It is widely believed that the trigonal β-form is favorable and effective for toughening isotactic polypropylene (iPP). Therefore, β-form content should be achieved as high as possible to realize excellent toughness in iPP. However, in this study, we demonstrate that the connection between crystallites might mainly determine the toughness of iPP instead of the β-crystal content. A new rare earth nucleator (WBG) was used to generate the rich β-crystalline structure in the compression-molded bars that were fabricated upon different molten temperatures (T f ). Interestingly, the increase in tensile elongation can be as large as 8 times for increased T f . The polymorphic composition and overall crystallinity of β-nucleated iPP are almost independent of T f . Nevertheless, the β-nucleated crystalline morphology has completely changed. Three types of β-crystalline morphology, namely, β-spherulite, β-transcrystalline entity, and "flower"-like agglomerate of β-crystallites, are sequentially obtained with increasing T f . From the morphological point of view, the connection between the crystallites in "flower"-like agglomerate is significantly better than that for the crystallites generated under lower T f . Therefore, it is concluded that the formation of β-nucleated iPP provides very good toughness only with sufficient connection between the crystallites. The result of this study clearly verifies the importance of crystal morphology on tuning the toughness of iPP. It provides important information for potential industrial applications.

It is still a challenge to fabricate polymer-based composites with excellent thermal conductive property because of the well-known difficulties such as insufficient conductive pathways and inefficient filler-filler contact. To address this issue, a synergistic segregated double network by using two fillers with different dimensions has been designed and prepared by taking graphene nanoplates (GNPs) and multiwalled carbon nanotubes (MWCNT) in polystyrene for example. In this structure, GNPs form the segregated network to largely increase the filler-filler contact areas while MWCNT are embedded within the network to improve the network-density. The segregated network and the randomly dispersed hybrid network by using GNPs and MWCNT together were also prepared for comparison. It was found that the thermal conductivity of segregated double network can achieve almost 1.8-fold as high as that of the randomly dispersed hybrid network, and 2.2-fold as that of the segregated network. Meanwhile, much higher synergistic efficiency (f) of 2 can be obtained, even greater than that of other synergistic systems reported previously. The excellent thermal conductive property and higher f are ascribed to the unique effect of segregated double network: (1) extensive GNPs-GNPs contact areas via overlapped interconnections within segregated GNPs network; (2) efficient synergistic effect between MWCNT network and GNPs network based on bridge effect as well as increasing the network-density.

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As part of a continuous effort to develop high performance isotactic polypropylene (iPP) based on β‐form crystalline and morphological change induced by rare earth nucleator (WBG), various WBG contents (from 0.025 to 1.0 wt%) were adopted to prepare β‐nucleated iPP at a fixed final molten temperature (240°C) in this study. The crystallinity, polymorphic composition, and crystalline morphology were inspected in detail by a series of crystallographic characterizations, including calorimeter, X‐ray diffraction, polarized light microscopy (PLM), and electron microscopy. Furthermore, the self‐organization and re‐crystallization behavior of β‐nucleating agent occurred during cooling was characterized by rheometry. Finally, the dependence of mechanical properties, including tensile strength, elongation at break, and impact strength, on WBG content was discussed based on the variations in β‐form content and crystalline morphology. Interestingly, it is found that while the WBG content is below 0.1 wt%, the toughness of β‐nucleated iPP increases with increase in WBG content due to additional β‐form content; as the WBG content is in range of 0.1–0.5 wt%, the toughness increases at a lower rate with increase in WBG content due to β‐crystalline morphological change. However, a decrease in toughness is observed while nucleator content is above 0.5 wt% as WBG remains undissolved in iPP upon the adopted processing conditions. The result of this study provides valuable information for potential industrial applications. Copyright © 2010 John Wiley & Sons, Ltd.

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