Improved charge stability in polymer electrets quenched before charging

The influence of heat treatment (heating followed by quenching prior to charging) on charge storage in fluoroethylenepropylene (FEP) and polypropylene (PP) foils is studied by a corona discharge or by a mono-energetic electron beam. The variables which affect the charge decay time and the TSD (thermally stimulated discharge) peak are discussed. It is found that quenching leads to a significant reduction of the average crystalline size and an increase of the number of crystal granules. The activation energies are determined by the initial rise method, and the attempt-to-escape frequencies at higher temperatures are estimated for FEP before and after quenching. The depth dependence of the hardening in quenched samples is studied by use of electron-beam charging and explained by the different cooling rates at different depths inside a 25- mu m thick teflon-FEP sample during quenching.<
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