Three-dimensional numerical simulation of encapsulation in polymer coextrusion

• Main Author: Borzacchiello, Domenico
• Language: ENG
• Published: Université Jean Monnet - Saint-Etienne 2012
• Subjects: [CHIM:OTHE] Chemical Sciences/Other; [CHIM:OTHE] Chimie/Autre; Polymer coextrusion; Encapsulation; Viscoelastic fluids; Phase-Field; Finite volumes
• Online Access: http://tel.archives-ouvertes.fr/tel-00976093; http://tel.archives-ouvertes.fr/docs/00/97/60/93/PDF/These-Borzacchiello-Domenico-2012.pdf

The objective of the present work is the analysis of coextrusion processes by numerical simulation based on phase-field modeling of stratified confined flows. The study of such flows is motivated by the presence of complex phenomena appearing in a vast range of industrial operational coextrusion conditions due to the differences in the components properties and their viscoelastic behavior. The basic idea in coextrusion is to combine several layers of different polymers in a common die, to form a unique product with enhanced properties. However, the existence of fluid stratification in the die is responsible of a severe distortion of the interface between the fluid components, causing a loss of efficiency for the whole process. Experimental data show that, even if a stratified initial configuration is imposed at the die entry, one fluid eventually encapsulates the other in most of the flow condition analyzed. The intrinsically three-dimensional nature of this phenomenon has required the development of a three-dimensional flow solver based on the finite volume discretization of the Navier-Stokes equations for incompressible and isothermal flow, together with differential nonlinear constitutive equations (Giesekus, PTT models). The presence of two fluid phases is taken into account by a phase field model that implies the solution of an additional scalar equation to describe the evolution of the interface on a fixed Eulerian grid. This model, unlike others of the same family, has a thermodynamic derivation and can be physically interpreted. The proposed method is tested against experimental data and solutions already available in literature and a study of coextrusion in rectangular dies is performed to identify the dependence of encapsulation on the flow parameters