CHAPTER 10 IMPROVING LIGHT FASTNESS OF REACTIVE DYED COTTON FABRIC WITH COMBINED APPLICATION OF ULTRAVIOLET ABSORBERS AND ANTIOXIDANTS

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1 166 CHAPTER 10 IMPROVING LIGHT FASTNESS OF REACTIVE DYED COTTON FABRIC WITH COMBINED APPLICATION OF ULTRAVIOLET ABSORBERS AND ANTIOXIDANTS 10.1 INTRODUCTION In the light fastness of dyes the impact of testing atmosphere, effect of covalent bond and admixture of dyes were studied by the researchers. The mechanisms by which dyes undergo photo degradation are thought to be complex process (Oakes 2001). However, most of the research papers on this subject suggest that UV light induced decomposition and visible light-induced photo-oxidation are the two most important pathways of fading, as shown in Equations (2.6) and (2.7). Many authors studied the chemistry and reactive species involved in photofading. Notably, Egerton & Morgan (1971b) in a series of papers showed that reactive oxygen species (ROS) were produced by irradiation of dyed fabrics which were capable of destroying dyes. Antioxidants are organic compounds that are added to oxidisable organic materials to retard auto oxidation (Cristea & Vilarem 2006). Antioxidants have been used only on fabric dyed with natural dyes for light fastness improvement.

2 167 UV photofading does not require oxygen (Batchelor et al 2003). Rich & Crews (1993) studied the ability of UV absorber to reduce fading of nylon coloured with acid dyes and concluded that UV absorbers were more effective at reducing colour change on lighter shades. Yang & Naarani (2007) studied improvement of the light fastness of reactive inkjet printed cotton and found that the water soluble UV absorber had better light fastness improvement than the water insoluble UV absorber. In the previous chapter, it has been established that UV absorber and antioxidant application shows improvement in light fastness. The light fading happened with ultraviolet light and visible light in the presence of oxygen. This chapter analyses the effect of combined application of antioxidants and ultraviolet absorbers on light fastness of reactive dyed fabrics. Nickel arylcarboxylates provide a greater improvement in the light fastness in sunlight of acid colours than did conventional stabilizers (Oda et al 1981). Nickel sulphonate or carboxylate group was therefore of interest to study the effectiveness of UV absorbers. Antioxidants containing these groupings improve the light fastness of dyes. The individual application of ultraviolet absorbers is not giving significant improvement on yellow dyed samples, so this dye is expected to fade by the visible light. Red dyed sample treated with vitamin C shows very less fading as compared to phenyl salicylate, benzophenone, cafeic acid and gallic acid treated samples. On blue dyed sample, both the antioxidant and ultraviolet absorber treatment show improvement in light fastness and vitamin C treatment shows good improvement on light fastness as narrated in the Chapter 9. In this Chapter, combined applications of antioxidants and ultraviolet absorbers were tried on reactive dyed materials by exhaust and pad-dry-cure application methods for improving light fastness properties. The

3 168 durability of the both after treatments is analyzed by subjecting the treated material to ten wash cycles and testing for light fastness MATERIALS AND METHODS Materials The materials used in this study and treatments to which they were subjected to are described in sections (single jersey fabric), (chemicals used for pretreatment), (dyes) and (chemicals used for dyeing). Antioxidants and ultraviolet absorbers used were listed in section and fastness chemicals in section of Chapter Methods The single jersey fabrics made using 30 Ne cotton yarn were pretreated by semi bleaching method ( ) and dyeing carried out by exhaust ( ) method. Antioxidants and UV absorber application methods were described in section Fastness to wash, rubbing and light were tested as per international standards explained in section 3.3. Colour strengths and colour differences were measured by colour matching system as described in and respectively RESULTS AND DISCUSSION Effect of Antioxidants on Light Fastness Improvement Visible light requires oxygen to degrade the dyes. Antioxidants like gallic acid, vitamin C and cafeic acid absorb the oxygen radicals available for photo degradation. Oxygen Radical absorbance capacity of ascorbic acid is found to be more than Gallic acid and cafeic acid. This is the reason for good

