Varnishes organic solvents

A varnish is often appHed on top of the paint layers. A varnish serves two purposes as a protective coating and also for an optical effect that enriches the colors of the painting. A traditional varnish consists of a natural plant resin dissolved or fused in a Hquid for appHcation to the surface (see Resins, natural). There are two types of varnish resins hard ones, the most important of which is copal, and soft ones, notably dammar and mastic. The hard resins are fossil, and to convert these to a fluid state, they are fused in oil at high temperature. The soft resins dissolve in organic solvents, eg, turpentine. The natural resin varnishes discolor over time and also become less soluble, making removal in case of failure more difficult (see Paint and FINNISH removers). Thus the use of more stable synthetic resins, such as certain methacrylates and cycHc ketone resins, has become quite common, especially in conservation practice. 

Tetrahydronaphthalene [119-64-2] (Tetralin) is a water-white Hquid that is insoluble in water, slightly soluble in methyl alcohol, and completely soluble in other monohydric alcohols, ethyl ether, and most other organic solvents. It is a powerhil solvent for oils, resins, waxes, mbber, asphalt, and aromatic hydrocarbons, eg, naphthalene and anthracene. Its high flash point and low vapor pressure make it usehil in the manufacture of paints, lacquers, and varnishes for cleaning printing ink from rollers and type in the manufacture of shoe creams and floor waxes as a solvent in the textile industry and for the removal of naphthalene deposits in gas-distribution systems (25). The commercial product typically has a tetrahydronaphthalene content of >97 wt%, with some decahydronaphthalene and naphthalene as the principal impurities. 

Natural resins are generally described as solid or semisolid amorphous, fusible, organic substances that are formed in plant secretions. They are usually transparent or translucent yeUow-to-brown colored, and are soluble in organic solvents but not in water. The principal uses for natural resins are in varnishes, printing inks, adhesives, paper size, and polymer compositions. The term natural resins includes tree and plant exudates, fossil resins, mined resins, and shellac. They often have been altered from their original state during isolation and processing. For some appHcations, the resins have been chemically modified to increase their industrial utiUty. 

The first synthetic polymers to be used as paint varnishes were acrylic and vinylic resins. Poly(vinyl acetate) (PVAc), commercialized under the name Mowilith by Hoechst and Vinylite by Union Carbide, has been used in conservation as an adhesive since 1932 and in 1937 it was proposed as a picture varnish by Stout and Cross [63]. PVAc was soon rejected as a varnish because, despite its light stability and good solubility in organic solvents, it demonstrated poor optical properties in terms of colour saturation and the tendency to pick up dirt due to its low glass transition temperature. 

A number of solid acrylic resins, all known under the commercial name of Paraloid, are used in art conservation, dissolved in organic solvents, as consolidants, coatings, or in varnish formulations these resins are generally copolymers formed by two acrylic/ methacrylic monomers [82], Paraloid B-72 is the most widely used acrylic resin in conservation, and is formed by a methyl acrylate/ethyl methacrylate (MA/EMA) copolymer with molar composition 70/30. 

Organic solvents inhaled by abusers include gasoline, glue, aerosols, amyl nitrite, butyl nitrite, typewriter correction fluid, lighter fluid, cleaning fluids, paint products, nail polish remover, waxes, and varnishes. Chemicals in these products include nitrous oxide, toluene, benzene, methanol, methylene chloride, acetone, methyl ethyl ketone, methyl butyl ketone, trichloroethylene, and trichloroethane. 

These dyes, already described in section 2.12, require adequate solubility for the coloration of various organic solvents and must be cheap [79]. The simplest and least polar dyes of this class are used for the coloration of petrol and ball-pen inks, with more polar types being used in lacquers, stains and varnishes. Some products of lower solubility are used in mass coloration. 

Enviromnent and health-related problems Bio varnishes , i.e. varnishes based on natural, renewable raw materials, were developed as close-to-nature alternatives (substitutes) i.a. as a reaction to the so-called German wood preservative scandal and indoor pollution due to chemical solvents. Nevertheless, they have until now had a relatively high content of volatile bio-organic solvents, which may cause irritations, allergic and neurotoxic reactions, and contribute to the formation of tropospheric ozone. 

