Tribological performance of poly(sodium 4‐styrenesulphonate) as additive in water–glycol hydraulic fluid

The tribological behaviour of poly(sodium 4‐styrenesulphonate) (PSS) as additive in the base fluid of water–glycol hydraulic fluid was evaluated with four‐ball machine and Optimol SRV‐IV (Optimol Instruments, Munich, Germany) oscillating friction and wear tester, and its viscosity‐enhancing performance was also investigated. The results show that PSS exhibits excellent friction‐reducing and anti‐wear properties in the base fluid and can significantly improve the latter's welding load and viscosity. The worn surfaces were characterised by scanning electron microscope and X‐ray photoelectron spectroscopy. The analytical results of typical elements on the worn surfaces demonstrate that PSS molecules adsorb on the rubbing surface and form a stable chemically absorbed film through the interactions between the sulphonate anions and surface metallic atoms during the sliding process, which contributed to improve the tribological properties of the base fluid.