Dyeing with Oxidation Dyes

The base readily penetrates the hair and promotes bleaching. The addition of stabilizers such as sodium pyrophosphate or sodium oxalate [16,17] retards the decomposition of hydrogen peroxide in the alkaline preparation and thus enhances the bleaching action. The same holds for complexing agents (seques-trants) such as ethylenediaminetetraacetic acid, which hinder decomposition due to traces of heavy metals. Thickening additives include carboxymethyl celluloses, xanthine derivatives, and synthetic polymers. Certain dyes can also be added. 

Dusting of bleaching powders has to be prevented to avoid inhalation of per-oxosulfates. This can be achieved by (1) Addition of oils to bind fine particles [18], (2) Granulation to enlarge particle size [19], or (3) Formulation of water-free, oil-containing pastes [20], 

In spite of the importance of bleaches in oxidation dyeing, very few technical improvements apart from formulation aspects have occurred recently in this field. The selective adsorption of metal ions [21], especially of iron(n) salts [22], on melanin has been proposed for gentler bleaching of human hair. This process has achieved no more acceptance than the use of peroxocarboxylic acids or their precursors, which are important as bleaching intensifiers in textile bleaching. 

Hair dyeing includes the use of permanent, semipermanent, and temporary dyes. A permanent dye lasts through any number of washings as well as permanent waving. A semipermanent dye is removed after two to ten washings, and a temporary dye is largely eliminated after one washing. 

The simultaneous bleaching process also allows hair to be dyed a lighter color only small amounts of dye intermediates are needed to offset the shade produced by bleaching. The degree of lightening is limited the color corresponds to that obtained by cream bleaching without peroxodisulfate (see Section 5.4.1). 

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Before dyeing with oxidation dyes, the furs are treated with the appropriate killing agents and then mordanted with metal salts. Iron, chromium, and copper salts, alone or in combination, are used for mordanting, and the uptake process requires several hours. Adjustment of the pH is effected with formic, acetic, or tartaric acid. The final dyeing process is carried out in paddles with the precursors and hydrogen peroxide until the actual dye lake is developed and adsorbed within the hair fiber. It takes quite a few hours at room temperature until the dyeing process is finished. 

After dyeing with oxidation dyes, the fur skin must be washed and rinsed thoroughly to remove all loose and incompletely oxidized dye. In working with oxidation dyes, certain precautions have to be taken, as some people are allergic to specific amines. 

Based on correlations between energy level positions and electrochemical redox potentials, it has been estabHshed that polymethine dyes with reduction potentials less than —1.0 V (vs SCE) can provide good spectral sensitization (95). On the other hand, dyes with oxidation potentials lower than +0.2 V ate strong desensitizets. 

Ana.lytica.1 Methods. Various analytical methods involve titration with oxidants, eg, hexacyanoferrate (ferricyanide), which oxidize dithionites to sulfite. lodimetric titration to sulfate in the presence of formaldehyde enables dithionite to be distinguished from sulfite because aldehyde adducts of sulfite are not oxidized by iodine. Reductive bleaching of dyes can be used to determine dithionite, the extent of reduction being deterrnined photometrically. Methods for determining mixtures of dithionite, sulfite, and thiosulfates have been reviewed (365). Analysis of dithionite particularly for thiosulfate, a frequent and undesirable impurity, can be done easily by Hquid chromatography (366). 

Although most DIR couplers are based on image dye-forming parents, universal DIR couplers have appeared in the Hterature. These materials react with oxidized developer to produce the inhibitor (or precursor) and either a colorless dye, an unstable dye, or a washout dye (100). Universal DIR couplers could be used in any layer with a need to match only image-modifying properties, not hue, to the given layer. 

