MULTILAYER FILM COEXTRUSION OF POLYMER MELTS: ANALYSIS
OF INDUSTRIAL LINES WITH THE FINITE ELEMENT METHOD
School of Mining Engineering
and Metallurgy
National Technical University
of Athens
Zografou, 157 80, Athens,
Greece
e-mail: mitsouli@metal.ntua.gr
Multilayer coextrusion is practiced increasingly today for many commercial plastic products. It is not uncommon to employ up to 11 layers in many combinations to set up a structure that meets certain requirements, especially for the food packaging industry. The structure usually consists of the middle barrier layer, adhesive layers on either side, the bulk layer to take up most of the structure, and skin layers to provide high and low temperature impact strength and high heat resistance. In this work, multilayer coextrusion of typical industrial lines to produce plastic sheets for food packaging is analyzed via the finite element method. All the necessary material data are collected, with the emphasis placed on shear viscosity data for a wide range of shear rates and temperatures. Two cases of 4 and 7 layers are thus analyzed by using the conservation equations of mass, momentum, and energy for industrial throughputs. For a given flow rate and flow rate ratios (or correspondingly total sheet thickness and individual layer thicknesses), the solution provides the interface locations and individual pressure drops that each extruder has to supply. The shear stresses at the channel walls are checked as a criterion to avoid melt fracture. Such an analysis provides a fast qualitative as well as quantitative insight into the proper design and melt combinations for multilayer sheet coextrusion of polymer melts.
Keywords: film coextrusion, numerical simulation, multilayer structures,
interfaces