Influence of coexisting functionalized polyalkylmethacrylates on the formation of ZnDTP-derived tribofilm

Although zinc dialkyldithiophosphate (ZnDTP) shows supreme antiwear performance by forming a thick polyphosphate-based tribofilm on the friction surface, it has been pointed out that the use of ZnDTP is accompanied by interference from the coexisting dispersant. For the maintenance of the good antiwear performance of ZnDTP when it is used with coexisting polar compounds, the effects of polar compounds on the tribofilm formation of ZnDTP should be clarified. Since the recent demand for minimizing energy consumption recommends applying lower-viscosity oil to reduce the viscous drag, the use of a good viscosity modifier (VM) that improves the temperature-viscosity characteristic of the oil is required. Here we tested several types of functionalized polymethacrylate (PMA)-VMs used with ZnDTP, and we discuss their effect on the tribofilm formation of ZnDTP. We observed that the PMA-series VMs with different functional groups influenced the tribofilm formation of ZnDTP. The amino-group-containing PMA in particular significantly reduced the formation of tribofilm.