6. CLASSIFICATION OF FIBRES NATURAL REGENERATED SYNTHETIC Vegetable Animal Cotton Wool Viscose Polyamide-Nylon Jute Silk Polynosic PET – Terylene Ramie Cellulose Acetate Acrylic – Orlon Linen Cashmelon & PP

7. CLASSIFICATION OF DYES Readymade dyes Ingrain dyes Pigment colours Water soluble dyes Water insoluble dyes APPLICATION OF COLORLESS COMPONENTS IN SOLUBLE FORM AND CONVERTING INTO INSOLUBLE COLOURING COMPONENT IN THE FIBRE Direct Vat Azoic colours Vat Acid Sulphur Oxidation colours Azoic Basic Disperse Mineral colours Phthalocyanine Reactive Mineral Optical whitening agents

8. MAIN DYE CLASSES AND THEIR SUITABILITY FOR DIFFERENT FIBRES Dye type (Solubility/ Ionic character) Fibre affinity Dyebath auxiliaris Fastnes properties End-uses Comments Direct Water Soluble (anionic) Cellulosics (cotton, viscose) Dye bath + salt Light poor/good Washing-poor Low Quality Apparel Fabrics/ Matress covers After Treatment Can Improve fastness

9. Acid levelling Water soluble (anionic) Protein fibres (wool, silk) Acid + glaubers salt Light-good/moderate Washing-moderate Carpet yarns, dress goods, Suitings, overcoats, knitting yarns Carpet yarns, dress goods, Suitings, overcoats, knitting yarns The difference between the two types of acid are less evident on nylon compared to wool, Acid dyes have a higher affinity for nylon and better fastness Acid milling Water soluble (anionic) Polyamide fibres (nylon), Wool Neutral/weakly acidic dyebath + levelling agent Light-good Washing-good

10. Vat Insoluble in water (nonionic) Cellulosic (cotton, viscose) Alkali + reducing agent - to produce the anionic LEUCO solubilised form Light-excellent Washing-excellent High quality curtains, furnishing, shirts, towels, sewing threads Expensive. Bright colours often difficult to achieve

11. Reactive Water soluble (anionic) Cellulosics (also protein and polyamide fibres) Applied to cellulosics from a dyebath subsequently made alkaline Light-good/excellent Washing-excellent Curtains, furnishings, apparel fabrics, towelling, sewing threads Excellent shade range. High fastness due to covalent dye/fibre bond

12. Basic Water soluble (anionic) Acrylics (also occasionally protein fibres) Weakly acidic dyebath Light-good/moderate Washing-good Furnishings, apparel fabrics Bright shades, excellent tinctorial strength

13. Disperse Insoluble in water (nonionic) All synthetics Apparel fabrics, bed sheets, carpets Best fastness on polyester, through this substrate is also the most difficult to dye. Good levelling properties

14. DYEING FORMS FIBRE YARN FABRIC GARMENTS

15. FIBRE TO FABRIC STEPS FIBRE YARN GREY FABRIC FINISHED FABRIC PRE-SPINNING SPINNING WEAVING CHEMICAL PROCESSING PRE-SPINNING ROVING SPINNING YARN WEAVING GREY FABRIC CHEMICAL PROCESSING FINISHED FABRIC

17. In this method the dyeing is carried out in small batches. About 500 – 2500 mts. of fabric can be at a time depending on the type of equipment used. The equipments avaliable are designed on three principles: IN THIS METHOD THE DYEING IS CARRIED OUT IN SMALL BATCHES. ABOUT 500 – 2500 MTS. OF FABRIC CAN BE AT A TIME DEPENDING ON THE TYPE OF EQUIPMENT USED. THE EQUIPMENTS AVALIABLE ARE DESIGNED ON THREE PRINCIPLES:

