PTFE based nano-lubricants

Polytetrafluoroethylene (PTFE) is known as a high performance engineering polymer as well as a solid lubricant. The literature contains several papers that report on the effects of nano-sized solid lubricant additives, but no systematic studies have been published on the effects of nano-sized PTFE particles. This paper first describes the methodology for preparing nano- and micro-PTFE particles that were blended into a 150 N API Group II base oil. The particle sizes were 50 nm, 150 nm, 400 nm and 12 µm, and the particle concentrations were 4, 8 and 12%. Formulations were characterized for physical properties and tribological behavior. Physical properties included density, viscosity, pour point, and flash point. Tribological characteristics were (1) weld load tests (a four-ball EP method to determine load carrying capacity), (2) anti-wear properties (using a different four-ball test method) and (3) friction (using an Optimol-SRV III oscillating friction and wear tester). Results from tribological testing of the experimental oils and bearing steel test specimens showed that PTFE particles can significantly improve the weld load, as well as anti-wear and friction reduction properties. The smaller the size of PTFE particles and the higher their concentration, the greater was the performance improvement. The topography and surface chemistry of the test specimens were examined using scanning electron microscopy, and the improved quality of the tribo-films formed on the counter faces was seen to correlate with performance improvements.