Rheological Study of Melt Elasticity on Extrusion Coating with Polyethylenes, 2003 European PLACE Conference Proceedings

The processability of polyethylene (PE) in extrusion coating applications is principally concerned with the degree of neck-in (NI), which is defined as the lateral reduction of film width as it is drawn down into the coating nip, and the drawdown ability (DD), the maximum line speed at which the PE web breaks. Molecular structures like long chain branching (LCB) and molecular weight distribution (MWD) have strong influence on these two processability parameters, which can be correlated with the melt elasticity of the polymer at processing conditions. The effects of these molecular structures on melt elasticity can suitably be studied by shear and extensional rheology. A range of extrusion coating PE grades have been rheologically characterised (e.g., dynamic-mechanical analysis, Rheotens melt strength analysis, etc) and two models relating their extrusion coating processability parameters (NI and DD) and their melt elastic properties have been established. These new rheological parameters and models enable rapid quality controls and evaluation of potential materials, from catalyst development to products scale-up, for extrusion coating applications with the desirable processability in terms of NI and DD.