Coloration Technology

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1 doi: /cote Mordant dye application on cotton: optimisation and combination with natural dyes Yi Ding * and arold S. Freeman Department of Textile Engineering, Chemistry and Science, orth Carolina State University, Raleigh, C, 27695, USA yding4@ncsu.edu Received: 4 January 2017; Accepted: 16 March 2017 Coloration Technology Society of Dyers and Colourists It is well known that cotton fibres can be dyed through the formation of coordinate bonds involving cellulose chains, mordants such as alum, and natural dyes such as alizarin. Similarly, synthetic dyes known as mordant acid dyes can be used to dye wool fibres. Unlike mordant dyes on wool, the fastnesses of natural dyes on cotton are often low. Although concerns surrounding textile sustainability have sparked renewed interest in the use of natural dyes, extensive replacement of synthetic dyes with natural dyes is neither practical nor fundamentally possible. owever, similarities in dyeing methods using mordant and natural dyes raise the possibility of using mordant dyes as alternatives to natural dyes in the dyeing of cotton. Further, the potential for combining suitable dyes from these two classes to expand the colour gamut currently available from natural dyes on cotton seem worthy of exploration. The results of this study indicate that shades comparable with those produced by natural dyes can be obtained on cotton using select mordant dyes following Fe 2+ and Al 3+ pretreatments. The best results were obtained using a two-step/twobath process and dyes such as CI Mordant Blue 13 and CI Mordant range 6. In evaluations of mordant and natural dye combinations using the two mordant dyes logwood and sage orange as prototypes, interesting fabric shades were obtained. owever, the fastness properties of these dyes must be improved in order to produce commercially viable dyeings. Introduction Although the use of natural dyes has an extensive history [1,2], particularly natural dyes such as Tyrian purple, logwood, pollen of saffron and indigo, their use is often limited by their scarcity and the labour-intensive processes involved in their production and application [3 5]. Except for indigo, the application of natural dyes largely involves the use of metal ions (mordants) capable of providing a chemical link between the polymer chain of textile fibres and the adsorbed dye [3,6,7] (cf. Figure 1) in order to improve the colour fastness of the dyed fibres [8]. Most of the mordants used prior to the nineteenth century contained transition metals such as Cu 2+ and Cr 6+ [9,10], the use of which is not presently recommended in view of their ecotoxicity [11 13]. With the aim of supporting an ecofriendly approach, Al 3+ and Fe 2+ salts have been employed to lower the potential for harm to human health and the environment [14 17]. In 1858, the discovery of diazo compounds laid the foundation for azo dye chemistry, and subsequent industrial-scale synthetic dye manufacturing opened the door to viable alternatives to natural dyes in the marketplace [18 20]. Diverse synthetic azo dyes that covered a larger range of the visible spectrum, were more economical, of higher uniformity and more readily applied to textile fibres than natural dyes were discovered [21 23]. The dominant family of synthetic dyes are azo compounds that include the direct, reactive, disperse, basic and acid dye application families. The acid dye family is a large group of colorants that are attracted to polyamide and protein fibres such as nylon, wool and silk [24], which leads to electrostatic interactions between the dye and fibre when dyeings take place under acidic conditions. They include mordant dyes that are typically treated with transition metal ions such as Cr 3+ or Fe 2+ after wool fabric has been dyed with the metal-free dye ligand, which leads to improvements in wash and light fastness [25]. As cotton fibres can be dyed by coordination bonding of cellulose molecules to natural dyes with the aid of various metal ions [26], it was of interest to determine whether this process could also be used to apply mordant dyes to cotton [24]. Moreover, if mordant dyes can be applied to cotton using the same procedure as natural dyes, will they show acceptable colour uptake and fastness properties? If the answers to these questions are in the affirmative, the use of