Thermal Ageing of an Extrudable Fluorinated Polymer for Aerospace Application

The use of fluorinated polymers is proving increasingly attractive in the context of the energy transition and the move to all-electric propulsion in the aerospace industry. The fluoropolymer investigated in this work is Perfluoroalkoxy (PFA), which is derived from PTFE and retains the same mechanical properties between
$-200^{\circ}\mathrm{C}$
and
$+250^{\circ}\mathrm{C}$
, although it has a significant advantage over PTFE in that it is compatible with extruded technology. We measured the conduction current of power cables insulated with PFA at various temperatures between
$150^{\circ}\mathrm{C}$
and
$260^{\circ}\mathrm{C}$
and by applying a DC voltage with positive and negative polarity as a function of ageing time. We report that from
$200^{\circ}\mathrm{C}$
and on, an asymmetry phenomenon appears between the transient currents under positive and negative polarity. This asymmetry is accompanied by a disproportionate increase in current levels under negative polarity as we approach the maximum operating temperature of
$260^{\circ}\mathrm{C}$
. The probable causes of this asymmetry and the increase in current levels under negative polarity relative to positive polarity are discussed. The migration of positive ions, thermal degradation and the release of trapped charges as well as the interface between the PFA electrodes could be the cause of this phenomenon.