Anbu dye[2] electrochemical dyeing

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Anbu dye[2] electrochemical dyeing

  1. 1. ARTICLE IN PRESS + MODEL 1 58 2 59 3 60 Dyes and Pigments xx (2005) 1e8 4 www.elsevier.com/locate/dyepig 61 5 62 6 63 7 64 8 Potentiostatic studies on indirect electrochemical reduction of vat dyes 65 9 6610 M. Anbu Kulandainathan a,*, A. Muthukumaran a, Kiran Patil b, R.B. Chavan b 6711 68 F a12 Electro Organic Division, Central Electrochemical Research Institute, Karaikudi-630 006, India 69 b13 Department of Textile Technology, Indian Institute of Technology, Delhi, Hauz Khas, New Delhi-1100016, India 70 OO14 Received 10 May 2005; received in revised form 12 July 2005; accepted 10 October 2005 7115 7216 7317 7418 75 Abstract PR19 7620 Dispersed vat dyestuffs can be electrochemically reduced by indirect electrolysis using ironetriethanolamine complex as a reducing agent. 7721 The application and mechanism of indirect electrolysis as a reduction technique are described in detail in this paper. Electrochemically reduced 7822 vat dye is tested on a laboratory scale in dyeing experiments, and the results of different reduction conditions are discussed. The influence of the 7923 concentration of the complex-system on the build-up of colour depth, shade and fastness is discussed and compared with samples of the standard 80 ED24 dyeing procedure using sodium dithionite as the reducing agent. The new process offers environmental benefits as well as prospects for improved 8125 process stability, because the state of reduction in the dye-bath can be readily monitored by measuring the reduction potential. 8226 Ó 2005 Elsevier Ltd. All rights reserved. 8327 8428 85 CT29 8630 1. Introduction a-hydroxyketone which meets requirements in terms of reduc- 8731 tive efficiency and biodegradability had been tried. However, 8832 Vat dye is most popular among dye classes used for colora- such compounds are expensive and their use is restricted to 89 E33 tion of cotton, particularly, when high fastness standards are closed systems due to the formation of strong smelling con- 9034 required to light, washing and chlorine bleaching [1]. Also, densation products in an alkaline solution [7,8]. Some other 91 RR35 from the commercial point of view, vat dyes (including indigo) sulphur containing compounds such as hydroxyalkyl sulphi- 9236 have acquired a large share in the dyestuff market for the col- nate, thiourea, etc., have also been recommended [9,10]. These 9337 oration of cellulosic fibres. The annual consumption of vat dyes compounds have relatively low amount of sulphur content and 9438 including indigo is around 33,000 metric tons since 1992 and it also lower equivalent mass which leads to lower sulphur-based 9539 holds 24% of cellulosic fibre dye market in value terms [2]. salt load in the wastewater. However, in these cases too, it is 96 CO40 Vat dyes being water insoluble have to be first converted not possible to dispense with sulphur-based problems totally. 