Evaluation of the antiwear and friction reduction characteristics of mercaptocarboxylate derivatives as novel phosphorous-free additives

Abstract

In order to improve environmental protection, there have been many recent advancements in the purification of exhaust gas from automobiles. In order to prevent poisoning of the catalyst used in after-treatment devices for exhaust gas, it is essential to reduce phosphorus in automobile engine oils. However, this phosphorus comes from the zinc dithiophosphate (ZnDTP) that is included in the oils in order to achieve anti-wear and anti-oxidation properties. In the present study, we examined anti-wear additives that do not include phosphorus as substitutes for ZnDTP. The effects of the number of sulfur atoms in the dimer of mercaptocarboxylate derivatives, the length of the alkyl group and the structure of the end alkyl group were investigated. We found that the disulfide bonding of the short intramolecular alkyl chain and the large end alkyl group not only reduced friction, but also showed the same extreme pressure and anti-wear properties as ZnDTP.