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  1. 1. RECENTDEVELOPMENT INREACTIVE DYE & DYEINGTECHNIQUEAuthors :P.ManikandanV.SuganIII yearDept of Textile TechnologyPavendar bharathidasan college ofEngg& 9994239932Abstract.Cotton textiles are dyed mostly withreactive dyes because they produce a widegamut of bright colours with excellentcolourfastness to washing. However, thereactive dyeing requires considerablequantities of inorganic salt and alkali forefficient utilization and application ofdyes. These salts and alkalis when drainedto effluent generate heavy amounts of totaldissolved solids leading to environmentalpollution.Substantial remedies are beingconsidered within the textile processingsector to reduce the effluent pollutionandto fulfil the environmental regulations.This paper is a part of such efforts andpresents results where any of the threebiodegradable alkaline polycarboxylicsodium salts, tetrasodium ethylene diaminetetra-acetate (namely sodium edate),trisodiumnitrilo triacetate(namelytrisodium NTA) andtetrasodiumN,Nbis(carboxylatomethyl)-L-glutamate (namely tetrasodium GLDA),can be used as alternative to traditionallyused non biodegradable inorganic salt andalkali in the dyeing solution. Two widelyused dyes, CI Reactive Red 147 and CIReactive Blue 250, and pad-steam dyeingmethod were used in this study. Thedyeing was carried out by impregnatingthe cotton fabric in the solution containingthe dye, salt and alkali, and squeezing it toa 70% pickup, followed by steaming fordye penetration and fixation to the fibres.It has been found inthis study that theultimate colour-yield and colourfastnessproperties obtained by using thebiodegradable organic salts were closelycomparable to those obtained withinorganic salt and alkali. A significantincrease in the colour-yield was obtainedwhen tetra sodium GLDA was used forCI Reactive Blue 250. The dyeing effluentshowed reductions in total dissolved solidscontent with sodium edate and trisodiumNTA.Keywords:Biodegradable organic salt, dyeing, cottontextiles, reactive dye1. Introduction
  2. 2. The textile colouration and finishingindustry is one of the major contributors toenvironmental pollution [1, 2]. This ismainly due to the discharge ofnonbiodegradable inorganic salts, alkalis,other processing aids and organic mattersuch as dyes to the effluent. The effluenttreatment can play a significantrole inreducing discharge pollution. However,these treatments are expensive andproduce highly concentrated solid wastes[3]. Therefore, the better approach wouldbe to improve the textile processingtechnologies and chemistry for reducingthe discharge pollution.Reactive dyes havebecome a default choice for colouration ofcotton textiles, because they provide awide range of inexpensive bright colourswith excellent washing fastness [4]. Theexcellent washing fastness is due to thecovalent bonding between the fibrepolymers and the dye molecules underalkaline pHconditions [5]. The inorganicsalt, such as sodium chloride or sodiumsulphate, for dye transfer to andpenetration into the fibre, and inorganicalkali, such as sodium bicarbonate, sodiumcarbonate or sodium hydroxide, for dye-fibre reaction, are required in substantialquantities to accomplish the dyeingprocess.Irrespective of the dyeing methodusing reactive dyes, just about all of thesalt and alkali is drained to effluent. Sucheffluents are characterised by high levelsof dissolved solids which isenvironmentally undesirable [2, 5-7]. Anumber of developments have beenproposed for reducing the effluentpollution bycotton dyeing systems withreactive dyes.Developments in dyestructures, dyeing processes andmachinery have offered reductions in theamount of inorganic salt and improved dyefixation [8-14]. Cationisation of cottonfibre before dyeing process has beenproved to be capable for abolishing therequirement of inorganic salt, and alsoalkali in few cases [15-19]. Nevertheless,cationisation is an extra process and hasyet to be taken on to industrial