Dipole polarization formed on surface of polypropylene electrets

The surface chemical composition and pyroelectric properties in polypropylene (PP) film poled by corona discharge in the air were estimated by Fourier transform infrared spectrophotometry (FTIR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), thermally stimulated depolarization current (TSDC), and pyroelectricity measurement. The corona discharge oxidized the PP chains at the surface into oligomers bearing C=O, C-O and COH groups, and formed hetero charge, and counter homo charge absorbed strongly on the surface. The pyroelectricity and surface potential were undetected after removing the polymer surface with solvent or scratching. TSDC curves indicated that the both homo and hetero charges were stable below the melting point of the oligomers. The stabilization mechanism of surface potential was investigated from the electric behavior and the chemical structure of poled PP films.