4 169 results of vitamin C (ORAC value 12.5) than cafeic acid (ORAC value 9.5) and gallic acid (ORAC value 11.7) Effect of UV Absorbers on Light Fastness Improvement The ultraviolet light is an important cause in the fading of all dyes, in the weakening of fibres and fabrics and in the photodegradation of many other substances. The mechanism was explained in the previous Chapter Light Fastness Results of Chemical Treated Samples Table 10.1 shows the colour difference (de) measured by keeping chemical treated sample as standard and 40 AFU light faded samples as batch. In dyeing industry, the tolerance for passing shade between standard and batch is de The grey scale or blue wool reading has wider denomination, so even the smallest variation in fading can be measured by colour difference de value. The statistical analysis is also possible with de value. Table 10.1 Effect of application methods on light fading in terms of (de) C.I. Reactive Yellow 84 C.I. Reactive Red 22 C.I. Reactive Blue 198 Treatment Exhaust Pad-dry- cure Exhaust Pad- dry- cure Exhaust Pad- dry- cure Without Treatment Phenyl salicylate + Vitamin C Benzophenone + Vitamin C Phenyl salicylate + Gallic acid Benzophenone + Gallic acid Phenyl salicylate + Cafeic acid Benzophenone + Cafeic acid

5 170 The ANOVA test for the chemical treatments for each three samples done and found that exhaust and pad-dry-cure shows (p-value 0.07 < 0.05) not significant. The chemical treatments with antioxidant and ultraviolet absorbers are (p-value 1.46 E -06 > 0.05) significantly different with 95% confidence level. Figure 10.1 Light fastness (40 AFU) of C.I. Reactive Yellow 84 with chemical treatment Figure 10.1 shows that light fastness results of C.I. Reactive Yellow 84 without treatment and after chemical treatment with exhaust and pad-drycure methods. The light fastness after 40 AFU light exposure is measured as de with computer colour matching. The colour difference (de) is measured by keeping dyed sample as standard and light faded samples as batch. Colour difference of dyed sample after 40 AFU light fading is found to be de 2.76, for phenyl salicylate +

6 171 vitamin C treated sample de is 1.23, for benzophenone + vitamin C treated sample de is 1.41, for phenyl salicylate + gallic acid treated sample de is 1.61, for benzophenone + galic acid treated sample de is 1.38, for phenyl salicylate + cafeic acid treated sample de is 1.55 and for benzophenone + cafeic treated sample de is The least colour difference de was observed in phenyl salicylate + vitamin C combination as the visible light induced photofading reduced by antioxidant. Oxygen radical observance capacity of the vitamin C is higher than the other antioxidants. Auto antioxidant by ultraviolet radiation is inhibited by the presence of phenyl salicylate (UV absorbers). Combination of the phenyl salicylate and vitamin C reduced the light fading from de 2.76 to Other combinations also give reduction in light fading. The nickel complexes of phenylester ultraviolet absorbers and phenolic antioxidants on light fastness in a polymer substrate are investigated and found to be showing improvement. The most positive protection was achieved in Acid dye by the presence of nickel carboxylate grouping, particularly in the case of nickel salt of salicylic acid salicylate (Oda 2004). The usage of ultraviolet absorbers or radical scavengers bearing a singlet oxygen quencher has not been investigated for improving light fastness of dyes by Oda (2004). These results correlate with our results. The ANOVA test for the yellow dyed sample helps to confirm the chemical treatments by exhaust and pad-dry-cure shows (p-value 0.63 > 0.05) that the difference are not significant. The chemical treatments with antioxidant and ultraviolet absorbers are (p-value 1.46 E -06 < 0.05) significantly different with 95% confidence level.

