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Colour fastness of optionally aftertreated acid levelling and milling dyes on nylon 6.6 during washing in an activated oxygen-bleach containing detergent. Part 1: Fading observed in the UK-TO test and after repeated domestic laundering

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Previous studies examining the fading exhibited by different classes of cellulosic dyes on cotton, during washing in an oxidative-bleach containing detergent, have been extended to acid levelling and the higher wet fast acid half-milling dyes and
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  © Color. Technol. , 117  (2001) 147Web ref: 20010305 ColorationTechnology Society of Dyers and Colourists Colour fastness of optionally aftertreatedacid levelling and milling dyes onnylon 6.6 during washing in an activatedoxygen-bleach containing detergent.Part 1: Fading observed in the UK-TO test and after repeated domestic laundering † Duncan Phillips, a  John Taylor, a  Rajesh Lakhanpal, a  John Scotney a and Geoff Bevan b a  Dept of Textiles, UMIST, PO Box 88, Manchester M60 1QD, UK  b  Lever Brothers Ltd, PO Box 69, Port Sunlight, Wirral CH62 4ZD, UK  Previous studies examining the fading exhibited by different classes of cellulosic dyes on cotton, duringwashing in an oxidative-bleach containing detergent, have been extended to acid levelling and thehigher wet fast acid half-milling dyes and acid milling dyes on nylon 6.6. It has been shown that acidlevelling dyes exhibit a much higher level of fading, both in the single cycle, stressed UK-TO test andafter repeated domestic laundering, than acid milling dyes. The observed fading in each case was dueto wash-down/desorption of dye rather than an oxidative-bleaching effect. † For part 2 of this study, see page 152 of this issue of ColorationTechnology  . Introduction A single, stressed wash test (UK-TO) has been developed[1] and internationally validated [2,3] which diagnoses thesusceptibility of dyed substrates to the activated oxygen-bleach present in domestic detergents. It is expected to beadopted as an ISO standard (ISO 105-C09) during 2001.The srcinal study focused on the oxidative-bleachfading of different dye classes on cotton [1], since cottonand its blends with synthetic fibres represent in excess of 70% of the loading that is domestically washed.This current study reports the fading of optionallyaftertreated (with a syntan) acid levelling and acid millingdyes on nylon 6.6 in both the UK-TO test and after multiplemachine washes in an oxidative-bleach detergent. Syntansare anionic, polyphenolic compounds which are absorbedonto the nylon fibre under acidic application conditions.The resulting matrix produces a ‘barrier effect’, making theremoval of dye during washing more difficult. Experimental Selection of dyes All the dyes used in this study (Table 1) were obtainedfrom Crompton & Knowles (now Yorkshire Chemicals) andwere applied to knitted nylon 6.6 (141 g/m 2 ) by themanufacturer’s recommended method. This involvedraising the temperature of the dyebath containing the Table 1  Details of the dyes used in this studyDepth of DyeCommercial nameshade a  (%)  Acid levelling  b  1Nylanthrene Yellow B-5R1.0 2Nylanthrene Blue B-2RF1.5 3Nylanthrene Red B-2BSA1.0 4Nylanthrene Red B-3GP1.0 5Nylanthrene Pink B-LRF2.0 6Nylanthrene Scarlet B-2GL2.0 7Nylanthrene Blue B-AR1.0 8Nylanthrene Blue B-NL1.5 9Nylanthrene Blue B-2GL1.510Nylanthrene Yellow B-4NGL1.0  Acid milling  b 11Nylanthrene Rubine C-5BL1.012Nylanthrene Orange C-SLF2.013Nylanthrene Yellow C-3RL2.014Nylanthrene Blue C-GLF1.515Nylanthrene Navy C-R2.016Nylanthrene Bordeaux C-B2.0 a The different applied depths were chosen, in consultationwith the supplier, to give approx. standard depth dyeings b Some of the dyes would be considered as half-milling dyesin the context of dyeing wool dyestuff, ammonium sulphate (2 g/l) and Intratex B(Crompton & Knowles) (anionic levelling agent, 1 g/l) atpH 5–6 from 30 °C to the boil over 40 min. The dyeing(carried out at a liquor to goods ratio of 10:1) wascontinued for 60 min before the bath was dropped. Thefabric was rinsed in cold water and dried before anaftertreatment was optionally conducted.  148 © Color. Technol. , 117  (2001)Web ref: 20010305 Syntan aftertreatment of nylon 6.6 dyed with acidlevelling and milling dyes The current study examines the effect of both Intrafix PA(Crompton & Knowles) (anionic) and Fixogene AC (a twostage treatment of, firstly, an anionic agent followed by acationic agent) (Uniqema).  