Charging properties and time-temperature stability of innovative polymeric cellular ferroelectrets

Abstract

After appropriate mechanical and electrical treatments, some cellular polymers become able to retain space charge for a long time, i.e. they acquire electret behavior. The electrical treatment consists of charging under high levels of DC electric field. The mechanical treatment, based on the application of stretching forces to cellular polymer slabs that were before expanded under pressurized gas, affects the cavity size and shape, and therefore also the effectiveness of the charging process itself. An investigation of charging mechanisms, as well as of mechanical treatment, is therefore fundamental for optimizing the ferro-and piezo-electret properties. The aim of this paper is to discuss the effect of the physical dimension of the cavities on the charging behavior of cellular ferroelectrets and to focus on the time-temperature stability for two families of polymeric cellular ferroelectrets based on polypropylene (PP) and on a cyclo-olefin copolymer (COC). Emphasis will be given to the stretching process and in particular to the expansion rate applied during the manufacturing process (which affects the radial dimension and the height of the cavities, respectively). Space-charge and partial-discharge measurements as a function of time and temperature are the main tools to infer the influence of the cavity size on charging and stability characteristics. . In 1988, he was awarded an ITG-Preis by the Informationstechnische Gesellschaft im VDE. In 1989, he received a Silver medal from the Stiftung Werner-von-Siemens-Ring. In 2001, he was awarded the first Technologietransfer-Preis by the Technologie-Stiftung Brandenburg and the Prof.-Adalbert-Seifriz-Preis by the Verein Technologie-Transfer Handwerk for his technological collaborations with small industrial companies. The main research areas of Prof. Gerhard-Multhaupt are polymer electrets and ferroelectrets, in particular the mechanisms of space-charge storage and dipole polarization in dielectric polymers and polymer composites, their ferro-, pyro-and piezoelectrical properties, and their applications in sensors and actuators, as well as the nonlinear optical properties of polymers, and more recently also the physics of musical instruments. He is a

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

“…Moreover, it has good fatigue resistance, which is an important property for piezoelectric materials. [71][72][73] Thin cellular PP films (50-100 μm thick with cells having a length of 100 μm and a height up to 10 μm) are considered as useful materials for piezoelectric applications. Hence, the development of piezoelectric cellular polymers started with PP.…”

“…Hence, the development of piezoelectric cellular polymers started with PP . Recently, this knowledge was developed for cellular films made from polyethylene, poly(ethylene terephthalate) (PET), poly(ethylene naphthalate) (PEN), poly(tetrafluoro ethylene) (PTFE), cross‐linked PP (XPP), as well as some cyclo‐olefins polymers and copolymers …”

Bringing an insulation to failure: the role of space charge

“…Beyond that, space charge plays important roles in many other fields involving dielectrics and electrical insulation, from, e.g., electrostatic electrifications (e.g. oil-paper cables and transformers [141]), to cellular ferroelectric/piezoelectric materials [142]. Nanofiller is montmorillonite at 5% wt density.…”

Charging behavior and thermal stability of porous and non-porous polytetrafluoroethylene (PTFE) electrets

“…Cellular electret films have been developed from polypropylene (PP) (see the reviews [1] and [2] and the references therein), polyethylene terephthalate (PET) [3,4], polyethylene naphthalate (PEN) [5] and cycloolefine polymers (COP) and copolymers (COC) [6,7]. These ferroelectrets [1,2,8,9] represent a new class of piezoelectric polymers in addition to polar, ferroelectric polymers such as polyvinylidene fluoride (PVDF) and some of its copolymers.…”