Lubricant Potentiality of Degraded Palm Oil and Effect of Free Fatty Acid Addition

Abstract

Lubricant potentiality of used cooking palm oil was examined through four-ball friction test with modified palm oils of two different types. One category of tested oils was the heat-treated type which is expected as degraded palm oil by heating during cooking. The degraded degree was controlled by the length of heating period, then the acid number, AN, was varied between 0 and 3.5[mgKOH/. For these oils, temperature dependence druing friction test was examined on friction and wear between 40-100 ̊C. Degraded palm oil of higher acid number showed wear much more, and the wear for AN=3.5 showed almost double of non-heat treaed oil, but half of mineral oil, VG32, up to 85 ̊C. Friction coefficient did not show strong dependence of the acid number, and the value was 20%-lower than VG32 between 40-100 ̊ C.The other was the free-fatty acid added type which is expected as degraded palm oil by hydrolysis during cooking where boiled water reacts with palm oil. Four model oils were prepared, and each of them contained one of major palm oil components, such as palmitic acid, stearic acid, oleic acid and linoleic acid, at 10mass% to refined palm oil. For these oils, friction test was performed at 40 and 100 ̊ C to examine the effect of temperature. Addition of stearic acid showed lowest wear and lowest friction at both temperatures among fatty acid added types. The experimental results are discussed with kinematic viscosity, apprent normal stress, and apprent tangential shear stress.