Investigating electret properties of cellular PP by means of space charge measurement

Electret materials have been manufactured recently through cellular polymers. The electret properties are obtained subjecting these materials to unipolar corona charging. A threshold field exists for this process, which is the field above which electret properties are gained. This paper shows how space charge measurements, carried out by the pulsed electroacoustic technique, PEA, can be very useful to establish the threshold for inception of electret behavior, when existing, and evaluate time and temperature stability of electret properties. Tests are performed on cellular polypropylene (PP), which is charged through poling at different electrical fields levels in the PEA cell, until macroscopic and steady polarization is not observed. Removal of poling voltage and short-circuit (volt off) at different temperatures allow time and temperature stability to be evaluated.