Formation of Anisotropic Flow-Induced Morphologies above the Equilibrium Melting Temperature in Isotactic Polypropylene

Shearing an isotactic polypropylene melt, even above its equilibrium melting temperature (T_m° ∼ 187 °C) leads to the formation of stable flow-induced precursors. Anisotropic structures result from shearing at temperatures as high as 220 °C (>30 °C above T_m°), and are no longer generated at shearing temperatures exceeding 230 °C. The long periods increase with deformation, accompanied by a change in structural morphology. The crystallization kinetics were strongly affected by flow at shearing temperatures near T_m° and persist at even higher shearing temperatures, as chains continue to be aligned and stretched with large deformations, perhaps further stabilized by stretched chains adsorbing onto heterogeneous impurities from polymerization.