7 172 Figure 10.2 Light fastness (40 AFU) of C.I. Reactive Red 22 with chemical treatment Figure 10.2 shows that light fastness of C.I. Reactive Red 22 after chemical treatment. The light fastness after 40 AFU light fading is measured as de with computer colour matching. The colour difference is measured by keeping dyed sample as standard and light faded samples as batch. Colour difference of dyed sample after 40 AFU light fading is found to be de 6.35, for phenyl salicylate + vitamin C treated sample de is 4.14, for benzophenone + vitamin C treated sample de is 3.16, for phenyl salicylate + gallic acid treated sample de is 4.54, for benzophenone + gallic acid treated sample de is 4.12, for phenyl salicylate + cafeic acid treated sample de is 4.65 and for benzophenone + cafeic treated sample de is The lower colour difference was observed in benzophenone + vitamin C combination de is 3.16 achieved. It is comparable against the fabric tested without treatment de is As the visible light induced photofading reduced by antioxidant oxygen radical absorbance capacity of the vitamin C is higher than the other antioxidants, auto antioxidant by ultraviolet radiation is

8 173 inhibited by the presence of benzophenone (ultraviolet absorbers). Other combinations also give reduction in light fading. The ANOVA test for the Red dyed sample helps to confirm the chemical treatments by exhaust and pad-dry-cure shows (p-value 0.07 > 0.05) that the difference due to dyeing method are not significant. The chemical treatments with antioxidant and ultraviolet absorbers are (p-value 1 E -06 < 0.05) significantly different from the sample tested without chemical with 95% confidence level. Figure 10.3 shows that light fastness of C.I. Reactive Blue 198 after chemical treatment. The light fading after 40 AFU is measured as de with computer colour matching. The colour difference is measured by keeping dyed sample as standard and light faded sample as batch. Colour difference of dyed sample after 40 AFU light fading is found to be de 5.32, for phenyl salicylate + vitamin C treated sample de is 2.43, for benzophenone + vitamin C treated sample de is 2.21, for phenyl salicylate + gallic acid treated sample de is 2.97, for benzophenone + gallic acid treated sample de is 3.45, for phenyl salicylate + cafeic acid treated sample de is 3.12, and for benzophenone + cafeic treated sample de is Figure 10.3 Light fastness (40 AFU) of C.I. Reactive Blue 198 with chemical treatment

9 174 The lower colour difference was observed in benzophenone + vitamin C combination de from 5.32 to The visible light induced photofading got reduced by antioxidant. oxygen radical absorbance capacity of the vitamin C is higher than the other antioxidants. Further auto antioxidant by ultraviolet radiation is inhibited by the presence of benzophenone (UV absorbers). All other chemical treatments also reduced the fading. The ANOVA test for the Blue dyed sample helps to confirm the chemical treatments by exhaust and pad-dry-cure shows (p-value 0.96 > 0.05) not significant effect on light fastness. The light fastness results of the chemical treated fabrics with antioxidant and ultraviolet absorbers are (pvalue 5.9 E -06 < 0.05) significantly different against without chemical treated fabric with 95% confidence level. The effect of application method of antioxidant and ultraviolet absorber on light fastness can be derived from Table All combined chemical treatments show reduction in fading than the untreated sample. Combined application of antioxidants and ultraviolet absorber gives better light fastness than the individual application results. The above improvement is due to the reduction in fading by both ultraviolet and visible light. Both exhaust and pad-dry-cure application methods do not give significant change in light fastness result. Lower fading was observed in yellow dyed samples which are treated with phenyl salicylate and vitamin C in combination. Improvement in light fastness of Red and Blue are found with Benzophenone and vitamin C treatment compared with other treatments. As vitamin C has higher ORAC value, that combination gives good results on light fastness. Figure 10.4 shows the effect of exhaust method of chemical application on light fading. It is found that the benzophenone and Vitamin C combination shows the reduction in fading Yellow, Red and Blue dyed fabric. Figure 10.5 shows the effect of pad-dry-cure method of chemical application

10 175 on light fading. It is found that the benzophenone and Vitamin C combination shows the reduction in fading of Yellow, Red and Blue dyed fabric. Figure 10.4 Effect of exhaust method of chemical application on light fading (40AFU) Figure 10.5 Effect of pad-dry-cure chemical application on light fading(40afu)

