Dye
affinity
Dye conc.
Electrolyte
conc.
pH
Temperature
Type of fiber
Liquor
ratio
10. Reactive dyes… Substantivity: Influencing parameters
Standart affinity of dye;
Like substantivity; is a measure for the distribution of a dye between fiber and dyebath.
Unlike substantivity; affinity is constant at dyeing conditions, it is dye-spesific characteristic.
The number of
conjugated double
bonds in chromophore
Substantivity
High affinity for cellulose (Direct dye)
Low affinity for cellulose (Acid dye)
11. Reactive dyes… Substantivity: Influencing parameters
Electrolyte Concentration;
Anion-anion repulsion
Electrolyte conc.
Direct dyes; high affinity, require 5-10 g/lt salt
Reactive dyes; medium to low affinity, require 40-100 g/lt
Substantivity
12. Reactive dyes… Substantivity: Influencing parameters
pH of dyebath;
Cell-O¯
Cell-OH + H2O
OH¯
H⁺
As the pH increases, the cellulose carries more and more negatively charge.
The amount of the OH ion in the dye bath increases.
Without alkaline addition
pH Substantivity
7
8
9
10
11
12
13
RS:
Cell-O¯ (in the fiber)
OH¯ (in the dyebath)
13. Reactive dyes… Substantivity: Influencing parameters
Dye concentration;
Because of the limited adsorption
capacity of fiber surface;
S=
[F] Cellulose
[F] Dyebath
Dye concentration Substantivity
Surface saturation occurs later with high affinity dyes
than low affinity dyes so,
the greater influence on substantivity of low affinity
dyes
14. Reactive dyes… Substantivity: Influencing parameters
Dyeing temperature;
At 80⁰C, speed of diffusion of a dye in cellulose is higher than at 40⁰C.
Dyeing equilibrium is therefore achieved much more rapidly at 80⁰C than 40⁰C.
Temperature Substantivity
Subsantivity seems to be lower at
40⁰C than at 80 ⁰C, but in fact it is
not.
15. Reactive dyes… Substantivity: Influencing parameters
Liquor ratio;
Liquor ratio Substantivity
Don’t forget that the decrease is
also related to :
Dye concentration
Dye own affinity
So;
The Liquor ratio increases, the probability of contact between the dye molecules and the
fiber surface decreases.
16. Reactive dyes… Substantivity: Influencing parameters
Liquor ratio;
Affinity of the dye
Dye concentration (L.R. 10:1=%100)
Dye :C.I. Reactive Red 180
Electrolyte :50 g/lt NaCl
Dyeing temperature :40⁰C
Dye concentration :3%
Electrolyte :50 g/lt NaCl
Dyeing temperature :40⁰C
17. Reactive dyes… Substantivity: Influencing parameters
Fiber type;
Although the fiber structure has some minor effect on substantivity, we will see differences
e.g.; Mercerized cotton dyes to a much deeper shade than non-mercerized
It is merely the result of different optical properties: mercerized cotton has a circular cross
section,which allows better light penetration, less random light reflection.
Therefore, mercerized cotton can be much more easily penetrated by photons, thus a larger
proportion of coming light is selectively adsorbed and this means higher color saturation.
Raw cotton Mercerised and stretched cotton
18. Reactive dyes… Diffusion rate: Influencing parameters
But fiber type has a significant effect on Diffusion Rate…
Fiber type
Dyeing temperature
Size and shape of dye molecule
Subsantivity of dye molecule
Electrolyte concentration in the bath
Dye concentration
19. Reactive dyes… Diffusion rate: Influencing parameters
Adsorption equilibrium diffusion
Dye uptake phase consist of successive
states of equilibrium.
Dye repeatedly makes
brief stops on the
crystallite walls
Diffusion rate of a dye , decides its
speed of exhaustion
20. Reactive dyes… Diffusion rate: Influencing parameters
So, speed of diffusion;
Speed of exhaustion
Levelness of dyeing
Fixation
Fastness properties
21. Reactive dyes… Diffusion rate: Influencing parameters
Fiber type;
Cellulose Viscose Modal
Such a large dye molecule can not diffuse into the
highly oriented and tightly packed crystallites.
Dyeing therefore proceeds at the outer walls .
Viscose is still stiff at 40-50⁰C, while at higher
temperatures (60-80⁰C ) the fibres mobility allows
the fibre bundle open.
