(250c) The Effect of Rheological Properties on Film-Casting Performance

Film-casting performance is defined by evaluating the degree of necking experienced. In film-casting, necking is the phenomenon in which a particular film would prefer a reduction in width as opposed to thickness. We evaluate six polyethylene resins with varying degrees of branching by characterizing their rheological properties in both shear and extension and by experimental production of film samples. It is noticed that an increase in strain-hardening as seen in the extensional rheology increases the necking phenomenon as experienced in the film study. Large amounts of die swell are also noticed in the more highly branched strain-hardening films, which negatively impacts the film-casting performance. Numerical analysis of the material rheology using the McLeish-Larson Pom-Pom model yields some insight on the branching characteristics of the different materials. Using these parameters an attempt at modeling the film-casting process is constructed for comparison to experimental samples.