Aniline Black & Mineral Khaki

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ANILINE BLACK DYEING


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INTRODUCTION

For jet black colour with direct, reactive, sulphur, vat and other classes of

dyestuff requires large amount of dyestuff

For example: whereas 23% of blue. Green or brown vat dye produce

deep dyeings, a jet black is obtained by using 8 to 10% of black vat dye If lower percentage of dye is used, a grey shade will be produced

For perfect shade, the cost will increase

For direct dye the cost would be not so high

The colour fastness to washing would be poor

Not suitable for certain applications like umbrella cloth


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Black dye from sulphur can be used

But tendering occurs due to the formation of sulphuric acid

A large amount of sulphur dye should be used to get the shade

A class of colour can be successfully used for producing jet black shades inthe cotton materials

Economical

Extremely fast to water and wet treatments

Known as ANILINE BLACK

Also known as oxidation colours


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Aniline black is produced by oxidation of aromatic amines inside the fibre

at elevated temperature in acidic medium

This class of dye is thus known as oxidation colours

So, aniline black is the oxidation product of aniline


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Method of Dyeing with Aniline Black

Impregnation of the textile material with a solution containing1. Soluble salt of aniline

2. An oxidizing agent

3. An acid liberating acid and a catalyst

Drying the textile material with hot air

Chroming treatment (with a dichromate solution) to get an

ungreenable black shade

Ageing or steaming the textile material


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Dyeing with Aniline Black

A solution is produced containing aniline and HCl + aniline oil + oxidizing agent(sodium chlorate) Aniline is not soluble in water

Aniline hydrochloride is soluble in water

Aniline oil is added so that no free acid is present in the solution

The free acid will liberate oxygen with sodium chlorate and prematureoxidation of aniline will take place

Acid is needed for activating sodium chlorate during the ageing or steamingstep

A deep black is produced after ageing, but the black shade produced is notpermanent

On reduction it will turn into bottle green. It is called greenable aniline black

A subsequent treatment with dichromate solution under slightly acidiccondition (called chroming) produces the final oxidation product, theungreenable aniline black


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A pad liquor may be prepared as followSolution A

Aniline salt 80 Kg

Aniline oil 5 Kg

Cold water 200 Litres

Tragacanth thickening 50 Kg

Solution B

Pottasium ferrocyanide 50 Kg

Water 200 Litres

Solution C

Sodium chlorate 30 Kg

Water 200 Litres

335 Kg

250 Kg

230 Kg


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Solution A, B and C are mixed and stirred together and adjusted to pH 7and diluted to 1000 litres

The cloth is padded with the above solution, dried carefully

The development is done by steaming for 20 seconds followed bychroming using sodium dichromate (3 gms/L) at 500C

Rinsing, soaping and washing complete the process

p-aminoazobenzene is added as catalyst during chroming operation


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Use of Chemicals

AnilineAniline is oxidised into black ingrain dyes after being

impregnated inside the textile material

HClHydrochloride acid is used to convert the insoluble aniline into

soluble aniline hydrochloride salt

Aniline oilthis is used so that no excess HCl remains in the bath Tragacanthused to increase the viscosity of the dye solution

Pottasium ferrocyanideused as catalyst for the ageing

Sodium chlorateused as oxidising agent

Pottasium dichromateused for chroming agent

P-aminoazobenzeneused as a catalyst during chroming operation


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MINERAL KHAKI


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Involves a series of chemical reaction to make the process

economical

A large amount of cloth is dyes by this process to makemilitary / police uniform

The insolubility of the metal oxides in water imparts excellent

water fastness


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IronHas two state

Ferrous

Ferric

Oxides of ferrous is known as ferrous oxide Oxides of ferric is known as ferric oxide

ChromiumOxides of chromium is known as chromium oxide


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Ferric oxide and chromium oxide gives the khaki colour

Fe2O3 + Cr2O3 Khaki Shade

(Ferric oxide) (Chromium oxide)