Crystalline
regions
22. Reactive dyes… Diffusion rate: Influencing parameters
When cotton is mercerized;
Fiber induces a higher orientation of crystallites, this should reduce the diffusion
rate but;
A large portion of of intermicellar spaces of the cotton is dissolved and extracted
by alkaline.
Large molecules can be penetrated more easily to the empty spaces so;
Mercerized cotton swells dye more than non-mercerized
Diffusion speed of a dye is much higher (Despite high orientation)
Higher speed of exhaustion
Stronger shade
Mercerized cotton
Raw cotton
23. Reactive dyes… Diffusion rate: Influencing parameters
Temperature;
Temperature Diffusion rate Temperature has by far the greatest
effect on diffusion
So greatest effect on;
Migration rate
Washing-off
Levelness
24. Reactive dyes… Diffusion rate: Influencing parameters
Size and shape of dye molecule;
Molecule size Diffusion rate
Larger and bulkier dye molecules have
a much slower rate of diffusion than
smaller ones
25. Reactive dyes… Diffusion rate: Influencing parameters
Size and shape of dye molecule;
Reactive Blue 15 (Turquoise)
Poor;
Diffusion
Levelling
Washing-off properties
Phthalocyanine
Chromophore tents to
be square and very
bulk in the structure.
Reactive Red 198
MCT/VS
Bifunctional Reactive Dye
>
Diffusion rate:
Reactive Red 198 > Reactive Blue 15
26. Reactive dyes… Diffusion rate: Influencing parameters
Substantivity;
It promotes adsorption equilibrium but impairs diffusion speed.
High subsantivity dyes while exhausting more completely from the dye bath, diffuse,
migrate and level more slowly.
e.g.; Everzol Yellow LX
27. Reactive dyes… Diffusion rate: Influencing parameters
Electrolyte concentration;
Diffusion rate
Electrolyte Conc. Subsantivity
There is a small exception to this rule;
At very low electrolytes concentration adding a
trace of electrolytes to the dye bath helps to
improve diffusion.
This exception is rarely encountered in real-life
dyeing operation.
29. Reactive dyes… Fixation
Alkali is necessary for;
the dyestuff reaction with the fiber (heterocyclic type)
formulation of reactive site and reaction of dyestuff with the cellulosic
fiber (vinylsulfone type)
Increasing alkali
………………………………
Decreasing reactivity
Soda ash
Soda ash/Caustic soda
31. Reactive dyes…
Fixation; Dye chemical structure
monofunctional
Chromophore Bridging
Reactive group
Functional groups ;
providing water solubility
RG
Chromophore Bridging RG RG
conjugated
bifunctional
Chromophore Bridging RG
Bridging
RG
isolated
bifunctional
32. Reactive dyes…
Fixation; Dye chemical structure
Reactive group chemistry;
Cl
•Low reactivity
•Sensitive to acid
•Stable to alkaline
•May generate AOX
N
N
N
rest
Monochlortriazin (MCT)
N
N
N
F
rest
Monofluortriazine (MFT)
N
N
F
F
•High reactivity
•Stable to acid and alkaline
•Splitting with peroxide and light
•AOX free
Cl
N
Cl
•High reactivity
•Sensitive to acid
•Not hydrolysable AOX
Dichlorchinoxaline (DCC)
N
Cl
•Medium reactivity
•Stable to acid
•Sensitive to alkaline
•Dischargeable, stripping is possible
•AOX free
Vinyl sulfone (VS)
SO2-CH=CH2
Chromophore
Bridge
Difluorochlorpyrimidine (FCP)
•Medium to high reactivity
•Sensitive to acid
•Stable alkali to alkaline
•AOX free
Increasing Reactivity
36. Reactive dyes… Fixation
Dye-fiber reaction:
1. Nucleophilic substitution (MCT, FT, DFCT, DFP, DCQ, DCT)
A mobile halogen atom in the reactive group is substituted by the ionized nucleophilic
group of the cellulose.
Reactive Red 1
37. Reactive dyes… Fixation
Dye-fiber reaction:
2. Nucleophilic addition
Reactive Blue 19
A proton and the ionized group of cellulose are added the active group of dye.
In this example there is no bridging group
The dyes react with cellulose by addition to
sulfur oxgen doble bond.
