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Polyurethane water-based varnish: Transparent or paints, all sheens from 1% to 80% Excellent protection. Newer products (2009) also UV stable when noted Durable after a two-day curing period Safer than oil-based polyurethane, fewer volatile organic compounds: Easy. Applied with brush, roller or sprayer.
Without elasticity, the varnish would soon crack, allowing water to penetrate the wood beneath. Prior to the development of modern polymer chemistry, varnish production was rudimentary. Originally, spar varnish was a "long oil" varnish, composed primarily of drying oil with a small proportion of resin, usually boiled linseed oil and rosin. [1]
Some systems use a drying oil varnish as described below, while others use spirit varnish made of resin(s) dissolved in alcohol. Touchup in repair or restoration is only done with solvent based varnish. Drying oil such as walnut oil or linseed oil may be used in combination with amber, copal, rosin or other resins.
Polyurethane synthesis, wherein the urethane groups −NH−(C=O)−O− link the molecular units A kitchen sponge made of polyurethane foam . Polyurethane (/ ˌ p ɒ l i ˈ jʊər ə ˌ θ eɪ n,-j ʊəˈr ɛ θ eɪ n /; [1] often abbreviated PUR and PU) refers to a class of polymers composed of organic units joined by carbamate (urethane) links.
Polyurethane varnish may also lack the "hand-rubbed" lustre of drying oils such as linseed or tung oil; in contrast, however, it is capable of a much faster and higher "build" of film, accomplishing in two coats what may require many applications of oil. Polyurethane may also be applied over a straight oil finish, but because of the relatively ...
Castor oil by itself has been used in making a variety of polyurethane products, ranging from coatings to foams, and the use of castor oil derivatives continues to be an area of active development. Castor oil derivatized with propylene oxide [9] makes polyurethane foam for mattresses and yet another new derivative is used in coatings [10]
Alkyd or oil-urethane binders are used in casting for the creation of sand-based moulds. The alkyd resin is mixed with a polymeric isocyanate and a metallic drier, which speeds up the reaction. [9] Unlike other no-bake mould technologies, the process yields no toxic fumes, but the moulds need more air-curing time. [10]
Satin spar, less commonly atlas spar, is a trivial, partly obsolete name for fibrous varieties of two minerals, gypsum and calcite, [1]: 40 possessing a characteristic silky luster. Despite their very low hardness (2 or 3 on the Mohs scale ), both atlas (satin) spars (especially selenite ) are widely used as ornamental stones.