Effect of crystalline and amorphous phases on the transfer of polytetrafluoroethylene (PTFE) onto metallic substrates

The transfer of polytetrafluoroethylene (PTFE) onto stainless steel (AISI 316) and silicon wafers in a static contact was characterized at temperatures ranging from 21 °C to 300 °C. The amount of transferred PTFE on AISI 316 substrate was found to be strongly time- and temperature-dependent, and reached a steady state after a certain period of contact time. On testing the effect of temperature on this steady transfer state, an almost temperature independent amount of PTFE was observed to be transferred onto AISI 316 at temperatures between 130 and 180 °C. This steady state started at the glass transition at about 127 °C. This was significantly consistent with an almost constant amorphous-to-crystalline phase ratio at about the same temperature range as determined using infrared spectrophotometry (IR). In general, the amount of the transferred PTFE on AISI 316 depended on the relative amount of amorphous phase in the PTFE contact area. Thus, the amorphous phase in semicrystalline PTFE evidently plays an active role in the transfer process.