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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 ...
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]
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.
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.
A thinned oil is easier and more reliable to apply. Such commercial mixtures also contain metallic driers to improve their performance. There are also mixtures sold as finishing oils. These are classed as 'long oils', predominantly oil with some varnish added or as 'short oils' which are predominantly varnish, with some oil. [2]
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 dispersion, or PUD, is understood to be a polyurethane polymer resin dispersed in water, rather than a solvent, although some cosolvent may be used.Its manufacture involves the synthesis of polyurethanes having carboxylic acid functionality or nonionic hydrophiles like PEG (polyethylene glycol) incorporated into, or pendant from, the polymer backbone. [1]
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]