level.Organic chemicals have been shown to bemeaningful substituent to inorganic salts inexhaust dyeings [20-23].Tetrasodiumethylene diaminetetraacetate (sodiumedate) is a biodegradable alkalinepolycarboxylic salt and has been studied asan alternative to inorganic salt and alkali inreactive dyeing of cotton by exhaustmethod[24]. However, the high alkalinityof sodium edate can cause reactive dyehydrolysis in the dye bath during dyeexhaustion. This can result in the difficultcontrol of dyeing and reduced dye fixation[22]. The use of the alkaline organic saltsin continuous dyeing of cotton withreactive dyes would be of interest Thispaper presents the results of a study wheresodium edate and two more alkaline
  3. 3. polycarboxylic sodium salts,trisodiumnitrilo-triacetate (trisodium NTA)and tetrasodium N N-bis(carboxylatomethyl)-Lglutamate(tetrasodium GLDA) have been used in thecontinuous pad-steam dyeing of cottonwith reactive dyes to improve effluentquality by replacing the traditionalinorganic salt and alkali. These salts arebiodegradable and are commonly used inthe detergent and the cosmetic industriesas chelating agents[25-27].2. Material and methodsA commercially prepared ready-to-dyecotton woven fabric (282 g/m2) and twowidely used commercial reactive dyes, CIReactive Red 147 and CI Reactive Blue250, were used for this study. A non ionicdetergent, Felosan RGN-S, was used forsoaping during washing-off. The sodiumedate,trisodium NTA, tetrasodium GLDA,sodium chloride, sodium carbonate andsodium bicarbonate were analytical grade.Fabric pieces were padded (70% pick-up,Benz padder) with aqueous dyebath having20 g/l dye and the related salt and alkali oran organic salt. The padded fabric pieceswere then subjected to steaming(100%moisture, 101 – 102oC, Mathissteamer) for 60, 90 and 120 sec. In case oftraditional dyeing processes, sodiumbicarbonate was used for CI Reactive Red147 and sodium carbonate for CI ReactiveBlue 250 as analkali. To remove unfixed dyes andresidual chemicals, the dyed fabrics wererinsed with cold water then with hot water,soaped with 2 g/l Felosan RGN-S at boil(15 min), and then rinse with hot wateruntil dye desorption stopped. Finally, thefabrics were washed with cold water andoven dried. The final fabric samples weretested for colour-yield, K/S value, using aData color 600 spectrophotometer andcolourfastness to rubbing (ISO 105 - X12),to washing (ISO 105 - C02) and to light(BS 1006: 1990 UK-TN).Each optimumdyeing recipe was diluted 100 times asrepresentative of the dyeing effluent. TheTDS of the representative dyeing effluentwas measured using a Eutech laboratoryTDS meter.3. Results and discussion3.1. Optimum inorganic salt and alkaliSalt is used for increasing dye levelnessthroughout the fibre and the resultantcolour-yield, in pad-steam dyeing [6, 28,29]. Fig. 1 (a) shows that the maximumcolour-yield was obtained with 50 g/lsodium chloride for 20 g/l dye. Thereaction between the reactive dyemolecules and the hydroxyl groups ofcotton cellulose occur at alkaline pHconditions. The dye can also react with thehydroxide ions in an aqueous dye solution
  4. 4. [6,28, 30]. The excessive amount of alkalican increase dye hydrolysis at the cost ofdye-fibre reaction, thus,reducing theultimate colour-yield. Fig. 1 (b) shows that15 g/l alkali provided the optimum colour-yield for 20 g/l dye.(a) Effect of sodium chloride concentrationon colour-yieldat constant alkali (15 g/l)(b) Effect of alkali concentration oncolour-yield atconstant sodium chloride (50 g/l)Fig. 1: Optimum sodium chloride andalkali sodium carbonate / sodiumbicarbonate) concentrations for 20 g/ldyeat 60 sec steaming3.2. Effect of biodegradable organic saltconcentrationFig. 