Photofading Mechanism of Reactive Blue Dyes on Cotton against Sunlight and Xenon-arc lamp
Abstract
The photofading mechanism investigates in this study for dyeing of cotton fabric with five different blue reactive dyes by exposing sunlight and xenon arc lamp. Fading rate has enhanced by prolonging the time period 24-120 hr and stabilized at 72 hr of irradiation. Furthermore, a significant color difference obtained with unexposed and exposed cotton fabric dyeing with di fluro pyrimidine azo (ΔE= 5.5) by irradiating xenon arc lamp. The structural characteristics of both the dye and substrates confirmed by using FT-IR and UV-Vis spectroscopy. Among five reactive blue dyes, the di fluro pyrimidine and copper metal complex azo dyes appeared most sensitive. However anthraquinone based reactive dyes showed the best stability for sunlight and xenon arc lamp.
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Purpose
The purpose of this paper is to compare light fastness assessments by exposure of fabric dyes with various dyes in daylight and an artificial xenon arc lamp.
Design/methodology/approach
Cotton fabric dyed with 66 reactive, vat, azoic and direct dyes dyed in different depths were exposed to daylight and Xenon arc lamp for assessment of light fastness by standard methods. The light fastness rating and fading hours by the two methods were analysed and compared statistically.
Findings
The correlation between the corresponding light fastness rating (LFR) measured in Xenotest and daylight is quite high (0.93). The logarithmic correlation coefficients between fading hour (FH) and LFR in Xenotest and daylight are 0.95 and 0.88, respectively. For Xenotest, the assessed LFRs are same as those predicted from geometric progression up to LFR of 5.5, and thereafter, the former is higher. On the other hand, in the case of daylight, the assessed LFR is lower. Assessments for three successive seasons showed high repeatability in case of Xenotest and moderate repeatability in case of daylight. Assessments for three successive seasons showed high repeatability in case of Xenotest and moderate repeatability in case of daylight.
Research limitations/implications
The exposure conditions in daylight cannot be controlled or standardised, whereas the exposure in Xenon arc lamp in the accelerated fading instrument can be strictly controlled. These differences in exposure control may affect the repeatability of experimental findings.
Practical implications
Inconsistent ratings may be because of little deterioration of samples during storage, as well as seasonal variation of daylight.
Social implications
There are no direct social implications.
Originality/value
The researches on the comparison of the two light fastness assessment methods have not been reported in any recent publication to the best our knowledge.
Activation energies of fading of three different dye-fiber systems have been measured by fading at different temperatures: (i) three acid dyes on gelatin film, (the behavior of wool is expected to be similar to that for gelatin); (ii) four reactive dyes on Cellophane film; and (iii) three reactive dyes on nylon film. Activation energies of fading range between about 3 and 18 kcal/mole and depend on the nature of the substrate and the class of the dye.
Activation energy values are found to decrease with loosening of the structure of the fiber, e.g. wool, which gives low values. Fading of wool seems to be almost insensitive to wide variations in humidity. Activation energy values of disperse dyes on nylon and disperse reactive dyes (Procinyl) on the same substrate are about the same, which tends to show that the reactive type of dye-fiber bond is not effective in lightfastness.
The fading rate curves and the characteristic fading curves of seven azo dyes on cellulose diacetate (CDA) and polyamide (PA) films were examined. Fading was enhanced by prolonging the time of irradiation and decreased by increasing dye concentration on the substrate, irrespective of the nature of the latter or the dye used. However, the magnitude of fading was governed by structural characteristics of both dye and substrate. The results obtained suggested that dyes of higher ability to aggregate forming large and uniform particles were more resistant to fading than those forming smaller and/or a non-uniform size of dye aggregates. Similarly, substrates of higher polarity and porosity acted in favour of association of dye molecules, thereby impeding fading. These suggestions were, indeed, substantiated by measurements of the extinction ratio after different irradiation periods.
The reductive and Oxidative photofading of Red 22 and Black 5 on cellulose on exposure in substrate solutions was kinetically examined by spectral analysis. In the presence of DL-mandelate and oxygen the oxidative and reductive fading of both the dyes occurred simultaneously from the beginning and later the oxidative fading was suppressed depending upon the concentration of oxygen. On exposure of Red 22 in the presence of lactate of high concentration and oxygen oxidation initially occurred and was followed by reduction with complete inhibition of oxidation. An increase in the concentration of oxygen promoted the initial oxidation and an increase in the concentration of substrate promoted subsequent reduction. On exposure of Black 5 in the presence of lactate of high concentration and oxygen similar fading behavior to that in DL-mandelate solutions was observed but the oxidation products formed were immediately further photo-reduced.
