Reactive Chemistry - Murat Şahinli's Blog

Reactive ChemistryTECHNICAL INFORMATION

12.11.2015

Murat ŞAHİNLİ

Cellulose… Cellulose structure

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

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

ShadeFastnessLevelnessSubstantivitySolubilityApplication temperature

FastnessDischargeabilityFixationApplication temperature

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¯ ⁺ NaReduce the repulsion

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

OtherIntermolecular

1.0

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

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

Reactive dyes… Substantivity: Influencing parameters

SubstantivityDye

affinity

Dye conc.

Electrolyteconc.

pHTemperature

Type of fiber

Liquorratio


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

SubstantivityHigh affinity for cellulose (Direct dye)

Low affinity for cellulose (Acid dye)


Electrolyte Concentration;

Anion-anion repulsion Electrolyte conc.

Direct dyes; high affinity, require 5-10 g/lt saltReactive dyes; medium to low affinity, require 40-100 g/lt

Substantivity


pH of dyebath;

Cell-O¯Cell-OH + H2OOH¯

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

78910111213

RS:Cell-O¯ (in the fiber)

OH¯ (in the dyebath)


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


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 at40⁰C than at 80 ⁰C, but in fact it is not.


Liquor ratio;

Liquor ratio Substantivity

Don’t forget that the decrease is also related to :

Dye concentrationDye own affinity

So;

The Liquor ratio increases, the probability of contact between the dye molecules and the fiber surface decreases.


Liquor ratio;

Affinity of the dyeDye concentration (L.R. 10:1=%100)

Dye :C.I. Reactive Red 180Electrolyte :50 g/lt NaClDyeing temperature :40⁰C

Dye concentration :3%Electrolyte :50 g/lt NaClDyeing temperature :40⁰C


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

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


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


So, speed of diffusion;

Speed of exhaustion Levelness of dyeing Fixation Fastness properties


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.

Crystallineregions


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


Temperature;

Temperature Diffusion rate Temperature has by far the greatest effect on diffusion

So greatest effect on;

Migration rate Washing-off Levelness


Size and shape of dye molecule;

Molecule size Diffusion rateLarger and bulkier dye molecules have a much slower rate of diffusion than smaller ones


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


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


Electrolyte concentration;

Diffusion rateElectrolyte 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.

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 cellulosicfiber (vinylsulfone type)

Increasing alkali………………………………Decreasing reactivity

Soda ash

Soda ash/Caustic soda


Then,

What is the meaning of heterocyclic or vinylsulfone…?How is the reactive dyes chemical structure…?

Reactive dyes…Fixation; Dye chemical structure

monofunctionalChromophore Bridging

Reactive group

Functional groups ;providing water solubility

RG

Chromophore Bridging RG RG

conjugated bifunctional

Chromophore Bridging RGBridgingRGisolated bifunctional

Reactive dyes…Fixation; Dye chemical structureReactive 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)

NNF

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


Hot-dyeing dyes Cold-dyeing dyes

Everzol dyes

Reactivity

Substantivity



Everzol Yellow NPN Everzol Red LX


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


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.

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


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


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)


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 tomonofunctional dyes;

more stable dye/fiber bond to acid and alkali

a longer shelf life much better chemical

stability

Reactive dyes… Washing



Easy Wash-Off

Less Effluent

Value-Adding

Fixed dye molecules

Unfixed dye molecules

Chemicals

Washing

Dyed fiber


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


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

Reactive dyes… Fastness of reactive dyes

-N=N-Reactiveanchor Fiber

water & lightperspiration & light

Light Fastness

Bleaching Fastness

Chromophore

ChlorinePeroxide

Wash Fastness

Detergent, heat, water

Heat

Acid Alkali


Reactiveanchor

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


Reactiveanchor

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


Rubbing Fastness

Material

Construction of material (knitted, textured..)

Dye (molecule size, chemistry…)

Dyeing method

Washing

Finishing

Wet/dry rubbing


Cotton;Raw material

Cotton; Dyeing reactive dyes, than wet rubbing


Viscose;Raw material

Viscose; Dyeing reactive dyes, than wet rubbing

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;


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.


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.

Reactive dyes… Exhaust dyeing method

Reactive Chemistry - Murat Şahinli's Blog

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