The dielectric polypropylene film is not only the core of dry DC capacitor

but also the “key” of new energy power generation and flexible DC transmission

which directly influences both quality and safety of electric energy conversion. The crystal structure of polypropylene film plays decisive role in the performance of capacitor. In this paper

the crystal structure of the dielectric film of capacitor (BOPP)

which is made of three kinds of polypropylene pellets by way of casting bi-axially drawing

is studied by such characterization method as wide-angle X-ray diffraction

Fourier transform infrared spectroscopy and differential scanning calorimetry. It is found by the characterization result that three kinds of BOPP dielectric films are predominantly composed of α-crystal structures. However

there are notable differences among the films in terms of their crystallinity

melting temperature and the crystallite size in various orientations. The melting point of dielectric film based on Borealis grains is minimum (169℃)

the degree of crystallinity is highest (59.8%) and the crystals size along the [060

]

direction is maximum. The result of infrared spectrum shows that in BOPP species based on Borealis grains the 3

1

helical chain segments with sequence lengths

n

=14 is maximum. It is found by the study of specimens after melting recrystallization of BOPP film that the crystalinity of three kinds of grains is almost identical (about 53%). However

the non-isothermal crystallization temperature of Borealis PP grains is highest (119℃) and obvious a β-phase melting peak is occurred during the melting period. In comparison

non-isothermal crystallization te

mperature of Sinopec PP grains is the lowest

which is 3℃ less than that of the Borealis grains.