Aniline black & amp; mineral khaki

Aniline Black Dying

1. ANILINE BLACK DYEING

2. INTRODUCTION For jet black colour with direct, reactive, sulphur , vat and other classes of dyestuff requires large amount of dyestuff For example: whereas 2 – 3% 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

3. 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 in the cotton materials Economical Extremely fast to water and wet treatments Known as “ANILINE BLACK” Also known as “ oxidation colours ”

4. 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

5. Method of Dyeing with Aniline Black Impregnation of the textile material with a solution containing Soluble salt of aniline An oxidizing agent 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

6. 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 premature oxidation of aniline will take place Acid is needed for activating sodium chlorate during the ageing or steaming step A deep black is produced after ageing, but the black shade produced is not permanent On reduction it will turn into bottle green. It is called greenable aniline black A subsequent treatment with dichromate solution under slightly acidic condition (called chroming) produces the final oxidation product, the ungreenable aniline black

7. Dyeing with Aniline Black A pad liquor may be prepared as follow Solution 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

8. Dyeing with Aniline Black Solution A, B and C are mixed and stirred together and adjusted to pH 7 and diluted to 1000 litres The cloth is padded with the above solution, dried carefully The development is done by steaming for 20 seconds followed by chroming using sodium dichromate (3 gms /L) at 50 C Rinsing, soaping and washing complete the process p- aminoazobenzene is added as catalyst during chroming operation

9. Use of Chemicals Aniline – Aniline is oxidised into black ingrain dyes after being impregnated inside the textile material HCl – Hydrochloride acid is used to convert the insoluble aniline into soluble aniline hydrochloride salt Aniline oil – this is used so that no excess HCl remains in the bath Tragacanth – used to increase the viscosity of the dye solution Pottasium ferrocyanide – used as catalyst for the ageing Sodium chlorate – used as oxidising agent Pottasium dichromate – used for chroming agent P- aminoazobenzene – used as a catalyst during chroming operation

10. MINERAL KHAKI

11. Involves a series of chemical reaction to make the process economical A large amount of cloth is dyes by this process to make military / police uniform The insolubility of the metal oxides in water imparts excellent water fastness

12. Iron – Has two state Ferrous Ferric Oxides of ferrous is known as ferrous oxide Oxides of ferric is known as ferric oxide Chromium – Oxides of chromium is known as chromium oxide

13. Ferric oxide and chromium oxide gives the khaki colour Fe 2 O 3 + Cr 2 O 3 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 can’t be directly applied

14. Soluble salts of iron and chromium is used For iron both ferrous sulphate and ferric sulphate can be used but 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 by sulphuric acid

15. So, a liquor is made which contains a mixture of chromium sulphate and ferrous sulphate The cloth is padded with the solution and dried in a hot flue The fabric is then passed through boiling alkali when the corresponding metal hydroxides are precipitated in the fabric This is then aired for the conversion of chromium hydroxide into chromium oxide and ferrous hydroxide into ferric oxide

16. 8Na 2 Cr 2 O 7 + 32H 2 SO 4 + C 12 H 22 O 11 8Na 2 SO 4 + 8Cr 2 (SO 4 ) 3 43H 2 O + 12CO 2 Cr 2 (SO 4 ) 3 + 6NaOH 2Cr(OH) 3 + 3Na 2 SO 4 2Cr(OH) 3 Cr 2 O 3

17. FeSO 4 + 2NaOH Fe(OH) 2 + Na 2 SO 4 Fe(OH) 2 FeO + H 2 O 4FeO + O 2 2Fe 2 O 3 Fe 2 O 3 + Cr 2 O 3 Khaki shade

18. 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

19. NATURAL DYEING

20. 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

21. Potential hazard in chemical production plants Risky process to produce the synthetic dyes As opposed natural dyes are considered to be less hazardous and eco-friendly

22. 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

23. 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

24. 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 plants are required to cultivate The agricultural land require to cultivate the same would be approx. 250 – 500 acres which is around 10 – 20% of the area cultivated for grain throughout the world

25. 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

26. 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

27. RED Dyes In the colour index there is a list of 32 natural dyes The prominent among the red dyes are madder, manjeet , brazil wood, lac dye Lac dye is extracted from the lac i.e from the secretion of the tiny insects and is based on acid dyes. Lac dyes are therfore used for protein fibres like wool and silk Lac dye has a very good light and washing fastness

28. 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

29. Sr. No. Common Name Dye Class 1 Indigo Vat 2 Madder Mordant / Disperse 3 Manjeet Acid / Mordant / Disperse 4 Lac Dye Acid / Mordant 5 Tesu Mordant / Disperse 6 Kamala Mordant / Disperse

30. Fastness Properties Poor wash fastness of natural dye is due to Weak dye- fibre bond between the natural dye and the fibre Change in the hue due to dye-metal complex during washing Ionisation of the natural dyes during alkaline washing Since most of the natural dyes have hydroxyl groups which get ionised under alkaline condition and change their colour

31. Washing fastness of some of the natural dyes can be improved by post treatment with alum or a dye fixing agent resulting in the formation of Dye complex Cross-link between dye and fibre Please note: Tannins being large molecular compounds do not diffuse into the fibre easily Hence dyeings based on tannins show poor rubbing fastness on cotton

32. 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