Small Strain-Induced Abrupt Drop in the Electrical Breakdown Strength of Polypropylene Insulation

Area of Science:

• Materials Science
• Polymer Science
• Electrical Engineering

Background:

• Electrical properties of polymer dielectrics are generally stable before mechanical yielding.
• Cavitation and microvoid formation in polymers typically occur near the yielding strain.

Purpose of the Study:

• To investigate the electrical breakdown strength of polypropylene (PP) under tensile strain.
• To understand the mechanism behind the decline in electrical properties at low strain.
• To explore methods for improving electrical performance stability in semicrystalline dielectrics.

Main Methods:

• In situ scanning electron microscopy (SEM) to observe microstructural changes.
• Mechanical tensile testing combined with electrical breakdown strength measurements.
• Preparation of modified PP samples with suppressed yield and higher elastic limit strain (εe).

Main Results:

• An unexpected 17.4% decline in electrical breakdown strength was observed at 4% tensile strain in PP, well below its yielding strain (16%).
• Microvoids were observed forming at 4% strain, contrary to the understanding that cavitation occurs near yielding strain.
• Modified PP samples with suppressed yield and higher elastic limit strain (5.4%) showed only a 5.1% decrease in breakdown strength at 6% strain.

Conclusions:

• Microvoid formation at low tensile strain significantly impacts the electrical breakdown strength of PP.
• Suppressing yield and increasing the elastic limit strain (εe) enhances the electrical performance stability of semicrystalline dielectrics under mechanical stress.
• This study provides insights into designing more robust polymer dielectrics for demanding applications.