Tung oil
Vernicia montana, Vernicia fordii, Aleurites cordata
China, Japan
Light yellow to dark brown, clear
Tung oil, also called Chinese wood oil, is a pale yellow to dark brown, tasteless, smelling of pork fat vegetable oil. It is produced in South Asia by squeezing the seeds tree -like species of the genera Vernicia and Aleurites. In China, most of the Tung- or Abrasinbaum ( Vernicia montana ) and the tung oil tree ( Vernicia fordii ), used in Japan Aleurites cordata. The oil of the related light tree ( Aleurites moluccana ) is called a kukui nut oil.
Properties and composition
Tung oil has a clear, light yellow to dark brown in color and is relatively thick. The smell is similar to that of pig fat and is therefore very characteristic and unpleasant. Of other vegetable oils is tung oil is distinguished by its unique chemical composition: it consists to a large extent ( about 80 %) from the glyceride a single, tri-unsaturated fatty acid, the α - elaeostearic. Further, oleic acid residues ( about 15 %), palmitic acid (approx. 4%) and stearic acid (about 1.3%) - each bound as glycerin esters - included. Small amounts contained in all spurge di-and triterpene make tung oil toxic.
Tung oil also has a very distinctive behavior when heated, which plays a role in the properties: it is strongly heated, this results in a strong increase in viscosity, which leads to a gelatinization. Here, the specific gravity is increased, while the refractive index is reduced.
Tung oil has been used for centuries as a water-repellent oil as it penetrates very deeply and even in the densest wood. It forms in comparison to most other oxidative oils a fine, durable film that retains its elasticity and moves with the wood.
Extraction
The recovery of the oil is done by pressing the seeds in the ripe fruit, which are previously exempt from the shell. It can be extracted both hot as well as cold. The cores comprise from 50 to 60% oil.
Use
Because of the toxic ingredients tung oil is not suitable for eating. Use is it mainly for the production of paint, partly also for the production of soap and linoleum, as lubricating oil and as binders in painting.
Polymerized tung oil and oxidized similar to linseed oil, but dries quickly and forms a resinous, hard, matte finish. In the painting there is a high risk of cracking or brittleness when used alone, the Tung oil. Therefore, it is mostly used in a mixture with linseed oil or boiled linseed oil. Up to 20 % added to the boiled linseed oil, it speeds up the drying process and reduces the swelling by water. When mixed with linseed oil, is achieved particularly good durability and weather resistance. In small amounts added to the final coat of linseed oil paints without solvents, it increases the gloss and abrasion resistance.