Investigating the rheological and tribological properties of polyurea grease via regulating ureido amount

The ureido amount of polyurea strongly influences the properties of polyurea grease. Here, four polyurea greases (diurea, tetraurea, hexaurea, and octaurea) were synthesized via regulating the proportion and adding order of reactants (diphenylmethane diisocyanate, octadecylamine, and 1,6–ethylenediamine), using polyalphaolefin (PAO 40) as the base stock. The effects of ureido amounts on the physicochemical, rheological and tribological properties were evaluated. More importantly, the correlation of structure and performance characteristics was explored. Results show that the tetraurea with a granular structure presents optimal physicochemical properties and structural strength. The diurea grease with rodlike structure presents the optimal tribological properties due to the synergies of polyurea deposited film and tribolchemical reaction film (ferric oxide and nitrides), as well as oil film.