HYDROLYTIC STABILITY OF SYNTHETIC OILS

Synthetic oils based on esters are highly hydroscopic and hence contain dissolved water at practically all times. The dissolved water, even when present in very small amounts, may produce hydrolysis of the esters or additives, forming corrosive compounds or other products that harm the service properties of the oil. However, the susceptibility of synthetic oils to hydrolytic decomposition is determined not only by the presence of water, but also by the chemical structure of the esters, the composition and properties of the additives, the presence of impurities in the oil, etc. In the reported research program, the authors studied the hydrolytic stability of ester-based synthetic oils as one of their important service properties. In the method, that has been specially developed for this purpose, a mixture of 75 g of the oil with 25 g of distilled water is thoroughly homogenized to obtain a uniform emulsion, which is then held in the presence of a copper strip in sealed stainless steel beakers at 100 plus or minus 2 degree C for 48 h. Determinations are made of the quantity of isooctane-insoluble sludge, the acid number of the oil, the pH and acidic number of the water, the -40 degree C viscosity of the oil, and the corrosion of the copper strip. Data are plotted, tabulated, and discussed.