19. SEMI – CONTINUOUS DYEING IN THIS METHOD THE FABRIC IS IMPREGNATED (ABOUT 500-1000 MTS.) WITH THE DYE LIQUOR BY PADDING AND IT IS WOUND ON A ROLLER KNOWN AS BATCH ROLLER, AFTER WINDING CERTAIN LENGTH OF CLOTH ON THE ROLLER THE PROCESS IS DISCONTINUED AND THE SUBSEQUENT LENGTH OF CLOTH ARE IMPREGNATED WITH THE SAME DYE LIQUOR OR OTHER DEPENDING ON THE SHADES REQUIRED. THUS SEVERAL BATCHES OF CLOTH ARE MADE IN THIS WAY, EACH BATCH IS THEN WRAPPED UP WITH POLYETHYLENE SHEET AND STORED FOR 2- 24 HRS., DEPENDING ON THE DYEING CONDITIONS. DURING THIS PERIOD THE FIXATION OF DYE WOULD TAKE PLACE. ALL THE BATCHES ARE THEN SUBJECTED TO WASHING. THIS PARTICULAR METHOD IS MOST SUITABLE FOR DYEING OF COTTON WITH REACTIVE DYE AND IS KNOW AS PAD – BATCH METHOD.

20. CONTINUOUS METHOD IN THIS METHOD OF DYEING, THE FIXATION OR DEVELOPMENT AND THE WASHING OF THE UNFIXED DYE IS CARRIED OUT IN A CONTINUOUS MANNER. THE UNDYED CLOTH FED AT ONE END OF THE M/C. COMES OUT FROM OTHER END IN COMPLETELY DYED AND DRY CONDITION. THE EQUIPMENT AVAILABLE IS KNOWN AS CONTINUOUS DYEING RANGE AND CONSISTS OF PADDING MANGLE FOR THE IMPREGANATION OF CLOTH WITH DYE LIQUOR, HOT FLUE OR FLOAT DRYER FOR THE DRYING OF CLOTH, DYE FIXATION UNIT, OPEN SOAPER FOR THE REMOVAL OF UNFIXED DYE AND DRYING CYLINDER FOR THE FINAL DRYING OF THE DYED CLOTH. ALL THESE EQUIPMENT RUN IN TANDEM AND THEIR SPEEDS ARE SYNCHRINISED. THE CONTINUOUS DYEING RANGE IS MOST ECONOIMICAL WHEN LARGE YARDAGES OF CLOTH ARE TO BE DYED IN A SINGLE SHADE.

21. DYEING OF COTTON AND VISCOSE DIRECT, VAT, SOLUBILISED VAT, SULPHUR, AZOIC, REACTIVE, DIRECT DYES THESE DYESTUFFS ARE WATER SOLUBLE AND A COMPLETE RANGE OF SHADES CAN BE OBTAINED AT A LOW COST OF DYEING. DIRECT DYES HAVE POOR FASTNESS TO WASHING; THEREFORE, THEIR USE IS RESTRICTED TO THE DYEING OF CHEAPER QUALITIES OF FABRICS OR THOSE FABRICS, WHICH ARE RARELY SUBJECTED TO WASHING DURING THEIR USE. THE FASTNESS PROPERTIES COULD BE IMPROVED TO SOME EXTENT BY CHEMICAL AFTER TREATMENTS OF THE DYED FABRIC WITH POTASSIUM DICHROMATE, COPPER SULPHUTE, HCHO, ETC.

22. VAT DYES: AMONG ALL THE CLASSES OF DYESTUFFS, VAT DYES POSSESS EXCELLENT FASTNESS PROPERTIES TO ALL THE AGENCIES. THEREFORE, THE INITIAL BRIGHTNESS I.E. FRESH LOOK AND THE DEPTH OF SHADE IS MAINTAINED THROUGH THE LIFE OF THE GARMENT OR THE FABRIC. VAT DYES ARE WATER INSOLUBLE HOWEVER, CAN BE CONVERTED TO WATER-SOLUBLE FORM BY REDUCTION TREATMENT WITH CAUSTIC SODA AND SODIUM HYDROSULPHITE. THE PROCESS KNOWN AS VATTING AND THE WATER-SOLUBLE FORM OF THE DYE IS KNOWN AS LEUCO COMPOUND. SO DURING THE PROCESS OF DYEING THE DYESTUFFS MUST BE CONVERTED INTO LEUCO FORM, FROM WHICH THE DYEING TAKES PLACES.