9741 into water soluble form (leuco dye) by reduction with a strong Fe(OH)2 being a strong reducing agent in alkaline medium, 9842 reducing agent like sodium dithionate. In its reduced form, the the possibility of using it has also been explored for reducing 9943 vat dye has substativity towards cellulosic fibres and, after organic dyestuffs. The reducing effect of Fe(OH)2 increases 10044 absorption, is reoxidised to the original water-insoluble form with increase in pH. However, Fe(OH)2 is poorly soluble in 101 UN45 in situ in the fibre [3,4]. The use of sodium dithionate is being an alkaline solution and gets precipitated. It has to be com- 10246 criticized for the formation of non-environment friendly plexed in order to hold it in solution [11]. A stable complex 10347 decomposition products such as sulphite, sulphate, thiosulphate with good reducing power is obtained with weaker ligand, 10448 and toxic sulphur [5,6]. such as gluconic acid. Regarding eco-friendliness, gluconic 10549 Attempts are being made to replace the sodium dithionite acid can be eliminated in the sewage tank through neutraliza- 10650 by ecologically more attractive alternatives. In this connection tion with alkali; free Fe(OH)2 can be aerated and converted to 10751 Fe(OH)3 which acts as a flocculent and brings down wastewa- 10852 ter load. Tartaric acid has also been tried as a ligand by Chak- 10953 raborty for complexing Fe(OH)2 in the presence of NaOH for 110 * Corresponding author. Tel.: þ91 4565 227772; fax: þ91 4565 227779.54 E-mail address: manbu123@yahoo.com (M.A. Kulandainathan). reduction and dyeing of cotton with indigo and other vat dyes 11155 11256 0143-7208/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. 11357 doi:10.1016/j.dyepig.2005.10.007 114 DYPI2176_proof Š 11 November 2005 Š 1/8 Š e-annotations
  2. 2. ARTICLE IN PRESS + MODEL 2 M.A. Kulandainathan et al. / Dyes and Pigments xx (2005) 1e8115 at room temperature [12]. Efforts have been made to complex chemicals. The mediator system necessary for indirect electro- 172116 Fe(OH)2 with single and double ligand systems using tartaric chemical reduction of vat dyes was prepared in an alkaline 173117 acid, citric acid and gluconic acid which have shown encour- medium from triethanolamine and ferric sulphate, which 174118 aging results [13]. were analytical grade chemicals. Potentiometric titrations 175119 Electrochemical reduction of vat, indigo and sulphur dyes were carried out to measure the dye reduction potential using 176120 is also suggested as an alternative route for ecological and eco- K4Fe(CN)6 as an oxidizing agent which was also an analytical 177121 nomic reasons. Electrochemical reduction can be achieved by grade chemical. Dye systems investigated were commercial 178122 direct and indirect electrochemical reduction. In direct electro- products from Atul Ltd.: Novatic Yellow 5G (CI Vat Yellow 179123 chemical reduction chemical reducing agents are replaced by 2), Novinone Brown RRD (CI Vat Brown 5), Novinone Green 180124 electrons from electric current, and effluent contaminating FFB (CI Vat Green 1), Novinone Blue RSN (CI Vat Blue 4), 181125 substances can be dispensed with altogether [14,15]. Although Novinone Blue BO (CI Vat Blue 20), Novinone Brown BR 182 F126 this technique is ideal, the stability of reduced dye species (CI Vat Brown 1), Novinone Black BB (CI Vat Black 36), 183127 formed is poor thereby affecting the colour yield and the Novinone Brill. Violet RR (CI Vat Violet 1) and Novinone 184 OO128 rate limiting step of electrochemical reduction is electron Black CH. 185129 transfer from the cathode surface to the surface of the micro- 186130 crystal of the dispersed dye pigment [16e20]. In indirect elec- 2.2. Dyeing procedure and process control 187131 trochemical reduction technique the reduction of dye is 188132 achieved through a redox mediator system [21,22]. This pro- 2.2.1. Conventional dyeing 189 PR133 cess is mediated by an electron carrier whereby reduction Conventional vat dyed samples were prepared in the labo- 190134 takes place between surfaces of the electrode and the dye pig- ratory, with a standard procedure using sodium dithionite 191135 ment instead of direct contact between both surfaces. Among and sodium hydroxide as described elsewhere [13]. 