Angerer J, Wulf H. 1985. Occupational chronic exposure to organic solvents. XI. Alkylbenzene exposure of varnish workers Effects on hematopoietic system. Int Arch Occup Environ Health 56 307- 321. 

Volatile organic chemicals are released during a number of industrial and manufacturing operations. For example, 1,3-butadiene is an important raw material in the manufacture of synthetic rubber During manufacture small amounts of the chemical escape into the air. Formaldehyde is a raw material used in the manufacture of a variety of building materials, such as phenol-formaldehyde and melamine resins. Many household products, such as cleaning products, varnishes, waxes, paints, and organic solvents, contain VOCs, which vaporize and escape easily into the atmosphere when they are used. For this reason, VOCs often build up indoors. 

In addition to its use as a chemical feedstock and intermediate, acetone is used extensively as an organic solvent in lacquers, varnishes, pharmaceuticals, and cosmetics. Nail polish remover is one of the most common products containing acetone. Acetone is used to stabilize acetylene for transport (see Acetylene). 

When the material is dissolved in an organic solvent and provided as a varnish, the varnish can be directly coated on the conductor. These methods can be optionally selected according to the thickness of the coating material and other desired properties. 

The nitrogen content should be within the range 11.0-12.3% N, i.e. within such limits that ensure complete dissolution in organic solvents. For cheaper varnishes, in which ethyl alcohol is used as a solvent, nitrocellulose of lower nitrogen value, e.g. 10-10.5%, is used. Such a nitrogen content endows the product with complete solubility in ethyl alcohol. 

Synonyms 2-propanone, dimethyl ketone Formula CH3COCH3 MW 58.08 CAS [67-64-1] used as a common solvent in many organic syntheses and in paint and varnish removers colorless liquid characteristic odor, sweetish taste boils at 56.5°C vapor pressure 180 torr at 20°C freezes at -94°C density 0.79 g/ML at 20°C readily mixes with water and organic solvent highly flammable. 

MW 93.14 CAS [62-53-3] used in the manufacture of dyes, varnishes, resins, pharmaceuticals, and photographic chemicals colorless oily liquid with characteristic odor boils at 184.5°C freezes at -6°C vapor pressure 0.3 torr density 1.02 g/mL at 20°C moderately soluble in water 3.5% at 20°C readily mixes with most organic solvents weakly alkaline. 

Uses The alicyclic hydrocarbons have numerous industrial applications. Cyclopropane (C3H6) is used as an anesthetic. Cyclohexane (CgH ) is used as a chemical intermediate as an organic solvent for oils, fats, waxes, and resins and for the extraction of essential oils in perfume manufacturing industries. Cyclohexene (C6H10) is used in the manufacture of maleic acid, cyclohexane carboxylic acid, and adipic acid. Methyl cyclohexane (C7H14) is used for the production of organic synthetics such as cellulose ethers. These compounds are used in different industries such as adipic acid makers, benzene makers, fat processors, fungicide makers, lacquerers, nylon makers, oil processors, paint removers, plastic molders, resin makers, rubber makers, varnish removers, and wax makers. 

Phenyl(chloromethyl)dichlorosilanes and methyl(chlorophenyl)-dichlorosilanes are colourless, transparent, motile liquids, which fume in air. Like all organochlorosilanes, they are easily hydrolysed with water and humidity in air and dissolve well in organic solvents. Phenyl(chloromethyl)- and methyl(chlorophenyl)dichlorosilanes are raw stock for preparing various silicone liquids, elastomers, and polymers for varnishes. 

Polydimethylphenylsiloxane and polymethylphenylsiloxane varnishes are transparent liquids with colour ranging from light yellow to light brown. They can be dissolved in toluene, benzene, xylene and other nonpolar organic solvents but are not soluble in water and alcohols. 

Much of the information about the harmful effects of organic solvents comes from studies of industrial exposure, although toluene abuse through sniffing of glues and other household sources of solvents (acrylic paints, adhesive cements, aerosol paints, lacquer thinners, shoe polish, typewriter correction fluids, varnishes, and fuels) has also been widely reported. 

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