Piezoelectric polymer cellular films have been studied since 1986. In recent years, they have improved the potential applications due to materials progress. Cellular polypropylene (PP) polymers are characterised by its high piezoelectric coefficient d 33 in comparison with other piezoelectric materials such as ceramics. One of the advantages of these films is their elasticity and flexibility. This study is based on the optimisation of the activation process and characterisation results of polymer cellular films. Samples were made of a commercially available PP film which was modified by a thermal biaxial stretching. Coefficient d 33 was measured by a quasi-static method and the frequency characterisation was made for validating all characterisations and their relations. Transducer coefficients around 700 pC/N were obtained with polymer cellular PP films with silver coating electrodes, activated by corona discharge. An approximation of the surface charge density in the polymer voids was obtained with a mathematical model. Thermal stability was checked by thermally stimulated discharge currents (TSDCs) showing a relationship between the TSDC and the coefficient d 33. Time stability was determined after 3000 h ageing, and finally was obtained a resonance frequency by interferometry measurement.@en

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.

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