23. AFTER THE DYEING OPERATION, THE WATER SOLUBLE LEUCO COMPOUND ON THE FABRIC IS CONVERTED TO PARENT WATER INSOLUBLE DYE BY OXIDATION TREATMENT OF THE FABRIC FOLLOWED BY WASHING AND SOAPING DURING WHICH TRUE SHADE OF THE DYE IS DEVELOPED. AT ONE TIME THE VAT DYES WERE VERY WIDELY USED. BUT AFTER THE DISCOVERY OF REACTIVE DYES, THEIR USE IS RESTRICTED TO THE DYEING OF SPECIAL TYPES OF FABRICS LIKE SUITINGS AND DYEING OF YARN TO GET COLOURED THREAD EFFECTS DURING WEAVING. THESE RESTRICTIONS ARE BECAUSE OF HIGH COST OF DYEING AND ALSO PARTLY DUE TO LACK OF AVAILABILITY OF COMPLETELY RANGE OF SHADES AND BRIGHTNESS AS COMPARED TO REACTIVE DYES.

24. SOLUBILISED VAT DYES THESE ARE WATER-SOLUBLE VAT DYES SO THAT THE PROCESS OF VATTING IS ELIMINATED FOR DUE SOLUBILISATION. AFTER THE DISSOLUTION OF THE DYE IN WATER AND APPLICATION OF THE FABRIC; THE ORIGINAL WATER INSOLUBLE FORM HAS TO BE PRODUCED BY THE OXIDATION TREATMENT OF THE FABRIC WITH SULPHURIC ACID AND SOD. NITRITE OR POTASSIUM DICHROMATE. THE PROPERTIES OF THIS CLASS OF DYES ARE SAME AS THOSE OF VAT DYES.

25. SULPHUR DYES THESE ARE ALSO WATER INSOLUBLE; HENCE DURING DYEING THEY ARE FIRST CONVERTED TO SOLUBLE FORM BY REDUCTION WITH SOD. CARBONATE AND SOD. SULPHIDE FOLLOWED BY SUBSEQUENT OXIDATION TREATMENT TO PRODUCE ORIGINAL WATER INSOLUBLE FORM OF THE FABRIC. ALTHOUGH THE DYES OF THIS CLASS ARE CHEAPER, THEY LACK IN BRIGHTNESS OF SHADE AND LIMITED FASTNESS TO LIGHT AND CHLORINE. ANOTHER DISADVANTAGE IS THAT WHEN THE SULPHUR DYED FABRIC OR GARMENT IS STORED FOR LONGER TIME THERE IS THE DANGER OF FABRIC TENDERING DUE TO LIBERATION OF SULPHURIC ACID FROM THE DYE.

26. AZOIC COLOURS AZOIC COLOURS ARE NOT READY MADE DYESTUFFS, BUT A COLOURED COMPOUND IS PRODUCED ON THE FABRIC ITSELF BY THE REACTION OF TWO COLOURLESS COMPOUNDS. ONE OF THE COMPOUNDS IS KNOWN AS NAPHTHOL OR COUPLING COMPONENT AND THE SECOND DIAZOTISED AMINE OR DIAZO COMPONENT. THEY REACT WITH EACH OTHER TO PRODUCE WATER INSOLUBLE DYE. THUS THE METHOD OF APPLICATION CONSISTS OF TREATMENT OF THE CLOTH FIRST WITH NAPHTHOL FOLLOWED BY TREATMENT WITH DIAZOTISED AMINE. AFTER THE DEVELOPMENT OF SHADE THE FABRIC MUST BE THOROUGHLY SOAPED TO REMOVE THE LOOSELY HELD PIGMENT.

