Crystallization and melting behaviour of polypropylene 'catalloys'

The crystallization and melting behaviour of polypropylene 'catalloys' (PP-cats) as well as pure polypropylene (PP) were investigated using differential scanning calorimetry. The results showed that, for PP-cats and PP, a single melting peak of PP appeared under slow cooling rate. When the cooling rate is fast enough in the non-isothermal case, or the crystallization temperature is relatively high in the isothermal case, a shoulder peak appears in front of the melting peak with increasing ethylene content in PP-cats. It is believed that this shoulder is induced by recrystallization of crystals initially formed during non-isothermal or isothermal crystallization. When the ethylene component in PP-cats reached a certain level, there existed a melting peak of polyethylene (PE) crystallized during the cooling process. Polarized optical microscopy (POM) showed that the spherulites formed by PP-cats were much smaller and had less perfect morphology compared with that formed by pure PP at the same cooling rate. And with the increase of the cooling rate, the spherulites could not be clearly observed. (C) 2004 Society of Chemical Industry.