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

Abstract

Isothermal crystallization of poly(phenylene sulfide) with three molecular weights (M w ¼ 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 ¼ 22k), the spherulite growth rate is independent on the shear rate and shear time; while for the higher ones (M w ¼ 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.

Molecular dynamics simulations of crystal nucleation in entangled polymer melts under start-up shear conditions

“…Commercially, polymer melts pass through fast shear or extensional flows during processing. Experimentally, intensive efforts have been made to understand the crystallisation process under quiescent conditions [1][2][3][4][5][6][7][8][9][10] and under the influence of external flow [11][12][13][14][15][16][17][18][19][20][21][22][23] . In these studies, the flow affects the nucleation and growth rates and morphological features including single and multiple shish.…”

Crystal nucleation mechanism in melts of short polymer chains under quiescent conditions and under shear flow

“…In spite of intensive research efforts since the early 1940s, the molecular mechanism of polymer crystallization is still not completely understood 1 . Experimental research has been carried out using a wide range of techniques both, on polymers under quiescent conditions [2][3][4][5][6][7][8][9][10][11] and in external fields [12][13][14][15][16][17][18][19] . Crystallization rates and critical shear rates have been measured for different polymeric materials, the morphological features of the final crystal structure and the effect of molecular weight on the crystallization kinetics have been studied.…”