Effects of high-energy electron radiation on polypropylene dielectric

Polypropylene, a polymeric materials widely used as the main dielectric in many high-voltage components such as capacitors and cables, was exposed to electron irradiation in air at room temperature. The 25.4-μm-thick dry polypropylene films were irradiated to different doses up to 108 rads with electron beam having energies of 0.5, 1.0, and 1.5 MeV. Monoisopropyl biphenyl (MIPB)-impregnated polypropylene films were also exposed to 1-MeV electron beam to doses up to 108 rads and the post-irradiation effects on the electrical, mechanical, and morphological and chemical properties of the films were evaluated. The electrical properties included the AC, DC and pulsed breakdown strengths, dielectric constant, dissipation factor, conductivity, and pulsed life-endurance. The mechanical properties comprised the Young's modulus, elongation-at-break, tensile strength, complex modulus, and mechanical loss. Finally, the morphological and chemical diagnoses carried out included surface morphology, elemental analysis, crystallinity changes, and identification of newly formed bonds and degree of oxidation. The results obtained indicate that the dry polypropylene films started to exhibit degradation at doses as low as 106 rads. The properties that were mostly affected included the film's tensile properties, pulsed life, dissipation factor, and electrical conductivity