(180an) Modeling Extrusion Film Casting Process Using Coarse-Grained Molecular Constitutive Equations

Extrusion film casting (EFC) is an important polymer processing technique that is used to produce several thousand tons of polymer films/coatings on an industrial scale. While significant research has been carried out to explain the film neck-in of viscoelastic melts in EFC, little is understood about the role of macromolecular chain architecture (for example long-chain branching) on influencing the neck-in behavior. In the present research we have used several commercial polyethylene (PE) resins of linear molecular architecture (LLDPE and HDPE) and long-chain branched molecular architecture (LDPE) to produce extrusion cast films under controlled experimental conditions. The neck-in profiles of the films were imaged and the velocity profiles during casting were monitored using particle tracking velocimetry (PTV) techniques. The EFC process was modeled using the 1-D flow model of Silagy et. al. (1) in which multi-mode molecular constitutive models such as the eXtended Pom Pom equation (XPP, for long chain branched polymer melts) and Rolie Poly equation (RP, for linear polymer melts) were incorporated. We show that the model captures the salient features of the experimental data in a semi-quantitative manner. Further, the numerical simulation results are used to elucidate the effect of chain architecture on the film flow and neck-in profiles. 

(1) Silagy, D., Demay, Y., & Agassant, J. F. (1996). Study on the stabilityof the film casting process. Polymer Engineering Science, 36, 2614.