Hiromi Motomura

Catalytic fading of vinylsulfonyl reactive dye mixtures on cellulose under wet conditions

Abstract 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.

Photofading of vinylsulfonyl reactive dyes on cellulose under wet conditions

Abstract The fading on cellulose of six vinylsulfonyl (VS) reactive dyes, an aminopyrazolinyl azo dye (1). C.I. Reactive Red 22 (2), a copper-complex azo dye (3), a copper phthalocyanine dye (4), C.I. Reactive Blue 19 (5) and Black 5(6) was investigated under wet conditions. The rate of fading for VS dyes on cellulose, except for dye 2, decreased with increase in the concentration; that for dye 2 increased. The rate of fading for the VS dyes examined was in the following order: 2 >1 >3 >6 >4 >5. This order was similar to that for the rate of fading for VS dyes on cellulose on which Rose Bengal was adsorbed, except for the reversal between dyes 1 and 2. The photosensitivity of VS dyes was confirmed by exposing films dyed with a mixture ofl with the other dyes and by shielding dye 1 by the use of a filter (510nm). No fading of these dyes on cellulose in deaerated water occurs under a nitrogen atmosphere. These results suggest a singlet oxygen mechanism for the fading of VS dyes on cellulose under wet conditions. The rate of fading for a VS dye was dependent mainly on the ease with which it was oxidized and secondly on its efficiency and that of the partner dye to generate singlet oxygen.

Fading of vinylsulfonyl reactive dyes on cellulose in admixture under wet conditions

Abstract The fading of vinylsulfonyl(VS) reactive dyes on cellulose in a binary mixture was investigated under wet conditions. Dyes with a high photosensitivity such as Rose Bengal, a copper phthalocyanine, C.I. Reactive Red 22 and Black 5, gave a positive concentration dependence on the fading of the partner dye or of its own, when the partner or itself was easily oxidized. A preferential surface fading model for reactive dyes on cellulose in a mixture is proposed to explain the fading behavior under wet conditions and the model was experimentally confirmed by the variation in the concentration profiles during the fading for both dyes on film dyed in admixture. A dye which underwent fading more readily when it was oxidized showed accelerated fading when present in a mixture with a dye having high fading sensitivity, compared with the fading of the single dyeing at the same concentration. A dye which faded with moderate ease, when present in a mixture with a dye which faded less readily, showed decreased fading.

Simultaneous Oxidative and Reductive Photofading of C.I. Reactive Red 22 and Black 5 on Cellulose in the Presence of Oxygen and Substrate under Wet Conditions

Abstract 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.

Adsorption behavior of reactive dyes on cellulose

Abstract The adsorption of three anionic dyes (CI Reactive Red 120, a monochlorotriazinyl red dye (Red E), and CI Direct Blue 1) on cellulose was investigated from a neutral dyebath at 80°C over a wide concentration range of sodium sulfate. Because of the apparent low substantivity, no accurate adsorption was determined at low electrolyte concentrations, where a higher apparent substantivity of the dyes was observed. The standard chemical potential differences between the cellulose and solution phases, or the standard affinity, − Δμ °, for these dyes were calculated on the basis of the Donnan equilibrium model. CI Reactive Red 120 and CI Direct Blue 1 showed saturation in the adsorption isotherm, while Red E had a likeness to the other dyes when a high salt concentration was used. The substantivity of several reactive dye ranges is discussed, comparing them with the present results.

Oxidative and reductive fading of monochlorotriazinyl reactive dyes on cellulose under wet conditions

Abstract The photofading of three monochlorotriazinyl (MCT) reactive dyes was examined in the absence or presence of oxygen and substrate under wet conditions. These dyes on cellulose showed no fading on exposure in deaerated water and oxidative fading in aerated water, whereas they underwent reductive fading in the presence of dl -mandelate in a nitrogen atmosphere. C.I. Reactive Blue 2 and a phthalocyanine dye showed a multi-step photoreduction. Their reduction intermediates were oxidized to re-form the original dyes as in the case of thermal reduction. The azo group nearer the triazine ring of a copper-complex disazo dye was readily photoreducible, and the other was oxidizable. The relationship for a phthalocyanine dye among the rates of fading in aerated water, the degree of association, and the concentration of dye on cellulose was examined. The fading behavior of C.I. Reactive Blue 19 was compared with that of Blue 2 under various conditions.

Photosensitization and simultaneous reductive or oxidative fading of monochlorotriazinyl reactive dyes on cellulose under wet conditions

Abstract The photosensitivity of ten monochlorotriazinyl (MCT) reactive dyes (three monoazo five disazo a copper phthalocyanine and an anthraquinone) was estimated by exposing the binary mixtures of each MCT dye and an aminopyrazolinyl azo dye on cellulose in aerated water. The ease with which MCT dyes were photo-oxidized was examined by use of Rose Bengal. MCT dyes on cellulose dyed in admixture underwent reductive or oxidative fading depending on the own properties and on the conditions of exposure, and sensitized the oxidative fading of the partner dyes at the same time. The concentration dependence of fading for two dyes on cellulose was examined under wet conditions.

Photofading of monochlorotriazinyl reactive dyes on cellulose under wet conditions

Abstract The fading of seven monochlorotriazinyl (MCT) reactive azo dyes (three monoazo and four disazo) on cellulose was investigated under wet conditions. It was shown by spectral analysis that these dyes on cellulose were faded via photoreduction on exposure in de-aerated water in spite of the absence of substrate. Oxygen suppressed the reductive fading for some of the dyes or inhibited it, resulting in oxidative fading. Thus four dyes were photoreduced on exposure in aerated water at a rate lower than that in de-aerated water, whilst the other dyes were photo-oxidized at a higher rate. The chemical structure of the dyes and the environmental conditions during exposure determine whether oxidative or reductive fading of MCT dyes on cellulose occurs under wet conditions.

Dissociation of hydroxyl groups of cellulose at low ionic strengths

Abstract According to Donnan equilibrium theory, the dissociation of the hydroxyl groups of cellulose (mercerized cotton) or alkaline adsorption can be treated as a function of the pH and ionic strengths of the external solution, and of the amount of fixed anionic groups in cellulose, by using 1:1- and 1:2-electrolytes as a neutral salt to adjust the ionic strength. The acid dissociation constant of the hydroxyl group for cellulose was estimated by Neale at 25°C, and this treatment therefore only holds for this temperature. The ratios of hydroxide ion concentrations in the inner solution and those in the external one, [OH − ] i /[OH − ] s , as well as [Cell-O − ] i /[OH − ] i [Cell-O − ] i : cellulosate ion concentration in the inner solution) decrease with a increase in the concentration of hydroxide ions in the external solution and the fixed anions in cellulose, and with a decrease in the ionic strengths in the external solution, but with little decrease of [Cell-O − ] i /[OH − ] i .

Diffusion/adsorption behaviour of reactive dyes in cellulose

The diffusion/adsorption behaviour in cellulose films of two monochlorotriazinyl (MCT) reactive dyes having high substantivity to cellulose was investigated from the dyebath using a wide concentration range of sodium sulphate at 80°C. Diffusion coefficients for these reactive dyes showed a large concentration dependence at low salt concentration and a smaller dependence with an increase in salt concentration. The concentration dependence of the diffusion coefficient or of the diffusion behaviour for reactive dyes in cellulose was essentially the same as that for direct dyes. From the results obtained the diffusion/adsorption behaviour of reactive dyes in cellulose could be explained by a variable porosity model in the low concentration range of the dyes. In the case of high salt concentration, the diffusion coefficients in cellulose increased with increasing dye concentration at which the saturated adsorption appeared.