Protective coatings organic

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. 

Asphalt Asphalt is used as a flexible protective coating, as a bricklining membrane, and as a chemical-resisting floor covering and road surface. Resistant to acids and bases, alphalt is soluble in organic solvents such as ketones, most chlorinated hydrocarbons, and aromatic hydrocarbons. 

Hence whilst in the past corrosion control has involved, in the main, the use of metal alloys, protective coatings, inhibitors, etc. corrosion problems may now often be circumvented by the use of self-supporting organic polymers in the form of either rubbers or plastics. It must however be immediately stressed that such materials are not invariably inert to chemicals and they display their own particular response to such materials. A consideration of such behaviour will be a prior object of this section. 

Organic Coatings. Organic coatings or lacquers protect the steel or tin from external or internal corrosion. The can interiors are coated to prevent undesirable reactions between the interior metal surface and the product. These reactions involve (1) corrosion of the tin coating caused by oxidants in the product, (2) color or flavor loss by the product because of metal ion pickup, or (3) staining of the metal by sulfur-con-... 

K. K. Stevens, and J. C. Warner, Organic Protective Coatings Paints, Varnishes, Enamels, Lacquers, in Chemistry of Engineering Materials, fourth ed., ed. J. C. Warner (New York McGraw-Hill, 1953), 544-590. 

The covalent bond between interface and polysiloxane is very stable towards higher temperatures and organic solvents and, therefore, guarantees the stress resistance of the protective coating. 

Natural and synthetic resins are organic compounds easily found in art objects either as varnishes and protective coatings or binding media, adhesives, consolidants and finishing layers. They are mainly used in manufacturing paintings, but also in pottery, furniture and wooden objects, sculptures, musical instruments and works on paper. In addition, natural and synthetic resins have widespread use as conservation materials. 

Hybrid polymer silica nanocomposites formed from various combinations of silicon alkoxides and polymers to create a nanoscale admixture of silica and organic polymers constitute a class of composite materials with combined properties of polymers and ceramics. They are finding increasing applications in protective coatings (Figure 7.1), optical devices, photonics, sensors and catalysis.1... 

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