brief history
Tung oil is one of the important forest by-products in China and has a long history of processing and utilization. Li Mingzhizhen's Compendium of Materia Medica records that "it is necessary for the people to harvest seeds and goods as oil." In Qing dynasty, tung oil was used as a tribute in Jiangsu and Zhejiang provinces. China tung oil 15 16 began to be exported, and 1869 tung oil exported to the United States reached 62.88 tons. Since then, Europe and Japan have successively imported tung oil from China. From the end of 19 to the beginning of the 20th century, the coating industry developed rapidly. The paint made from tung oil is cheap, and the export of tung oil increases rapidly, which promotes the development of tung oil production in China. According to statistics, from 1922 to 1936, the output of tung oil increased from more than 54,900 tons to145,700 tons; Tung oil exports increased from more than 37,200 tons to more than 43,400 tons. At the end of 1940s, the output of tung oil once shrank. From 1950s to 1970s, production gradually recovered. Since 1980, the annual export volume of tung oil is about 20,000 tons.
Raw material tree species
(1) tung tree (three-year-old tung tree, tung tree); 2 Millennium paulownia (wood oil tree, wrinkled paulownia); (3) Japanese tung oil (Jatropha curcas, Jatropha curcas).
The bearing age of tung oil varies with species and varieties. Three-year-old paulownia began to blossom and bear fruit after three years of sowing; It takes 5-6 years for Millennium Tung to blossom and bear fruit after sowing. Its fruit ripens after cold dew and before the first frost. The collected paulownia fruits are stacked in outdoor wet places or indoors to rot. If the weather is dry, cover with straw and sprinkle with water for about 15 days, then peel the tung seeds and dry them. Tung kernel contains 36.4 ~ 66.3% oil; It contains crude fat 6 1.5%, crude protein 0/6.5%, crude fiber 4.35%, water 3.74%, and soluble nitrogen-free extract 0/1.23%. After combustion, the ash content accounts for 2.6% of Jatropha curcas.
nature
Tung oil is a yellow to brownish yellow liquid with a special smell and toxicity. The main components are α -triethylene oleate (72.8%) and oleic acid (13.6%). It also contains linoleic acid triglyceride (9.7%), palmitic acid (3.7%) and stearic acid (1.2%). The chemical properties of tung oil are very unstable. A white solid fatty substance (β tung oil) will be produced under sunlight, which can be dried by itself after brushing teeth. Storage time is too long, and the surface is oxidized and crusted or even dry. The drying strength is higher than linseed oil, and the oxidation speed is several times faster than hemp seed oil.
process
There are two kinds of direct oil extraction and shell oil extraction. Oil press equipment has manual wood press; Screw oil press (model 200, model 95); Hydraulic oil presses (Model 90 and Model ZWY- 100) (see Tea Oil).
Wood pressing technology is backward, the pressed tung oil is dark in color and poor in oil quality, and the oil yield of tung oil seeds is low (22 ~ 25%). Most of them are replaced by mechanical pressing.
The production procedures and principles of screw oil press and hydraulic oil press are basically the same as those of wood press. Only the most labor-intensive processes in wood pressing, such as shelling, crushing, blank making and pressing, are changed into mechanical operations. Compared with wood pressing, the work efficiency is improved by more than 5 times, the oil yield is 25 ~ 30%, the oil yield can reach 32%, and the residual oil rate of bran meal is low. Many processes from feeding, shelling, crushing, cooking, pressing to processing into oil are controlled by instruments. The production process is as follows:
In addition to mechanical pressing, there is also leaching, which is to extract residual oil from wood pressing and mechanical pressing bran meal. 7 ~ 10% tung oil was extracted from wood bran meal, and 5 ~ 8% tung oil was extracted from machine-pressed bran meal. The residual oil rate of leached bran meal is about 65438 0%.
Low-acid light-colored tung oil export can be made by pressing tung kernel with a wood press at low temperature.
quality
People's Republic of China (PRC) tung oil inspection standards are as follows:
The color, orange yellow and transparency should be no deeper than the newly prepared 0.4 g potassium dichromate 100 ml solution; Smell, no different from smelly, not rancid; Specific gravity (15.5℃), 0.9400 ~ 0.9430; Refractive index 4 12365,1.5168 ~1.5200; Iodine value (Wechsler method),163 ~173; Acid value, up to 8.0; Saponification value,190 ~195; Moisture impurities, up to 0.35%; Concentrated seed doping test, without adding other oil; Warst test, solidified into a solid in 7.5 minutes, and did not stick to the knife when cutting; β tung oil experiment, no precipitation.
use
Tung oil is a good natural drying oil, which has the characteristics of fast drying and film formation, good waterproof performance, acid and alkali corrosion resistance, electrical insulation and so on. It is an important industrial oil. Widely used in industry, agriculture, fishery and national defense industry. Tung oil can be used not only for ordinary paint, but also for making aviation paint, enamel and insulating paint. Tung shell is rich in potassium and can be made into high-grade fertilizer (potassium dihydrogen phosphate); Bran is a high-quality organic fertilizer.