Fibrillation to Radically Reduce the Wear and Friction of Unfilled PTFE

Polytetrafluoroethylene (PTFE), a material best known for low friction and adhesion, nevertheless suffers from high wear rates. To date, the only demonstrated solution to this high wear problem is to fill the PTFE with other reinforcing materials. We propose a fundamentally distinct approach to reducing PTFE wear by leveraging its natural fibrillability to improve transfer film stability, friction, and wear without the need for adulteration. The primary challenge is that melt processing of parts also destroys the crystalline order needed for fibrillation. Our approach addresses this challenge by combining premelted PTFE matrix particles with unmelted particles. By processing the parts at an intermediate temperature that falls between the melting temperatures of the premelted and unmelted PTFE, we achieve a dual-phase part with a nonfibrillating primary phase and a fibrillating secondary phase. We created dual-phase (with 20% fibrillating content) parts, confirmed the presence of virgin crystalline structure and fibrillation, and observed remarkable improvements in tribiological performance over the control, including: (1) transfer film coverage, alignment, and robustness; (2) 30% reduced friction; (3) 95% reduced wear. To our knowledge, this is the first paper to demonstrate that chemically unmodified PTFE is capable of such properties without fillers. We propose that shear-induced fibrils anchor the transfer film to the counterface, which directly reduces friction and wear independently of subsurface reinforcement. This approach offers a fundamentally distinct design lever for PTFE-based tribomaterials. When integrated with intelligent subsurface reinforcement and trace nanofillers that catalyze favorable tribochemistry, it has the potential to radically improve upon the current state of the art for solid lubrication.