Numerical modeling of nonisothermal polymer crystallization kinetics: Flow and thermal effects

Abstract

A numerical model able to simulate polymer crystallization under nonisothermal flows is developed. It is based on the assumption that the trace of the extra‐stress tensor, calculated according to a viscoelastic multimode Upper Convected Maxwell (UCM) model, is the driving force of the flow‐induced extra nucleation. Two distinct sets of Schneider equations are used to describe the growth of thermally and flow induced nuclei. The model is then coupled with the momentum equations and the energy equation. As an application, a shear flow configuration between two plates (Couette flow) is simulated. The relative influence of the mechanical and thermal phenomena on the crystallization development as well as the final morphology distribution is then analyzed as a function of the shearing intensity and the cooling kinetics, in terms of nucleation density and crystallite mean sizes. POLYM. ENG. SCI., 50:2044–2059, 2010. © 2010 Society of Plastics Engineers

Process and Structure Interactions in Polymer Materials: the Case of Non-Isothermal Crystallization Kinetics during Processing

“…The solidification model, based on the concentrated suspension theory, assumes that the evolution of the viscosity is equivalent to that of the concentration. See more details in Zinet (7) .…”

“…In the present work, a numerical model able to simulate the crystallization of polymers under non-isothermal flow condition (7) has been developed. The flow causes the macromolecular chains to stretch, thus increasing the melt elastic free energy.…”

“…Following our previously published work (7) , the first invariant (i.e. the trace) of the viscoelastic extra-stress tensor tr(τ VE ), which quantifies the molecular orientation, is used as the driving force of flow-induced nucleation according to the following proposed relationship:…”

“…The spherulitic growth process is modeled using two sets of Schneider rate equations (7,10) , i.e. one set for each type of nucleation:…”

“…This additional nucleation rate can be linked to various parameters: free energy related quantities (3) , shear rate (4) , combination of shear strain and shear rate (5) , and recoverable strain tensor (6) . For a more detailed survey on crystallization kinetics modeling, see the previous paper by the present authors (7) .…”