Triboelectrification and thermal stability of positive charge on polytetrafluoroethylene electret films

It is known that triboactivation of polymer surfaces does not only lead to electrification, but may also result in mechano-chemical modifications. In the present work, the influence of triboelectrification on the thermal stability of positive charge on subsequently corona-charged PTFE films is investigated. As rubbing materials cotton or low-density polyethylene (LDPE) fibers were employed. LDPE is near to PTFE in the triboelectric series, whereas cotton is on the positive side of the series. As a result of triboelectrification, PTFE films always attained a negative charge the magnitude of which strongly depended on the treatment conditions (time, pressure, etc.). After triboelectrification, the PTFE films were charged in a positive corona discharge. The thermal stability of the electret charge was investigated by means of thermally stimulated surface-potential-decay measurements. It could be shown that the rubbing treatment generally improves the thermal stability of positive charge on the PTFE films. The improvement depends on the rubbing material and on the magnitude of the resulting negative tribocharge.