Shear-induced crystallization in phase-separated blend of isotactic polypropylene and poly (ethylene-co-octene)

The Journal of Chemical Physics
Kun MengCharles C Han

Abstract

Isothermal crystallization after shear in a blend of isotactic polypropylene (iPP) and poly (ethylene-co-octene) (PEOc) was investigated by in situ optical microscopy and shear hot stage under various thermal and shear histories. Crystalline cylindrites during growth were observed in phase-separated iPPPEOc blends for the first time. According to our results, the very long cylindrites are formed which are much longer than the dimensions of the liquid-liquid phase-separated domains under shear, and the cylindrites appear to grow through noncrystallizable domains, as well as through crystallizable ones. Obviously, the nuclei ("shish") come from the oriented and entangled network strands instead of pulled-out long chains. The number of cylindrites and the distortion and breakup of the cylindrites are related to the shear rate and shear time. On the other hand, the number of spherulites increases not only with shear rate but also with liquid-liquid phase separation time. Spherulites always form with longer induction time than cylindrites due to the different nucleation mechanism. The shish is nucleated through the shear-induced mechanism, and most of the spherulites are nucleated through liquid-liquid spinodal decomposition and cro...Continue Reading

References

Mar 5, 2004·Physical Review Letters·Liangbin Li, Wim H de Jeu

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Methods Mentioned

BETA
x-ray scattering
light
atomic force microscopy
optical microscopy

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