LUBRICATION PROPERTIES OF CASTOR-OIL POTENTIAL BASESTOCK FOR BIODEGRADABLE LUBRICANTS

Viscosity, oxidative stability, deposit formation, volatility, lubrici ty and additive compatibility of castor oil (88+% ricinoleic) were com pared to super-refined mineral oil (SRMO) and high oleic sunflower oil (HOSO). A satisfactory viscosity index (VI) of 90 and the extraordina rily high viscosity of castor oil can be related to hydrogen bonding o f hydroxy monounsaturated triglycerides. When oxidized in thin film mi crooxidation test on a steel surface at 225 degrees C under controlled air flow, castor oil showed deposit forming tendencies lower than HOS O but much higher than SRMO. Both vegetable oils had low volatility an d demonstrated similar high molecular weight oxidation product formati on tendencies at 175 degrees C. Castor oil solubilized higher concentr ations of antioxidants, but the oxidative stability of the formulation was lower when compared to HOSO. Without additives castor oil was com parable to other vegetable oils and superior to SRMO in performance on the four-ball wear tester.