ENVIRONMENT FRIENDLY DYEING OF COTTON

R.B.CHAVAN

Department of Textile Technology

Indian Institute of Technology

Hauz-khas, New Delhi 110016

E-mail: rbchavan@hotmail.com

PRESENT CONCEPTPOLLUTERS MUST PAY

CRADLE TO GRAVE WOMB TO TOMB NOT ONLY FINAL PRODUCT BE ECO FRIENDLY RAW MATERIALS, PRODUCTION PROCESSES,

PACKAGING, ECO FRENDLY EVEN AFTER DIPOSAL MEET EMS 14000 AND SAS 1800 STANDARDS ECO FRIENDLY PRODUCTS INDENTIFIED BY ECO

LABLES• GREEN MINDED CONSUMER PREFER ECO PRODUCTS

EVEN AT HIGH COST

ENVIRONMENT FRIENDLY CHEMICAL PROCESSING

Input / output analysis of Textile chemical Processes

Textile Auxiliaries

Dyes

Base chemicals(e.g. acid, Alkali, sodium chloride)

Textile EnergyNatural Fibres; 10-20 MJ/kgChemical Fibres: 5-50 MJ/kg

Water60-360 l/kg textile

Polluted Air

Water Effluent

WasteSewage sludge:

60-70 g/kg textile

Wet Processing (pre-treatment,

dyeing, printing, finishing.)

ENVIRONMENT FRIENDLY DYEING

• DYE CLASSES FOR CELLULOSIC• REACTIVE• VAT• DIRECT• AZOIC• SULPHUR

• EFFLUENT• RESIDUAL DYE• SALT• ALKALI• REDUCING AGENT• OXIDIZING AGENT• DETERGENT

REACTIVE DYES

ENVIRONMENTAL PROBLEM

• COLOUR IN EFFLUENT

• SALT IN EFFLUENT

Typical dye fixation on different fibres

ALTERNATIVE METHODS FOR LOW COLOUR IN EFFLUENT

• DYEING AT LOW LIQUOR RATIO

• CAREFUL FOLLOW UP OF DYESTUFF MANUFACTURERS RECOMMENDATION FOR

DYEING CONDITIONS FOR OPTIMUM DYE FIXATION

• RIGHT FIRST TIME APPROACH TO AVOID

• SHADING ADDITIONS

• STRIPPING AND REDYEING OF OFF SHADES

• USE OF HIGH FIXATION BIFUNCTIONAL REACTIVE DYES

BIFUNCTIONAL REACTIVE DYES

HOMO BIFUNCTIONAL REACTIVE DYES• ORIGINALLY PROMOTED BY ICI (NOW ZENECA) AS PROCION

SUPRA DYES FOR PRINTING AND THEN PROCION H-E DYES FOR DYEING (HOMO BIFUNCTIONAL MONO CHLORO TRIAZYNYL)

HETRO BICUNTIONAL REACTIVE DYES• CHARACTERIZED BY THE PRESENCE OF TWO REACTIVE

GROUPS OF DIFFERENT REACTIVITIES• CAN BE APPLIED OVER A TEMPERATURE RANGE OF 60-800 c• BETTER SHADE REPRODUCIBILITY EVEN WITH

TEMPERATURE VARIATION• AVAILABLE FROM MAJOR DYESTUFF MANUFACTURERES

BIFUNCTIONAL REACTIVE DYES

LOW SALT REACTIVE DYES

SALT REQUIREMENTCONVENTIONAL REACTIVE DYES 60-80 g/lLOW SALT REACTIVE DYES 20 g/l

FEATURES (CIBACRON LS)• BIFUNCTIONAL REACTIVE DYES• TWO CHROMOPHORES CONTRIBUTE HIGH

AFFINITY AND HIGH COLOUR STRENGTH• HIGH FIXATION• STABLE DYE-FIBRE BOND

EFFECT OF SALT ON ENVIRONMENT

• EFFLUENT TREATMENT REMOVES ONLY SMALL QUANTITY OF SALT

• MAJOR QUANTITY OF SALT REMAINS IN WATER• RIVERS AND LAKES GET POLLUTED WITH

EFFLUENT CONTAINING HIGH SALT CONCENTRATION

• FRESH WATER ORGANISMS CAN SUFFER TOXIC EFFECTS

• IN REGIONS WITH SCARCE FRESH WATER RESOURCES SUCH WASTE WATER HAS TO BE USED FOR LAND IRRIGATION

• REDUCTION IN LAND FERTILITY AND ULTIMATELY HAVE TO BE ABONDONED

APPROACHES TO SOLVE PROBLEMS OF SALT LOAD

• DYEING AT LOWEST POSSIBLE LIQUOR RATIO

• USING DYE CLASSES OTHER THAN REACTIVE SUCH AS VAT REQUIRING LOW SALT CONCENTRATION FOR DYEING

• USING REACTIVE DYES GIVING HIGH EXHAUSTION AND FIXATION AT LOW SALT CONCENTRATION

GENERAL STRUCTURE OF LOW SALT REACTIVE DYES

CHROMOPH-ORE

CHROMOPHORE

BRID-GE

REACT-IVE

GROUP

REACT-IVE

GROUP

ADVANTAGES OF HIGH DYE FIXATION

Conventional dyes60 % fixation

Cibacron LS (bireactive)