27. THE AZOIC DYES PRODUCE VERY BRIGHT SHADES. SOME OF THE BRIGHT RED, ORANGE, YELLOW, NAVY BLUE AND BLACK SHADES COULD BE OBTAINED AT REASONABLE COST. THE LIMITATION OF THESE CLASSES OF DYES IS UNSATISFACTORY RUBBING FASTNESS PARTICULARLY WHEN THE SOAPING OF THE FABRIC AFTER DYEING IS NOT THOROUGH. SECONDLY, THESE DYES ARE SUITABLE FOR DYEING ONLY DEEP SHADES AS IN LIGHTER SHADES THE LIGHT FASTNESS IS FATHER POOR.

28. REACTIVE DYES THIS IS THE LATEST CLASS OF DYES INVENTED IN 1956 BY ICI AND SINCE THEN CONSIDERABLE DEVELOPMENT TOOK PLACE AND NOW A DAYS MOST OF THE DYE MANUFACTURERS ARE MANUFACTURIG THESE DYES BASED ON ONE REACTIVE SYSTEM OR THE OTHER. THESE DYES ARE CHARACTERIZED BY THE FORMATION OF CHEMICAL LINKAGE BETWEEN DYE AND FIBRE AND HENCE THESE KNOW AS REACTIVE DYES. BECAUSE OF THIS LINKAGE THIS DYES PRODUCE DYEING OF EXCELLENT WASHING FASTNESS. IN ADDITION A COMPLETE RANGE OF SHADES WITH EXCELLENT BRIGHTNESS COULD BE OBTAINED AT REASONABLE COST AND THEREFORE, THIS CLASS OF DYES HAS BECOME VERY POPULAR.

29. THE DYEING PROCESS IS NORMALLY CARRIED OUT IN THREE STAGE: APPLICATION OF THE DYE ON FABRIC, CHEMICAL REACTION OF DYES AND FIBRE UNDER ALKALINE CONDITIONS AND THE SOAPING TO REMOVE UNREACTED DYE FROM THE FABRIC. THE DRAW BACK OF THIS CLASS OF DYES IS POOR FASTNESS TO CHLORINE AND THEREFORE, GARMENT DYED WITH REACTIVE DYES SHOULD NOT BE SUBJECTED TO LAUNDRY WASH WHERE CHLORINE IS USED BLEACHING.

30. DYEING OF WOOL AND SILK DIRECT, ACID, BASIC, METAL COMPLEX AND REACTIVE DYES. WOOL AND SILK CONTAIN BOTH ACID (COOH) AND BASIC (NH2 AND CONH) GROUPS AND THEY RETAIN THE DYE MOLECULES BY MEANS OF ELECTROSTATIC ATTRACTION. THE FASTNESS PROPERTIES PARTICULARLY THE WASHING FASTNESS DEPEND ON THE STRENGTH OF THE ATTRACTIVE FORCES BETWEEN THE DYES AND THE FIBRE. THE REACTIVE DYES FORM CHEMICAL LINKAGE WITH THE FIBRE IN ADDITION TO THE ELECTROSTATIC ATTRACTION. EXCEPT BASIC DYES, ALL CLASSES OF DYESTUFFS SHOW GOOD WASHING FASTNESS.

31. THE FASTNESS TO OTHER AGENCIES WOULD VARY WITH THE INDIVIDUAL MEMBER OF EACH CLASS. BASIC DYES THOUGH PRODUCE VERY BRIGHT SHADES LACK IN WASHING AND LIGHT FASTNESS PROPERTIES. THE GENERAL METHOD OF APPLICATION OF THESE CLASSES OF DYES CONSIST OF EXHAUSTION OF THE DYE FROM THE ACIDIC SOLUTION IN PRESENCE OF AN ELECTROLYTE LIKE COMMON SALT. THE DYEING IS NORMALLY CARRIED OUT AT BOIL FOLLOWED BY WASHING.

