Effect of Thermal History and Shear on the Viscoelastic Response of <i>i</i>PP Containing an Oxalamide-Based Organic Compound

Abstract

We report on the role of temperature and shear on the melt behavior of <i>i</i>PP in the presence of the organic compound <i>N</i>1,<i>N</i>1'-(propane-1,3-diyl)bis(<i>N</i>2-hexyloxalamide) (<b>OXA3,6</b>). It is demonstrated that <b>OXA3,6</b> facilitates a viscosity suppression when it resides in the molten state. The viscosity suppression is attributed to the interaction of <i>i</i>PP chains/subchains with molten <b>OXA3,6</b> nanoclusters. The exact molecular mechanism has not been identified; nevertheless, a tentative explanation is proposed. The observed viscosity suppression appears similar to that encountered in polymer melts filled with solid nanoparticles, with the difference that the <b>OXA3,6</b> compound reported in this study facilitates the viscosity suppression in the molten state. Upon cooling, as crystal growth of <b>OXA3,6</b> progresses, the decrease in viscosity is suppressed. Retrospectively, segmental absorption of <i>i</i>PP chains on the surface of micrometer-sized <b>OXA3,6</b> crystallites favors the formation of dangling arms, yielding <b>OXA3,6</b> crystallites decorated with partially absorbed <i>i</i>PP chains. In other words, the resulting <b>OXA3,6</b> particle morphology resembles that of a hairy particle or a starlike polymer chain. Such hairy particles effectively facilitate a viscosity enhancement, similar to branched polymer chains. This hypothesis and its implications for the shear behavior of <i>i</i>PP are discussed and supported using plate-plate rheometry and slit-flow experiments combined with small-angle X-ray scattering analysis.