mordant dyes might help to address two longstanding disadvantages of vegetable-based natural dyes that refer to, respectively, their lack of homogeneity from one geographic region to another and from 1 year to another, and the large volume of waste plant material that remains after the extraction of vegetable-based dyes. Based on these considerations, a group of mordant dyes were screened for use on cotton. Examples of these are shown in Figure 2. This group of dyes included ligands with medially metallisable ortho, ortho -bis-hydroxyazo and ortho-hydroxy, ortho -carboxyazo groups. Also used was a terminally metallisable azo dye derived from salicylic acid (CI Mordant range 6). The selection of mordant dyes and their initial amounts was based on results from our previous work involving the use of Fe 2+ and Fe 3+ salts in the post-treatment of mordant dyes on wool, in which medium shades were obtained [25,27]. Five natural dyes were also selected for this study, examples of which are also shown in Figure 2. Following dye application, L*a*b* and K/S values were measured. Different dyeing methods were also explored to determine the effects of mordanting prior to and during dye 2017 The Authors. Coloration Technology 2017 Society of Dyers and Colourists, Color. Technol., 0, 1 7 1

2 C 2 C 2 M n+ Dyeing methods Mordant dye Trial 1 Al 2 (S 4 ) 3 or FeS 4 ( g) was dissolved in distilled water (300 ml). Cotton fabric (5 g) was added at 50 C and the bath was heated to 100 C with agitation, held for 45 min, and reduced to 80 C. Mordant dye powder ( g) was dissolved in distilled water (10 ml) and added to the bath. The bath was heated to 100 C and held for 50 min. The fabric was removed after the bath temperature had fallen to 50 C, rinsed with distilled water at 25 C and air-dried. application, as well as the potential benefits of combining tannic acid (tannin) with a metal mordant a process shown to enhance natural dye wet fastness on cotton. It is known, for instance, that alum does not bond as readily with cotton as it does with wool. Tannin bonds readily with cellulose molecules and alum interacts well with the tannin cellulose complex. Experimental Figure 1 Bonding of a natural dye to cellulose by means of a mordant (M n+ ) as illustrated with alizarin Materials Bleached cotton and multi-fibre fabric o. 10 were obtained from Testfabric, Inc. (USA). CI mordant dyes were obtained from Standard Dyes (USA) and were used as received. Samples of natural dyes were obtained from Jeffrey Krause (College of Textiles, orth Carolina State University) and included logwood, sage orange, cochineal and chestnut. Aluminium sulfate [Al 2 (S 4 ) 3 ], sodium dihydrogen phosphate monohydrate (a 2 P 4 2 ), tannic acid, dimethyl formamide (DMF), sodium carbonate (a 2 C 3 ) and iron sulfate (FeS 4 ) were obtained from Fisher Scientific (USA). An Ahiba Texomat dyeing machine was used to dye the cotton fabrics. The open beakers of this machine were ideal for adding dyeing auxiliaries, as well as for observing fabrics and solution throughout the procedure. An Atlas launder-ometer and a Ci3000+ Xenon weather-ometer were used to assess wash and light fastness, respectively. An Atlas crockmeter was used to assess crock fastness and an X-Rite Colorimeter was used to measure L* a* b* and K/S values. The software was set to use illuminant D 65 with the ultraviolet (UV) light included and the CIE 10-degree supplementary standard observer. The samples tested were folded twice and measured twice by rotating the sample 90 degrees between each measurement. The average value was recorded. The K/S value of each sample was calculated by adding the K/S value of each 10 nm over the nm region as follows: Sum K k¼700 ¼ X K S S k¼400 UV-visible (UV-Vis) spectra were recorded using a Cary 300 spectrophotometer (Agilent Technologies, USA) coupled with Cary Win UV software. k Mordant dye Trial 2 Mordant ( g) was dissolved in distilled water (300 ml) and heated to 50 C. Cotton fabric (5 g) was added and the bath was heated to 80 C and held for 45 min. The fabric was removed from the bath when the temperature had cooled to 50 C and placed in 300 ml Mordant dye solution containing g dye. The bath was heated to 80 C and held for 50 min. The fabric was removed after the dye bath temperature had reached 50 C, rinsed in water at 25 C and air-dried. Two mordant levels (19 and 109 vs Trial 1) were used