Nonisothermal crystallization and multiple melting behaviors of ß-nucleated impact-resistant polypropylene copolymer

As a substitute of isotactic polypropylene in applications requiring excellent fracture resistance, impact-resistant polypropylene copolymer (IPC) has attracted much attention in recent years. In this study, a highly effective beta-form nucleating agent (beta-NA; an aryl amide compound) was introduced into IPC, and our attention was focused on the nonisothermal crystallization and subsequent melting behaviors of the nucleated samples. The nonisothermal crystallization behaviors were investigated on the basis of the different cooling rates and different concentrations of beta-NA with differential scanning calorimetry, wide-angle X-ray diffraction (WAXD), and polarized optical microscopy. The results show that both the cooling rate and concentration of beta-NA greatly determined the nonisothermal crystallization process and subsequent multiple melting behaviors. Further results show that the multiple melting behaviors were related to the transition in beta crystallites and those between the beta and a crystallites. The morphologies of the dispersed particles and the supermolecular structure of the matrix were characterized with scanning electron microscopy. Finally, the effect of the beta-NA concentration on the fracture resistance of IPC was evaluated by measurement of the notched Izod impact strength. (c) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012