Charge Storage Properties And Piezoelectricity Of Chemically Modified Cellular Polypropylene Electret Films

Cellular polypropylene (PP) film is one of the piezoelectric electret materials with important commercial application potential in recent years. Some commercial applications are already available from cellular PP films because of their strong piezoelectricity, but the rather low working temperature (60℃) restricts their further applications. Therefore, how to improve cellular PP films' thermal stability of piezoelectricity and charge storage becomes one of the focuses in the field of the functional dielectric materials. But it is difficult to improve those properties significantly only by physical preparation methods such as heat treatment or being charged at elevated temperatures. In this thesis, a chemical method was firstly proposed and its influences on the thermal stability of piezoelectricity and charge storage of cellular PP films were investigated.Firstly, the electret properties of virginal cellular PP (PQ50) films were systematically studied by measuring the open-circuit thermally stimulated discharge (TSD) current spectra and charge TSD spectra. Then, cellular PP films were modified by extraction, oxidation and fluorination in a hydrofluoric acid (HF) solution. The results of the attenuated total reflection infrared (ATR-IR) spectrum for the surface layer and the energy-dispersive X-ray spectrum (EDS) for the cross section of the chemically modified cellular PP films indicted that a layer containing fluorine element was formed after chemical treatment and it had a considerable reaction depth. By the means of TSD current spectra, charge TSD spectra and isothermal charge decay measurements, the charge storage properties of the virginal and the chemically modified cellular PP films were comparatively investigated. The results pointed out that the technology and parameters of chemical modification have obvious effects on the thermal stability of charge storage of the cellular PP film. With optimized chemical modification, the thermal stability of charge storage of the cellular PP film was significantly improved in comparison with that of the virginal one.In addition, the influences of the above-mentioned chemical modification on the...