Halogen-Free Poly(Ionic Liquid) Water-Based Lubricant Additive with Superior Viscosity-Building and Lubricating Properties

A protic poly(ionic liquid) (PPIL), PPDG, was synthesized by using a copolymer as the cationic component and halogen-free octanoylglycine as the anionic counterpart. The viscosity-enhancing and tribological properties of the PPDG additive were systematically characterized. In addition, scanning electron microscopy (SEM), electrical contact resistance (ECR), X-ray photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectrometry (ToF-SIMS) analysis were employed to elucidate the lubrication mechanisms of PPDG. The results indicate that the addition of PPDG in deionized water significantly enhances the viscosity, anticorrosion, and tribological performance of the water-based lubricant. The coefficient of friction (COF) and wear volume (WV) of the water-based lubricant with 8% PPDG were reduced by approximately 68 and 75%, respectively, compared with deionized water. The synergistic action of the physical adsorption film and the tribochemical reaction film formed at the friction interface endows the lubricant with superior lubrication and anticorrosion properties. This type of PPIL lubricant additive is free of sulfur, phosphorus, and halogen elements, making it environmentally friendly. It demonstrates significant potential for application in fully synthetic water-based metalworking fluids or nonflammable hydraulic fluids.