The Study Of Crystallization Behavior For Polypropylene Catalloys

The isothermal and non-isothermal crystallization behavior of polypropylene (PP) catalloys was studied by using differential scanning calorimetry (DSC), polarized optical microscopy and wide angle X-ray diifraction (WAXD) in this dissertation.In the isothermal crystallization experiments, it was found that the Avrami exponent n of PP and PP catalloys are nearly the same, which suggested that they shared the same heterogeneous nucleation mode. Crystallization rate coefficient k showed that the crystallization rate of PP catalloys is faster than that of PP homopolymer. And the crystallization rate increased with the increase of the ethylene component in PP catalloys, indicating that the ethylene component increased the nucleation rate and therefore the crystallization rate. The melting curves of the isothermally crystallized PP catalloys showed that the melting peak temperature is the same to that of PP homopolymer isothermally crystallized under the same conditions. When the ethylene component in PP catalloys increased to a definite degree, there is a shoulder peak in front of the melting peak in the DSC curves. And with the crystallization temperature increasing, the dominance and the shoulder peak both shift to the higher temperatures.The study of the non-isothermal crystallization kinetics showed that there was the crystallization peak of polyethylene (PE) around 120, during the cooling process when the ethylene component in PP catalloys increases to a definite degree (such as PEP60). At the same cooling rate, the crystallization peak of PP catalloys shifts to higher temperatures as compared with PP homopolymer. The melting curves of the non-isothermal crystallization showed that there was a shoulder peak in front of the PP melting peak with the increasing of the cooling rate and the ethylene component in the PP catalloys, but the melting peak temperature are of the same for PP catalloys. As compared with PP homopolymer, the degree of crystallinity for PP catalloys is much smaller, but, there is no notable difference in the degree of crystallinity for different PP cataloys.By using polarized optical microscopy, we found that the spherulites of PP catalloys appeared at higher temperatures as compared with those for PP homopolymer during cooling processes. On the other hand, the average spherulitic size of PP catalloys is much smaller than that of the PP homopolymer.