| Vegetable oils are environmentally friendly base stocks and renewable feedstocks. They have excellent lubricity and biodegradability. However their practical application is limited because of the poor oxidative stability (there are double bonds in the molecular) and bad low-temperature fluidity. So we improved the oxidative stability and low-temperature fluidity of vegetable oils through chemically modification in this paper.1. Rapeseed oil ethyl ester was synthesized through optimizing test. They produce oil-soluble linear polymer after oxidized, so their oily sludge content is obviously less than rapeseed oil. However they still have double bounds in the molecule. Rapeseed oil ethyl ester with high viscosity index value (VI≥200) can be used as VI improve portion.2. A series of chemically modified soybean oils were synthesized by epoxidizing soybean oil and different carbon chain length fatty acids (which can saturate the double bonds to enhance the oxidative stability). They have high viscosity index(VI107～132), good viscosity-temperature characteristics, however their pour point(-4～-12℃) no obvious improve. The chemically modified soybean oils with different acyl chain length have different viscosity, and the higher the viscosity is, the better lubrication characteristics become. The propionyl-chemically-modified soybean oil synthesized through optimizing test has the best integrative characteristics: V40℃=1145 mm2/s,VI 114,pour point is -12℃,PB744.8N,D294N30 '0.52mm. The wear scare based on acetyl-chemically-modified soybean oil is smoother, leveler and smaller than 250BS and soybean oil. The tribological mechanism of them was discussed through AES and XPS analysis combined with reflectance IR spectrum analysis.3. A series of chemically modified rapeseed oils were synthesized by epoxidizing rapeseed oil and different carbon chain alcohols (which can saturate the double bonds to enhance the oxidative stability). They have high viscosity index(VI107～132), good viscosity-temperature characteristics, pour point is between -6～-29℃. The pour point of iso-octanol modified rapeseed oil (-29℃) is obviously improved. The pour point of chemically modified rapeseed oils increases with the length of carbon chain of linear alcohol, and gradually decreases with the degree of isomerization of the molecule; the tribological characteristics increase with the length of carbon chain decrease with the degree of isomerization at the same length of carbon chain. The iso-octanol modified rapeseed oil has the best integrative properties of the chemically modified rapeseed oils (V40℃=25.2mm2/s, VI 140, pour point is -29℃, PB 862.4N, D294N30 '0.50mm). The wear scare based on iso-octanol modified rapeseed oil is smoother, leveler and smaller than 32# mineral oil and rapeseed oil, and the tribological mechanism of them was discussed through AES analysis.4. The chemically modified castor oil 1 was synthesized by epoxidizing castor oil and iso-octanol (which can saturate the double bonds to enhance the oxidative stability). And the chemically modified castor oil 2 ( V40℃=64.16 mm2/s,VI 117,pour point is -58℃,PB695.8N, D294N30 '0.57mm) was synthesized by chemically modified castor oil 1(V40℃=90.12 mm2/s,VI 105,pour point is -46℃,PB785.0N,D294N30 '0.44mm) and acetic anhydride. The viscosity index and pour point of these two kind of chemically modified castor oils were improved, even be better than which of pentaerythritol ester of market Selling. The viscosity index and pour point of chemically modified castor oil 2(VI 117, P.P. -58℃) is better than chemically modified castor oil 1(VI 105, P.P. -46℃). The wear scare based on chemically modified castor oil 1 is smoother, leveler and smaller than castor oil, however which of chemically modified castor oil 2 is worse than castor oil, the tribological mechanism of them was discussed through AES analysis.Biodegradability of propionyl-chemically-modified soybean oil, iso-octanol modified rapeseed oil and chemically modified castor oil 2 was evaluated according to L-33-A-93, they are biodegradable lubricants because their biodegradability can satisfy the norm of German"Blue Angle".The feasibility of application of propionyl-chemically-modified soybean oil and chemically modified castor oil 2 was evaluated. The propionyl-chemically-modified soybean oil with high viscosity, could be used to blend the lubricating oils with diversified viscosity levels instead of bright stock. These blended lubricating oils, prepared by propionyl-chemically-modified soybean oil and polyether, have low pour point, good tribological characteristics, and excellent oxidation stability, which can be used as high-grade synthetic lubricant. The chemically modified castor oil 2 has excellent low-temperature property and oxidative stability, which have the wide application prospect. The aviation turbine engine lubricating oils based on chemically modified castor oil reach or close to the norm of MIL-L-7808L, which could be applied in aviation turbine engine.
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