Dependence of mechanical properties on β-form content and crystalline morphology for β-nucleated isotactic polypropylene

As part of a continuous effort to develop high performance isotactic polypropylene (iPP) based on beta-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 beta-nucleated iPP at a fixed final molten temperature (240 degrees 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 beta-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 beta-form content and crystalline morphology. Interestingly, it is found that while the WBG content is below 0.1 wt%, the toughness of beta-nucleated iPP increases with increase in WBG content due to additional beta-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 beta-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 (C) 2010 John Wiley & Sons, Ltd.