Is replacement of aromatic compounds with alkyl ones really the effective way toward developing greener lubricants?

The present work designs a series of cycloalkyl ester oils and reports a comparative study on their physicochemical and tribological properties, phytotoxicity, and biodegradability. From the perspective of molecular structure, the factors affecting their physicochemical, tribological properties, phytotoxicity, and biodegradability were discussed, including steric hindrance, group polarity, and so on. The results demonstrated that cycloalkyl ester oils had better thermal stability and viscosity -temperature property than the reference oils. Additionally, their friction -reducing and anti -wear performances were superior to the reference samples. Unexpectedly, the cycloalkyl ester oils were found to have higher phytotoxicity to the experimental plants (wheat and Pak Choi) due to the introduction of the cycloalkyl group, which enhanced the lipophilicity of corresponding oils and then strengthened the damaging of the oils to plant cell. On the other hand, some of cycloalkyl ester oils were proved to be more biodegradable than the reference samples. By and large, developing green lubricants by replacing aromatic rings is not entirely successful. Lubricants' biodegradability can be improved with this replacement, but their phytotoxicity cannot be reduced. Howsoever, the present work provides a specific benchmark for the subsequent development of environment friendly, high-performance synthetic ester lubricants.