Non-isothermal Crystallization Kinetics of AB3 Hyper-branched Polymer/Polypropylene Blends

The non-isothermal crystallization kinetics of pure polypropylene (PP) and AB3 hyper-branched polymer (HBP)/PP blends (with 5% HBP content) were investigated with various cooling rates by differential scanning calorimetry (DSC) method. The Avrami analysis modified by Mandelkern and a method combined with Avrami and Ozawa equations were employed to describe the non-isothermal crystallization kinetics of the samples. The conclusion showed that at the same cooling rate, hyper-branched polymer could accelerate crystallization effectively. Furthermore, in the blends, the crystallization rate decreased when the higher molecular weight of HBP was added. An increase in the Avrami exponent showed that the addition of HBP influenced the mechanism of nucleation and the growth of PP crystallites. The possible reason and explanation could be attributed to the fractal structure of hyper-branched polymer which has an influence on the diffusion mode of crystallizable segments towards the growing nuclei. The polarized micrographs showed that the number of effective nuclei increased obviously in the HBP/PP blends where, HBP acts as a heterogeneous nucleation agent during the crystallization of the blends. In addition, the activation energy of crystallization was also obtained according to the Kissinger method and the results showed that the crystallization activation energy decreased remarkably in HBP/PP blends.