Nickel sulfate can be produced from either pure or impure sources. The pure source involves the reaction of pure nickel or nickel oxide powder (combined or separately) with sulfuric acid to produce nickel sulfate that is filtered and crystallized to produce a solid product. The impure raw material may be spent industrial liquor that contains a high percentage of nickel sulfate. The impurities in the liquor are precipitated by sequential treatment with oxidizers lime and sulfides can later be filtered out. The treated liquor, which is a pure solution of nickel sulfate, can be packaged in a drum or further crystallized and dried to produce solid nickel sulfate. Nickel sulfate is used mainly in the metal plating industries. Other uses include dyeing and printing of fabrics and production of patina, an alloy of zinc and brass. 

Dithionite and derivatives Minimising the concentration by optimising Oxidation of sulphite to sulphate (isothermal dyeing with oxidation in the dyebath for pale shades)... 

The aluminium is white and shiny before applying the potential. A critical potential exists below which no electro-oxidation will commence. At more extreme potentials, the surface atoms of the aluminium oxidize to form Al3+ ions, which combine with oxide ions from the water to form AI2O3. This electro-precipitation of solid aluminium oxide is so rapid that molecules of dye get trapped within it, and hence its coloured aspect. 

Scheme 1 illustration of the interfacial charge-transfer processes in nanocrystalline dye sensitized solar cell. S, S, and S represents the sensitizer in the ground, oxidized, and excited states, respectively. Visible light absorption by the sensitizer (1) leads to an excited state, followed by electron injection (2) onto the conduction band of TiO2. The oxidized sensitizer (3) is reduced by the I /I redox couple (4). The injected electrons into the conduction band may react either with the oxidized redox couple (5) or with oxidized dye molecule (6). 

Another class of ballasted dye releasers is represented by the sulfonylhydrazone (88). These compounds interact with oxidized p-phenylenediamines to give sulfinate-solubilized dyes (89). Y can be the residue of an azo, anthraquinone or phthalocyanine dye (73BRP1321046, 75BRP1407362). 

In other types of metallizable conventional dyes, the chelating site is not part of the chromo-phore, and thus there is not a large hue shift on metallization. In the yellow (66),133 magenta (67)134 and cyan (68)135 couplers the metallizable site is the l//-imidazo[4,5-/i]quinoline substituent. This allows the option for metallization before or after the generation of the azamethine dyes by reaction with oxidized / -phenylenediamine. Advantages of improved light stability and acid fastness are reported for the metallized dyes. 

As with oxidation dyes, the actual dye in the Phthalogen process-the insoluble phthalocyanine pigment-is formed in the fiber itself. The dyeing is performed with precursors. There are two main processes. 

Disperse and other synthetic dyes can only be taken up by the hair at elevated temperatures, and for this reason the skins must be chrome-tanned. The shrinking temperature of suede has to be at least 20° C higher then the dyeing temperature. No mordant is required, unlike with oxidation dyes, and killing need be far less intensive, too. In actual fact the operation is more hair cleaning than a killing process. The suede portion is not dyed and can be cleaned very easily with standard washing auxiliaries. 

Permanent hair colors can be achieved with tint shampoos. The shampoo base is adjusted to an alkaline pH and contains oxidation dye intermediates. Before application, it is mixed with hydrogen peroxide or a hydrogen peroxide addition compound. In comparison with oxidation hair dyes, tint shampoos employ lower concentrations of base and oxidant. This suppresses the simultaneous bleaching process that occurs during dyeing (see Section 5.4.2). As a result, damage to the keratin in hair is diminished, but the uniform coloring action is lost. 

The rate of electron transport in dye-sensitized solar cells is a major element of the overall efficiency of the cells. The injected electrons into the conduction band, from optically excited dye, can traverse the Ti(>2 network and can be collected at the transparent conducting glass or can react either with oxidized dye molecule or with the oxidized redox couple (recombination). The reaction of injected electrons into the conduction band with the oxidized redox mediator gives undesirable dark currents, reducing significantly the charge-collection efficiency, and thereby decreasing the total efficiency of the cell (Fig. 7). 

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