Both the ferric and chromium oxide are insoluble in water and

thus a very good washing fastness property is achieved

Since, these oxides are insoluble in water so they cant be

directly applied


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Soluble salts of iron and chromium is used

For iron both ferrous sulphate and ferric sulphate can be usedbut ferrous is preferable since it is cheaper

For chromium soluble chromium sulphate can be used

But sodium dichromate is used which is cheaper

Sodium dichromate is converted into chromium sulphate bysulphuric acid


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8Na2Cr2O7 + 32H2SO4 + C12H22O11

8Na2SO4 + 8Cr2(SO4)3 43H2O + 12CO2

Cr2(SO4)3 + 6NaOH 2Cr(OH)3 + 3Na2SO4

2Cr(OH)3 Cr2O3


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FeSO4+ 2NaOH Fe(OH)2+ Na2SO4

Fe(OH)2 FeO + H2O

4FeO + O2 2Fe2O3

Fe2O3 + Cr2O3 Khaki shade


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Please Note

Mineral khaki- dyed cloth is often over dyed (topped) with Vat

Khaki

If the entire shade is built up with these vat dyes, the dyeing

process becomes costly

In order to reduce the cost of dyeing, a major part of the

shade is produced by the mineral khaki and topped with a

small percentage of the vat dye


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NATURAL DYEING


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Introduction

Natural dyes are derived from the natural sources

Plant

Mineral

Animal

Problems with the synthetic dyes

Pollution

Ozone gas hole

Greenhouse gasses

Azo dyes

Allergic disperse dyes


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Limitations of natural dyes Availability

Colour yield

Complexity of dyeing process

Reproducibility of shades

Applicable only on wool, natural silk, linen and cotton

Great difficulty in blending dyes

Non-standardized

Inadequate degree of fixation

Inadequate fastness properties

Water pollution by heavy metals


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Advantage of natural dyes

Obtained from renewable sources

No health hazards

Practically no or mild chemical reactions are involved in

there preparation

No disposable problems


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Estimate of Dye Requirements

The consumption of synthetic dye ---- one million tonnes /year

Maximum production of natural dyes ------ 90, 000 tonnes /

year

To produce one million of natural dye about 100 million plantsare required to cultivate

The agricultural land require to cultivate the same would beapprox. 250500 acres which is around 1020% of the areacultivated for grain throughout the world


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Some Important Natural Dyes

One can get colouring matter from almost all vegetable

matter

Only a few of these sources yields colourants which can be

extracted and commercially viable

Similar in the case of animal origin

Basically three colours are require to give any given hue

These type of approach has been worked out for synthetic

dyes

In case of natural dyes, the dyeing procedures are different for

different dyes and they cannot be blended to get the require

colour easily


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BLUE Dyes

In the colour index there are only 3 natural blue dyes

Natural indigo

Sulphonated indigo

Flowers of Japanese Tsuykusa

Indigo is the most widely used and most popular

Indigo is derived from plant

The production of natural indigo has decreased after the

invention of synthetic indigo

The dyeing process of natural indigo is same as that of the

synthetic indigo

It comes under the classification of vat dyes


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Yellow Dyes

Yellow dye is the most common in natural dye

In the colour index there is a list of 28 yellow dyes

Some of the important yellow dyes are

Barberry

Tesu flower

Kamala

Black oak

Turmeric


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Fastness Properties

Poor wash fastness of natural dye is due to

Weak dye-fibre bond between the natural dye and thefibre

Change in the hue due to dye-metal complex duringwashing

Ionisation of the natural dyes during alkaline washing

Since most of the natural dyes have hydroxyl groupswhich get ionised under alkaline condition and changetheir colour


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Light fastness is poor

Post treatment with a metal salt can result in an

improvement in the light fastness of some natural dyes

However, a post treatment with metal salt also results in

change of hue

Aniline Black & Mineral Khaki

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