32. DYEING OF SYNTHETIC FIBRES DYEING OF NYLON DIRECT , ACID, METAL COMPLEX, DISPERSE AND REACTIVE THE DYEING IN GENERAL IS CARRIED OUT AT 85 - 900 C UNDER ACIDIC CONDITIONS, WHICH MAY BE ADJUSTED WITH THE ADDITION OF ACETIC ACID OR FORMIC ACID OR ACID LIBERATING SALT LIKE AMMONIUM SULPHATE.

33. DYEING OF POLYESTER PET IS HIGHLY HYDROPHOBIC AND THERE ARE NO REACTIVE SITES IN THE FIBRE. ALONG WITH THESE FACTORS, ITS HIGHLY CRYSTALLINE COMPACT STRUCTURE MAKES THE DYEING OPERATION VERY DIFFICULT. THE ONLY CLASSES OF DYE SUITABLE FOR THE DYEING OF POLYESTER IS DISPERSE DYES. THERE ARE THREE METHODS AVAILABLE FOR THE DYEING OF POLYESTER WITH DISPERSES DYES. BEFORE DYEING HEAT SETTING SHOULD BE CARRIED OUT TO PREVENT FABRIC SHRINKAGE.

35. 3. THEMOSOL DYEING THIS IS A CONTINUOUS METHOD OF DYEING AND IS BASED ON THE PRINCIPAL THE DISPERSE DYES WHEN SUBJECTED TO HIGH TEMPERATURE SUBLIME OR VAPOURISE AND THESE DYE VAPOURS HAVE HIGH AFFINITY FOR POLYESTER. THUS WHEN THE POLYESTER FABRIC CONTAINING DISPERSE DYE IS SUBJECTED TO HIGH TEMPERATURE (180 –210 0C); THE DYE VAPOURS ARE TAKEN UP BY THE FIBRE IT GETS DYED. THUS

36. THE SEQUENCE OF OPERATIONS IN THIS METHOD CONSIST OF PADDING THE FABRIC WITH DISPERSE DYE DISPERSION CONTAINING SUITABLE THICKENER OR A MIGRATION INHIBITOR, DRYING AT 90-1000C AND CURING AT 180-2100C FOR 45-60 SECONDS FOLLOWED BY WASHING. ALL THESE OPERATIONS CAN BE CARRIED OUT CONTINUOUSLY AND THUS THE METHOD IS ECONOMICAL WHEN LARGE YARDAGES ARE TO BE DYED IN A SINGE SHADE.

37. DYEING OF ACRYLICS THE MOST COMMONLY USED DYE CLASS FOR THE DYEING OF ACRYLICS IS BASIC DYES. THESE DYES GIVE BRIGHT SHADES ALONG WITH GOOD FASTNESS PROPERTIES. THE DYEING IS CARRIED OUT UNDER ACIDIC CONDITIONS AT BOIL FOR 1-2 HRS. HOWEVER ABOVE 85-90 0 C THE TEMPERATURE MUST BE RAISED VERY SLOWLY TO BOIL, BECAUSE ABOVE 90 0 C THE DYE UPTAKE IS VERY RAPID AND THERE ARE LESS CHANCES OF DYE MIGRATION WITH THE DANGER OF UNEVEN DYEING.

38. MANY TIMES TO CONTROL THE SLOW DYE UPTAKE DYEING RETARDERS ARE USED SO THAT UNIFORM DYE UPTAKE AND SHADES ARE OBTAINED. IN ADDITION TO BASIC DYES DISPERSE DYES, VAT, SOLUBILISED VAT AND ACID DYES MAY ALSO BE USED. HOWEVER, THEIR FASTNESS PROPERTIES ARE INFERIOR AS COMPARED TO BASIC DYES.

