Polymer Composition and Film Morphology Affecting Polypropylene Electret Charge Stability

Electret charge stability has been examined by thermally stimulated surface potential decay for corona charged polypropylene films. Pressed and extruded samples have been analyzed with their initial morphology and after annealing at 120°C for 15 min. Notwithstanding the typically low amounts of additives used by polymer manufacturers, already distinct differences in charge stability have been observed for polymer compositions with different anti-oxidant packages. Charging with positive corona has provided the most stable electret films for all analyzed sample compositions. Next to the additive related peculiarities, a major discrepancy on electret stability has been noticed between extruded and pressed films. It is found that pressed films have a better electret stability in respect to the extruded films. Annealing has improved the electret stability, but doesn't affect all samples equally. Biggest gains in electret stability have been obtained by annealing quench cooled extruded films, even though the improvements are both composition and polarity dependent.