Formation Mechanism and Morphology of β-Transcrystallinity of Polypropylene Induced by Two-Dimensional Layered Interface

The β-nucleated polypropylene (β-PP) and polypropylene (PP) were coextruded to form the alternating layered structure with different layer number. During the isothermal crystallization of layered samples at 130 °C, the high-density β-nuclei at the two-dimensional layered interfaces between β-PP and PP layers grew asymmetrically. In the β-PP layer, the growth of β-lamellae was quickly terminated by other β-spherulites. In the PP layer, because the formation of α-crystals delayed, all β-lamellae could freely grow perpendicular to the interface and finally form the β-transcrystallinity (β-TC) layer with about 25 μm thickness. If the thickness of PP layer was lower than 50 μm, PP layer would be almost occupied by β-TC. The ordered arrangement of β-TC led to an orientation of molecular chains of β-TC layer parallel to the interface. With the increase of layer number, the content of β-TC and orientation degree of layered samples increased. This paper provided a simple and effective method to prepare continuous,...