as a step towards optimising the amount of mordant needed to apply the dyes to cotton. Mordant dye Trial 3 Cotton fabrics (5 g) were placed into Texomat dyeing machine beakers containing 300 ml tannic acid solution (1.5 g/l) and the solution was heated to 70 C. The fabrics were agitated for 2 h while the temperature was lowered to 25 C. The fabrics were removed, rinsed with water, added to a preheated (70 C) solution (300 ml) containing a mixture of g/l Al 2 (S 4 ) 3 and 2 g/l soda ash, and agitated periodically for 2 h. The fabrics were removed, squeezed, dried for 24 h at 40 C, and used in the dyeing step. Dye baths were prepared using g dye in 300 ml distilled water. After the mordanted fabrics were added, the baths were heated to 70 C, held for 60 min, cooled to room temperature and left overnight. Subsequently, the fabrics were rinsed in water and washed free of residual unfixed dye using 300 ml a 2 P 4 2 (7.4 g/l) at 70 C for 30 min. They were then rinsed again in distilled water and hung to dry in an oven at 40 C. This set of experiments was run in triplicate. ptimised dyeing procedure for natural dyes and mordant dyes Cotton fabrics (5 g) were placed into beakers of 300 ml tannic acid (1.5 g/l) solutions and the baths heated to 70 C. The fabrics were agitated for 2 h while the temperature dropped to room temperature. Fabrics were removed, rinsed with distilled water, placed in a preheated (70 C) solution containing a mixture of g/l Al 2 (S 4 ) 3 and 2 g/l soda ash, and agitated periodically for 2 h. The fabrics were removed, squeezed, dried for 24 h at 40 C, and used in the dyeing step. Pretreated cotton fabrics (5 g) were added to 300 ml baths containing sage orange, logwood, cochineal, chestnut or Mordant dye (1.25 g). The baths were heated to 70 C and held for 60 min. Each dye bath was cooled to room The Authors. Coloration Technology 2017 Society of Dyers and Colourists, Color. Technol., 0, 1 7

3 C 2 a Cl a 3 S CI Mordant Blue 13 S 3 a a 3 S CI Mordant Brown 40 a 3 S C 2 a CI Mordant range 6 S 3 a C 2 a 2 S C 2 a C 2 a 3 C 3 C CI Mordant Yellow 30 CI Mordant Yellow 8 R R =, sage orange dye (Scandenone and Auriculasin) Logwood dye (aematein) C 3 C 2 Cochineal dye (Carminic acid) Chestnut dye (Cutch) Figure 2 Chemical structures of the mordant and natural dyes used in this study temperature, after which fabrics were left in the baths for another hour. The fabrics were rinsed with distilled water, washed free of unfixed dye using 300 ml a 2 P 4 2 (7.4 g/l) at 70 C for 30 min, rinsed, and hung to dry in an electric oven at 40 C. Combination dyeing with mordant and natural dyes CI Mordant Blue 13, CI Mordant range 6, logwood and sage orange were selected for this component of the study. An Ahiba Texomat dyeing machine (Ahiba AG, Switzerland) was used to dye the cotton fabrics in triplicate. Twelve samples of mordanted fabrics (5 g) were added to 300-ml dye baths containing g or 1.25 g dye. The baths were heated to 70 C, held for 60 min and then cooled to room temperature. Fabric was left in the dye baths overnight. After dyeing, the fabrics were rinsed in distilled water and washed using 300 ml a 2 P 4 2 (7.4 g/l) at 70 C for 30 min to remove any remaining surface dye. Fabrics were then rinsed in water and hung to dry in an electric oven at 40 C. Measurements Fastness measurements Fastness tests performed on the dyed fabric samples were the Colour Fastness to Laundering: Accelerated (AATCC Test Method ), Colour Fastness to Light (AATCC 2017 The Authors. Coloration Technology 2017 Society of Dyers and Colourists, Color. Technol., 0, 1 7 3

4 Test Method ) and Colour Fastness to Crocking (AATCC Test Method ). Colour analysis An X-Rite Color i7 benchtop spectrophotometer (X-Rite, USA) equipped with Color imatch Professional software was used to obtain average values for L*a*b* and K/S at k max of the fabrics. The colorimetric information was also recorded using a DataColor SF600X spectrophotometer (DataColor, Switzerland) equipped with Color icontrol software. The CIE L*a*b* colour system and illuminant D65-10 mode were selected. Fabric sample colours were generated by the software automatically. Dye bath exhaustion To determine dye bath exhaustion levels, 50 ll dye bath aliquots were removed, diluted to 6.0 ml using DMF, and absorbance measurements made before and after dyeing. An Agilent Technologies Cary 300 UV-Visible spectrophotometer