3 years ago

Structure and Function of Transfer Film Formed from PTFE/PEEK Polymer Blend

Structure and Function of Transfer Film Formed from PTFE/PEEK Polymer Blend
Momoji Kubo, Koshi Adachi, Kazue Kurihara, Kenji Kawasaki, Jun Nunoshige, Tasuku Onodera
Improving the tribological performance of polytetrafluoroethylene (PTFE) resin is important for industrial use of PTFE. An effective way to do this is to blend pure PTFE with another resin material to improve the quality of the transfer film, i.e., adhesion to a counter metallic surface. It is well-known that PTFE/polyetheretherketone (PEEK) polymer blends show significantly less wear than pure PTFE and PEEK. However, the structure and function of the transfer film formed from the blend, which is the key process for reducing friction and wear, have not yet been understood well. Accordingly, the tribological properties and the structure of transfer film of PTFE/PEEK polymer blends were investigated. The blends were prepared by compression and calcination of mixed powders, and a conventional pin-on-disk friction test was performed using pure aluminum as a counter material. Both the friction coefficient and wear rate of the polymer blends were lower than those of pure PTFE and PEEK, respectively. This is consistent with the results of an earlier study [Burris and Sawyer, Wear 2006, 261, 410–418]. The present study especially focused on the microstructure and function of the transfer film formed from the PTFE/PEEK polymer blend. The microstructure of the transfer film was analyzed by X-ray photoelectron spectroscopy (XPS) with argon etching. The XPS depth profile of the carbon 1s and fluorine 1s photoelectrons in the transfer film revealed the existence of a unique microstructure. The film was probably heterogeneous: the PTFE content was on the topmost surface of the film, and the PEEK content was mainly inside the film. To gain a better understanding of this transfer film formation, a density functional theory simulation was performed, and the results indicated that PEEK is more likely to adsorb onto an aluminum surface than PTFE. The PEEK contents in the polymer blend apparently migrated to the counter aluminum surface prior to PTFE addition. Subsequent investigation of the tribological function of the transfer film by molecular dynamics simulation showed that the PEEK prevents detachment of the film and that the PTFE reduces friction by interlayer sliding. These findings clarify the tribological advantage of PTFE/PEEK polymer blends in terms of elucidating the structure and function of the transfer film.

Publisher URL: http://dx.doi.org/10.1021/acs.jpcc.7b02860

DOI: 10.1021/acs.jpcc.7b02860

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