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In this work, isotactic polypropylene and high density polyethylene blends with tailored crystalline structures were prepared through an accessible injection-molding method. Two hierarchic structures, i.e., shish-kebab structures and epitaxy structures, were both successfully obtained among the whole range of samples, which were carefully characterized through polarized light microscopy, scanning electron microscopy, differential scanning calorimetry and small-angle X-ray scattering. It was found that the special epitaxy crystalline structure showed better mechanical properties than the shish-kebab one. The inclined polyethylene lamellae among the oriented polypropylene matrix not only enhances the interfacial adhesion but also facilitates the transmission of external force within matrix. Consequently, the tensile strength of the sample with epitaxy structures is around 46.58 MPa and its impact strength reaches up to 63.33 kJ/m2. These results provide a new method to industrially manufacture samples with tailored crystalline structures, making it possible for preparing general polymer materials with advanced properties.

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In the past few decades, some modified injection molding technologies aiming to fabricate highly oriented superstructure as "self-reinforcement" phase in injection molded samples, such as SCORIM, DPIM, and PVIM, have been extensively proven to be effective in improving mechanical properties of polyolefin. However, there is rare report focus on applying these technologies on reinforcing products with a more complex geometry structure until now. The vibration injection technology is currently researched at lab scale rather than wildly used in industry. Here we designed a lid-shaped part, of which the geometry structure is completely different from the rectangle or dumbbell used in the previous studies, and a novel multiflow vibration injection technology was hired to control the content of shish-kebab successfully. The self-reinforcement effect induced by shish-kebab was remarkable, indicated by the overall improvement in mechanical properties. This work gave a new insight into the practical application prospect of vibration injection technology.

In this article, epitaxial structures have been successfully obtained in the isotactic polypropylene (iPP)/polyethylene (PE) blends by an accessible injection molding methods. By studying a series of iPP/PE blends, the evolution of the epitaxial growth of PE lamellae on the oriented iPP lamellae has been detailedly discussed via wide‐angle X‐ray diffraction, small‐angle X‐ray scattering, scanning electron microscopy and differential scanning calorimetry. Unexpectedly, the exactly epitaxial angles between peculiarly arranged PE lamellae and oriented PP lamellae are all larger than the classical epitaxy theory value of 50°, and it even increases gradually with increasing PP content. It is inferred that the special crystallization of PE is the consequence of joint construction of the oriented PP crystals and the continuous intense shear field provided by pressure vibration injection molding. The epitaxial structures play a positive role in the interfacial connection between two components; thus, the mechanical properties of the blends are improved. This work provides an insight understanding on the formation mechanism of the epitaxy crystallization under shear field. Copyright © 2017 John Wiley & Sons, Ltd.

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Various annealing temperatures below, near, or above the melting temperature were used to anneal polypropylene with oriented shish kebab and isolated spherulite structures in this work. The results showed that a high annealing temperature decreases the time needed to achieve the ideal material property. When the annealing temperature is near or above the melting temperature, the impact strength would be 1.6 times improved by partial melting and recrystallization. The crystal structure of the oriented shish kebab or isolated spherulite structures was improved when annealed at 150 °C, whereas annealing at 165 or 170 °C recombined the crystal lamellae of the structure. Moreover, the high crystallinity and thick lamellae improved the impact and yield strength values of the spherulite structure. However, excessively high crystallinity and thick lamellae in the oriented shish kebab structure did not result in good mechanical performance. Therefore, the prediction of mechanical properties for the shish kebab structure based on crystallinity and lamellar thickness is not feasible. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46465.

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