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

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.