Effect of molecular weight on crystallization of semirigid poly(phenylene sulfide) under shear flow

摘要

Isothermal crystallization of poly(phenylene sulfide) with three molecular weights (M _w = 22k, 48k, and 52k, respectively) under shear condition has been investigated. It appears that shear can induce all these three PPS samples to form a thread-like crystal structure which consists of the numerous stable nuclei that align tightly in the direction of shear. Crystallization kinetics of PPS has been greatly influenced by shear flow. Higher shear rate and long shear time can lead to decrease of spherulite growth rate of PPS. Also, the spherulite growth rate of PPS is affected by supercoolings and molecular weight. For the lower molecular weight (M _w = 22k), the spherulite growth rate is independent on the shear rate and shear time; while for the higher ones (M _w = 48k and 52k), with the increasing of shear rate, the spherulite growth rate of PPS increases to reach maximum at first, and then decreases. The lower the crystallization temperature is, the more the spherulite growth rate changes, showing that higher orientation of molecular chains can be obtained more easily with increased supercooling. A model has been proposed to explain the mechanism of thread-like crystal formation under shear flow.