Enhancement of Electro-Mechanical Properties of Thin Semicrystalline Polypropylene Films

Mechanical property enhancements in ultra-thin polymer films are becoming increasingly important in applications ranging from packaging to nanotechnology. Recent studies have demonstrated dramatic increase in electrical breakdown properties of ultra-thin non-crystalline entangled polymer films when the film thickness is reduced to range between 1 mm to 0.1 mm,

an effect attributed previously to a mechanical stiffening of the polymer film based upon prior independent dynamical mechanical modulus measurements of non-crystalline entangled polymer films under large deformation conditions.  In the present paper, we show a direct correlation between the enhancement of electrical breakdown strength and the Young’s modulus enhancement in progressively semi-crystalline isotactic polypropylene (PP) films in a similar thickness and deformation range and interpret this phenomenon as arising from physical cross-links as argued before for amorphous glass-forming polymers. Our results have important ramifications for applications of ultrathin PP films, especially as flexible capacitors for high-power energy storage.