The Effect of Crystal Forms on Dielectric Properties of Polypropylene

In the present paper, the dielectric properties of polypropylenes with different crystal forms were investigated. The space charge distribution was measured by using electro-acoustic pulse and the effect of space charge on short circuit breakdown was analyzed by using DC pre-stress voltage. Relative crystallinity of the beta crystal in beta crystal form polypropylenes was analyzed by using DSC, and morphology of the polypropylenes was observed by using POM. The results show that the conventional dielectric properties are almost same, however the space charge density in beta crystal form polypropylene homopolymerized is much smaller than that in the alpha crystal form polypropylene homopolymerized, and its decay with time is more rapid than that in the alpha crystal form polypropylene homopolymerized. The beta crystal form effectively inhibits the space charge effect, which improves space charge induced breakdown