Effect of nucleating duality on the formation of gamma-phase in a beta-nucleated isotactic polypropylene copolymer

BACKGROUND: It is a challenge for polymer processing to promote the formation of gamma-phase under atmospheric conditions in isotactic polypropylene (iPP) copolymer containing chain errors. Incorporation of an alpha-nucleator in iPP copolymer seems reasonable since it can enhance non-isothermal crystallization. Up to now, however, the issue regarding a beta-nucleated iPP copolymer still remains unclear, which is the subject of this study. RESULTS: The results indicate that the gamma-phase indeed occurs in a beta-nucleated random iPP copolymer with ethylene co-unit (PPR) sample and becomes predominant at slow cooling rates (e.g. 1 degrees C min(-1)) where the formation of the beta-form is suppressed to a large extent. With detailed morphological observations the formation of gamma-phase in the beta-nucleated PPR sample at slow cooling rate is unambiguously attributed to the nucleating duality of the beta-nucleator towards alpha-and beta-polymorphs. The alpha-crystals, induced by the beta-nucleator, serve as seeds for the predominant growth of the gamma-phase. Moreover, the presence of the beta-nucleator, acting as heterogeneous nuclei, promotes the formation of gamma -phase in the nucleated PPR sample, at least to some extent. CONCLUSION: The findings in this study extend our insights into the formation of gamma-phase in beta-nucleated iPP copolymer and, most importantly, provide an alternative route to obtain iPP rich in gamma -phase. (C) 2008 Society of Chemical Industry