Antiwear Film Formation by ZnDTP, Detergent, and Dispersant Components of Passenger Car Motor Oils, Part II. Effects of Low Molecular Weight Dispersant on Film Formation

摘要

Passenger Car Motor Oils (PCMOs) are undergoing a rapid evolution. Studies have found that some exhaust emission catalysts may be deactivated by phosphorus, largely derived from zinc dialkyldithiophosphate (ZnDTP), the mainstay antiwear and antioxidant agent in PCMO formulations for 50 years. Consequently, future engine oils will contain significantly reduced phosphorus levels. Since ZnDTP is the dominant antiwear and antioxidant in current PCMOs, lower phosphorus content will impact engine oil formulation strategies. To better understand the effects of ZnDTP reduction on wear control, Electrical Contact Resistance (ECR) studies have been carried out on blends containing ZnDTP, detergent, and low molecular weight (LMW) succinimide dispersant. In contrast to previous results obtained with high molecular weight (HMW) dispersant, the combination of ZnDTP and LMW dispersant gave an ECR trace closely resembling that of ZnDTP alone. Thus, the chemical structure of the succinimide dispersant can have a profound effect on ZnDTP antiwear film formation. ECR experiments on three-way combinations of ZnDTP + LMW succinimide dispersant + overbased phenate detergent provided a much better film than that from a similar formulation using a HMW succinimide dispersant. This study demonstrates that the ECR experiment is sensitive to the chemical structures of components controlling the function of modern Passenger Car Motor Oils, making ECR a convenient tool to optimize the performance of the remaining ZnDTP in lower phosphorus PCMO formulations.