A numerical treatment of crystallization in tube flow

A viscosity-oriented, flow-induced crystallization model is used to predict the rate of crystal layer growth in a tube at high shear rates. A combined strain and strain rate dependence of the enhancement of crystallization kinetics was proposed that showed excellent agreement with viscosity measurements at low deformation rates in simple shear, and it is here considered in the more complex Poiseuille flow. Suspension mechanics is used to link the relative crystalline volume fraction to the viscosity of the semicrystalline polymer. The microstructure is directly related to the thermomechanical histories and this was accounted for in the total volume fraction using the Avrami-Kolmogorov model. The key characteristic of our model is the coupling of the flow history to induced crystallization and the linkage of the flow-enhanced nucleation with viscosity. In this way, the flow is described in terms of changes in crystallization due to changes in rheological behavior. A finite volume numerical treatment was employed using the ANSYS CFX software to model the layer growth. The model is further tested with the presence of an organic nucleating agent in which the sensitivity of the rheological properties of the pigment–polymer blend to stress and temperature was evident. Reasonable agreement with experiments was observed. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers