Tribological properties of radiation cross-linked polytetrafluoroethylene sheets

A polytetrafluoroethylene (PTFE) sheet was cross-linked by electron beam irradiation at 335 ± 5 °C in a nitrogen gas atmosphere. With increasing dose, the cross-linked PTFE (X-PTFE) sheet became transparent, and the melting point and the heat of crystallization decreased gradually. The tribological behavior of the X-PTFE sheet was investigated on a ring-on-ring tribometer and a block-on-ring friction tester under dry friction conditions. It was shown that the friction coefficient of X-PTFE increased with the absorbed dose, and that the increase was about 5% for cross-linking at a dose of 3000 kGy. The substantial improvement of the wear resistance of X-PTFE is of particular interest. The wear resistance of X-PTFE was improved by three orders of magnitude at a dose of 150 kGy. Scanning electron microscopy (SEM) analysis revealed that, after the tribological test, the ground surface of the virgin PTFE sheet was smooth, and the debris was in the form of flakes; while the worn surface of X-PTFE was rough, and the abraded debris was in the form of a fine powder. The three-dimensional network of X-PTFE is responsible for its excellent wear resistance behavior.