Dyes featuring two reactive groups or one bifunctional group, when applied to wool and silk, can reduce the solubilities of these fibers in appropriate solvent systems. This is consistent with the formation of crosslinks during dyeing. Of the nine dyes studied, the most effective crosslinker possessed two well separated reactive groups. On wool, dyes with more closely located reactive sites were comparable in effect to formaldehyde. The reduced solubility of wool dyed with dyes containing one α-bromoacrylamide group indicates a bifunctional reaction of this group; this is in agreement with a hy pothesis stating bifunctionality.
On silk, α-bromoacrylamide dyes undergo bifunctional reactions to a limited extent only, if at all. With other bifunctional dyes, the number and distribution of cnosslinks on silk depend on the type of reactive group and the method of dyeing. The inhibition of dye penetration after crosslink formation on silk in dyeings with a difluorochlo ropyrimidine dye at 40°C can be greatly alleviated by dyeing at 90°C, and thereby distributing the crosslinks more evenly throughout the fiber. The effectiveness of the highly reactive dichlorotriazine system in crosslinking depends on the method of dyeing used on wool and on silk.
The effects of xenon-arc radiation, using an Atlas Weather-Ometer and a clear glass pyrex filter system, on the breaking strength, extension-to-break, and the energy-to-break for several nylon, polyester, and polyester/cotton yarns were compared to these of outdoor exposure behind window glass. Both types of exposure resulted in similar, related rates of loss for these properties for all yarns. Lamp age in the Weather-Ometer intluenced degradation rates in some cases. All nylon yarns degraded slowly during Weather-Ometer exposure and rapidly outdoors behind window-glass, in com parison to polyester, while the polyester/cotton yarns degraded at similar rates in both locations. Yarn-denier variation and the presence of an optical, brightener had no detectable effect on degradation rates. Sensitization by anatase in nylon and polyester yarns occurred during outdoor exposure, but not during Weather-Ometer exposure.
The fading of nine reactive dyes on cotton fabrics under light and perspiration was investigated using the ATTS standard and many factors affecting the stability of these dyes were discussed, viz. exposure environment, chromophores of dyes, the pH value and components of the artificial perspiration. The experimental results show that reactive dyes exhibit lowest stability under simultaneous exposure to light, perspiration and oxygen in a wet state. Among all selected dyes, Cu-complex azo reactive dyes appear to be the most sensitive, whereas anthraquinone reactive dyes show the best stability. The pH value of perspiration may also greatly influence the fading of dyes by affecting the hydrolytic stability of dye–fibre bonding. Furthermore, the study on the contribution of artificial perspiration components discloses that some acidic components play major roles in the fading of the dyes and inorganic salts usually decelerate the fading extent.
Poly(ethylene terephthalate) films having different morphologies have been coloured with some azo dyes. Isotropic and anisotropic films showed an inversion in dyeing behaviour as well as in light fastness, always at crystallinity β=0.5. We have interpreted the phenomenon in terms of a different localisation of the dye in going from a structure of PET corresponding to a free-volume model to a structure corresponding to a pore model. It was found that polymer morphology strongly affected dye photofading whilst the thermal cis-trans isomerisation of azo dyes in the PET matrix depended only on the amorphous region; below the glass transition temperature isomerisation proceeded in a way that was determined by the effects of restrictions in the mobility of the photochrome itself.
Self-sensitised and Methylene Blue-sensitised photo-oxidation of 4-arylazo-1- and 1-arylazo-2-naphthols gives 1,4- and 1,2-naphthoquinone, respectively, via the reaction of singles oxygen with the hydrazone tautomeric forms. The reactivity in both cases decreases with increasing electron-withdrawing strength of substituents in the aryl ring.
Vinylsulfonyl reactive dyes on cellulose, present as a mixture of an aminopyrazolinyl azo yellow dye (1) and a phthalocyanine blue dye (2) showed marked catalytic fading of dye 1 under wet conditions, but only a slight fading under dry conditions. The fading was almost completely suppressed in the absence of oxygen and considerably by the addition of the singlet oxygen quencher 1,4-diazabicyclo[2.2.2]octane. Dye 1 on cellophane showed catalytic fading by adsorbing Rose Bengal on the film under wet conditions. The photosensitized fading of dye 1 on cellophane dyed in a mixture was proved by exposing only dye 2 or Rose Bengal to light of wavelength above 520 nm, and was also confirmed to be due to the singlet oxygen mechanism by diagnostic tests. The phenyl groups of dye 1 were not split off from the substrate during the fading of the dye.