Cellular Polymer Ferroelectret: A Review on Their Development and Their Piezoelectric Properties

Because of their ability to show ferroelectret behavior when exposed to an external electric field, cellular polymers have been recently considered for ferroelectret applications. These cellular polymer films can be produced by stretching or foaming, but depending on the application and conditions, different polymers, such as polypropylene (PP), poly(ethylene terephthalate), poly(ethylene naphthalate), poly(tetrafluoro ethylene), cross-linked PP, and some cyclo-olefines, have been considered. Nevertheless, cellular PP was the most investigated material because of its outstanding properties such as high piezoelectric d(33)coefficient, flexibility, good fatigue resistance, good charge trapping properties, and low cost. In this review, recent advances related to the materials used for ferroelectret applications and their processing are discussed. The effect of different parameters such as pressure, electrical breakdown strength of the gas phase, presence of fillers, and service temperature on the d(33) coefficient is presented and discussed.