Preparation of microcapsules using ionic liquid and their tribological behavior for epoxy composites

Thermosetting epoxy resins are widely used as bearings, gears, gaskets, and other components. The tribological properties of epoxy resins play an important role in ensuring the life and reliability of the components. A novel self-lubricating microcapsule was synthesized in this study by in situ polymerization using ionic liquid as the core material and polyurea formaldehyde (PUF) as the wall material. The effects of the ionic liquid microcapsule content on the coefficient of friction, wear rate, and surface morphology of the epoxy resin composites were investigated under dry friction conditions. The results showed that the incorporation of self-lubricating microcapsules significantly improved the friction and wear properties of the composites, and the 5 wt.% microcapsule/epoxy composites had the best tribological properties, with the coefficient of friction decreasing from 0.634 to 0.062 and the wear rate decreasing from 6.64 x 10-4 mm3/(N m) to 1.64 x 10-5 mm3/(N m). Compared with the pure epoxy resin, the friction coefficient of the composites was reduced by 90.22% and the wear rate was reduced by 97.53%. The wear mechanism of epoxy resin changes from severe fatigue wear and adhesive wear to slight abrasive wear. This is because after friction destroys the composite, the embedded microcapsules rupture, releasing the lubricant and forming a transfer film that lubricates the friction surface. At the same time, the addition of microcapsules enhances the tensile strength and hardness of the epoxy resin. This study would provide the experimental basis for the design and performance enhancement of epoxy composites with high self-lubricating properties. The prepared epoxy composites are expected to be applied to self-lubricating spherical plain bearings and other mechanical parts.