Flow-induced crystallization of polypropylenes in capillary flow

Abstract

In this paper, the flow-induced crystallization (FIC) behavior of various polypropylenes with different molecular characteristics was investigated using a capillary rheometer. The Cogswell analysis was applied on the capillary data to obtain the apparent extensional strain rate and strain as well as the apparent extensional viscosity. The extensional viscosity obtained using this method was in good agreement with the zero shear viscosity obtained using a cone-and-plate rotational rheometer (Anton Paar MCR-502). Extensional flow parameters did not influence crystallization kinetics in the capillary die. FIC was found to depend strongly on the length-to-diameter (L/D) ratio of the capillary die that is directly related to the residence time. It was also found that the crystallization kinetics were enhanced with increasing molecular weight, indicating the importance of high-end tail of molecular weight distribution (MWD) on FIC. Finally, temperature impacted the FIC behavior significantly since it alters the activation energy needed for the formation of macroscopic structures.