Characterization of piezoelectric films of foamed polyethylene obtained by extrusion

Foamed polyethylene (MDPE) films obtained by extrusion have been characterized by X-ray diffraction, thermogravimetric analysis and tensile tests. The piezoelectric properties have been determined by calculation of piezoelectric constant d(33), thermally stimulated depolarized current method and calculation of activation energy depolarization of electrets. It has been found that the crystallinity and internal morphology, including cellular structure, affect the possibility of an effective polarization in order to obtain a piezoelectric material from foamed MDPE. The conditions of processing have a great influence on the piezoelectric properties. The value of piezoelectric constant attains similar to 18 pC/N and similar to 75 pC/N for low stress range and diminishes for higher stresses, temperature T-m similar to 72 A degrees C and similar to 82 A degrees C, approximate activation energy attains 2.67 and 3.28 eV, for compacted and non-compacted film, respectively. Because of the simple and cheap method of foaming PE films of piezoelectric properties it is worthy to take care regarding their application for pressure sensors.