RADIATION HARDENING OF POLYTETRAFLUOROETHYLENE AGAINST CHEMICAL ETCHING

Exposure of polytetrafluoroethylene (PTFE) to MgKα x-rays (1253.6 eV) for times as short as 10 min is observed to lead to permanent radiation hardening toward chemical etching. X-ray-dosed surfaces are visibly less etched, and the loss of F is over a factor of 2 smaller. For PTFE itself, the x-ray photoelectron spectrum shows only slight changes for x-ray exposures up to several hours, but thermal desorption spectroscopy yields a direct correlation between the desorption of low-molecular-weight fluorocarbons and x-ray exposures down to the order of minutes. Irradiation of PTFE does not lead to molecular weight degradation and branching and/or crosslinking through free radical reactions. The degradation reactions are the source of the low-molecular-weight fluorocarbons which desorb at elevated temperatures. Branching and/or crosslinking, which produce a more rigid, thermally stable structure, are proposed as the mechanism for resistance to chemical etching.