192136 the various mediator systems suggested in the literature, irone 193137 triethanolamine complex (ironeTEA) seems to be promising 2.3. Electrochemical dyeing 194 ED138 [23e29]. In order to meet all requirements in an economical 195139 way, a multi-cathode cell with a large number of cathodes, 2.3.1. Design of the electrochemical cell 196140 electrically connected with one or two anodes, has been sug- The two-compartment electrochemical cell consists of 197141 gested [30,31]. This configuration allows the operation of a rectangular polyvinyl chloride vessel containing the capacity 198142 the cell with a maximum area cathode and minimum area an- of 1 l catholyte and 0.1 l anolyte and the separator used was 199 CT143 ode [32e34]. Very recently, Bechtold et al. have demonstrated 423 Nafion membrane. The anode used was a thin stainless 200144 that mediator system obtainable by mixing one or more salts steel rod with the surface area of 6 cm2. A three-dimensional 201145 of a metal capable of forming a plurality of valence states copper wire electrode with a surface area of 500 cm2 served as 202146 with at least one amino-containing complexing agent and at the cathode. The cathode compartment was thus providing po- 203 E147 least one hydroxyl-containing but amino-devoid complexing rous flow through electrode filling the cathode compartment as 204148 agent in an alkaline medium has the improved capacity to coil. The catholyte was agitated by an analytical rotator at 205 RR149 reduce the vat dyes [35,36]. a constant speed to create homogeneous and stable conditions 206150 Both the electrochemical reduction techniques are not yet in the cathode chamber. The dye-bath of the dyeing apparatus 207151 commercialized and research and developmental efforts are was circulated through the electrochemical reactor for contin- 208152 in progress in this direction. Here, the most challenging engi- uous renewal of the reducing capacity of the dye-bath. 209153 neering task is to achieve a dye reduction rate and a current A schematic drawing of the dye-bath circulation through 210 CO154 efficiency, which are high enough to make electrochemical the laboratory dyeing unit and the catholyte circulation 211155 reaction industrially feasible. through the electrochemical cell is given in Fig. 1. 212156 In the present study attempts are being made to understand 213157 the fundamentals of indirect electrochemical reduction of 2.3.2. Determination of reduction potential of vat dyes 214158 selected vat dyes using ironeTEA complex as a mediator. Here, the reduction potential of the dye is referred as the 215 UN159 Essential requirements for the design of electrochemical cell potential developed on the bright platinum electrode vs the ref- 216160 are suggested. IroneTEAeNaOH molar ratio has been stan- erence electrode when dipped in the dye-bath in which the dye 217161 dardized to get the dyeing of cotton by indirect electrochemi- gets just solubilised. In order to measure the reduction poten- 218162 cal reduction technique. Colour yields are compared with tial of vat dyes, a titration was carried out using bright plati- 219163 those of conventional sodium dithionate method. Repeated num electrode with Hg/HgO/OHÿ as a reference electrode. 