Variation of non-isothermal crystallization behavior of isotactic polypropylene with varying β-nucleating agent content

The non-isothermal crystallization behavior, the crystallization kinetics, the crystallization activation energy and the morphology of isotactic polypropylene (iPP) with varying content of beta-nucleating agent were investigated using differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The DSC results showed that the Avrami equation modified by Jeziorny and a method developed by Mo and co-workers could be successfully used to describe the non-isothermal crystallization process of the nucleated iPPs. The values of n showed that the non-isothermal crystallization of alpha- and beta-nucleated iPPs corresponded to a tridimensional growth with homogeneous and heterogeneous nucleation, respectively. The values of crystallization rate constant showed that the rate of crystallization decreased for iPPs with the addition of beta-nucleating agent. The crystallization activation energy increased with a small amount (less than 0.1 wt%) of beta-nucleating agent and decreased with higher concentration (more than 0.1 wt%). The changes of crystallization rate, crystallization time and crystallization activation energy of iPPs with varying contents of beta-nucleating agent were mainly determined by the ratio of the content of alpha- and beta-phase in iPP (alpha-PP and beta-PP) from the DSC investigation, and the large size and many intercrossing lamellae between boundaries of beta-spherulites for iPPs with small amounts of beta-nucleating agent and the small size and few intercrossing bands among the boundaries of beta-spherulites for iPPs with large amounts of beta-nucleating agent from the SEM examination. (C) 2010 Society of Chemical Industry