Classification &

Identification of Dyes

by

K.PrasenjitJr. Quality Assurance Officer

Textiles CommitteeMumbai.

CLASSIFICATION OF TEXTILES FOR DYEING TEXTILES

Cellulosic•Cotton•Linen•Jute•Hemp•Ramie•Viscose rayon•Cupra - rayon

Protein•Wool•Silk

Synthetic •Polyester •Polyamides•Polyacrylonitrile•Polyurethane•Polyolefin•Cellulose Acetate•Aramid

Colours are sensory perceptions Produced to the eyes when light was reflected from an object .

There are three primary colours viz.RED,BLUE,GREEN

Different shades can be prepared by additive or subtractive mixing of these primary colours .

When all the three primary colours mixed together white colour is obtained .

Colourants of the textiles materials may be classified as either as dyes or pigment.

The term dye and pigment , almost interchangeable in common use have different meaning in colouraion of textiles .

DYES

A dye is substance which at least during stage of its application has inherent affinity for the textile material. Dyes are soluble in the dyeing medium during or at least in some stage of the dyeing process.

Dyes can diffuse into fibres and interacts with the polymer structure of the fibre.

All textile dyes are organic chemical sythesised from coal tar chemicals.

PIGMENTSA pigment is a substance used to impart colour and which does not have inherent affinity for the textile material.

Pigments simply bonded to the surface of the fibre , fabric or yarn by other chemical agents.Pigments can be either organic or inorganic substance.

CLASIFICATION OF DYESTUFF

COLOURING MATTER

Synthetic Dyes Natural Dyes Pigments O.B.A.

Ready-made Dyes Ingrain Dyes

Water Soluble

Water Insoluble

•Sulphur•Disperse•Vat

Vat Azoic Mineral

Phthalo-cyanine

•Azoic•Mineral•Oxidation

•Direct•Basic•Acid•Reactive

Dye Classes by method of application

Eight major dye classes are commonly used in textiles according to method of application .

The five classes used mainly on cellulose fibre are Direct dyes, Sulphur dyes, Azoic dyes, Reactive dyes and Vat dyes .

The three classes of dyes used mainly for protein fibres and synthetic fibres are Acid dyes, Basic dyes and Disperse dyes .

All of them are sythesised from coal tar.

Direct dyes:

Are named so because they have natural affinity for the cellulose and can be applied directly without auxiliary chemicals.

In practice ,the dyeing rate and colour yield can be greatly improved by adding inorganic salts such as sodium chloride or sodium sulphate to the dye bath.

The greatest advantage of direct dyes is simplicity of its application .

The greatest limitation of direct dyes is that their poor wash fastness.

Wash fastness of direct dyes can be improved by resin treatment of dyed or various after treatments.

Sulphur dyes

Are complex organic compounds sythesised by heating simple amines or phenolic compounds in the presence of sulphur.

Sulphur dyes exist as a pigment form , which does not have affinity for cellulose . They are converted to a water soluble form having affinity for cellulose by treatment with a reducing agent under alkaline conditions. After application to the fibre sulphur dyes must be oxidized back to their pigment form .

The greatest advantage of sulphur dyes is relatively low cost.

The biggest limitation of sulphur dyes is that they are not bright enough in colour for many use.

Azoic dyes

Are pigments that are sythesised inside the fibre by coupling of two component neither of which is dye itself(insitu dyeing).

The two components are an aromatic diazonium salt and an aromatic hydroxy compounds often a naphthol. Because of the use naphthol as a component in the reaction , this class is some time called as naphthol dyes.

Although the coloured material produced in azoic dyeing is pigment , the azoic are classified as dye because the naphthol component has affinity for the cellulose and is applied like a dye before the azo component is added.

The greatest advantages of azoic dyes is that they provide an economical way to obtain certain shade , especially red .

The greatest limitation of azoic dyes is that they sometimes posses fastness to crocking and containing banned amines .

Reactive dyes

Are relatively new class of dye , which have been developed in

the 1950s

As the name implies the reactive dyes chemically reacts with

the fibre forming covalent bonds between the dye and fibre

since the covalent bonds between the dye and fibre are strong ,

reactive dyes have excellent wash fastness property.

Outstanding fastness is greatest advantage of reactive dyes .

Vat dyes

Are like sulphur dyes in that they are pigments which must be

reduced and oxidized during application.

They are named so because of dyeing carried out in wooden

vats .

Vat dyes have outstanding wash fastness and light fastness as

a class (exception indigo vat dyes )

The biggest disadvantage of vat dyes is their relatively high

cost.

Acid dyes

Are so called because they contain acidic group in their structure .

The acidic groups reacts with basic groups in protein and polyamide fibres forming organic salts .

Individual acid dyes vary greatly in properties and

compatibility.

Basic dyes

Are sometimes called cationic dyes because the chromophore in basic dye molecule contain positive charge.

These basic or cationic group react with acidic groups in acrylic ,cationic dyeable polyester, cationic dyeable nylon or occasionally protein fibres .

The salt linkage formed are similar to those formed between acid dyes and fibre containing basic groups.

A limitations of basic dyes is that their fastness to light is sometimes not satisfactory especially on protein fibres.

Disperse dyes

Are used mostly for polyester , nylon and cellulose acetate although they will dye some other fibres also .

The name disperse dye comes from the fact these dyes are almost insoluble in water and have to be dispersed in water to make the dye bath.

Disperse dyes were developed when cellulose acetate was first marketed.

Disperse dyes are the only acceptable dye class for acetate and unmodified polymer.