11 Durability of Chemical Treatment for Ten Wash Cycles The durability of chemical treatment application method after ten washing cycles is analysed. Table 10.2 and Figure 10.6 show the de of the faded sample before and after ten washing cycles. It is found that the durability is good in pad-dry-cure method and not up to the expected level in exhaust method. In exhaust method, there is no bond formed between cotton and applied chemicals. Chemicals are applied only on the surface which is the reason for poor stability. The durability of pad-dry-cure application method is much better than the exhaust application. In this method, acrylic based binder helps to retain the applied chemicals on the surface of fabric. Table 10.2(a) Stability of chemical treatment after ten washing cycles in terms of light fastness (de) for Yellow 84 Exhaust Pad-Dry-Cure Treatment on Reactive Yellow 84 dyed sample Before After Before After wash wash wash wash without treatment Phenyl salicylate +Vitamin C Benzophenone+ Vitamin C Phenyl salicylate +Gallic acid Benzophenone+Gallic acid Phenyl salicylate+cafeic acid Benzophenone +Cafeic acid

12 177 Table 10.2(b) Stability of chemical treatment after ten washing cycles in terms of light fastness (de) for Red 22 Exhaust Pad-Dry-Cure Treatment on Reactive Red 22 Before After Before After dyed sample wash wash wash wash without treatment Phenyl salicylate +Vitamin C Benzophenone+ Vitamin C Phenyl salicylate +Gallic acid Benzophenone+Gallic acid Phenyl salicylate+cafeic acid Benzophenone +Cafeic acid Table 10.2(c) Stability of chemical treatment after ten washing cycle in terms of light fastness (de) for Blue 198 Exhaust Pad-Dry-Cure Treatment on Reactive Blue 198 dyed sample Before After Before After wash wash wash wash without treatment Phenyl salicylate +Vitamin C Benzophenone+Vitamin C Phenyl salicylate +Gallic acid Benzophenone+Gallic acid Phenyl salicylate+cafeic acid Benzophenone +Cafeic acid

13 178 (a) C.I. Reactive Yellow 84 (b)c.i. Reactive Red 22 Figure 10.6 Stability of application method of chemical treatment after ten washing cycles in terms of light fastness

14 179 (c) C.I. Reactive Blue 198 Figure 10.6 (Continued) Effect of Chemical Treatment on Wash Fastness The effect of chemical treatment of staining on cotton fabrics during wash fastness is shown in Table The wash fastness of Yellow, Red, Blue dyed samples are tested. The staining on adjacent fabrics is measured by grey scale. The colour change during wash fastness is also measured and no significant difference is observed. The result shows that the chemical treatment does not affect the wash fastness. Table 10.3(a) Effect of chemical treatment on wash fastness of Yellow 84 Without treatment wash fastness is 4.0 Treatment C.I. Reactive Yellow 84 Exhaust Pad-Dry- Cure Phenyl salicylate + Vitamin C Benzophenone+ Vitamin C Phenyl salicylate + Gallic acid Benzophenone+Gallic acid Phenyl salicylate+ Cafeic acid Benzophenone + Cafeic acid

15 180 Table 10.3(b) Effect of chemical treatment on wash fastness of Red 22 Without treatment wash fastness is 4.0 C.I. Reactive Red 22 Treatment Exhaust Pad-Dry- Cure Phenyl salicylate + Vitamin C Benzophenone+ Vitamin C Phenyl salicylate + Gallic acid Benzophenone+Gallic acid Phenyl salicylate+ Cafeic acid Benzophenone + Cafeic acid Table 10.3(c) Effect of chemical treatment on wash fastness of Blue 198 Without treatment wash fastness is 4.0 C.I. Reactive Blue 198 Treatment Exhaust Pad-Dry- Cure Phenyl salicylate + Vitamin C Benzophenone+ Vitamin C Phenyl salicylate + Gallic acid Benzophenone+Gallic acid Phenyl salicylate+ Cafeic acid Benzophenone + Cafeic acid Effect of Chemical Treatment on Rubbing Fastness Figure 10.7 and Table 10.4 show the effect of chemical treatment on dry rubbing fastness. The chemical treatment does not give any significant influence on dry rubbing fastness. The dry rubbing fastness is slightly

