Relationship between thermo-stimulated discharge currents and piezoelectric d33 constants in PP and PE foams

Abstract

Cellular polymers films have a too soft mechanical characteristic, like elastic compliance due of the internal porosity structure and their high electric insulation that gives the ability of hosting internal electrical dipoles. If a corona discharge is applied to the surface, the high electrical field induces internal discharges which leave a permanent static charge in the polymer cells. A macro dipole of cell dimension is generated producing a quasi-piezoelectric response. The d33 piezoelectric constant can reach values of about many hundreds of pC/N. Thermally stimulated discharge currents (TSDC) are widely used to characterize charge density and stability of dielectric materials. In our work the relationship between TSDC and d33 piezoelectric constant of two cellular polymers based on polyethylene and polypropylene films is investigated. Samples were thermally stretched, charged by corona discharge and metallized on both sides. The d33 piezoelectric constant by quasi-static method was measured and then TSDC were registered. A strong relation between d33 constants and TSDC curves on both cellular polymers was obtained.