Deliani Lovera

Recent Advances in the Improvement of Polymer Electret Films

Polymer electret materials are electrically charged dielectric polymers capable of quasi-permanently retaining their electric field. However, environmental influences such as temperature and humidity reduce their charge stability and restrict applications. Therefore it is of great importance to provide a broad pool of polymer electret materials and to enhance further the charge storage behavior. In this context we report on concepts, measures, and solutions to improve the electret performance of commodity and high performance thermoplastic polymers, which was carried out at the University of Bayreuth in recent years. It is demonstrated that the commodity polymer polypropylene can be manufactured into excellent electret films when certain trisamide additives are incorporated in very low concentrations. Polypropylene can be employed at temperatures up to its continuous service temperature of 70 ∘C. To achieve higher temperature windows we investigated the commodity blend system of poly(phenylene ether) (PPE) and polystyrene (PS). We demonstrate that especially PPE/PS blend films with a composition of 75/25 exhibit remarkably good charge storage retention during the isothermal surface decay (ITPD) tests at 120 ∘C. In addition, the commercially available high performance thermoplastic polyetherimide (PEI) resin containing special phosphorus(III) additives shows very good electret properties at elevated temperatures. These properties can be further enhanced by physical aging; resulting in a charge retention after 24 h at 120 ∘C as high as 95%. The same beneficial effect of physical aging can be used to advance PPE and PPE/PS blends. Polymer electret materials with such charge storage properties have the potential to be employed in microphones, sensor devices, and electret filters.

Charge storage of compact and fibrous blends based on polyphenylene ether

The charge storage behavior is a fundamental property of polymers used in electromechanical-transducer applications. Polymer blends can potentially show a higher charge storage capability than the neat constituents, since the phase boundaries between the individual components can act as trapping sites. In this work, the charge storage behavior of polyphenylene ether (PPE) is enhanced by the addition of selected amounts of polystyrene (PS) and poly(styrene-isobutylene-styrene) (SIBS). While the binary blends PPE/PS are miscible and are expected to form one homogeneous phase, the ternary blends PPE/PS/SIBS are multiphasic. The blend charge storage behavior was related to the macro- and micro- morphology as well as to the charging method.

Influence of the polymer chemical structure on the charge storage of polymer blends

In this study, multiphasic blends were prepared by the addition of different styrene-based-copolymers to a blend PPE/PS of 75/25 composition. The aim is to give insights into the influence of the polymer chemical structure on the charge storage of polymer blends.