was used for these measurements and the Beer Lambert law was used to determine the final dye concentration in the bath as follows: A = Cel where A is absorbance, C is the concentration of the sample in mol/l, e is molar absorptivity, and l is the path length in cm [28]. The absorbance of solutions before and after dyeing was used to determine dye uptake levels as follows: C 1 /C 2 = A 1 /A 2 dye uptake = 1 (C 1 C 2 )/C 1 where C 1 and C 2 represent the concentrations of the dye bath before and after dyeing, respectively, and A 1 and A 2 represent absorbance values at k max before and after dyeing, respectively. Results and Discussion Mordant dye trials In Trial 1 studies, mordant treatments using predissolved Al 3+ gave visually brighter shades on cotton than those using Fe 2+, which is consistent with results reported elsewhere [29]. As a transition metal, Fe has empty d- orbitals capable of participating in backbonding, which enhances the photostability of azo dyes, unlike Group III metals such as Al. Further, both sets of dyeings were more uniform than those arising from the addition of solid mordants to dye baths following exhaustion of mordant dye onto cotton at 100 C. Results from K/S and L*a*b* measurements are presented in Table 1. K/S results indicate that Fe 2+ gave a greater depth of shade than Al 3+ when CI Mordant range 6, a terminally metallisable salicylic acidbased azo dye ligand, and CI Mordant Blue 13, an ortho, ortho -bis-hydroxyazo ligand, were used. It is also clear that CI Mordant range 6 (a terminally metallisable dye with a salicylic acid end group) and CI Mordant Blue 13 (a medially metallisable azo dye with ortho, ortho -hydroxy groups) gave greater depths of shade than the three other mordant dyes, giving K/S values of 8.3 and 4.0, respectively, using the Fe 2+ mordant. Although Al 3+ gave brighter shades, the depths (K/S values) were low in each case, suggesting a weaker interaction between the ligands and this mordant. The three dyes with ortho-hydroxy, ortho - carboxy groups forming the metallisable ligand were outperformed. In Trial 2 experiments, the dye bath temperature was lowered from 100 C to 80 C in an effort to increase exhaustion levels. In addition, separate baths were used to apply the mordant and dye in order to enhance shade uniformity on cotton. Dye bath concentrations were carried over from Trial 1 and two mordant levels were used. Results from these experiments are presented in Table 2 and indicate that pastel to medium shades were obtained, and that CI Mordant range 6 and CI Mordant Brown 40 provided the darker shades. At the 1.6% (omf) Al 3+ level, CI Mordant range 6 gave a K/S value of 3.0 and CI Mordant Brown 40 gave a K/S value of 2.7. Al 3+ gave slightly higher dye uptake on cotton than it had in Mordant dye Trial 1. Further, all mordant dyes gave level shades in Trial 2 studies. Interestingly, shade depth from Fe 2+ mordant were decreased by using the lower dye bath temperature and the dyeings obtained were generally duller and darker than those from Al 3+ (supporting information, Figure S1, online). Lowering the temperature to 80 C significantly increased the exhaustion of dyes following the Al 3+ mordant pretreatment. owever, both yellow dyes gave pastel shades on cotton. L* values of were noted. Both of these dyes have an anthranilic acid-based azo pyrazolone structure, whereas CI Mordant Blue 13 and CI Mordant Brown 40 have arylazo-naphthol structures, and CI Mordant range 6 has a salicylic acid-based end group as the metallisation site. As a step towards optimising the amount of Al 3+ mordant needed to apply mordant dyes to cotton and in order to capitalise on its provision of brighter shades, a comparison of 1.6% (omf) Al 3+, the amount used initially in Trial 2, and a 10-fold mordant level (16% omf) was conducted. It is clear Table 1 Colour values obtained from dye and mordant levels used in mordant dye Trial 1 Fe 2+ Al 3+ CI Mordant dye Bath concentration a FeS 4 or Al 2 (S 4 ) 3 b L* a* b* K/S L* a* b* K/S Blue % range % Yellow % Yellow % Brown % a Based on a 300 ml dye bath. b Percentage omf (on mass of fibres) The Authors. Coloration Technology 2017 Society of Dyers and Colourists, Color. Technol., 0, 1 7

