Analysis of the chemical composition of the PTFE transfer film produced by sliding against Q235 carbon steel

• Changes of the chemical component for PTFE transfer film are confirmed.
• DFT calculation is of benefit for revealing the change of PTFE transfer film.
• Defluorination of PTFE transfer film is mostly prone to take place.
• Chain scission of PTFE transfer film is difficult to occur.
• Based on carbonyl group formation, the hydroxyl group can be easily formed.

Polytetrafluoroethylene (PTFE) transfer films formed on the surface of Q235 carbon steel were studied using scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X-ray photoelectron spectroscopy (XPS), molecular dynamics (MD), and density functional theory (DFT) calculations. Changes in the chemical composition of the transfer film were analyzed using XPS measurements. Mechanisms of defluorination, chain scission, and formation of carbonyl and hydroxyl groups were elucidated using DFT transition state calculations. Of these four reactions, defluorination, which has an energy barrier of only 1.0 kcal/mol, is most likely to occur. The formation of a carbonyl group, with an energy barrier of 23.1 kcal/mol, can more easily take place than the chain scission, which has an energy barrier of 44.6 kcal/mol, and is a precursor to the simplest path to the formation of a hydroxyl group.