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

Abstract

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, highly ordered and content-controlled β-TC. As a result, the sample with high content of β-TC exhibited good mechanical properties.

Excellent toughness, crystal morphology and crystallization mechanism of transcrystallization of polypropylene induced by layered interface

“…The high‐light β‐TC can be observed at the interface between iPP and β‐iPP layers. Yang and coworkers declared that once the crystallization temperature was fixed, the theoretical thickness of β‐TC layer would be constant . In this work, the average thickness of β‐TC layers was close to 120 μm.…”

“…(in “Wide angle X‐ray diffraction (WAXD)” section), and the results are listed in Table . Meanwhile, the content of β‐TC ( K β‐TC ) can be obtained according to the following equation, which derived from Yang's work : where K β‐0 is the content of β‐crystal in β‐1 sample, r is the thickness ratios of iPP, and β‐iPP layers listed in Table .…”

“…β‐TC located in iPP‐layers and β‐spherulites located in β‐iPP layers. For identical cooling rates, the growth rate of β‐crystal and the time interval between the appearance of the β‐nuclei and the α‐nuclei were fixed, therefore the thickness of the obtained β‐TC was also fixed . With an increasing cooling rate, the temperature decreased rapidly from the temperature which was beneficial for the growth of β‐crystal to the temperature favorable for α‐crystals.…”

“…Whereas, the “self‐assembly” behavior of β‐NA had been investigated by numbers of researchers , and a special shish‐kebab structure was observed . Recently, a special β‐transcrystallinity (β‐TC) was formed by forcing the β‐NA distributed in specific layered spaces of iPP matrix through microlayered coextrusion . Other than the fiber‐induced TC structure, which described in 1952 by Jenckel and coworkers , the layered interface induced β‐TC was continuous, highly ordered and high‐content.…”

Largely enhanced mechanical properties and heat distortion temperature of β-nucleated isotactic polypropylene by adding ultrafine full-vulcanized powdered rubber

“…In order to exhibit the structure of crystal bundles clearly, the size of the selected supermolecular units in I0.05G is smaller than most of crystals, so it is meaningless to compare the size of superstructures between I0.05G and I0.05G1R. 34,35 The self-assembly process is usually driven by weak intermolecular interactions, such as van der Waals interactions, hydrogen bonds, aromatic interactions, and electrostatic interactions. However, it is interesting to nd that interconnected crystals are obtained in I0.05G1R.…”