A new insight into the effect of β modification on the mechanical properties of iPP: The role of crystalline morphology

Highlights: • Three types of crystal morphologies was obtained. • The impact strength of the sample contained leaf-like transcrystallinity is almost 3 times higher than that of pure iPP. • The β nucleating agent not only improves the content of β phase, but also enhances the orientation extent of α crystals. • The azimuthal spreads curve of (300)_β plane of sample PP0.1 shows a six-peak structure. It is well established that the trigonal β-form is favorable and effective for toughening isotactic polypropylene (iPP). The content of β-phase, based on the conventional view, should be achieved as high as possible to realize excellent toughness in iPP. Nevertheless, in this study, it is demonstrated that the morphology plays a more important role in improving the impact strength of iPP than β-crystal content. Variable crystal morphologies in the inner regions of the samples are acquired by the variation of nucleant concentrations. Three types of β-crystalline morphologies, β-spherulite (0.02 wt.% and 0.05 wt.%), leaf-like transcrystalline entity (0.1 wt.%), and bundle like one (0.2 wt.% and 0.5 wt.%), are sequentially generated. The leaf like transcrystalline iPP wins the best impact strength. Testing by 2D-WAXD, furthermore, the special six-peak structure of (300) azimuthal diffraction arc is presented with the sample PP0.1 which also has the longest long period.