Application of Intrafix PA Nylon 6.6, dyed with acid levelling and milling dyes, wasaftertreated for 20 min at 70 °C in a fresh bath at 20:1 liquorratio containing 2% owf Intrafix PA at pH 4.5 (addition of acetic acid). The samples were rinsed in cold water for 10min and then air-dried.  Application of Fixogene AC  An acid bath was first prepared using a 10 g/l stocksolution of 80% glacial acetic acid to achieve pH 4.5–5.5.2% owf Fixogene A-XF was added to this bath and stirred.Nylon 6.6 was added (to give a liquor ratio of 20:1) andthe bath temperature raised to 90 °C and maintained for30 min. The samples were rinsed in cold water for 10 minand then air-dried. A fresh bath was prepared with 2% owf Fixogene C-XF. The samples were aftertreated at 40 °C for15 min, after which they were rinsed in cold water for 10min and then air-dried. Wash test methodology The wash tests used in this study are outlined in Table 2and were conducted on nylon 6.6 dyed with the selectedacid levelling and milling dyes and optionally aftertreated. Table 2  Wash test methods used in this studyTestConditionsC06 a  [4]A2S (40 °C), B2S (50 °C), C2S (60 °C)UK-TO50 °C, 60 °CBlank UK-TO50 °C, 60 °C20 MMW b 50  CBlank 20 MMW50 °C a See ref. 4 b 20 MMW refers to 20 multiple machine washes  Blank UK-TO test  The methodology was the same as above except that only10 g/l ECE non-phosphate reference detergent was used perlitre of water (no perborate or TAED).  Multiple machine washing (20 MMW) test  A Miele washing machine model W698 was used for allwashing machine testing. The programme selector was seton cotton main wash (no pre-wash) at either 40 or 50 °Cusing medium to hard water (100 to 150 ppm calciumcarbonate) and a spin speed of 1100 rpm. The main washwas conducted for 50 min, making a 2 h total washingcycle.A 100   100 mm specimen was cut out of an optionallyaftertreated, dyed nylon fabric, and sewn onto a whitecotton backing cloth. Similar shades were attached to agiven backing cloth, thereby avoiding the problem of cross-staining (i.e. reds were kept separate from blues). Theweight of the load was adjusted to 3.0 kg using cottonsheeting for ballast, giving a liquor ratio of approximately4:1.The detergent dosage was prepared by mixing 116.0 gof ECE reference detergent (non-phosphate), 30.0 g of sodium perborate tetrahydrate and 4.86 g of TAED (92%activity).The quantities of base detergent, oxidising agent andbleach activator are typical of those used when conductinga domestic laundering operation using a commonlyavailable proprietary powder detergent. This wasdispensed via the washing machine’s dispenser drawer.  Blank 20 MMW test  The methodology was exactly as above except that only116.0 g of ECE non-phosphate reference detergent was used(i.e. no perborate or TAED). UK-TO test  A 50   100 mm test specimen was cut out of an optionallyaftertreated dyed nylon 6.6 fabric. The sample wasweighed and the appropriate volume of wash liquor wasadded to a stainless steel container of a Roaches WashtecP machine to maintain a mass to liquor ratio of 1:100.The wash liquor was prepared by dispersing 10.0 g of ECE reference detergent (non-phosphate), 12.0 g of sodiumperborate tetrahydrate and 1.94 g of tetraacetylethylene-diamine (TAED) (92% activity) per litre of water. Thesolution was stirred vigorously for 10 min at 20 °C (  2 °C)before being used for the test. The Washtec P washingmachine was programmed to raise the temperature at agradient of 2 °C/min to either 50 or 60 °C (as specified),and then run for a further 30 min. At the end of the testthe samples were rinsed under a cold running tap for 10min, after which they were air-dried. Results and Discussion Fading of a series of untreated acid levelling and millingdyes on nylon 6.6 The UK-TO test has been established using a temperatureof 60 °C, primarily to predict the fading exhibited bycellulosic-based substrates during domestic laundering attemperatures up to 60 °C. Since nylon 6.6 is likely to bedomestically laundered at somewhat lower temperatures(40 or 50 °C), the diagnostic nature of the UK-TO test forthe fading of dyed nylon during laundering was studiedat both 50 and 60 °C (Figure 1).This figure shows that all the dyes satisfy the previouslyspecified pass limit for a CIELab colour change (   E  ) < 4 [1]when the UK-TO test is conducted at a temperature of 50  C. However, when the test is conducted at 60  C, threeacid levelling dyes (dyes 2, 7 and 8) fade more dramatically(i.e. record a ‘fail’). The fading of the acid milling dyes re-mains below this limit, i.e. all ‘pass’ at both 50 and 60  C.The fading of dyed, untreated nylon 6.6 as a result of conventional C06/A2S (40 °C), C06/B2S (50 °C) and C06/ C2S (60 °C) wash fastness tests were determined [4] andare shown in Figure 2. It can be observed that the resultsare very similar to those of the UK-TO test carried out atthe same temperature.  © Color. Technol. , 117  (2001) 149Web ref: 20010305 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 0246810 Dye no.        E  ,   C   I   E   L  a   b  u  n   i   t  s  Acid levellingAcid millingPass/fail threshold in UK-TOUK-TO 50 o CUK-TO 60 o C Figure 1  Fading of untreated acid dyes on nylon 6.6 in theUK-TO test at 50 and 60 °C 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Dye no. 0246810        E  ,   C   I   E   L  a   b  u  n   i   t  s  Acid levellingAcid millingC06/A2S (40 o C)C06/B2S (50 o C)C06/C2S (60 o C) Figure 2  Fading of untreated acid dyes on nylon 6.6 in the C06/ A2S, B2S and C2S tests Since the UK-TO test is a stressed test (relative to thesingle-cycle C06/C2S test), a similar level of fading can beattributed to a wash-down/desorption effect and not anoxidative-bleach effect, which is similar to the behaviourof direct dyes on cotton [5]. Oxidative-bleach fading effect of a series of untreatedacid levelling and milling dyes on nylon 6.6 The fading exhibited by nylon 6.6 dyed with acid dyes inthe UK-TO test may be considered to consist of two com-ponents; a wash-down effect due to dye desorbing (bleed-ing) into the wash liquor plus an oxidative-bleach effectresulting from chromophoric destruction. Consequently a‘blank’ UK-TO test (using only 10 g/l ECE, non-phosphatedetergent) was conducted on dyed, untreated nylon 6.6 toestimate the amount of fading due to dye desorption alone(   E  desorp ). Subtraction of this level of fading from thatobserved in a conventional UK-TO test (   E  fade ) indicates thelevel of inherent bleach sensitivity (   E  bleach ) of the acid dyechromophore (Eqn 1): bleachfadedesorp.  EEE       (1)Figure 3 shows that none of the 16 acid dyes are inherentlyoxidative-bleach sensitive. The small negative value (i.e. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Dye no. 0–2246810        E  ,   C   I   E   L  a   b  u  n   i   t  s  Acid levellingAcid millingBleach effect (50 o C)Bleach effect (60 o C) Figure 3 Fading due to oxidative-bleaching of untreated aciddyes on nylon 6.6 in the UK-TO test 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Dye no. 0246810        E  ,   C   I   E   L  a   b  u  n   i   t  s  Acid levellingAcid milling Figure 4 Fading of acid dyes on nylon 6.6, aftertreated withIntrafix PA, in the UK-TO test at 50 and 60  C; for key seeFigure 1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Dye no. 0246810        E  ,   C   I   E   L  a   b  u  n   i   t  s  Acid levellingAcid milling Figure 5 Fading of acid dyes on nylon 6.6, aftertreated withFixogene AC, in the UK-TO test at 50 and 60  C; for key seeFigure 1   E  blank  >   E  full ) in many cases is probably explained bythe lower ionic strength at which the ‘blank’ test wasconducted. Fading of a series of aftertreated acid levelling andmilling dyes on nylon 6.6 The fading of acid dyes aftertreated with Intrafix PA andFixogene AC are shown in Figures 4 and 5, respectively.Comparing these two figures with the results in Figure 1  150 © Color. Technol. , 117  (2001)Web ref: 20010305 indicate that the use of an aftertreatment can reduce thefading of acid dyes in the UK-TO test. Indeed it can allowsome acid levelling dyes to record a ‘pass’ in the UK-TOtest even when carried out at 60  C. The study indicatesFixogene AC to be marginally superior to Intrafix PA, apartfrom in the case of dye 5, whose seemingly anomalousbehaviour (for both aftertreatments) is due to a change inhue caused by the presence of this aftertreatment. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Dye no. 010203040        E  ,   C   I   E   L  a   b  u  n   i   t  s  Acid levellingAcid millingPass/fail threshold in MMWUntreatedIntrafix PAFixogene AC Figure 6 Fading of acid dyes on nylon 6.6 after 20 machinewashes at 40  C 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Dye no. 010203040        E  ,   C   I   E   L  a   b  u  n   i   t  s  Acid levellingAcid milling Figure 7 Fading of acid dyes on nylon 6.6 after 20 machinewashes at 50  C; for key see Figure 6 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Dye no. –10010203040        E  ,   C   I   E   L  a   b  u  n   i   t  s  Acid levellingAcid millingUntreatedIntrafix PAFixogene AC Figure 8  Oxidative-bleach fading of acid dyes on