Tribochemical Degradation of Polytetrafluoroethylene Catalyzed by Copper and Aluminum Surfaces

• Published in: Journal of physical chemistry. C Vol. 120; no. 20; pp. 10857 - 10865
• Main Authors: Onodera, Tasuku, Nakakawaji, Takayuki, Adachi, Koshi, Kurihara, Kazue, Kubo, Momoji
• Format: Journal Article
• Language: English
• Published: American Chemical Society 26.05.2016
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.6b00799

The tribochemical reaction of polytetrafluoroethylene (PTFE) resin sliding against a metallic surface was investigated for a purpose of improving its tribological performance. The tribochemical reaction between PTFE and aluminum surface has been investigated experimentally and theoretically [ Onodera et al., J. Phys. Chem. C 2015, 119, 15954−15962 ]. One of the important results is that the wear and self-lubrication properties can be controlled by the catalytic activity of the oxidized aluminum surfaces with different crystal structures (α- and γ-alumina). In particular, the amount of wear was higher on the γ-alumina surface because it easily activates tribochemical degradation of PTFE and suppresses the formation of transfer film (a necessary phenomenon for reducing wear). Accordingly, for controlling catalytic activity a copper surface was tested as a model surface exhibiting a weaker reactivity than an aluminum surface. A thermogravimetric analysis proved that the copper surface showed a weaker catalytic effect in regard to PTFE degradation in comparison with an aluminum surface. Metallic fluoride, causing less transfer film to form, appeared on the aluminum surface but hardly any was observed on the copper surface. An experiment and density functional theory (DFT) calculations showed lower catalytic activity on copper surfaces. A friction test was also carried out to determine the relationship between the catalytic activity of metallic surfaces on PTFE and the resultant wear properties. A rubbed copper surface was fully covered with flakelike PTFE transfer film, and no metallic fluoride was detected. Transfer film was less abundant on an aluminum surface because aluminum fluoride tribochemically formed. Reflecting these chemical changes, the wear amount of PTFE on the copper surface was less than that on the aluminum surface. The results of this investigation indicate that suppressing the catalytic effect during friction process of PTFE is a promising way to improve its tribological performance. The use of a copper-based material will be effective in industrial uses of PTFE, because it suppresses catalytic tribochemical degradation.