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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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Dyeing with Aniline Black
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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Dyeing with Aniline Black
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
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