nylon 6.6 after20 machine washes at 50  C Fading of a series of optionally aftertreated acidlevelling and milling dyes on nylon 6.6 after 20 MMW Figures 6 and 7 show the fading of the selected range of acid dyes, either untreated or in the presence of anaftertreatment, after 20 domestic washes at 40 and 50  C,respectively.From Figure 6 it is clear that after 20 washes at 40  C,all untreated acid levelling dyes exhibit significant fading[   E   (CIELab) > 10] and ‘fail’ the criterion set for a dyestuff whose shade is insensitive to multiple machine washing.Aftertreatment with either Intrafix PA or Fixogene ACdramatically reduces the level of fading after 20 machinewashes at 40  C, allowing some dyes to ‘pass’ the setcriterion. The performance of Fixogene AC is almostidentical to that of Intrafix PA.After 20 washes at 50  C (Figure 7), essentially all theacid levelling dyes exhibit unacceptably severe levels of fading, irrespective of whether an aftertreatment has beengiven.With the exception of dye 13, all the acid milling dyesexhibit acceptable levels of fading [   E   (CIELab) < 10], atboth 40 and 50  C, irrespective of whether an after-treatment has been applied. Oxidative-bleach fading effect of a series of optionallyaftertreated acid levelling and milling dyes on nylon 6.6after 20 MMW at 50  C The fading due to oxidative-bleaching after 20 MMW at 50  C was determined by subtracting the fading observed ina blank MMW test from that observed after a conventionalset of 20 launderings (Figure 8).Generally no net oxidative-bleaching effect wasobserved. This is consistent with the results shown inFigure 3 for the single cycle UK-TO test. The negativeoxygen-bleach fading observed by all the dyes except dye6 is attributed to an enhanced wash-down effect as a resultof the lower ionic strength of the wash liquor used in theblank MMW test. The large ‘fading’ effect of dye 6 isactually due to a severe hue change. [Since the dyeregistered a ‘pass’ in the UK-TO test (see Figure 3) it mustbe assumed that the shade change is a cumulative effect,built up over 20 washing cycles.] Conclusions In the UK-TO test, acid levelling dyes, irrespective of whether an aftertreatment had been applied, exhibited alevel of fading of less than   E   = 4 (CIELab units) at 50  C(i.e. a ‘pass’), but showed greater fading at 60  C. Meetingthe pass criterion at 60  C would be dependent on thedyestuff concentration and the aftertreatment used. Underthe same test conditions, acid milling dyes exhibited anacceptably low level of fading at both 50 and 60  C, evenin the absence of an aftertreatment. The results showedthat syntan aftertreatment offered some protection againstfading in the UK-TO test. This improvement was mostnoticeable for acid levelling dyes when the UK-TO test wasconducted at 60  C.After multiple machine washing, acid levelling dyesexhibited unacceptably high levels of fading [     E   (CIELab)< 10] when washed 20 times at 50 °C, irrespective of   © Color. Technol. , 117  (2001) 151Web ref: 20010305 whether an aftertreatment had been given. Fading after 20washes at 40  C was dye–aftertreatment dependent. Acidmilling dyes, with the exception of one dye, exhibitedacceptably low levels of fading at both 40 and 50 °C,irrespective of whether an aftertreatment had been given.Thus, the   syntan aftertreatment dramatically reduced thefading of acid dyes when tested at 40 °C. Any beneficialeffect from the syntan was marginal when the repeatwashing was carried out at 50 °C.Thus, from the results of this work, it can be concludedthat the fading of the selected acid levelling and millingdyes can be attributed to a wash-down/desorption effectrather than an oxidative-bleach effect.***The authors greatly acknowledge the support from Dr JBailey, Dr S Askew (Procter and Gamble), Dr J Lloyd(Unilever Research), Dr J Hoffmeister (Henkel), Mr KDunkerley (Yorkshire Chemicals) and Mr D McKelvey(Marks and Spencer) in the preparation of this paper. References 1.D A S Phillips, M Duncan, E Jenkins, G Bevan, J Lloyd and J Hoffmeister,  J.S.D.C  ., 112  (1996) 287.2.D A S Phillips, M Duncan, A Craydon, G Bevan, J Lloyd,C Harbon and J Hoffmeister,  J.S.D.C  ., 113  (1997) 281.3.D A S Phillips, G Bevan, J Lloyd, R Hall and J Hoffmeister,  J.S.D.C  ., 115  (1999) 100.4.  Methods of test for colour fastness of textiles and leather  (BS1006:1990) 5th Edn (Bradford: SDC, 1990).5.D A S Phillips, J Taylor, R Lakhanpal, R Hall, J Bailey,G Bevan, J Lloyd, J Hoffmeister and D McKelvey,  J.S.D.C  ., 116 (2000) 229.
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