Anomalous Suppression of Orientation and Crystallization in Semicrystalline Polymers under Flash Shear Flow

Abstract

Flow-induced crystallization (FIC) typically governs the performance of semicrystalline polymers through accelerated crystallization and produces shish-kebab-like structures (typically under steady or strong shear flow conditions; shear rate < 102 s−1). However, FIC behavior under realistic and extreme shear flow conditions remains unclear because of FIC apparatus limitations. Here, flash flow (shear duration < 1.5 s, shear rates of 102−105 s−1, and Weissenberg numbers up to 3.9 × 104) is realized using a self-developed X-ray characterization platform for FIC, revealing anomalous suppression of orientation and crystallization in a set of polymer systems (e.g., poly(l-lactic acid)). The physical origin of this suppression is attributed to the competition between stretching and tumbling motions. We propose a refined microrheological model that incorporates both free energy and diffusion dynamics to overcome the shortcomings of the classical FIC model (i.e., prediction of unbounded FIC), enabling the successful capture of anomalous FIC behavior under flash flow. These results can supplement the current theoretical considerations of FIC and gain deep understanding of FIC mechanism in real polymer processing.