220164 use of dye-bath after dye separation is also explored. A solution of 100 mg vat dye was prepared which was then re- 221165 duced with 25 ml of 0.1 M NaOH and 100 mg Na2S2O4. This 222166 2. Experimental solution was then diluted to 50 ml with distilled water and then 223167 titrated against 0.05 M K4[Fe(CN)6]. The K4[Fe(CN)6] solu- 224168 2.1. Materials tion was added in the steps of 0.5 ml and the dye solution po- 225169 tential was measured at every step. The volume of 0.05 M 226170 The sodium dithionite and sodium hydroxide used for vat K4[Fe(CN)6] solution is then plotted against the dye solution 227171 dyeing by conventional method were laboratory grade potential in order to find out dye reduction potential. 228 DYPI2176_proof Š 11 November 2005 Š 2/8 Š e-annotations
  3. 3. ARTICLE IN PRESS + MODEL M.A. Kulandainathan et al. / Dyes and Pigments xx (2005) 1e8 3229 Analytical rotator 286230 287231 + - 288232 289233 290234 291235 292236 293237 294238 295239 296 F240 Anode: SS Cathode: Cu Peristaltic 297 Anolyte: Catholyte: Pump 1 Dye bath Peristaltic241 Mediator 298 OO (Mediator system 175 ml/min Pump 2242 100 ml 299 + dye) 1200ml 175 ml/min243 300244 301245 Electrochemical 302246 cell 303 PR247 304248 305 Cu wire to measure solution potential w.r.t. Reference electrode249 306250 307 Reference electrode (Hg / HgO/OH-)251 308 ED252 Fig. 1. Schematic representation of the electrochemical flow cell. 309253 310254 311 2.3.3. Dyeing procedure mediator system should be made as low as possible. High con-255 312 Selected vat dyes were dyed under the standardized condi- centrations of chemicals in the dye-bath enable more stable re-256 313 CT tions of the mediator system as described in Section 3. While duction conditions and prevent the oxidation of the reduced257 314 following the electrochemical dyeing technique, the dye-bath dyestuff. However, if we use the mediator solution towards258 315 was circulated through the cathodic compartment of the elec- its higher concentration end then there will be an eventual in-259 316 trolytic cell for continuous renewal of the reducing capacity. crease in the loss of chemicals in the recycling loop and also260 317 All the experiments were performed under potentiostatic con- carried along the fabric at the end of dyeing operation. This E261 318 ditions (ÿ1050 mV vs Hg/HgO/OHÿ) at room temperature. makes the process uneconomical.262 319 The catholyte was called as a mediator solution which com- RR263 320 prised triethanolamine, ferric sulphate and sodium hydroxide. Table 1264 321 The potential prevailing in the catholyte, during electrolysis, Different composition of the mediator solutions used for dyeing experiments265 322 was measured with a copper wire vs a reference electrode Mediator solution pH Mediator solution composition266 323 (Hg/HgO/OHÿ). The catholyte was agitated in the catholyte Fe2(SO4)3 (M) TEA (M) NaOH (M)267 324 compartment itself and was also circulated through the dye- CO268 Group I 325 bath continuously. When the potential achieved in the catho- 1.1 14 0.025 0.30 0.357269 326 lyte was equivalent to the reduction potential of the dyestuff, 1.2 14 0.03 0.35 0.434270 327 the dyestuff was introduced into the catholyte compartment. 