5 Table 2 Colour values obtained from dye and Al 3+ mordant levels used in mordant dye Trial 2 Al 3+ (1.6%) b Al 3+ (16%) b CI Mordant dye Bath concentration a L* a* b* K/S L* a* b* K/S Blue % range % Yellow % Yellow % Brown % a Based on a 300 ml dye bath. b Percentage omf (on mass of fibres). Table 3 Results of mordant dye Trial 3 studies Mordant dye Bath concentration a L* a* b* K/S WF b LF b CF b CI Mordant Blue % CI Mordant range % CI Mordant Brown % WF, wash fastness; LF, light fastness; CF, crock fastness. a Based on a 300 ml dye bath. b Rating scale: 1 (poor) to 5 (excellent). from the L* and K/S values in Table 2 that a 10-fold increase in Al 3+ did not increase shade depth. Instead, except for CI Mordant Yellow 8, a perceptible decrease in shade depth occurred. This suggests dye desorption from the fabric occurred, in favour of a dye mordant interaction in the bath rather than on the fibre. Further, the 1.6% (omf) Al 3+ treated CI Mordant Blue 13-dyed fabric had a brighter and more reddish blue colour compared with the 16% (omf) Al 3+ sample. Further, the a* and b* values for CI Mordant Brown 40-dyed fabric were much higher for the 16% (omf) Al 3+ treated sample than for the 1.6% (omf) Al 3+ pretreatment. In this case, a reddish and yellowish brown shade was produced. Mordant dye Trial 3 experiments employed a tannic acid treatment step in front of an Al 3+ pretreatment, prior to dye application, in an attempt to enhance mordant dye fixation in the knowledge that tannic acid has been used to improve natural dye uptake, as well as wash fastness, on cotton [30]. Because of the very low uptake of the mordant yellow dyes during Trials 1 and 2, they were omitted from this component of the study. In addition, dyeing experiments involving increasing concentrations of dye to levels twoand four-fold those used in Trials 1 and 2 were conducted. Colour values from mordant dye Trial 3 are shown in Table 3. The results show that tannic acid improved the shade depth for CI Mordant Brown 40 only, a dye containing and C 2 groups in the ortho, ortho -positions adjacent to the azo bond. Colour fastness data for the dyeings were also recorded; the results are shown in Table 3. Generally, wash fastness was low, but was slightly better using CI Mordant Blue 13, and light fastness was moderate, except when CI Mordant Brown 40 was used. Crock fastness was good in each case. With references to dye bath exhaustion levels, the best results were obtained with the use of CI Mordant Brown 40, which gave about 68% exhaustion, and CI Mordant range 6, which gave exhaustion of 38%. In view of the low percentage exhaustion values, a set of experiments to determine the effects of two- and four-fold increases in mordant dye concentrations in the dye bath were conducted. At the four-fold dye level, percentage exhaustion levels increased from 27% to 56% for CI Mordant Blue 13 and from 38% to 55% for CI Mordant range 6. owever, CI Mordant Brown 40 exhaustion dropped to 28% for reasons that remain unclear. ptimised dyeing procedure for mordant and natural dyes Duplicate runs were conducted for this component of the study. The resulting L*, a*, b* and K/S values and fastness properties are shown in Table 4. Results show that sage orange gave the highest K/S value of 8.8. CI Mordant Blue 13 provided the second deepest shade with a K/S value of 6.8. CI Mordant Brown 40 and CI Mordant range 6 also provided interesting pastel shades, which is typical of natural dyes. A comparison of a* and b* values indicated that the orange dyes, CI Mordant range 6 and sage orange, gave similar hues. In addition, the mordant dye shade on cotton was brighter, but the natural dye shade was deeper. Table 4 shows that the highest wash fastness rating belonged to chestnut, which was rated at 4 5 on a scale of 1 5. Wash fastness ratings for logwood and CI Mordant Blue 13 were in the 3 4 range. CI Mordant Blue 13 provided K/S values of 6.8 before washing and 2.9 after washing, and a colour shift from purple blue to blue was observed. In this case, a* values shifted from 9.2 to 1.7. This was also consistent with the wash water, which was red after washing, indicating that the more soluble unmetallised dye was removed during washing. The light fastness ratings of fabrics resulting from the optimised dyeing procedure were comparable for the two dye classes, ranging from 2 3 to 5, with the best results 2017 The Authors. Coloration Technology 2017 Society of Dyers and Colourists, Color. Technol., 0, 1 7 5

