关键词: 静磁场, 交变磁场, 极化, 磁偶极子, 显微形态

Abstract: The changes of crystal structure of polypropylene thin films in their melting-crystallization process under the action of static and alternating electromagnetic fields were investigated and compared with each other by polarizing microscopy. The results showed that the melted polymer is liable to be affected by electromagnetic field so as to form inducible dipoles and its morphology of molecular linkage is different from that as not acted by the field in crystallization process. Spherulites are stretched by the magnetizing force and tend to orientate their crystallization along the direction of the field, thus forming an additional whisker zone in the leading-edge crystallization region due to the traction effect of electromagnetic field. Meanwhile, the polarization effect causes the radiated lamellar crystals to grow from twist form to stretch form, so that the ring-like extinction contour disappears. On the other hand, the magnetostatic field restrains the nucleation in the polymer, thus decreasing the nucleation rate and increasing the spherulite size. It was also revealed that the alternating electromagnetic field has a slight effect on the morphology of spherulites but plays an electromagnetic stirring role in crystallization process to improve nucleation rate and decrease spherulite size.