1.3 14 0.035 0.40 0.500271 1.4 14 0.04 0.45 0.570 328 In all the experiments 2% of weight of fabric dye was used272 1.5 14 0.045 0.50 0.643 329 UN in the dyeing recipe. The fabric sample was introduced into273 Group II 330 the dye-bath after 10 min of introduction of dyestuff in order274 2.1 10.5 0.03 0.35 0.185 331 to allow reduction of the dyestuff. Experiments were carried275 2.2 12 0.03 0.35 0.225 332 out at a relatively large liquor ratio i.e. 240:1. The dyeing 2.3 13 0.03 0.35 0.275276 333 was continued in the dye-bath for 1 h with constant agitation 2.4 14 0.03 0.35 0.315277 334 of the fabric sample with glass rods, while electrolysis and cir- 2.5 14 0.03 0.35 0.375278 2.6 14 0.03 0.35 0.429 335 culation of the catholyte were in progress. After dyeing the279 2.7 14 0.03 0.35 0.480 336 sample was withdrawn from the dye-bath, air oxidized, cold280 337 rinsed, soaped at boil, cold rinsed and air dried. Group III281 3.1 14 0.025 0.30 0.43 338282 3.2 14 0.025 0.315 0.43 339283 2.3.4. Optimization of mediator solution 3.3 14 0.025 0.33 0.43 340284 In order to make the indirect electrochemical dyeing tech- 3.4 14 0.025 0.345 0.43 341 3.5 14 0.025 0.360 0.43285 nique eco-friendly and economical, the concentration of the 342 DYPI2176_proof Š 11 November 2005 Š 3/8 Š e-annotations
  4. 4. ARTICLE IN PRESS + MODEL 4 M.A. Kulandainathan et al. / Dyes and Pigments xx (2005) 1e8343 Table 2 400344 Reduction potential of selected vat dyes 401345 Dye Reduction potential (V) Dye Reduction potential (V) Dye Reduction potential (V) 402346 Novatic Yellow 5G ÿ0.818 Novinone Blue RSN ÿ0.880 Novinone Black BB ÿ0.952 403347 Novinone Brown RRD ÿ0.841 Novinone Blue BO ÿ0.903 Novinone Brill. Violet RR ÿ0.953 404348 Novinone Green FFB ÿ0.850 Novinone Brown RR ÿ0.935 Novinone Black CH ÿ0.964 405349 Reduction potential (V vs Hg/HgO/OHÿ). 406350 407351 Indirect electrochemical dyeing was carried out with the se- 3. Results and discussion 408352 lected dyestuffs at different mediator solution concentrations 409353 in three sets of mediator systems as shown in Table 1. In group 3.1. Reduction potential of vat dyes 410 F354 I, the ferric sulphate to TEA and ferric sulphate to sodium hy- 411355 droxide molar ratio was kept constant as 1:11.48 and 1:14.3, The reduction potential of vat dyes gives an idea about the 412 OO356 respectively as described elsewhere [13]. In group II, the ferric level of difficulty involved in their reduction. Higher the 413357 sulphate to TEA molar ratio was kept constant at 1:11.48 reduction potential of the dye, higher is the reducing power 414358 while the ferric sulphate to sodium hydroxide molar ratio required in the dye-bath for its reduction. Thus, from the 415359 was varied. Whereas in group III, the ferric sulphate to sodium reduction potential values, we can group the dyes under con- 416360 hydroxide molar ratio was kept constant at 1:14.3 and the fer- sideration in three groups viz. easy to reduce, normal to reduce 417 PR361 ric sulphate to TEA molar ratio was varied (Table 2). and difficult to reduce. 418362 The mediator solution was prepared according to the proce- While following the indirect electrochemical dyeing tech- 419363 dure described elsewhere [14]. Caustic soda was dissolved in nique, three dyestuffs such as, Green FFB (an easy to reduce 420364 a small amount of water in which TEA was added. Ferric sul- dye), Blue RSN (a normal to reduce dye) and Violet RR (a 421365 phate was separately dissolved in a small amount of water and hard to reduce dye) were selected. 