Solvent bleaches

The first step in the restoration process is dry cleaning with soft erasers. Old mounts or supports, usually highly acidic, are removed. Immersion in water is prescribed for removal of discoloration in the more stable forms of art on paper etchings, prints, engravings, and some drawings. For specific stains that cannot be removed with water or other solvents, bleaching agents are applied locally. Deacidification by total immersion is preferred a spray is used when this is not possible. 

Bleaches are sometimes used to reduce the density of black-and-white images by removing silver, in solutions that are confusingly known as reducers . These bleaches can be solvent bleaches, where the oxidized silver dissolves in the bleach, essentially without complexation. Alternatively they can contain a silver complex-ing agent and act as a bleach-fix. 

As can be seen by inspection, there are only a few oxidising agents that are likely to be suitable for making a solvent bleach dichromate, permanganate, persulfate and hydrogen peroxide. The last two in the list are very poor bleaching agents as their oxidation appears to be kinetically hindered. They can only be used in the presence of a suitable catalyst, which will be described later. 

Bleaching based on dichromate as the oxidant has been used extensively in the past and is useful for providing solvent bleaches as the dichromate has sufficient potential (see Table 10) without the need to add halide or a silver complexing agent. Solvent bleaches are especially useful for black-and-white reversal systems where they are still used extensively. 

Chemical inertness to a wide variety of acids, solvents, bleaches, and so on. 

Polyester fibers have exceUent resistance to soap, detergent, bleach, and other oxidiziag agents. PET fibers are generally iasoluble ia organic solvents, including cleaning fluids, but are soluble ia some phenoHc compounds, eg, (9-chlorophenol. 

The amount of oxygen evolved is not related to the degree of bleaching (40). Oxidative decoloring is caused by hydrogen peroxide or by the HO ions present in alkaline solution. Hydrogen peroxide is also an effective solvent for melanin (41). 

Raw lac is first treated to remove water-soluble carbohydrates and the dye that gives lac its red color. Also removed are woody materials, insect bodies, and trash. It is further refined by either hot filtration or a solvent process. In the heat process, the dried, refined lac is filtered molten through cloth or wine screens to produce the standard grades of orange shellac. In the solvent process, lac is dissolved and refluxed in alcohol solvents, filtered to remove dirt and impurities, and concentrated by evaporation. The lac can be further decolori2ed in this process to produce very pale grades. Bleached shellac is prepared by treatment with dilute sodium hypochlorite and coalesced into slabs. 

Rice-Bran Wax. Rice-bran wax [8016-60-2] is extracted from cmde rice-bran oil. It can be degummed, the fatty acid content reduced by solvent extraction, and bleached. The wax is primarily composed of esters of lignoceric acid (43 wt %), behenic acid (16 wt %), and 22 02 alcohols (28 wt %). Rice-bran wax may be used in some food apphcations under the regulations described in 21 CFR 172.890. 

The refining process most commonly used involves treatment with hot aqueous alkaH to convert free fatty acids to soaps, followed by bleaching, usually with hydrogen peroxide, although sodium chlorite, sodium hypochlorite, and ozone have also been used. Other techniques include distillation, steam stripping, neutralization by alkaH, Hquid thermal diffusion, and the use of active adsorbents, eg, charcoal and bentonite, and solvent fractionation... 

Dichlorine monoxide is an intermediate in the manufacture of calcium hypochlorite. It has been used in sterilization for space appHcations (70) (see Sterilization techniques). Its use in the preparation of chlorinated solvents (71) and chloroisocyanurates has been described. Chlorine monoxide has been shown to be effective in bleaching of pulp (qv) and textiles (72—74). 

The relatively low pX values seen for the benzoyl acetanilides, especiaHy as two-equivalent couplers, minimize concerns over slow ionization rates and contribute to the couplers overaH reactivity. But this same property often results in slow reprotonation in the acidic bleach, where developer carried over from the previous step can be oxidized and react with the stiH ionized coupler to produce unwanted dye in a nonimage related fashion. This problem can be eliminated by an acidic stop bath between the developer and the bleach steps or minimized by careful choice of coupling-off group, coupler solvent, or dispersion additives. 

In hair coloring a light ash blond shade may require as Httie as 0.5—1% of intermediates, whereas a tme black may require up to about 5%. In principle, the formulator blends precursors that yield red, blue, and yellow dyes. The base in which the components are dissolved or suspended is similar to that used in simple bleaches and may include alkanolamides, various types of surfactants, thickening agents, and solvents. Removal of undesirable dyes is achieved by treating the discolored hair with a powerful reductant of the sulfite family. 

In addition to being the most widely used disinfectant for water treatment, chlorine is extensively used in a variety of products, including paper products, dyestuffs, textiles, petroleum products, pharmaceuticals, antiseptics, insecticides, foodstuffs, solvents, paints, and other consumer products. Most chlorine produced is used in the manufacture of chlorinated compounds for sanitation, pulp bleaching, disinfectants, and textile processing. It is also used in the manufacture of chlorates, chloroform, and carbon tetrachloride and in the extraction of bromine. Among other past uses, chlorine served as a war gas during World War I. 

Much of the CI2O manufactured industrially is used to make hypochlorites, particularly Ca(OCl)2, and it is an effective bleach for wood-pulp and textiles. CI2O is also used to prepare chloroisocyanurates (p. 324) and chlorinated solvents (via mixed chain reactions in which Cl and OCl are the chain-propagating species).Its reactions with inorganic reagents are summarized in the scheme opposite. 

Other examples of concentrated laundry liquids have been described in the literature [53]. These might be called nonaqueous or low-water formulations. They may contain nonionic and anionic surfactants, inorganic builders, enzyme and bleach additives, and an organic solvent such as a low mole AE [54]. Surfactant levels may range from 30% up to 80%. In some cases, the builder salts are dispersed as solid particles in the non-aqueous phase [55]. 

Chlorine is used in a number of industrial processes, including the manufacture of plastics, solvents, and pesticides. It is used as a bleach in the paper and textile industries and as a disinfectant in water treatment (Section 15.6). 

Uses Chlorine is used for water purification and in decreasing amounts for pulp and paper bleaching. Some is used for metallurgical purposes such as metal extraction. Its largest use is for the production of organic compounds used in plastics, pesticides, herbicides, refrigeration fluids, solvents, and others. 

Sulphur dioxide is used as a preservative for beer, wine and meats in the production of sulphites and hydrosulphites in solvent extraction of lubricating oils as a general bleaching agent for oils and foods in sulphite pulp manufacture in the cellulose and paper industries and for disinfection and fumigation. 

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