Tung oil o Chinese wood oil is a dried oil obtained by squeezing the seed of the tung tree (Vernicia fordii). Tung oil hardens upon exposure to air (through polymerization) and the resulting coating is clear and has a deep, almost moist appearance. Mainly used for finishing / protecting wood, after several coats the finish can also look similar to plastic.
Raw tung oil tends to dry out to a fine roughness. The tung tree is native to southern China during the Song dynasty, tung oil was used to waterproof ships. The word "tung" derives etymologically from the Chinese 桐 tóng. The earliest references to the Chinese use of tung oil are found in the writings of Confucius around 500-400 BC.

The name is often used by paint and varnish manufacturers as a generic name for any wood finishing product that contains real tung oil and / or provides a finish that resembles the finish obtained with tung oil.

Composition
The main fatty acids in tung oil and their concentration are
Alpha-Eleostearic Acid 82.0%
Linoleic acid 8.5%
Palmitic acid 5.5%
Oleic acid 4.0%

The primary constituent is a fatty acid with a chain of 18 linked carbon atoms or methylene units containing three conjugated double bonds. They are particularly sensitive to self-oxidation which encourages cross linking of neighboring chains and thus hardening of the base resin.

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Other names
China wood oil; sirloin oil;
tung oil paraformaldehyde; tungmeal; tungoel

CAS number8001-20-5
ECHA InfoCard 100.029.338
EC number 232-272-3

Property
Density 0.937 g / ml at 25 ° C
Refractive index (nD)1.52 (20 ° C)
Flash point> 110 ° C

Except where otherwise noted, data is provided for materials in their standard state (at 25 ° C [77 ° F], 100 kPa).
Wood finishing

Tung oil is very popular today for two properties:
it is natural or "green" and after application (5 to 30 days, time / temperature), the result is a very hard and easily repairable finish. This is why it is used on pontoon decks and now on floors. The oil is often diluted with thinner so that the viscosity is very low and allows the oil to penetrate into the finer grain woods. This thinning vehicle evaporates in 15-20 minutes and results in a totally natural residual finish. As previously mentioned, when applied in many thin layers on wood, tung oil slowly hardens and has a "wet wood" satin appearance with a slight golden tinge. Tung oil is water resistant better than any other pure oil finish and does not darken too much with age and is said to be less susceptible to mold than linseed oil. More importantly, of all oil finishes, tung oil is the only drying oil that cures 100% (fully cured). Linseed oil, for example, does not harden completely.

As tung oil has become popular as an environmentally friendly wood finish, some products labeled as "tung oil" are actually blends of cured linseed oil and solvents.

Heating the tung oil to about 260 ° C in an oxygen-free environment substantially increases the viscosity and quality of the product. Most cured tung oils are sold mixed with mineral spirits to make them easier to process. L-limonene and D-limonene are less toxic alternatives to mineral spirits.
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