6 Table 4 Results obtained from the optimised dyeing procedure Dye L* a* b* K/S WF a LF a CF a CI Mordant Blue CI Mordant Brown 40 CI Mordant range 6 sage range Chestnut Cochineal Logwood WF, wash fastness; LF, light fastness; CF, crock fastness. a Rating scale: 1 (poor) to 5 (excellent). obtained from CI Mordant range 6. Typically, the absence of structural features giving protection to the azo bond via steric and electronic effects [31] makes azo dyes more susceptible to degradation upon exposure to UV light. owever, certain simple diazo dyes that contain a phenol end group (e.g. Disperse Yellow 23 and Disperse range 29) are known to have better light fastness than the mono-azo counterparts. Results from crock fastness assessments indicated CI Mordant Blue 13 gave the best crock fastness, followed by CI Mordant Brown 40, CI Mordant range 6 and logwood, with ratings of 4 5. The lowest rating was associated with sage orange (3 4), but was still acceptable. In each case, it is clear that the resultant fibre coloration is not merely a surface adsorption process. Dye penetration into the fibre has occurred. Mordant and natural dye combinations CI Mordant dyes Blue 13 and range 6 and natural dyes logwood and sage orange were used in this component of the study. Results from triplicate experiments are summarised in Table 5, where B/L 1 6 and / 1 6 represent CI Mordant Blue 13 logwood and CI Mordant range 6 sage orange combinations, respectively. Whereas a two-fold increase in dye bath concentration from 0.2% to 0.4% (owb) increased K/S levels for both combinations, the shade Table 5 Results obtained from mordant natural dye combination trials Fabric L* a* b* K/S WF a LF a B/L B/L B/L B/L B/L B/L / / / / / / B/L, CI Mordant Blue 13 logwood combination; 1 3, 0.2% (owb) dye bath concentration; 4 6, 0.4% (owb) dye bath concentration. /, CI Mordant range 6 sage orange combination; 1 3, 0.2% (owb) dye bath concentration; 4 6, 0.4% (owb) dye bath concentration. WF, wash fastness; LF, light fastness. a Rating scale: 1 (poor) to 5 (excellent). depth obtained from CI Mordant Blue 13 logwood increased by 70%, but the corresponding CI Mordant range 6 sage orange shade depth rose by only 22%. It is also evident that the fabrics dyed with the CI Mordant Blue 13 logwood combination had significantly darker shades (L*) than those achieved with CI Mordant range 6 sage orange. Results from fastness testing are also presented in Table 5. Both dye combinations gave poor wash fastness, with grey scale ratings of no higher than 2. Similarly, the highest rating for light fastness was 2 3 and was achieved using CI Mordant range 6 sage orange at either shade depth. A comparison of these results with those from assessments of CI Mordant Blue 13 and logwood individually clearly shows that combining the two dyes led to a significant reduction in wash and light fastness (cf. B/L 1 6 vs Table 4). Dyeing with CI Mordant range 6 and sage orange individually also resulted in better light fastness than that observed with the combination, and in greater wash fastness. The wash fastness results suggest that mordant dye?mordant natural dye interactions occur at the expense of dye?mordant fibre interactions, which facilitates the removal of dye from the fibre. The reason for reductions in light fastness is not evident, but it seems that important excited state internal conversion processes are inhibited when the dye combination is applied. To assess the effects of dyeing machine type on dye uptake in combination dyeings, our studies included the use of the closed (pressure) chamber of an Eco Ahiba uance dyeing machine in awareness of the wide use in industry of pressure machines vs atmospheric dyeing machines. Measurements of shade depths and fastness properties of the dyed fabrics showed that K/S levels achieved with the CI Mordant Blue 13 logwood combination ranged from 3.3 to 5.1, which are comparable with those obtained using the Ahiba Texomat machine. The CI Mordant range 6 sage orange combination gave K/S values a full unit lower than those obtained using the atmospheric Ahiba Texomat machine. This was an unexpected outcome because greater fibre swelling in the pressure dyeing environment and enhanced dye penetration might be expected. It appears that instead the solubility of the dye is enhanced in the bath, which reduces dye exhaustion. A comparison of the fastness properties of fabric samples dyed in the two machines revealed a slight