Summary: A novel method for the tailoring of unique three‐phase crystalline systems in isotactic poly(propylene) has been proven. It is based on a synergistic application of a specific β‐nucleating agent and high pressure during crystallization. The formation of a γ phase was supported by elevated pressure and high temperature during crystallization; under these conditions the growth of both β and α phases was significantly suppressed. Nevertheless, during the course of crystallization at lower pressure and/or lower temperatures, strong β‐nucleation efficiency favored the formation of a β phase. magnified image

Structural transformations of semicrystalline polymers form an important field of current scientific research. The preparation of controlled supermolecular structure may lead to significant improvements in mechanical, thermal and optical properties. As for isotactic polypropylene (iPP), its properties essentially depend on its crystalline phase composition, which is due to polymorphism of iPP. Thus, the aim of this work is to analyze the influence of the β-phase content in polypropylene and of its spatial arrangement on mechanical properties, in particular on its impact strength. Commercially available isotactic polypropylene (iPP) was modified by various amounts of a specific β-nucleating agent (N, N'-dicyclohexylnaphtalene-2,6-dicarboxamide). From the prepared mixtures standard impact testing bars were injection molded. The structure of the specimens was studied by X-ray diffractometry, and impact properties were determined using Charpy impact tester. It was found that addition of the nucleator led to β-phase content increase, especially in the core region of the injection molded samples. The skin (surface layer of the samples) contained lower amount of β-phase. Furthermore, notch impact strength dramatically increased with increasing concentrations of the β-nucleating agent. The concentration of 0.03 wt.% of the nucleator can be considered a “boundary value” due to the fact that the maximum notch impact strength value was reached. With further addition of the nucleating agent the impact strength slowly decreased. Therefore it should be noted that the improvement of impact properties is not only due to the presence of β-phase, but also there are some synergy-applied factors – such as the structural heterogeneity and spatial arrangement of the β-phase in injection molded samples.

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Tensile and Flexural Properties of b-Nucleated PolypropylenesResuming our previous work on b-nucleated polypropylenes, namely on their impact strength, our present work directs attention towards a flexural and tensile behavior of b-nucleated polypropylenes (b-iPP). For the purposes of this work, commercially available isotactic polypropylene was modified using various amounts of a specific nucleating agent based on N, N 'dicyclohexylnaphtalene-2,6-dicarboxamide (NU100). From the prepared blends test specimens were prepared by injection molding. Structural characterization (crystallinity and the content of b-phase) was carried out by X-ray diffractometry. A multipurpose mechanical property tester was used for determination of tensile and flexural properties. It was found that b-phase content decreased both tensile and flexural strength; on the other hand, the presence of b-phase dramatically raised cold drawability of the injection-molded specimens; addition of 0.03 wt.% of NU100 in the injection-molded parts led to a more than 800 % increase of the draw ratio of specimens tested at the testing speed of 100 mm/min. Furthermore, tensile testing carried out using various strain speeds (10 and 100 mm/ min) revealed that higher ductility of the material containing b-phase is particularly pronounced by faster deformation processes, such as fast drawing or impact load.International Polymer Processing downloaded from www.hanser-elibrary.com by Kungliga Tekniska on August 18, 2015For personal use only.