80 % fixation

200 gm into the waste water

800 gm on the fibre

1 kg dye

+ 33% %

- 50% %

1 kg dye

600 gm on the fibre

400 gm into the waste water

ECOLOGICAL BENEFITS OF LOW SALT REACTIVE DYES

Property Benefit

• High fixation rate Low dye concentration in effluent

• Low electrolyte concentration Low salt effluent and cost/time saving

• Good wash off Less water and energyLow BOD values

• Halogen-free chromophores No AOX in effluent• Free from carcinogenic amines No health risk to dyes

No risk of ban

• High repeatability of dyeing Less shading and stripping

ECO FRIENDLY REDUCING AGENTS FOR VAT DYES

• SODIUM HYDROSULPHITE IS UNIVERSALLY USED

• DURING DYEING CONVERSION TO SULPHITE AND SULPHATE

• SULPHITE IS TOXIC TO FISH AND BACTERIA

• SULPHATE IS NON-TOXIC TO FISH AND BACTERIA IT MAY CAUSE CORROSION OF CONCRETE PIPES

ALTERNATE REDUCING SYSTEMS

HYDROXY ACETONE

• CAN TOTALLY REPLACE HYDROSULPHITE

• BIO-COMPATIBLE

• GIVE 20% HIGHER COLOUR YIELD WITH

INDIGO

• EXPENSIVE

• NOT READILY AVAILABLE

• YET TO USE ON COMMERCIAL SCALE

ELECTROCHEMICAL REDUCTION

• DIRECT REDUCTION OF DYE BY CONTACT BETWEEN DYE DISPERSION AND ELECTRODE

• ADDITION OF SMALL QUANTITY OF HYDROSULPHITE IS ESSENTIAL TO MAINTAIN DYE IN REDUCED STATE

• METHOD PRODUCES LIGHTER SHAED COMPARED TO HYDRO SULPHITE

IRON COMPLEXES

• USE OF Fe(OH)2 AS REDUCING AGENT

• COPPERAS METHOD KNOWN FOR LONG FOR DYEING OF

INDIGO

• USE OF FeSO4 AND Ca(OH)2

• Fe(OH)2 HAS VERY LOW WATER SOLUBILITY

• PRECIPITATES IN DYEBATHN NO REPRODUCIBLE RESULTS

• NOT SUITABLE FOR VAT DYES OTHER THAN INDIGO

• USE OF GLUCONIC ACID IS SUGGESTED IN GERMAN

LITERATURE FOR ENHANCING SOLUBILITY OF Fe(OH)2

• GLUCONIC ACID IS EXPENSIVE

STUDY AT IIT DELHIR.B.chavan, J.N.chakraborty

• USE OF CITRIC ACID, TARTARIC ACID AND TRIETHANOL AMINE TO ENHANCE SOLUBILITY OF Fe(OH)2

• REDUCTION POTENTIAL HIGHER THAN HYDRO SYLPHITE

• POSSIBLE TO REDUCE VAT DYES AT ROOM TEMPERATURE

• DYEING AT ROOM TEMPERATURE• COLOUR YIELD AND FASTNESS PROPERTIES

COMPARABLE TO HYDROSULPHITE• TOTAL REPLACEMENT OF HYDROSULPHITE• ENVIRONMENT FRIENDLY AND ENERGY SAVING

SYSTEM

SULPHUR DYES

• Na2S IS COMMONLY USED REDUCING AGENT

• NO ODOUR NUISANCE ABOVE pH 9• LIBERATION OF H2S UNDER ACID

CONDITIONS• FOUL SMELL OF ROTTEN EGGS• TOXIC WHEN INHALED• ODOUR THRESHOLD LIMIT 10 ppm• TOXIC TO FISH

OXIDATION

• USE OF HALOGENATED COMPOUNDS LIKE BROMATE, IODATE PRODUCE ORGANIC HALOGEN COMPOUNDS RESPONSIBLE FOR ADSORBABLE ORGANIC HALOGEN (AOX)

• AOX IS TOXIC TO AQUATIC LIFE• DICHROMATE IS MORE RISKY, HEALTH

HAZARDS

SAFE OXIDIZING AGENT IS H2O2

Na2S REPLACEMENT

β – MERCAPTOETHANOL MARKETED BY

BASF AS MOLESCAL SF

• LOWER COLOUR YIELD COMPARED TO Na2S

• INCOMPLETE DISSOLUTION OF SOME

SULPHUR DYES

• SUITABLE FOR LIMITED RANGE OF

SULPHUR DYES

• COSTLY

GLUCOSE

• CAN BE USED AS REDUCING AGENT FOR SULPHUR DYES

• GIVES REDUCTION POTENTIAL SUITABLE FOR

REDUCTION OF SULPHUR DYES UNDER ALKALINE CONDITIONS ABOVE 600 c

• CENTURY MILL (MUMBAI) HAS SUCCESSFULLY REPLACED Na2S WITH GLUCOSE ON INDUSTRIAL SCALE

• HYDROL, VISCOUS LIQUID AVAILABLE COMMERCIALLY AT LOW COST

CONCLUSION

• USE OF BIFUNCTIONAL REACTIVE DYES FOR LOW COLOUR IN EFFLUENT

• USE OF LOW SALT REACTIVE DYES FOR REDUCTION OF SALT IN EFFLUENT

• REPLACEMENT OF Na2S WITH GLUCOSE IN SULPHUR DYEINGREPLACEMENT OF HYDROSULPHITE IN VAT DYEING BY

• IRON COMPLEXES

• ELECTROCHEMCAL REDUCTION METHOD