Effects of multistress aging (radiation, thermal, electrical) on polypropylene

Capacitor-grade polypropylene films were aged under multiple stresses (electrical, thermal, radiation). The aging experiments were performed for singular stresses as well as a combination of any two stresses and finally for simultaneous application of all three. The radiation was applied by suspending a capsule in one of the reactor's stand pipes. Polypropylene film 25.4 ;Based on this work it is found that the mechanical properties of polypropylene undergo much greater changes upon exposure to radiation and thermal stress than the electrical properties. It can be concluded that the failure mechanism of the electrical insulation under multistress aging conditions could be a mechanical failure rather than direct homogeneous decay in the dielectric strength or thermal breakdown of polymer.;The most pronounced changes were observed in the mechanical properties of the film. There is a significant decrease in elongation at break and tensile strength proving deterioration of the polypropylene under combined neutron-gamma radiation. The temperature stress had an opposite effect causing an increase in above mentioned properties and offsetting, therefore, the negative effect of radiation. For the electrical properties, the changes were not as significant as for the mechanical characteristics. The breakdown voltage increased slightly because of radiation, while thermal and electrical stresses lowered it. A similar trend was also observed for volume resistivity. The combination of either thermal or electrical stress with the radiation is overshadowed by the latter and overall increase in the above properties is observed. The radiation stress is therefore a dominant factor in the degradation of the polypropylene film. The effect of electrical stress was very little on both the mechanical and electrical properties, due to relatively low applied field.