Zenzo Morita

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.

Reactivity of phenylazonaphthol sulfonates, their estimation by semiempirical molecular orbital PM5 method, and the relation between their reactivity and azo-hydrazone tautomerism

Abstract With respect to 4-phenylazo-1-naphthols and 1-phenylazo-2-naphthols, the azo-hydrazone tautomerism (AHT) of the undissociated and dissociated (UD&D) species for their p-sulfo derivatives (Orange I and Orange II) was analysed estimating their enthalpies of formation in both the gaseous phase and water using semiempirical molecular orbital (MO) (PM5 and COSMO) methods. The reactivities of these phenylazonaphthols against oxidizing agents including singlet molecular oxygen were examined using simple frontier orbital theory. The hydrazone tautomers (HTs) of the UD species of the two orange dyes had higher stability in water than the azo tautomers (ATs), while the two tautomers of the D species had similar stability. Both the UD&D species of the dyes resulted in AHT and furthermore both the tautomers of the dyes displayed an acid–base equilibrium. The assumption that the HTs had smaller pKa values than the ATs explained some of the experimental results observed. Frontier orbital theory showed that the azo and hydrazone tautomers (A&HTs) for the UD and D species of two orange dyes as well as the A&HTs for phenylazonaphthols with several substituents had similar reactivity towards oxidants in terms of the interaction between HOMO and LUMO, although the positions of reaction changed in the tautomers used. The dissociation of hydroxyazo dyes and/or oxidants changed their mutual reactivity due to a rise in EHOMO and ELUMO, although the A&HTs for the D species of orange dyes had almost the same electronic structure as each other, irrespective of the different sites of ionization.

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.

The aggregation of triphenodioxazine reactive dyes in aqueous solution and on cellulosic and nylon substrates

Abstract Monomer–dimer equilibriums of triphenodioxazine (TPDO) reactive dyes with vinylsulfone anchors (PVS-TPDO) and monochlorotriazine anchors (MCT-TPDO) were investigated in water, in aqueous organic solvent, and on a cellulosic substrate. The aggregation tendency of PVS-TPDO in water was promoted by the addition of neutral electrolyte and suppressed by that of 1-methyl-2-pyrrolidone (MP). The dimerization constants, K , for PVS-TPDO were estimated in water and in aqueous sodium chloride solution; PVS-TPDO showed also aggregation on a cellulosic substrate. The apparent value of K on dry cellulose was two orders of magnitude smaller than that in water, and was increased by about ten times by water. The aggregation of PVS-TPDO in aqueous sodium chloride solution was suppressed by the addition of both MP and poly(vinylpyrrolidone). Four TPDO dyes examined showed the same order of aggregation tendency on cellulosic and nylon substrates as that in aqueous solution.

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.

Relationship between photochemical properties and colourfastness due to light-related effects on monoazo reactive dyes derived from H-acid, γ-acid, and related naphthalene sulfonic acids

Abstract Photofading of 15 reactive azo dyes derived from H- (seven), J-, L-, R-, 2R-, γ-acids (three), pyrazoline and a reactive copper-complex dye on cellophane under wet conditions was examined to estimate the essential properties: photo-oxidisability ( k 0 : the reactivity with molecular singlet oxygen), photosensitising ability ( f ) and photo-reductivity. The relationships between the essential properties of these dyes and the lightfastness (LF) as well as the perspiration-lightfastness (PLF) on cotton fabrics are discussed. A linear correlation between the logarithmic product, log ( f k 0 ), and the LF ratings of dyes on dry cotton fabric was found when plots of reactive dyes with low LF and those of the vat dyes examined in a previous paper were added because the ratings of 11 red dyes out of 15 dyes examined had a narrow range. It showed that LF of monoazo red reactive dyes on dry cotton fabric is very dependent on photo-oxidative fading. A linear correlation was also found between logarithms of f -values and the relative initial rates of photo-reductive fading, except for dyes with very high photosensitising ability. A conflicting relationship between the k 0 -values and the photo-reductivity could be shown for dyes derived from H- and γ-acids, an unsolved restriction on synthesis of azo dyes with excellent LF as well as PLF. Azo dyes derived from γ- and 2R-acids possess smaller f but larger k 0 values than those derived from H-acids. The photofading of dyes on cotton fabrics in the presence of artificial perspiration was explained in terms of the essential properties. The substrates promoted photo-reduction and suppressed photo-oxidation.

Photofading, photosensitization and the effect of aggregation on the fading of triphenodioxazine and copper phthalocyanine dyes on cellulosic film

Abstract The photosensitized oxidation of four triphenodioxazine (TPDO) reactive dyes and a copper phthalocyanine (CuPc) reactive dye on cellulosic films by Rose Bengal (RB) was examined in aqueous solution under aerobic conditions. The rates of photo-oxidation of 4,11-bis(vinylsulfonyl)TPDO dyes were smaller than those obtained for 3,10-bis(disubstituted triazinyliminoethylimino)TPDO dyes. The rates of photofading of the four TPDO dyes and a CuPc dye on cellulose were similar in the order to the rates of the photosensitized oxidative fading with RB. Photo-oxidation left the aromatic residue from TPDO ring along with the reactive anchor bound to cellulose. No aggregation effect was observed on the fading of TPDO dyes and a CuPc dye on cellulose. The photosensitivity of the TPDO dyes was very small, this being estimated by the photosensitized fading of an aminopyrazolinylazo dye (Yellow dye) on cellulosic films dyed in admixture with TPDO dyes by use of a yellow filter to shield Yellow dye on exposure. It is concluded that the good light-fastness of the TPDO dyes on cellulosic substrate is attributed to the very small photosensitivity in spite of their relatively large ease with which they are oxidized.

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.

Photo-oxidation and -reduction of vat dyes on water-swollen cellulose and their lightfastness on dry cellulose

Abstract Photostability of nine (seven anthraquinone and two thioindigoid) vat dyes on cellulosic films was examined. The ease ( k 0 ) with which the dyes were photo-oxidized was estimated by the relative fading of vat dyes on cellophane immersed in aqueous Rose Bengal solution on exposure, a condition resulting in only the photo-oxidative fading. The photosensitivity ( f ) was estimated by the relative fading of an aminopyrazolinyl azo vinylsulfonyl dye on cellophane dyed in admixture with vat dyes examined under the same conditions as above. The values of k 0 were small, compared with those of reactive dyes, while those of f comparable. The lightfastness of nine vat dyes on dry cotton fabric had close correlation with log ( f k 0 ). This fact shows that the fading of vat dyes on dry cellulose occurs mainly by photo-oxidation on exposure in air. On exposure of vat dyes on cellulosic substrate in an aqueous anaerobic dl -mandelate solution, a condition resulting in only the photo-reduction, vat dyes displayed a colour change in the direction of the acid leuco-compounds, many of which returned to the original dyes by re-oxidation. Vat dyes with high photoreductivity showed the same colour change on dry cellulose by long exposure, implying that photo-oxidation occurs in the superficial part of fibre substrate and photo-reduction in the inner part. The photofading properties of anthraquinone vat dyes were attributed to the excited triplet T 1 (nπ*) state of the carbonyl groups. The quantum yields to T 1 (ππ*) was very small by an effective internal conversion of the exited singlet states. Since the ππ* absorption of the annelated anthraquinones with the large extinction coefficients shielded the carbonyl groups with the small coefficients from the nπ* absorption, the photofading of the vat dyes with the highest lightfastness became very small. As a result, those vat dyes perform the highest lightfastness.