Effect of Thermal History and Shear on the Viscoelastic Response of PP Containing an Oxalamide-Based Organic Compound.

We report on the role of temperature and shear on the melt behavior of PP in the presence of the organic compound 1,1'-(propane-1,3-diyl)bis(2-hexyloxalamide) (). It is demonstrated that facilitates a viscosity suppression when it resides in the molten state. The viscosity suppression is attributed to the interaction of PP chains/subchains with molten 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 compound reported in this study facilitates the viscosity suppression in the molten state. Upon cooling, as crystal growth of progresses, the decrease in viscosity is suppressed. Retrospectively, segmental absorption of PP chains on the surface of micrometer-sized crystallites favors the formation of dangling arms, yielding crystallites decorated with partially absorbed PP chains. In other words, the resulting 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 PP are discussed and supported using plate-plate rheometry and slit-flow experiments combined with small-angle X-ray scattering analysis.