Electret stability related to the crystallinity in polypropylene

Through mixing isotactic-polypropylene (i-PP) and atactic-polypropylene (a-PP), we have demonstrated the importance of the crystallinity in polypropylene as an electret material. Samples with crystallinities between 7 % and 47 % were used. A high degree of crystallinity in polypropylene, used as an electret, gives a better charge stability with respect to temperature and humidity changes. The semicrystalline i-PP significantly outperforms a-PP regarding charge stability. a-PP is an amorphous polymer. By mixing a-PP and i-PP, the degree of crystallinity can be controlled, while all other sample preparation processes and characteristics can be identical. This is important since the performance of an electret material is sensitive to its previous process history. Activation energies used for predicting the thermal potential decay are determined from thermally stimulated current and isothermal potential decay experiments. Activation energies from 0.98 eV to 1.41 eV were determined. From these values, a very good agreement was achieved between the experimental potential decay at room temperature for more than 290 days, and a theoretical estimation of the potential decay.