Factors driving the properties of PEEK transfer films

Debashis Puhan and Janet Wong

Tribology Group, Department of Mechanical Engineering,

Imperial College London, London, SW7 2AZ, UK.

Abstract

Polyetheretherketone (PEEK) is one of the most commonly used high performance polymers for engineering components. Its popularity is due to its low density, relatively good thermal and chemical stability. This work focuses on using PEEK as a tribological material. As moving parts, PEEK components often rub against metal or ceramic components and as a result, PEEK materials are transferred to the metal counterface. Understanding the material transfer process and properties of transfer materials would be crucial for developing materials with better tribological performance.  This understanding is achieved by observing in-situ PEEK materials transfer process to counterface. A rotating PEEK disc was rubbed against a stationary steel or sapphire ball under ambient conditions. Surface analysis were conducted on transferred materials. In-situ imaging showed PEEK debris accumulated around PEEK-counterface contact, some of which were detached and removed, while some re-entered the contact, creating local hot spot under more shear. FITR and Raman spectroscopies confirmed that transferred PEEK materials have all undergone changes due to oxidation, crosslinking or orientation that suggests ion irradiation. Mechanical shear, elevated temperature and plasma bombardment, all contribute to PEEK degradation. The role of plasma on transfer film was further explored with optical emission spectroscopy (OES) which shows the plasma luminescence observed during rubbing were nitrogen ions along with CH and C2 radicals. These radicals abstract hydrogen from adjacent phenylene units, or terminate by combination to produce crosslinks.