16 181 decreased in the phenyl salicylate + gallic acid combination treatment. There is no change in the dry rubbing fastness by the application technique of chemicals. Figure 10.7 Effect of chemical treatment on dry rubbing fastness Table 10.4(a) Change of dry rubbing fastness by chemical treatment of Yellow 84 Without treatment dry rubbing fastness is 4.5 C.I. Reactive Yellow 84 Treatment Exhaust Pad-Dry-Cure Phenyl salicylate + Vitamin C Benzophenone+ Vitamin C Phenyl salicylate + Gallic acid Benzophenone+Gallic acid Phenyl salicylate+ Cafeic acid Benzophenone + Cafeic acid

17 182 Table 10.4(b) Change of dry rubbing fastness by chemical treatment of Red 22 Without treatment dry rubbing fastness is 4.5 Treatment C.I. Reactive Red 22 Exhaust Pad-Dry-Cure Phenyl salicylate + Vitamin C Benzophenone+ Vitamin C Phenyl salicylate + Gallic acid Benzophenone+Gallic acid Phenyl salicylate+ Cafeic acid Benzophenone + Cafeic acid Table 10.4(c) Change of dry rubbing fastness by chemical treatment of Blue 198 Without treatment dry rubbing fastness is 4.5 C.I. Reactive Blue 198 Treatment Exhaust Pad-Dry-Cure Phenyl salicylate + Vitamin C Benzophenone+ Vitamin C Phenyl salicylate + Gallic acid Benzophenone+Gallic acid Phenyl salicylate+ Cafeic acid Benzophenone + Cafeic acid

18 183 Figure 10.8 Effect of chemical treatment on wet rubbing fastness Figure 10.8 and Table 10.5 show the effect of wet rubbing fastness by chemical treatment. The Exhaust method of chemical treatment does not improve the wet rubbing. But, the pad-dry-cure method with acrylic binder gives 0.5 rating improvement in wet rubbing fastness. It is due to the bonding of surface dyes by binding chemicals. Table 10.5(a) Effect of wet rubbing fastness by chemical treatment of Yellow 84 Without treatment wet rubbing fastness is 4.0) C.I. Reactive Yellow 84 Treatment Exhaust Pad- Dry- Cure Phenyl salicylate + Vitamin C Benzophenone+ Vitamin C Phenyl salicylate + Gallic acid Benzophenone+Gallic acid Phenyl salicylate+ Cafeic acid Benzophenone + Cafeic acid

19 184 Table 10.5(b) Effect of wet rubbing fastness by chemical treatment (without treatment wet rubbing fastness is 3.5) Treatment C.I. Reactive Red 22 Exhaust Pad- Dry- Cure Phenyl salicylate + Vitamin C Benzophenone+ Vitamin C Phenyl salicylate + Gallic acid Benzophenone+Gallic acid Phenyl salicylate+ Cafeic acid Benzophenone + Cafeic acid Table 10.5(c) Effect of wet rubbing fastness by chemical treatment (without treatment wet rubbing fastness is 4.0) Treatment C.I. Reactive Blue 198 Exhaust Pad-Dry-Cure Phenyl salicylate + Vitamin C Benzophenone+ Vitamin C Phenyl salicylate + Gallic acid Benzophenone+Gallic acid Phenyl salicylate+ Cafeic acid Benzophenone + Cafeic acid Effect of Chemical Treatment on Light Fastness of Combination Shades The Figure 10.9 shows the effect of chemical treatment on light fastness of trichromatic shades. The light fastness for 20 AFU is tested and compared in computer colour matching system against unexposed sample. It was found that the chemical treatments reduce the colour fading. The trend of

