Enhanced biodegradability and lubricity of mineral lubricating oil by fatty acidic diethanolamide borates

The impacts of two fatty acidic diethanolamide borates, viz. oleic diethanolamide borate and lauric diethanolamide borate, as additives on biodegradability and lubricity of an unreadily biodegradable mineral lubricating oil were studied. The biodegradabilities of neat lubricating oil and its formulations with the borate esters were evaluated on a biodegradation tester. Furthermore, the anti-wear and friction-reducing abilities of neat oil and the formulated oils were determined on a four-ball tribotester, respectively. The tribochemical species of the worn surfaces were analyzed by an X-ray photoelectron spectroscope (XPS). The results indicated that oleic diethanolamide borate and lauric diethanolamide borate markedly enhanced biodegradability and lubricity of the lubricating oil. The improvement of anti-wear and friction-reducing abilities of the mineral oil by the borates was mainly ascribed to the formation of a composite boundary lubrication film thanks to the adsorption and tribochemical reactions of the borates on the friction surfaces.