422 ED366 then added to the TEA/caustic soda mixture with continuous 423367 stirring with the magnetic stirrer. After the complete dissolu- 424368 tion of the precipitated iron oxide, the solution was diluted 3.2. Dyeing results 425369 to the full volume. The solution was subjected to constant stir- 426370 ring for 90 min. The rates of potential development while carrying out po- 427 CT371 tentiostatic electrolysis in the group I, II and III dyeing experi- 428372 ments with Violet RR dye only are shown in Figs. 2, 3 and 4, 429 2.3.5. Material to liquor ratio experiments373 respectively. In each dyeing experiment, the dye was intro- 430 As the electrolysis cell was not optimized with regard to374 duced in the cathodic chamber as soon as the reduction poten- 431 short liquor ratios, experiments were carried out at a relatively E375 tial of Violet RR had reached i.e. ÿ953 mV. The final dye-bath 432 large material to liquor ratio i.e. 1:240. To understand the ef-376 potential attained at the end of dyeing in few cases was lower 433 fect of the various materials to liquor ratios on the colour RR377 than that attained during the course of dyeing, especially while 434 depth developed on the fabric samples by indirect electro-378 dyeing with Green FFB and Blue RSN. 435 chemical dyeing, experiments were also carried out with379 436 1:120, 1:80 and 1:60 material to liquor ratios by making380 437 appropriate modifications in the system.381 438 CO382 1000 439 Solution Potential (-mV vs Hg/HgO/OH-)383 2.3.6. Recycling of mediator solution experiments 440384 After completing the dyeing experiment, the remaining dye 441385 and reduced mediator were oxidized by bubbling air though 900 442386 the solution to form an insoluble dye. 443 UN387 The oxidized dye particles can be segregated out through 444 800388 the vacuum filtration using G3 type of porcelain membrane. 445389 The clear filtered out mediator solution was recycled further 446390 to carry out dyeing experiments. 700 Mediator index: 1.1 447 Mediator index: 1.2391 448 Mediator index: 1.3392 2.3.7. Dyed samples evaluation 600 Mediator index: 1.4 449393 Results of the dyeing experiments were characterized by Mediator index: 1.5 450394 colour measurement in the form of K/S and CIELab coordi- 451395 nates with the help of spectrophotometer X4000 (Jaypak) us- 500 452 -50 0 50 100 150 200 250 300 350396 ing D65 light source, 10 viewing angle. 453 Time (min)397 Dyed samples were also evaluated for wash fastness 454398 (SOURCES: IS 764; 1979), light fastness (SOURCE: IS Fig. 2. Dye-bath potential development with varying ferric sulphate concentration 455399 2454; 1985) and rubbing fastness (SOURCE: IS 766; 1988). (group I) electrolysis with Violet RR dye. 456 DYPI2176_proof Š 11 November 2005 Š 4/8 Š e-annotations
  5. 5. ARTICLE IN PRESS + MODEL M.A. Kulandainathan et al. / Dyes and Pigments xx (2005) 1e8 5457 Table 3 514 Mediator index:2.1 Comparison of colour yield and colour coordinates of conventional and458 1000 515 Solution Potential (-mV vs Hg/HgO/OH-) Mediator index:2.2 electrochemical dyeing with Green FFB459 Mediator index:2.3 516460 Mediator solution Final dye-bath potential K/S L* a* b* 517 900 Mediator index:2.4 index (V vs Hg/HgO/OHÿ)461 Mediator index:2.5 518462 With dithionite* 15.4626 35.44 ÿ35.20 ÿ0.98 519 Mediator index:2.6 800 1.1* ÿ0.860 5.1460 55.37 ÿ39.92 ÿ2.67463 Mediator index:2.7 1.2* ÿ0.880 4.7258 53.39 ÿ32.58 ÿ6.24 520464 1.3* ÿ0.870 5.6865 52.95 ÿ38.25 ÿ3.72 521465 700 1.4* ÿ0.874 3.3465 58.97 ÿ33.46 ÿ4.71 522466 1.5* ÿ0.996 4.1874 57.42 ÿ36.84 ÿ3.27 523467 600 Initial dye-bath potential before starting the electrolysis in each case was 524 F468 ÿ0.350 V vs Hg/HgO/OHÿ. 525469 526 OO 500470 527471 cell due to the deposition of a block material as a hard layer on 528 0 50 100 150 200 250 300 350472 Time (min) the cathode. As can be seen from the corresponding K/S values 529473 in Table 3, the colour depth appears to be increasing with an in- 530474 Fig. 3. Dye-bath potential development with varying sodium hydroxide crease in NaOH concentration above pH 13. 