2 shows the effect of alkalinepolycarboxylic sodium salt concentrationon colour-yield of the fabric dyed with 20g/l dye. The yield passed throughmaximum values with increasingconcentration of the salt.For CI Reactive Red 147, the optimumconcentration was around 100 g/l of thesodium edate or trisodium NTA and 75 g/lof the tetrasodium GLDA. And for CIReactive Blue 250, the concentration was125 g/l of the sodium edate or trisodiumNTA and 100 g/l of the tetrasodiumGLDA. Lesser concentrations oftetrasodium GLDA were required toachieve optimum yield which was betterthan that obtained with the other twoorganic salts. The colour-yield of CIReactive Blue 250 obtained by usingoptimum tetrasodium GLDA wassignificantly higher than that obtained withother organic salts. This is highlysignificant increase comparing to thepossible lower colour-yield in thetraditional reactive dyeing of cotton bypad-steam process because of excessivedye hydrolysis and lower ultimate dye-fixation levels [28]. This may beattributedto the higher ionic-strength and betterstability (at elevated pH) of tetrasodium
  5. 5. GLDA for reaction between abis(sulphatoethylsulphone) dye and thecotton cellulose.3.3. Dyeing using organic salt versusconventional dyeingComparative effect of steaming timeSteaming time of the range of 60–120 secwas selected. This is because industrialpad-steam dyeing machines generallyfunction within this range. Fig. 3 showsthe effect of steaming time on colour-yieldhaving the optimum concentrations ofinorganic and organic chemicals. Thefigure shows that the colouryieldscontinuously increase slightly withsteaming time in all cases. The steamingtime to maximum yield at longer steamingtime was not determined because the timeexceeds standard industry practice.Comparative colour-yield andcolourfastnessFig. 4 shows the comparative colour-yieldsfor the alkaline polycarboxylic sodiumsalts and traditional dyeing’s. The figureshows that the colour-yield results for thealternate and traditional dyeing’s wereconsiderably comparable. However,interestingly, the tetrasodium GLDA gaveconsiderably higher yield with CI ReactiveBlue 250, as described in an earlier sectionfor Fig. 3. These results obtained by usingtetrasodium GLDA for thebis(sulphatoethylsulphone) dye worth afurther study.Table 1 shows that the rubbing, washingand light fastness achieved by of the
  6. 6. organic salt dyeing’s are generally verygood and the same as those obtained by thetraditional dyeing’s. These results aremotivating. The lower light fastness of CIReactive Blue 250 is same as that notifiedon the dye manufacturer’s literature. The40 g/l of tetrasodium GLDA (not anoptimum concentration) was used forcolourfastness testing to havethe matchingcolour-yields with traditionally obtainedyields.Comparative effluent analysisTable 2 shows that sodium edate andtrisodium NTA provided around 24–29%TDS reduction in the effluent of CIReactive Red 147 and around 8–14%reduction in the case of CI Reactive Blue250. The lower percent reduction in TDSfor CI Reactive Blue 250 is due to thehigher concentration of alkalinepolycarboxylic salt needed to obtainoptimum colour fixation and ultimatecolour-yield. Tetrasodium GLDA did notprovide any significant reduction in theeffluent TDS. However, tetrasodiumGLDA is still safer interms ecologicalfootprint than sodium edate and trisodiumNTA principally because of its betterbiodegradability [27]. Further, it providedsignificantly higher colour-yields for CIReactive Blue 250. This means the amountof unfixed dye washed-off to effluent willbe reduced significantly.4. ConclusionsThis research has revealed that thebiodegradable alkaline polycarboxylic sodiumsalts, such as sodium edate, trisodium NTAand tetrasodium GLDA, can effectively beused for reactive dyeing of cotton by padsteamprocess to reduce the dyeing-effluentpollution. The alternate dyeing systemproduced colour-yields and colourfastnesscomparable to those obtained using traditionalsalt and alkali. Further, increased colouryieldof the CI Reactive Blue 250 was achieved withtetrasodium GLDA. This was a significantly
  7. 7. higher increase in colour-yield with no changein the colourfastness of dyed fabricscomparing to the lower yields obtainedtraditionally because of lower dye-fixationlevels.