20 185 the colour fading is found similar for grey, brown and olive colour dyed fabric. The best light fastness improvement in individual chemical application was observed with Vitamin C treatment. Figure 10.9 Effect of chemical treatment on light fastness of combination shades antioxidants, In the combination treatment with ultraviolet absorbers and the light fading is reducedcompared with the individual treatment of dyed samples. The best result was found in phenyl salicylate + vitamin C combination and benzophenone + vitamin C combination. The reasons for the improvement are 1. Reduction in ultraviolet induced unimolecular colour decomposition by ultraviolet absorber. 2. Reducion in visible light induced photo oxidation of colour by removal of oxygen with antioxidants.

21 186 The Table 10.6 shows the effect of chemical treatment on light fastness of combination shades. The above treatments are statistically checked by two way ANOVA with 95% confidence level and found that the treatments are (p value 3.21E-11) significantly different from each other. The best treatment to improve the light fastness is found to be the phenyl salicylate and vitamin C combination. Table 10.6 Effect of chemical treatment on light fastness of combination shades in terms of de Colour change in de Light Grey Light Brown Light Olive Without Treatment Phenyl salicylate Benzophenone Vitamin C Cafeic acid Gallic acid Phenyl salicylate + Vitamin C Benzophenone+ Vitamin C Phenyl salicylate + Gallic acid Benzophenone+Gallic acid Phenyl salicylate+ Cafeic acid Benzophenone + Cafeic acid Effect of Chemical Treatment on Light Fastness of Combination Shades by AATCC 16E 20 AFU Method Table 10.7 shows the effect of chemical treatment on combination shades by AATCC 16E method. For the dyed sample and phenyl salicylate + vitamin C treated samples, light fastness was tested as per AATCC 16E 20 AFU method. The result shows a reduction in fading up to one rating. This will help to save the processor from any claim from the buyer for lower light fastness.

22 187 Table 10.7 Effect of chemical treatment on combination shades by AATCC 16E 20 AFU method Treatment Sample Rating Grey shade without treatment 2-3 Grey shade with Phenyl salicylate + vitamin C 3-4 Brown shade without treatment 2-3 Brown shade with Phenyl salicylate + vitamin C 3-4 Olive shade without treatment 3.0 Olive shade with Phenyl salicylate + vitamin C 4.0

23 CONCLUSION Visible light requires the oxygen to degrade the dyes. Usage of antioxidants like gallic acid, vitamin C and cafeic acid absorb the oxygen radicals available for photo degradation. The ultraviolet light is an important cause for fading of dyes and this reaction does not require oxygen. The combined application of antioxidants and ultraviolet absorbers improves the light fastness of reactive dyed fabric. The combination treatment with ultraviolet absorber and antioxidant reduces the light fading better than the individual treatment of dyed samples. The best result was found in phenyl salicylate + vitamin C combination and benzophenone + vitamin C combination. The reduction in light fading up to one rating is achieved. This research will help to save the processor to avoid claim from the buyer for lower light fastness. The chemical treatment does not change the staining on adjacent fabric during wash fastness. The chemical treatment does not give significant change in dry rubbing fastness. The dry rubbing fastness is slightly decreased on treatment with the phenyl salicylate + gallic acid in combination. There is no change in the dry rubbing fastness by the application technique of chemicals. Treating with chemicals gives 0.5 rating decrease in some of the chemical treatments. The lower wet rubbing fastness was observed only in blue shade. The red shade is treated with phenyl salicylate and vitamin C combination gives 0.5 rating improvement whereas other treatments do not alter the wet rubbing fastness. The pad-dry-cure with acrylic binder also gives 0.5 rating improvement in wet rubbing fastness due to the bonding of surfacr dyes by binding chemicals.

24 189 It is observed that the durability of the chemical treatment is better in pad, dry and cure method than the exhaust method of application. The reason is that the acrylic binder helps to bind the ultraviolet absorber and antioxidants better on to the fabric surface.