531 PR475 concentration (group II) during electrolysis with Violet RR dye. There is no effect of the TEA concentration variation in the 532476 mediator solution in the given range of group III experiments 533477 on the colour depth and shade. Also the solution potential de- 534478 From the variation of the CIELab coordinates from the velopment rate is found to be unaffected (Fig. 4). However, at 535479 group I experiments as shown in Table 3, it becomes clear 44.75 g/l TEA, the iron complex becomes unstable and ferric 536 that the colour depth and shade did not show strong depen- ED480 hydroxide is found to be precipitating. 537481 dence on the iron salt concentration in the mediator solution. 538482 However, the depth appears to be good around 12e14 g/l fer- 539 ric sulphate concentration. The potential development rate ap- 3.2.1. Influence of MLR on colour yield483 540 pears to be increasing with increase in ferric sulphate All the dyeing experiments for mediator solution optimiza-484 541 CT concentration as can be seen in Fig. 2. tion were carried out at 1:240 material to liquor ratio. The485 542 In case of group II experiments, the solution potential could depth of the dyed samples was very low as compared to the486 543 not be developed above ÿ953 mV vs Hg/HgO/OHÿ while conventionally dyed samples which were dyed at 1:30 material487 544 working up to pH 13. Therefore dyeing was not possible during to liquor ratio. In order to investigate the possibilities of im-488 545 working with NaOH concentration below 11 g/l in the mediator proving the colour depth, dyeing experiments were carried E489 546 solution. During electrolysis of the solution with pH below 13, out with Blue RSN dye at 1:240, 1:120, 1:80 and 1:60 material490 547 the complex formed was found to be unstable and caused addi- to liquor ratios using 1.2 mediator index solution. RR491 548 tional problems in the proper functioning of the electrochemical Values of K/S and CIELab coordinates of dyeing experi-492 549 ments are given in Table 4 which show marginal improvement493 550 in colour depth of the dyed samples with shorter material to494 551 liquor ratios.495 552 CO496 1000 553 Solution Potential (-mV vs Hg/HgO/OH-)497 3.2.2. Recycling of mediator solution 554498 Dyeing without effluent i.e. dye-bath recycling seems to 555 900499 be very attractive in the present environment conscious era. 556500 557 UN501 800 558 Mediator index:3.1502 Table 4 559 Mediator index:3.2 Comparison of colour yield and colour coordinates of conventional and503 700 560 Mediator index:3.3 electrochemical dyeing Blue RSN504 Mediator index:3.4 561505 Mediator solution Final dye-bath potential K/S L* a* b* 562 600 Mediator index:3.5 index (V vs Hg/HgO/OHÿ)506 563507 With dithionite 9.1666 35.94 6.62 ÿ38.03 564 500 1.1 ÿ0.875 2.6641 52.92 ÿ3.29 ÿ27.93508 565 1.2 ÿ0.900 3.6045 48.44 0.58 ÿ32.87509 1.3 ÿ0.890 2.2319 55.17 ÿ2.25 ÿ28.24 566 -20 0 20 40 60 80 100 120 140 160510 1.4 ÿ0.905 2.5897 52.71 0.23 ÿ31.25 567 Time (min)511 1.5 ÿ0.983 1.9702 56.10 ÿ1.10 ÿ27.58 568512 Fig. 4. Dye-bath potential development with varying TEA concentration Initial dye-bath potential before starting the electrolysis in each case was 569513 (group III) during electrolysis with Violet RR dye. around ÿ0.350 V vs Hg/HgO/OHÿ. 570 DYPI2176_proof Š 11 November 2005 Š 5/8 Š e-annotations