38. Reactive dyes… Fixation; influencing parameters
Chromophore
Reactivity of reactive groups
The more unstable the leaving group, the more reactive dye
pH of the dyebath
With every increase bye one unit of the pH, the concentration of ionized nucleophilic
groups on cellulose increase, so the speed of reaction increase
Temperature of the dyebath
Substantivity of the dye
The reaction speed increasing as temperature rises and substantivity
39. Reactive dyes… Fixation
Dye-fiber reaction:
Competitive reaction results; Inactivation of the reactive groups
OH¯
N
N
N
Cl
Cl
N
N
N
OH
OH
+
Dye-SO2- CH=CH3 + OH¯ Dye-SO2- CH=CH2CH2OH
40. Reactive dyes… Fixation
Bireactivity and its consequences;
When considering:
A is a mono reactive dye with fixation of about 60%
B is a bireactive dye which have two reactive groups, each capable of achieving a
fixation of 60%
For B; fixed 84%
hydrolyzed 16%
For A: fixed 60%
hydrolysed 40%
Residue dyestuff (unfixed) in the dyebath
R-R can be either the same (homo-bireactive)
or different (hetero-bireactive)
41. Reactive dyes… Fixation
Bireactivity and its consequences;
Skillful combination of two different reactive groups can ensure elimination of each
group’s spesific fastness weakness.
MCT; stable to alkali
VS; stable to acid By comparison to
monofunctional dyes;
more stable dye/fiber
bond to acid and alkali
a longer shelf life
much better chemical
stability
44. Reactive dyes… Washing
As a general rule of thumb;
The best results are obtained if washing off is carried out;
Substantivity of the dye is as low as possible and diffusion rate as high as possible.
-at high temperatures
-with lowest possible electrolytes conc.
-at higher liquor ratio
to reduce the affinity/substantivity
of dye molecules to fiber
45. Reactive dyes… Washing
Dye with low affinity and good diffusion;
Most of dye extracted cold, which shows that it was only adhering to the fibre surface.
An insignificant amount of unfixed dye remains inside the fiber matrix.
30⁰C 60 ⁰C 98 ⁰C 80 ⁰C 60 ⁰C 30 ⁰C
47. Reactive dyes… Fastness of reactive dyes
Reactive
anchor
Fiber
Wash Fastness
Problems may result from;
1. uncomplate washed off hydrolyzed dyestuff
2. washing conditions which destroy the Chromophore e.g. washing
detergents with bleaching agents
3. conditions which split the dyestuff-fibre bond
Chromophore
Light Fastness
Highly dependent on chromophore
48. Reactive dyes… Fastness of reactive dyes
Reactive
anchor
Fiber
Bleaching Fastness
1. Strong dependent on chromophor
2. Chromophore class is important with pattern on substituent adjacent to the azo
group
3. Even similar elements in the chemical structure big differences in chlorinated and
bleaching fastness
Chromophore
Oxidation agent
49. Reactive dyes… Fastness of reactive dyes
Rubbing Fastness
Material
Construction of material (knitted, textured..)
Dye (molecule size, chemistry…)
Dyeing method
Washing
Finishing
Wet/dry rubbing
50. Reactive dyes… Fastness of reactive dyes
Cotton;
Raw material
Cotton;
Dyeing reactive dyes, than wet rubbing
51. Reactive dyes… Fastness of reactive dyes
Viscose;
Raw material
Viscose;
Dyeing reactive dyes, than wet rubbing
52. Reactive dyes… Hints
The molecules of most colored organic compounds
contain two parts:
i) An aromatic ring such as benzene, naphthalene or
anthrhracene
ii) Conjuge double bond system containing unsaturated
groups
The intensity of color can be increased in a dye molecule
by addition of substituents;
53. Reactive dyes… Hints
For Printers…
Pint-paste is should be stable several days without any noticeable inactivation (hydrolysis)
of the reactive dye. MCT reactive groups are suitable with;
Hydrolyze slowly at room temperature
Fix rapidly under the usual steaming conditions.
For Viscose…
MCT is a good choice when dyeing viscose by the exhaust method at 80°C .
The higher temperature reduces the risk of poor levelness because:
The swollen viscose is more accessible to the dyebath than at lower temperatures
and the dye more evenly distributed in the material.
The levelling effect of dye diffusion is more effective at high temperatures.
54. Reactive dyes… Hints
For Cold Pad-Batch dyers…
Prefer dyes that are;
completely fixed at room temperature at (pH: 11.5-12.5)
To be resistant to hydrolyze
these conditions are met for example by VS, MFT, DFP or DFCP bireactive dyes
which combining two reactive groups of similar, medium reactivity.