Effect of Dicarboxylic Acid Chain Length on the Tribological Properties of Aqueous Polyether Esters

Abstract

This article presents the preparation of environmentally friendly water-soluble lubricant additives. Adipic acid (AA), sebacic acid (SA) and dodecanedioic acid (DA) were individually subjected to esterification reactions with polyethylene glycol 1500 (PEG1500) to prepare a class of water-soluble polyether esters (AAPEE1500, SAPEE1500 and DAPEE1500) (referred to as XAPEE1500s) that exhibit excellent water solubility and do not contain environmentally harmful elements. First, the molecular structure characterisation and functional group analysis of these additives will be conducted using an infrared spectrometer and a nuclear magnetic resonance spectrometer. Subsequently, the frictional properties of the additives in the base liquid (deionised water) will be investigated using an SRV-V tribometer, Falex pin-on-disc tribometer and screw torque tester. The surface morphology of wear scars will be characterised and analysed using scanning electron microscopy (SEM) and a non-contact 3D profilometer. Finally, the lubrication mechanism of the DAPEE1500 additive will be analysed using X-ray photoelectron spectroscopy (XPS). The results indicate that the optimal lubrication performance is achieved when the added mass fraction of DAPEE1500 is at 3%. Compared with 0.5 wt% DAPEE1500, the average friction coefficient of 3 wt% DAPEE1500 decreased from 0.285 to 0.122, and the wear volume decreased from 25.52 × 10⁻⁵ μm³ to 10.96 × 10⁻⁵ μm³. The lubrication mechanism of polyether ester is the result of the combined action of its polar ester functional groups and long carboxylic acid chains in the structure. These polar functional groups can form a relatively firm adsorption film on the friction surface, while the long carboxylic acid chains act as a brush-like isolating layer, thus demonstrating superior anti-wear and anti-friction performance.