39. ASSESSMENT OF FASTNESS PROPERTIES DURING THE USE OF FABRICS/GARMENTS THEY ARE LIKELY TO BE SUBJECTED TO VARIOUS AGENCIES SUCH AS WASHING, RUBBING, LIGHT, PERSPIRATION, IRONING, CHLORINE, DRY-CLEANING ETC. THEREFORE, THE RESISTANCE OF DYED OR PRINTED MATERIAL MUST BE TESTED BEFOREHAND TO ASCERTAIN THE QUALITY OF DYEING. STANDARD TEST SPECIFICATIONS ARE READILY AVAILABLE TO DETERMINE THE FASTNESS PROPERTIES TO DIFFERENT AGENCIES, THEREFORE, INSTEAD OF GOING INTO THE DETAILS OF TEST PROCEDURES,

40. IT SHOULD BE INTERESTING TO TAKE THE TYPICAL CASE STUDIES OF THE COMPLAINTS WHICH ONE NORMALLY RECEIVES FROM THE CONSUMERS. IT IS NECESSARY TO ANALYZE THESE COMPLAINTS CAREFULLY ASSUMING THAT THE CLAIMS MADE BY THE CONSUMER ARE VALID, BECAUSE IT SPEAKS FOR THE BEHAVIOR OF THE DYED MATERIAL DURING ACTUAL USE. SOME OF THE DYED COMPLAINTS ARE:

41. LOSS OF DEPTH OF SHADES OR CHANGE IN TONE AFTER WASHING LOSS OF DEPTH OF SHADES DURING THE FIRST TWO OR THREE WASHES IS CERTAINLY DUE TO POOR WASHING FASTNESS OF THE DYED MATERIAL. IT MAY BE DUE TO THE FACT THAT THE CHOICE OF THE DYE WAS NOT CORRECT OR THE DYEING PROCEDURES WERE NOT FOLLOWED CAREFULLY. IN SUCH CASES, THE ATTEMPTS SHOULD BE MADE TO IDENTIFY THE DYE CLASS AND EVALUATES ITS GENERAL PROPERTIES.

42. SECONDLY, MANY TIMES IT WOULD BE NOTICED THAT THE DYED FABRIC LOOSES ITS TONE AFTER WASHING E.G. THE REDDISH TONE OF THE FABRIC BECOMES DULL BLUE OR GREENISH BLUE. THIS IS DUE TO THE MATERIAL IS BASICALLY DYED WITH FAST BLUE DYES, BUT IN THE FINAL OPERATION IT IS TINTED WITH A SMALL QUANTITY OF RED DYE TO GIVE REDDISH TONE. THE FASTNESS PROPERTY OF THE RED DYE IS OBVIOUSLY POOR AND THEREFORE, WASHED AWAY IN THE FIRST ONE OR TWO WASHINGS.

43. RUBBING AND PERSPIRATION FASTNESS THE CHANGE IN SHADES OR THE LOSS OF DEPTH OF SHADES AT COLLARS OR CUFFS IS THE TYPICAL CASE OF POOR RUBBING OR PERSPIRATION FASTNESS, BECAUSE AT THESE AREAS THE GARMENT IS EXCESSIVELY SUBJECTED TO RUBBING OR THE ACTION OF PERSPIRATION. THE MATERIAL COULD BE TESTED INDEPENDENTLY FOR THESE TWO FASTNESS PROPERTIES AND THE TRUE CAUSE COULD BE ASCERTAINED. THE IDENTIFICATION OF THE DYE CLASS WOULD ALSO THROW SOME LIGHT ON THE BEHAVIOR OF THE SHADE. FABRIC DYED WITH PIGMENT OR AZOIC COLOUS WOULD GIVE LOW RUBBING FASTNESS .

44. LIGHT FASTNESS DURING THE USE OF GARMENT THEY ARE CONTINUOUSLY SUBJECTED TO THE ACTION OF LIGHT. IF THE DYE IS NOT FAST TO LIGHT THEN ONE WOULD OBSERVE THAT THE PORTIONS OF THE GARMENT WHICH ARE NOT EXPOSED TO LIGHT RETAIN THEIR ORIGINAL SHADE, WHEREAS, THE EXPOSED PORTIONS ARE ALTERED CONSIDERABLY. THIS CAN BE CONFIRMED BY SUBJECTING THE DYED MATERIAL UNDER STANDARD CONDITIONS TO THE ACTION OF SUNLIGHT OR ARTIFICIAL LIGHT IN LABORATORY.