Performance properties of lithium greases with PTFE particles as additive: Controlling parameter- size or shape?

The tribo-performance of Lithium-based synthetic greases based on poly-alpha olefin as a base-stock and Polytetrafluoroethylene particles (4 wt%) of different sizes viz. 50 nm, 6 μm, 9 μm and 12 μm and shapes as a functional additive were developed and tribo-investigated. Tribo-results revealed that the smaller the size, better was the performance in general. However, there was a strong competition between small particles 6 μm and nano-particles (50 nm) for best performance. The 6 μm particles showed slightly better performance, mainly because of their spherical shape. It was concluded that both the size and shape of particles were the controlling factors. •Size effect of PTFE nanoparticles (NPs) as l additive in lithium-based grease was I time studied.•Enhancement in performance was observed for EP (74%), AW (75%) and AF (30%).•Spherical particles of 6 μm performed slightly better than NPs with cylindrical shape.•PTFE in grease reacted chemically with steel surface to form tribo-film of FeF2.