improvement in light fastness when the Ahiba uance was used to apply the CI Mordant Blue 13 logwood combination, whereas wash fastness was a little lower. For the CI Mordant range 6 sage orange combination, there was no change in wash fastness, but light fastness was lowered by using the Ahiba uance. Conclusion Results from a systematic study of CI Mordant dye application on cotton indicate that shades comparable with those obtained from the typical natural dye can be generated with these synthetic (mordant) dyes, following Fe 2+ and Al 3+ pretreatments. The best results were obtained using a twostep, two-bath process that involved the addition of mordant and dye to cotton fabric in separate baths. Good The Authors. Coloration Technology 2017 Society of Dyers and Colourists, Color. Technol., 0, 1 7

7 crock fastness was obtained with each dye evaluated, and acceptable light fastness was achieved with CI Mordant Blue 13 and CI Mordant range 6. Unlike the natural dye application process, tannic acid did not have a clear beneficial effect on the wash fastness of the mordant dyes, which was low in all cases. Further, no clear correlation between mordant dye structure and light or wash fastness was observed. Interestingly, the diazo dye CI Mordant range 6, which has a salicylic acid end group as the ligand, gave the best light fastness. As promising shade depths and fastness properties were obtained in cotton with the use of certain individual mordant dyes, Mordant dye and natural dye combinations such as CI Mordant Blue 13 logwood and CI Mordant range 6 sage orange were examined. Initial results show that dyes in both pairs exhaust onto cotton. owever, the production of a commercially feasible process will require enhanced fastness properties. References 1. Zollinger, Color Chemistry, 3rd Edn (Weinheim: Wiley-VC Verlag, 2003) J Dean, A eritage of Colour: atural Dyes Past and Present (Tunbridge Wells: Search Press, 2014) J Dean, Wild Color: The Complete Guide to Making and Using atural Dyes (ew York, Y: Watson-Guptill, 2010) S V Singh and M C Purohit, Universal J. Environ. Res. Technol., 2 (2012) E Tsatsaroni and M Liakopoulou-Kyriakides, Dyes Pigm., 29 (1995) M Montazer, M Parvinzadeh and A Kiumarsi, Color. Technol., 120 (2004) S Freeman and A T Peter, Colorants for on-textile Applications (Amsterdam; ew York, Y: Elsevier, 2000) K Prabhu and M D Teli, Int. Dyers, 196 (2011) M Sugar, The Complete atural Dyeing, (Lemoyne, PA: J Richard oel, 2002) P S Vankar, andbook on atural Dyes for Industrial Applications (Delhi: ational Institute of Industrial Research, 2007) M Tutak and E Korkmaz, J. at. Fibers, 9 (2012) R Siva, Curr. Sci., 92 (2007) A T Peter and S Freeman, Physico-Chemical Principles of Color Chemistry (London; ew York, Y: Blackie Academic & Professional, 1996) D Cardon, atural Dyes: Sources, Tradition, Technology and Science (London: Archetype Publications, 2007) M M Kamel, F Abdelghaffar and M M EI Zawahry, J. at. Fibers, 8 (2011) Y Lee and D Kim, Fiber Polym., 5 (2004) P S Vankar, R Shanker and A Verma, J. Clean. Prod., 15 (2007) Ali, Water Air Soil Pollut., 213 (2010) M Bulut and E Akar, J. Clean. Prod., 32 (2012) P Leitner, C Fitz-Binder, A Mahmud-Ali and T Bechtold, Dyes Pigm., 93 (2012) R S Blackburn and S M Burkinshaw, Green Chem., 4 (2002) M Asgher, Water Air Soil Pollut., 223 (2012) S Divaniyan, D Kharb, C Raghukumar and R Kuhad, Water Air Soil Pollut., 219 (2010) M Kamel, M M Kamel, B M Youssef and G M Shokry, J.S.D.C., 114 (1998) A Bardole, S Freeman and A Reife, Text. Res. J. 68 (1998) A K Samanta, P Agarwal and S Datta, J. at. Fibers, 6 (2009) A Bardole, Iron (II) and iron (III) as alternatives to chromium in the metallization of mordant dyes, Masters thesis, orth Carolina State University (1996) A D Broadbent, Basic Principles of Textile Coloration (Bradford: Society of Dyers and Colourists, 2001) J ooker, D inks and Freeman, Color. Technol., 119 (2003) L Rudkin, atural Dyes (London: A & C Black Publishers, 2001) P F Gordon and P Gregory, rganic Chemistry in Colour (eidelberg, Berlin: Springer-Verlag, 1987) 291. Supporting Information Additional Supporting Information may be found in the online version of this article: Figure S1. Computer-generated images of cotton fabrics from mordant dye Trial 2 using (left) Al 3+ and (right) Fe The Authors. Coloration Technology 2017 Society of Dyers and Colourists, Color. Technol., 0, 1 7 7