Analysis of isothermal two‐layer blown film coextrusion

Abstract

The mechanics of a bicomponent two‐layer blown film coextrusion is studied theoretically. As a first step for the modeling of this complex process, we adopt a simple system in which the flow is assumed to be isothermal and the two layers are a Newtonian and an upper‐convected Maxwell fluid (UCM), respectively. The two fluids are chosen to investigate the relative influence of viscous and viscoelastic forces on the flow mechanics of the process. For a given total flow rate, blow‐up ratio, freeze‐line height, and film gage, the radius and the melt thickness profiles of the blown film are determined numerically for various values of the flow rate ratio of the two fluids. When the relaxation time of the UCM layer is small, the flow mechanics including the shape of the bubble (or the radius profile) is not much different from that of a Newtonian single‐layer flow. With increasing relaxation time, the viscoelasticity effect of the UCM layer becomes more and more pronounced and eventually dominates the bubble dynamics even though its layer thickness may be smaller than that of the Newtonian layer.

A model for the two-layer blown film process with flow-enhanced crystallization

“…Similar to previous approaches for modeling single-layer film blowing (Doufas and McHugh, 2001a;Muslet and Kamal, 2004), and two-layer film blowing (Yoon and Park, 1992), the kinematics are assumed to be purely extensional. Thus the axial velocity does not vary radially and, in consequence, the appropriate continuity and momentum balance equations are the area-averaged forms.…”

Investigation of convective heat transfer in 9-layer film blowing process by using variational principles

“…In spite of a rapid growth of a blown film coextrusion in the last decades, the number of experimental and modeling studies for this process is very limited [27][28][29][30][31][32][33][34] as well as number of works focused on modeling of heat transfer in film blowing process [30,[35][36][37][38][39][40][41][42]. In order to extend the knowledge in this area, the main goal of this work is to investigate different heat transfer coefficient models for multi-layer film blowing process by using variational principles based model [43], which can be viewed as a simple and useful alternative to Pearson and Petrie thin-shell model.…”

Evaluation of Stresses in a Two-Layer Co-Extruded LDPE Melt Blown Film

“…Surprisingly, despite the fast growth of co-extruded film production, relatively few studies have been done to numerically describe this process. The main effort has been done by Yoon and Park [14] in 1992 who studied a bicomponent film composed of a Newtonian inner layer and an upper-convected Maxwell outer layer. They illustrated the effect of the relaxation time and the flow rate ratio on the bubble shape.…”