Studies on additive‐additive interactions: Effects of dispersant and antioxidant additives on the synergistic combination of overbased sulphonate and ZDDP

Abstract

Abstract A strong synergism between overbased sulphonate (OBS) and zinc dialkyldithiophosphate (ZDDP) in a proven diesel engine oil formulation has been reported in an earlier communication. 1 In continuation of these studies, the effect of different types of dispersant, of varying nitrogen content, and an antioxidant, on a synergistic combination of OBS‐ZDDP has been investigated. Both detergency and dispersancy of the optimised formulation were improved with high nitrogen‐content dispersants, which also increased strongly the wear tendencies. The antioxidant, though it improved detergency, did not show any positive effect on antiwear performance. Detailed IR and 31 p‐NMR spectroscopic analyses on interactive additive pairs, namely, ZDDP‐PIBS and ZDDP‐antioxidant, indicated the formation of association complexes and hydrogen bonding respectively.