  6. 6. ARTICLE IN PRESS + MODEL 6 M.A. Kulandainathan et al. / Dyes and Pigments xx (2005) 1e8571 Table 5 Table 7 628572 Comparison of colour yield and colour coordinates of conventional and Regeneration of mediator solution 629 electrochemical dyeing with Violet RR Recycling step Fresh solution Absorbance573 630574 Mediator solution Final dye-bath potential K/S L* a* b* addeda (ml) Before oxidation After filtration 631 index (V vs Hg/HgO/OHÿ) and filtration575 632576 With dithionite 15.73 23.10 16.93 ÿ23.13 Original 0 1.384 0.072 633 1.1 ÿ0.922 0.2810 77.92 10.16 ÿ9.76577 1 30 1.533 0.027 634 1.2 ÿ0.996 3.0499 47.82 22.82 ÿ28.25 2 41 1.403 0.050578 1.3 ÿ0.994 3.2752 47.87 26.70 ÿ30.07 635 3 28 1.417 0.079579 1.4 ÿ0.979 2.4236 52.75 26.42 ÿ27.63 4 42 1.420 0.070 636580 1.5 ÿ0.1001 2.9228 49.78 26.78 ÿ29.23 637 a 2.1 ÿ0.539 Dyeing not possible Fresh solution was added to make the total volume to 1 l before starting581 each experiment. 638 ÿ0.545 F 2.2 Dyeing not possible582 2.3 ÿ0.584 Dyeing not possible 639583 2.4 ÿ0.987 2.0706 54.97 25.45 ÿ26.87 640 OO584 2.5 ÿ0.993 2.2632 53.53 25.15 ÿ26.66 641585 2.6 ÿ0.1001 3.1007 48.72 26.54 ÿ30.03 642586 2.7 ÿ0.1001 4.4808 43.71 28.11 ÿ30.84 643 3.1 ÿ0.1002 2.8823 49.71 26.59 ÿ30.50587 3.2 ÿ0.992 3.5124 47.04 27.51 ÿ30.79 Table 8 644588 3.3 ÿ0.997 3.9246 45.32 27.49 ÿ31.02 Colour yield and CIELab coordinates for repeated dyeing with regenerated 645 PR589 3.4 ÿ0.1001 3.0499 47.82 22.68 ÿ28.25 mediator solution 646590 3.5 ÿ0.995 3.1660 48.79 26.99 ÿ28.83 Recycling step Final dye-bath potential K/S L* a* b* 647591 Initial dye-bath potential before starting the electrolysis in each case was (V vs Hg/HgO/OHÿ) 648592 around ÿ0.350 V vs Hg/HgO/OHÿ. Original ÿ0.995 2.4954 52.95 0.62 ÿ31.06 649593 1 ÿ0.965 2.3803 53.82 ÿ0.97 ÿ29.35 650 2 ÿ0.950 2.8766 51.25 ÿ0.55 ÿ30.31 ED594 3 ÿ0.958 2.6414 52.39 ÿ0.39 ÿ29.67 651595 4 ÿ0.953 3.0783 50.65 ÿ1.09 ÿ30.50 652596 653597 654 Table 6598 655 CT Effect of ML ratios on colour yield and CIELab coordinates599 656 MLR Final dye-bath potential K/S L* a* b*600 (V vs Hg/HgO/OHÿ) 657601 658 1:240 ÿ0.900 3.6045 48.44 0.58 ÿ32.87602 1:120 ÿ0.958 2.9914 50.85 ÿ0.72 ÿ30.43 659 E603 1:80 ÿ0.950 3.0879 50.49 ÿ1.65 ÿ29.25 Table 9 660604 1:60 ÿ0.965 4.0401 46.55 ÿ1.01 ÿ29.91 Comparison of fastness properties of electrochemical and conventional dyeing 661 RR605 Reduction/mediator Washing Light Rubbing fastness 662606 system fastness fastness Wet Dry 663607 a 664 With dithionite 4e5 5 4 5608 With dithioniteb 4e5 5 4 5 665609 With dithionitec 4e5 5 4 4e5 666 CO610 0.025 M Fe2(SO4)3 þ 4e5 4e5 4e5 5 667 1000 0.345 M TEA þ 0.45 M611 668 Solution Potential (-mV vs Hg/HgO/OH-) NaOH (MLR 1:240)a612 669 0.025 M Fe2(SO4)3 þ 4 4e5 4 4e5613 900 0.345 M TEA þ 0.45 M 670614 NaOH (MLR 1:240)b 671 UN615 0.025 M Fe2(SO4)3 þ 4e5 5 4 4e5 672 800616 0.345 M TEA þ 0.45 M 673 NaOH (MLR 1:240)c617 Mediator Index:1.2 674 0.025 M Fe2(SO4)3 þ 4 4e5 4e5 5618 700 Original 0.345 M TEA þ 0.45 M 675619 First Recycle NaOH (MLR 1:60)a 676620 600 Second Recycle 0.025 M Fe2(SO4)3 þ 4 4e5 4e5 5 677621 Third Recycle 0.345 M TEA þ 0.45 M 678 NaOH (MLR 1:60)b622 Fourth Recycle 679 500 0.025 M Fe2(SO4)3 þ 4 4e5 4e5 5623 0.345 M TEA þ 0.45 M 680624 NaOH (MLR 1:60)c 681 0 20 40 60 80 100 120625 a With Green FFB. 682 Time (min)626 b With Blue RSN. 683 c627 Fig. 5. Effect of mediator recycling on the dye-bath potential development. With Violet RR. 684 DYPI2176_proof Š 11 November 2005 Š 6/8 Š e-annotations

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