Correlation of dielectric behaviour with chemical structure in aged polypropylene

Results are reported for 50 μm films of isotactic polypropylene in three different forms: additive-free and containing either 0.25% or 1% of a hindered amine light stabiliser. Oxidation of the materials was achieved by irradiating them in air at room temperature in a Co-60 gamma source at a dose rate of 0.16 kGy/h. After irradiation, samples were left in air at room temperature for a period in excess of 1 year. Chemical analysis was performed using FTIR spectroscopy and spectrophotometry. The electrical analysis consisted of monitoring thermally stimulated discharge currents. It was found that the oxidation from the ageing procedure produced changes in both the chemical structure and the electrical response