Effect of ultraviolet and gamma sterilization on charge storage stability for porous PTFE film electrets

Medical products of PTFE electret that come in contact with the body or bodily fluids must be sterilized before use. That sterilization method is selected is important because the stability of space charge in electrets may be affected differently to various forms of sterilization. In this paper, charge storage stability in porous polytetrafluoroethylene (PTFE) film electrets were investigated by means of corona charging at room or elevated temperature, isothermal and thermal stimulating surface potential decay, as well as open-circuit thermally stimulated discharge (TSD) current spectra after ultraviolet (UV) and gamma (cobalt 60) radiation sterilization. The results showed that the surface potential remain above 95% of the original level in porous PTFE after UV-irradiation in the range of 3.2 mW/cm² for 2 hours, however, the charges injected in porous PTFE were almost completely removed after radiation with gamma-radiation at doses of 15 kGy. UV-irradiated porous PTFE films, one side coated with aluminum electrodes and negative corona charged, show peak position shifts towards the higher temperature in their TSD curves as compared with those of unirradiated samples. It is available for sterilizing medical electret products of porous PTFE films by UV radiation.