Wear, 96 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA (1984) 109 -119 109 zyxwvutsrq STORAGE STABILITY OF SULPHURIZED REPLACEMENTS SPERM OIL I: ORIGIN AND NATURE OF THE SLUDGE G. S. CHOLAKOV and K. KAISHEV Department of Fuels and Lubricant Technology, Higher Institute of Chemical Tech- nology, bul. ‘Kliment Ohridsky” no. 8, Darvenitza, Sofia 1156 (Bulgaria) (Received November 11,1983;accepted M ay 17,1984) Sulphurized sperm oil has been used in numerous lubricant formula- tions to improve their extreme pressure and antiwear properties. In the beginning of the 197Os, sperm oil became an almost unavailable and expen- sive raw material. Replacements have been developed, but they are also expensive. Many lubricant manufacturers seem to have turned to sulphurized glycerides, when possible since natural fats and oils are cheaper and more readily available than the synthetic replacements. The greatest limitation on the wider use of sulphurized glycerides in lubricating fluids is their low storage stability in compositions based on paraffinic mineral oils. This has not yet been an object of systematic inves- tigation. The purpose of the experiments presented in the present paper was to examine and suggest the origin and nature of the sludge formed by sulphurized esters of fatty acids in paraffinic mineral oils. The storage stability of sulphurized soya bean oil, lard oil and a mixture of n-butyl and diethylene glycol esters of long-chain fatty acids in three paraffinic base oils was studied. Samples of sludge obtained from the addi- tives after 12 months of storage were characterized. The experimental results confirm earlier observations with model additives that there are less than two sulphur atoms per double bond both in the bulk additive and in the sludge that it forms. The sludge samples were found to have substantially higher acidity than the bulk additives. 1. Introduction Sulphurized esters of fatty acids can be used in more than 100 lubricant formulations (for cutting fluids, gear and slideway oils, greases etc. [l]) to improve their extreme pressure and antiwear properties. The most popular of these additives, a sulphurized sperm whale oil with a lo%, 12% or 17% S content, is stable during storage in any mineral-oil-based formulation. It has a predominately monounsaturated monoester composition, which is unique 0043-1648/84/$3.00 @ Elsevier Sequoia/Printed in The Netherlands