Structure effect of thin film polypropylene view by dielectric spectroscopy and X‐ray diffraction: Application to dry type power capacitors

Abstract

This work reports on the relationship between structure and dielectric properties of biaxially oriented polypropylene. The morphology of semicrystalline bioriented isotactic polypropylene films is investigated using wide angle X-ray diffraction and Polarized Optical Microscopy. A b-orthorhombic structure, with a crystallinity ratio of about 46%, and "Crater" morphology of the b-form is identified. Dielectric properties are measured by Broadband Dielectric Spectroscopy over a wide temperature range (2150 to 1258C). Since the dissipation factor of the PP is very low, special care was taken to obtain valid data. Two main relaxation processes are observed: a a-relaxation peak associated to the glass transition temperature (Tg) at temperature about 278C, and a broad b*-relaxation at about 2608C, partly attributed to CH orientation. The variation of the dissipation factor versus sample thickness (from 3.8 to 11.8 mm) is correlated and partly explained by the increase of crystallinity ratio and lamella size at larger thicknesses. It comes out that the thinnest film seems perfectly meet the application requesting, namely lowest dissipation factor and highest permittivity.

Morphology Development, Structure and Dielectric Properties of Biaxially Oriented Polypropylene

“…Interestingly, with an increase in film porosity, the dielectric losses should decrease in tandem with the permittivity [19]; such a trend was however not very clear for the BOPP films here. In contrary, the BOPP films showed slightly elevated dielectric losses in comparison to the corresponding cast films-to our current knowledge, this could be attributable substrate heating and/or other stresses occurring during the electrode deposition [21]. Nevertheless, the dielectric losses of the BOPP films (mean 4.38×10 −4 ) are in line with the values reported elsewhere for BOPP films with evaporated Auelectrodes [22].…”

Discharge Characteristics and Plasma Erosion of Various Dielectric Materials in the Dielectric Barrier Discharges

“…The PP is an inexpensive polymer material made of carbon (C) and hydrogen (H) [38][39][40][41] that is used in a variety of fields such as packaging films, fibers, and daily goods. The PP film is prone to oxidation (or degradation) when it is exposed to heat or the ultraviolet light.…”

Ageing: Causes and Effects on the Reliability of Polypropylene Film Used for HVDC Capacitor

“…Thus, the crystallinity of BOPP films plays an important role in mitigating these phenomena [20]. The structural and morphological development of films during manufacturing can be considered as the main determinant of the final properties of the films [21]. In particularly, a high-quality film includes the high isotactic (97 to 99%), 30 ppm (or less in ash content) with an optimum molecular weight distribution, minimum thermal shrinkage (or high thermal stability), homogenous thickness, controlled surface roughness, tensile strength and tearing resistance and smallest amount of residual catalyst content in the raw material [20], [22].…”