A model for post-flow induced crystallization: General equations and predictions

Abstract

The aim of this work is to model the flow-enhanced crystallization and the flow-induced morphological changes of semi-crystalline materials during and after shearing flow. A FENE-P dumbbell model and a rigid dumbbell model are used to describe the molecular chain conformation and the orientation evolution for the amorphous phase and the semi-crystalline phase, respectively. The effect of flow on crystallization is considered by relating excess free energy and flow-induced orientation to crystallization kinetics. The crystallization of the material couples back to influence the solidification rheology of the crystallizing system. An isotactic polypropylene is used as an example to illustrate model predictions. We predict a pronounced effect of short-term shear treatments in accelerating nucleation and changing rheological behavior. Results are compared with available experimental data.

Kinetics and Morphology of Flow Induced Polymer Crystallization in 3D Shear Flow Investigated by Monte Carlo Simulation

“…E a /R g is the constant and can be determined by experiment. The stress contributed by amorphous phase can be written as [8,23]…”

“…Here, we adopt the idea of Zheng and Kennedy [8] and use a two-phase suspension model to deal with the crystallizing system. According to Zheng and Kennedy [8], the crystallizing system can be treated as a suspension of semi-crystalline phase growing and spreading in a matrix of amorphous material. The amorphous phase can be described as the FENE-P dumbbell model and the semi-crystalline phase can be described as the rigid dumbbell model.…”

“…The relaxation time of the fluid λ a (T) is a function of temperature and can be calculated by the shift factor a T (T) as follows [8] …”

“…For example, Doufas et al [4], Tanner [5], and Ziabicki [6] applied a multiplying factor function of stress, shear rate, and orientation, respectively, to modify the crystallization kinetic constant in the original Nakamura model to take into account the effect of flow on crystallization. Eder [1], Kosher and Fulchiron [7], and Zheng and Kennedy [8] molded the effect of flow on crystallization by considering nucleation and modified the original Avrami-Kolmogorov model. The modified Nakamura model does predict well in FIC, however, it has the disadvantage that it cannot reveal the details of crystal morphology.…”

Mold deflection effects on the prediction of packing pressure decay and shrinkage of semi-crystalline polymers

“…In addition to the standard flow analyses, simulation analyses were also performed using the flow-induced crystallization model of Zheng and Kennedy [10][11] which includes the influence of crystal growth rates, flow induced nucleation and cooling rates on the phase transition. With this model, the polymer evolves from melt to solid state according to the calculated relative crystallinity, which means that the fixed transition line seen in Figure 1 is not applied.…”