Unusual rheological characteristics of polypropylene/organoclay nanocomposites in continuous cooling process

Abstract

The cooling process of isotactic polypropylene (iPP)/organoclay nanocomposites was followed by dynamic rheometry. Contrasting to typical linear increment of log G 0 with decreasing temperature (log G 0 ! 1/ T) occurred on the melts for neat iPP and nanocomposites with small amounts of organoclay, an unusual rheological behavior was identified for composites with relative high organoclay content (!5 wt %) as that: increasing of log G 0 positively deviates to linear relation during cooling within certain high temperature region, thus yields an additional enhancement in viscoelastic properties. Furthermore, such unusual rheological phenomenon was found to be strongly impacted by initial dispersion level of organoclay, cooling rate, and construction of organoclay network. The origin of this unusual rheological phenomenon could be cautiously explained as due to the existence of unstable state of organoclay nanostructure, which could go further intercalation or exfoliation in some high temperature ranges. This might be a new rheological character and is meaningful for understanding the essentially structural behavior of polymer/layered clay nanocomposites, particularly containing mesoscopic clay network. V C 2012 Wiley Periodicals, Inc. J Appl Polym Sci 125: E292-E297, 2012