IDENTIFICATION OF CLASS OF DYES ON CELLULOSIC FIBRES:

(Source :IS: 4472 – (PART :I): 1967

Preliminary Test:

Group: I

Specimen +1.50%DMF

2.Conc .DMF3.Glacial AcOH+ETOH

No Stripping / Partial Stripping

Reactive and Ingrain Dyes (except azoic )may be present

Specimen +1% NH4OH

Bleads of Dye ,Solution distinctly coloured

Colour solution +Bleached Cotton +NaCl

Colour solution + 10%AcOH +Wool piece

White Cotton is approx. Dyed to original Shade

Wool piece Dyed

Direct dye may be present Acid dye may be present (If direct dye and basic dyes

are absent)

Specimen +1% NH4OHGroup II

1.

Coloured Solution + Mordant Cotton

Mordant Cotton Dyed

Basic dye may present

Note : MORDANT COTTON - cotton is mordanted with tannic acid

Specimen +Glacial AcOH H2O 2.

Dye Strips

Test for Direct dye if it is +ve

Direct dye after treated with resin

Specimen +1 % HCL 3.

Group III

Specimen +Na2 S2O4+ 44% Na OH

Dyes decolourises or change in shade

Oxidation (with H2O2 / AIR )

Group III Present Group IV Present

Coloured Solution +NaCl +Bleached Cotton

Place the test specimen +White cotton on filter paper and reoxidize dye

White cotton is redyed and restore to original shade

Specimen +H2O + Na2 CO3 +Na2SO4

1.Test for Sulphur dyes

Sulphur dye may be present

Extract + H2O

Spot the Filter Paper with 10 % OH

Spot turns red

Specimen +H2SO4+ Shake Extract the dye

2.Test for Oxidation Black (Aniline Black)

Oxidation Black (Aniline Black) may be present

Filter

Specimen Decolourises

Original Colour restored on oxidation

Vat dye may be present

Specimen +Formosul –G + 44% NaOH

2. Test for Vat Dyes

Formosul – G : 20 gm SODIUM SULPHOXYLATE FORMALDEHYDE + 75 ML HOT WATER + DIL WITH COLD WATER +50 GM MONO OR DIETHYLENE GLYCOL

Hot : Orange yellowCold :Greenish yellow

Specimen ash in porcelain dish + flux Fused

Group IV1.Direct dye after treated with chromium salt

Direct dye after treated with chromium salt

Blue colour

Ash + Conc. HNO3

Group IV2.Direct dye after treated with copper salt

Direct dye after treated with Copper salt

Blue Precipitate

Specimen + 5% H2 SO4 cool

Dropwise add 1%cabriole solution

Group IV3. Direct dye after treated with Formaldehyde

Direct dye after treated with Formaldehyde

Specimen + 2.3ml Pyridine

Repeat

Group IV4.Test for azoic dyes / diazotised dyes and developed dyes

Azoic dyes may be present

Specimen bleads and continuous to do so

Specimen does not bleads

Diazotised and developed dyes may be present

Confirmatory Test:Direct dyes:1. Specimen +5%NaOH

Mercerized Cotton + NaCl

10min.

Dye on the mercerized cotton not strip by 1% NH4OH

Direct dye is confirmed

Specimen + cold Ethlylerndiamine Shake

Colour Extract + H2O + cotton piece + NaCl 80 0c Cotton stained evenly and stain not

removed by 1% NH4OH

Direct dye is confirmed

2.

2.Basic Dye : Specimen + 5%NaOH 5%NaCl

Extract Dye

Extract +Undyed wool

Extract +10%AcOH +

Tannin Reagent

Extract +10%AcOH +Ferric chloride

Dye taken up by Wool Coloured ppt. Black ppt.

Basic Dye Confirmed

3.Sulphur dyes:

Specimen + Stannous chloride soln. lead acetate paper

Brown stain on lead acetate paper

Sulphur Dye confirmed

4.Vat dyes

Specimen Decolourises

Vat dye is confirmed

Specimen +Ethylene diamine + glucose

5.Azoic dyes: Specimen +Ethylenediamine

Extract + Na2 S2O4 Extract +H2O

Decolourisation Liquid becomes turbid & the flakes of coloured pigment settled down on standing

Azoic Dyes confirmed

Extract dye

IDENTIFICATION OF CLASS OFDYES ON PROTEIN FIBRES: (Source :IS: 4472 – (PART :II): 1967

GROUP :I Specimen +1. 50%DMF2. Conc .DMF3. Glacial AcOH+ETOH

No Stripping / Partial Stipping

Reactive and Ingrain Dyes (except azoic )

may be present

GROUP:II

Specimen +Glacial AcOH + H2O

Coloured Solution

Basic dye may present

GROUP:III Specimen +1% NH4OH

Bleeds of Dye ,Solution distinctly coloured

Colour solution +Bleached Cotton +NaCl cool

White Cotton is approx. Dyed to original Shade

Colour solution + 10%AcOH +Wool piece

Acid dye may be present(If direct dye and basic dyes are absent)

Wool piece Dyed

GROUP:IV

Test for presence of chromium / cobalt

Metal Complex / Mordant dyes may be present

Specimen ash in porcelain dish + Flux Fused

1.

SPECIMEN +1% NH4OH COOL +HCL

EXTRACT WITH ETHER

ETHER IS COLOURED

METAL COMPLEX DYE MAY BE PRESENT

MORDANT DYE (CHROME )

MAY BE PRESENT

ETHER IS NOT COLOURED

Group:V

 Specimen + 10% Na OH

to dissolve 

Na2 S2O4+NaCl +Bleached Cotton cool

Oxidised with NaNO3+ AcOH

Cotton is dyed Cotton is not dyed

Azoic dye is presentVat dye is present