PP-based blends for electret filters-an appraisal

Corona-charged polypropylene-based polymeric materials for electret filters were studied. Blending of PP with polycarbonate was found not to improve its performance, despite claims made elsewhere. The electret properties were characterized with several techniques, including one that allows the determination of the fine structure of all trap-depth energies. Trapping near the crystallites provides most of the deep traps in PP-based polymers. A more perfect crystallite structure thus enhances the charge stability. This fact offers better opportunities for producing longlasting electret filters than blending with PC. A crucial factor is that the PP-blend should remain nonpolar in order to guarantee a low conductivity and high water repellency.